Final Report Summary - AENEAS (Aquired Environmental Epigenetics Advances: from Arabidopsis to maize)
Executive Summary:
Interest in plant epigenetics is increasing both as an area of fundamental research and a source of new traits for breeding. DNA methylation, histone modifications and histone variants play a key role in regulating gene expression during the formation of epigenetic gene variants or epialleles, which can be propagated through mitosis and transmitted to the progeny, often remaining stable for several generations. Project AENEAS aimed to assess the impact of environmental conditions on epigenetic states and in the formation of epialles in the model plant Arabidopsis thaliana and then transfer the knowledge to maize (Zea mays) an important European crop.
The first general objective of AENEAS was to provide advances in understanding the detailed mechanisms of epialleles formation in response to environmental cues and their heritable maintenance in the model plant Arabidopsis, for which molecular and genetic tools were already available at the beginning of the project. Concomitantly, the constitution of an “environmental epigenetic platform” for maize has started with the development of tools indispensable for the shift of epigenetic research from Arabidopsis to maize, to achieve the second main objective of AENEAS: the transfer of knowledge from model to maize.
Both Arabidopsis and maize research has been sustained by application of genome wide technologies and bioinformatics analysis. The project focused on three epigenetic regulatory pathway: the autonomous, the small RNA and the CpG methylation pathway. These refer to how epiregulators perceive strong environmental change, by which environmentally-induced epialleles are formed and to what extent and how the newly formed epialleles are inherited trough generations.
Outstanding scientific article on Arabidopsis epigenetics were produced and published during the project aiming at: i) understanding the effect on destabilization of A. thaliana genome induced by environmental constrains; ii) elucidating the role of two RNA binding proteins FCA and FPA in Arabidopsis autonomous pathway; iii) producing a genome wide comparison of DNA methylation among ten A. thaliana lines, derived 30 generations ago from a common ancestors. Moreover, in Arabidopsis a new working model for the establishment of DNA methylation at endogenous loci were developed, characterizing different types of sRNAs and focussing on different RNA silencing factors.
In maize, a dataset on response to various environmental stresses previously tested in Arabidopsis was collected and analysed. Plants from both the B73 maize inbred line and maize mutants of epiregulators of the three epigenetic pathways under investigations in AENEAS were then used for preparing small RNAs , RNAs, ChIP-seq and BS-seq libraries. These were sequenced and the data was analysed in order to investigate, at genome-wide level, the effect of stress application on transcription, gene regulation and some epigenetic marks. Specific maize epitargets were identified and are currently under characterization.
In parallel a series of tools for maize were developed, protocols and mutants for epiregulators, some of which were characterized at molecular level in order to determine whether the three pathways are acting in the same way as in Arabidopsis. Indeed, the results indicated that some epiregulators belonging to these pathways have different targets in the maize genome and newly-produced mutants have been characterized and are now available at the Scientific Community.
It is already clear that the novel epigenetic mechanisms present in plants constitute unique opportunities for research into the development of the crops of the future. However, the extent to which species specific epigenetic marks are related to difference in genomic organization, and how they are linked to distinct responses remains to be seen. The comparison that AENEAS has made of the behaviour of Arabidopsis and maize epitargets in response to specific stress treatments will pave the way for further identifications of the similarities and differences between two evolutionarily distinct plant species.
AENEAS come to a close in March 2013 and the Final Meeting was held in Padova, where novel and important evidences produced during the project were discussed in view of new researches towards Horizon 2020.
Project Context and Objectives:
The project entitled AENEAS (Acquired Environmental Epigenetics Advances: from Arabidopsis to maize) aimed to investigate environmentally-induced epigenetic changes as the “new frontier” of natural and artificial variability. Epigenetics is defined as the study of heritable traits that are not encoded in the primary sequence of DNA and epigenetic mechanisms act through DNA and chromatin modifications. Environmental cues are thought to activate specific epigenetic mechanisms, which add epigenetic marks and in consequence alter spatial and temporal patterns of gene expression, destabilizes the plant genome and cause phenotypic changes that may be transmitted to the progeny, sometimes remaining stable for several generations.
The first general objective of AENEAS was to provide advances in understanding the detailed mechanisms of epiallele formation in response to environmental cues and their heritable maintenance in the model plant Arabidopsis. To this end, the project focuses on three epigenetic regulatory pathways, which have been well characterized for their interaction with environmental signals in mediating changes into the epigenome. They are the autonomous, the small RNA and the CpG methylation pathways. Cytosine methylation is one of the best characterised epigenetic mechanisms. Methylation occurs in CpG sequence context (mCpG) both in higher plants and animals, but plants differ from animals by significant levels of methylation at symmetric CpNpG (where N can be any nucleotide) and asymmetric CpHpH (where H is an A, C or T) sites. Two essential roles have been ascribed to DNA methylation: defending the genome against transposons and regulating gene expression. There is good evidence that siRNAs, which are generated by the sRNA pathway, can provide sequence specificity to guide cytosine methylation as well as other types of epigenetic modifications. In the Arabidopsis genome, there are thousands of loci for production of endogenous small RNAs that, in turn, can epigenetically modify the loci of origin. The epigenetic modifications involve DNA methylation, chromatin silencing or both. The autonomous pathway represents a good example of an interaction between environmental cues and the plant epigenome. This pathway was initially characterised because it regulates the switch from vegetative to reproductive development in Arabidopsis. However, more recent advances indicate that this pathway plays important, genome-wide roles and, in several cases, its function overlaps with other pathways mediating chromatin regulation.
Indeed, several bodies of evidence indicate that these three epigenetic regulatory pathways play a pivotal role in mediating epigenomic change in response to environmental cues. A large part of the information on the environmental-related epialleles formations is arising from studies carried out on the Arabidopsis model plant. In this model, it is well-documented that environmental cues, particularly stresses and shocks, strongly affect gene and genome activity. It is also evident that the environment, in addition to inducing genetic variability due to mutation of the DNA nucleotide sequence, also induces formation of stably inherited epialleles with relevant effects on the phenotype. Importantly, more preliminary results indicate that their function is also conserved in maize.
On the initial bases described above, AENEAS research activity has led to the generation of a genetic system(s) responding to a set(s) of environmental conditions, which affect the epigenome to favor adaptive selection of new epi-variants. This objective has been pursued through activity in work package 1 (WP1). Concomitantly, the constitution of an “Environmental Epigenetic platform” for maize has started with the development of tools indispensable for the shift of epigenetic research from Arabidopsis to maize and this has been directly followed by the second main objective of the AENEAS project: the transfer of knowledge from model plant to maize, an important European crop (WP2 and WP3 activity, respectively). Throughout the achievement of these two general objectives of the AENEAS project, we have started to make available for the scientific community a series of deliverables that can be the “progenitors” for the “next-generation” of breeding programs, based on the exploitation of the environmentally-induced epigenetic variability. For instance, it is thought that the ability to respond to abiotic stresses represents the main constraint on maize production. Thus the future release of maize varieties with high yield and stability will largely depend on the possibility to increase tolerance to environmental stresses. In plant improvement, breeders select for a consistent phenotype that is often conditioned by many genes with incremental effects, rather than single large effect mutations. Therefore, two important questions to address were: how much of this available variation exploited in breeding programs is caused by epigenetic processes, and how it is possible to increase epigenetic diversity from which advances in crop research and development can be drawn.
Furthermore, the main objectives of AENEAS research on Arabidopsis were the characterization of the epigenetic mechanisms involved in mitotically and meiotically heritable changes of epigenetic information in response to environmental cues and the development of reliable assays to efficiently monitor environmentally induced epigenomic alterations in this model plant. Each of the three WP1’s participants (P4, P5, and P6) focused their research activity on three selected pathways and applied different stress treatments, on the basis of their specific expertise and tools. They were interacting by using comparable developmental stages of plants for stress treatment and recovery, as well as comparable strategies for subsequent genomic analyses, which comprise RNA profiling, DNA methylation and siRNAs analyses. The research on Arabidopsis showed that the autonomous pathway has a general role on gene transcription termination and sRNA pathway is involved in controlling both genome stability and abiotic stress response. The next-generation sequencing of Arabidopsis and bioinformatics support for the AENEAS project were guaranteed by activity in WP4 coordinated by P7. P7 has previously developed the SHORE pipeline for mapping of short reads and a graph method, GenomeMapper, for effective mapping of variant sequences and adopted GenomeMapper in the context of SHORE for the analysis of reads that come from bisulfite conversion of Arabidopsis gDNA. P7 has compared genome wide. DNA methylation among 10 A. thaliana lines, derived 30 generations ago from a common ancestor, showing that CpG methylation marks is partially maintained across generations.
A further main objective of AENEAS research was to generate the molecular and genetic tools in a crop, maize, for the exploitation of the epigenetic regulation of gene expression in response to environmental stresses.. The objective of WP2 is to identify maize transcriptomic and epigenomic changes induced by stress treatments and analyze how the above mentioned epi-regulatory pathways (autonomous, small RNA and CpG methylation) will contribute to these changes. To achieve this objective, after preliminary investigations and considering the indications from Arabidopsis that provided some evidences on the effectiveness of specific treatment in the formation of trans-generationally stable epialleles, different stresses were applied to maize B73 and to maize mutants in epi-regulators by P1, P2 and P3. To address the role of stress-induced epigenetic gene and TE regulation P1 has analyzed the salt and drought stresses effects on transcriptional modulation (RNA-seq), transposon activity and on associated smallRNAs (sRNA-seq) and epigenetic marks (ChIP-seq for these histone modifications H3K4me3, H3K9ac and H3K27me3 in collaboration with P2), both in B73 inbred line and the epiregulator mutant rmr6. A collaboration between P3 and P7 was set to identify stress epi-targets, using a genome-wide approach. The meristematic area (MA) from cold and heat stressed and control populations at different time points was collected by P3 to produce Illumina libraries for sequencing: - P3 prepared and sequenced mRNA and small RNA (sRNA) libraries, P7 prepared libraries for BIS-seq form gDNA. In the time course of the project maize mutants for environmental epi-regulators were identified and characterized: insertional lines for five epi-regulators (one mutant for each pathway) were identified by P8 and introgressed by P1 in B73 background. P8 has also produced transgenic mutants of the three epigenetic pathways using a RNAi approach. Finally P2 has has deeply characterized an epiregulator mutant of the autonomous pathway and studied the effect of stress in maize genome destabilization.
While significant leaps in understanding of epigenetic phenomena had been made before AENEAS’ inception in 2009, several key questions remained, and the project has made solid progress towards finding workable answers. For instance, it has helped to clarify the interactions between the environment and epigenetic mechanisms and is already applying knowledge from its basic research to environmentally induced and epigenetic-related sources of variability. At the beginning of the project it was not clear whether different abiotic stresses and treatments cause distinct changes in the epigenome; since then, AENEAS has established protocols for the most effective stress treatments in epiallele formation in Arabidopsis and maize, where a genome-wide evaluation of their effects has produced interesting results.
Despite these successes, it is clear that there will be challenges ahead, as maize exhibits some characteristics not present in Arabidopsis, necessitating further characterizations and the development of unique tools. During the last part of AENEAS, the Consortium had the opportunity to start the comparison between the information produced on the model plant (Arabidopsis) and those coming from the crop (maize). This opened an interesting discussion both from an evolutionary and applicative point of view. The Consortium stressed the importance of crossing the data produced by the participants in order to depict a picture as much complete as possible on epialle formation in maize. A further effort is now needed for understanding the hereditability of epialles in maize, for their future exploitation in breeding programs. AENEAS research into the correlation between environment and epigenetics in maize is relatively young and only few epi-regulatory pathways have been characterised at a functional level, but the project has created a valuable collection of tools and information which together constitute the maize environmental-epigenetics platform.
The objectives of AENEAS WP5, the coordination WP, was to collect and coordinate all the activities related to the management of the project, the dissemination of the results, the staff exchange and the technology transfer among laboratories. P1, the Coordinator, was the responsible for maintaining the contact with the members of AENEAS Advisory Board, which was appositely constituted to guarantee the appropriate execution of the planned work within the project and to further exploit potential impacts from the project, throughout collaborations with non-EC Institutes of excellence. At the end of the project, it was a general opinion that one of the outstanding feature of AENEAS research project was the constitution of a consortium in which European groups, leaders in Arabidopsis research, were combined with groups working on maize. This combination has allowed a very fruitful collaboration making the ideas circulating among the people and driving the research on the right direction: AENEAS succeeded very well in the realization of the idea “ transfer of knowledge from model to crop”.
Project Results:
AENEAS Final Report
Description of the main S & T results/foregrounds
Participant
number Participant short name Beneficiary Name of Principle Investigator
1 coordinator UNIPD Università degli Studi di Padova Serena Varotto
2 CRAMAC CRA Unità di Ricerca per la maiscoltura Vincenzo Rossi
3 UNIWA University of Warwick Josè Gutierrez Marcos
4 UNIGE University of Geneva Jerzy Paszkowski
5 JIC John Innes Centre Caroline Dean
6 UCAM University of Cambridge David Baulcombe
7 MPG Max Planck Institute Tubingen Detlef Weigel
8 BIO BIOGEMMA Jacques Rouster
Work package 1
Work package number 1 Start date or starting event: Month 1
Work package title Epigenetic responses to environmental signals in Arabidopsis
Activity Type1 RTD
Participant number 4 5 6 7
Participant short name UNIGE
WP coordinator JIC UCAM MPG
General Objectives:
The objectives of WP1 are the characterization of epigenetic mechanisms involved in mitotically and meiotically heritable changes of epigenetic information in response to environmental and development of reliable assays to efficiently monitor environmentally induced epigenomic alterations.
Specific objectives of WP1 for the period are:
1. To characterize the global transcript changes in mutants affected in the autonomous, small RNA (sRNA) and CG methylation (mCpG) pathways – aiming to determine chromosomal targets affected by each of the pathways and thus the extent of their overlap. For certain mutants such as met1, and fca/fpa these data are available already, thus can be used directly for the comparative analysis.
2. To characterize the changes in RNA processing and in populations of small RNAs due to the deficiencies in each of the above mentioned pathways, allowing the overlaps between the pathways to be described in terms of RNA metabolism and RNA directed regulation. For certain mutants such as fca/fpa and nrpd1a small scale analysis have been completed and these data can be used directly for the comparative analysis.
3. To characterize genomic DNA methylation, chromatin properties and possibly direct targets of selected components of each of the pathways. For certain mutants (met1 at a genome-wide level and fca/fpa on a small number of selected targets) these data are available already, thus can be used directly in the comparative analysis.
4. To examine the influence of environmental cues/stresses/shocks of progressive severity on chromosomal targets regulated by a specific pathway, and targets controlled by multiple pathways (selected from objectives 1, 2 and 3). We aim to establish the most effective stress condition influencing each of the studied pathways (or several of them simultaneously). Plant material subjected to specific environmental triggers will be reassessed for genome-wide transcriptional responses, DNA methylation and chromatin analyses.
Summary of progress towards objectives:
1. Utilization of Affymetrix Whole Genome Tiling Array to investigate the genome-wide mis-expression profiles of the autonomous, mCpG and RNAi pathways. Comparative analysis of genome-wide differential expression profiles of mutants of the autonomous pathways (fcafpa double mutants), RNAi mutants ( dcl1, dcl23, hyl1, serrate and rdr6) and previously published data of the Arabidipsis DNA methylation mutants (drm1-1drm2-2cmt3-11ddc triple mutant).
2. Analyses of small RNA profiles in Arabidopsis wt and fcafpa double mutants (autonomous pathway) after cold stress application and comparison with previously published ddm1 mutant (mCpG pathway).
3. Studies on the destabilization of transcriptional gene silencing (TGS) in wt Arabidopsis and in mutants compromised in mCpG and siRNA pathways.
4. Development of a variety of different stress assays (high temperature, low temperature, high salt, osmotic stress, drought, Cu++, Cd++) to determine the effect of stress on Arabidopsis seed germination and seedling growth. The nrpd1a mutant and the respective wild-type were compared in these assays.
Task 1 Discovery of epigenetic mechanisms involved in stress mediated modulations of the autonomous pathway (P5 Lead participant; other participants P4– P6– P7)
Background:
FCA and FPA have been identified as RNA binding proteins that have important roles in vegetative to floral transition in Arabidopsis thaliana. It has been previously shown that FCA and FPA have widespread roles in silencing transgenes and transposons as well as single copy genes.
Sub-task 11 and 1.2: Transcriptome regulation by autonomous pathway and validation of the transcriptome data.
In order to investigate the extent of FCA and FPA targets in the Arabidopsis genome, P5 employed the Affymetrix Whole Genome Tiling Array Chip in collaboration with P7. Genome-wide transcript levels of Arabidopsis thaliana Columbia (Col-0) accession were compared to fcafpa double mutant seedlings from 7 and 17-day old plants, respectively. The results indicate a developmental difference in number of targets misregulated at two different time points. Performed analysis revealed that FCA and FPA have genome-wide targets not restricted to a certain class of genes or transcripts that belong to a single pathway/process. A number of upregulated segments from the fcafpa microarray analysis were selected for further verification.
Initially, P5 focused on unannotated segments that were novel transcripts in fcafpa double mutants. P5 selected a number of upregulated segments from the fcafpa microarray analysis for further verification. Out of 82 annotated segments, 27 were tested for verification via one-step RT-PCR and 18 were confirmed (~67%). Of these 18, 15 were further selected for analysis via quantitative RT-PCR. Particularly transcriptional changes were analyzed in the 15 selected targets in fcafpa double as well as fca and fpa single mutants compared to wild type Col-0. FCA and FPA show functional redundancy and they have differential interaction on different loci. P5 analyzed the 15 verified upregulated segments either using RT-PCR followed by sequencing or 5′ and 3′ rapid amplification of cDNA ends (RACE) analysis. This revealed a complex picture, with every misexpressed segment resulting from a slightly different event at each locus. Loss of FCA and FPA led to increased transcript read-through that continued several kilobases downstream to the adjacent gene, i) through an adjacent gene, ii) into an intergenic sequence, iii) into transposon rich regions, iv) or in convergently transcribed genes. Northern analysis of the misexpressed transcripts suggested that loss of FCA and FPA resulted mainly in increased transcriptional read-through. Northern blot also revealed accumulation of high molecular weight transcripts in fpa single and fcafpa double mutants, which was not detected by the RT-PCR or 3′ RACE analyses. In summary, P5 investigations showed that transcriptional read-through, alternative polyadenylation, and alternative splicing result in apparently unannotated genomic segments being misexpressed in the fcafpa double mutant. In some cases, the transcriptional read-through significantly reduced expression of the associated genes. Furthermore FCA/FPA dependent changes in DNA methylation were found at several loci, supporting previous associations of FCA/FPA function with chromatin modifications and suggesting that extensive read-through transcription because of defective 3′ processing is associated with chromatin changes and that FCA and FPA are involved in the interplay of these co-transcriptional mechanisms. Finally, data suggest that FCA and FPA play important roles in the A. thaliana genome in RNA 3′ processing and transcription termination, thus limiting intergenic transcription.
C Sonmez, I Bäurle, A Magusin, R Dreos, S Laubinger, D Weigel and C Dean (2011) RNA 3’ processing functions of Arabidopsis FCA and FPA limit intergenic transcription. PNAS 108 (20): 8508-13
In collaboration with P7, P5 employed the Affymetrix Whole Genome Tiling Array in order to do a comparative analysis of genome-wide differential expression profiles of mutants of the Autonomous pathway (i.e. fcafpa double mutants), RNAi mutants (i.e. dcl1, dcl234, hyl1, serrate and rdr6) and previously published data of the Arabidopsis DNA methylation mutants (drm1-1drm2-2cmt3-11 (ddc) triple mutants) (Kurihara et. al. Biochem Biophys Res Commun 2008 Nov 21;376(3):553-7).
P5 and P7 observed that the percentage of differentially expressed segments is quite similar between Autonomous, RNAi and DNA methylation pathways at 2 weeks. However, only ~9 % of the segments were misregulated in 1-week old fcafpa mutants. These results indicate a developmental bias in differential expression profiles of fcafpa mutants.
Of the total number of misregulated segments in fcafpa mutants, ~27% were in common with the RNAi and DNA methylation mutants irrespective of the time point. At 2-weeks, the autonomous pathway shared ~15 and 12% segments in common with the RNAi and DNA methylation pathways, respectively. When RNAi and DNA methylation pathways are compared alone, the percentage of the segments that were commonly misregulated was ~15%. These results show the extent of commonality between the Autonomous, RNAi and DNA Methylation pathways and suggest a genome-wide role of the autonomous pathway in gene silencing.
The tiling array analysis of the genome-wide targets of FCA and FPA with P7 in wild type Columbia and fcafpa mutants at two different time points identified a series of target sequences that comprised several unannotated segments (UAs). The detailed analysis of these targets showed that upregulation of UA segments/downregulation of genes in fcafpa can partly be explained by a “switch” in polyadenylation site.
The analysis of the antisense transcript of Helitron1 (AT1TE93275) that is upregulated in fcafpa mutants demonstrated a possible overlap of the Autonomous pathway with other silencing pathways, such as the DNA methylation and the sRNA pathway. This last observation was also confirmed by the analysis of several others UAs. Furthermore it was observed that DNA Methylation at the Helitron 1 locus is perturbed in fcafpa double mutant.
To better characterized the fcafpa double mutant In collaboration with P5 , P4 performed RNA-seq using Illumina technology for the genome-wide analysis of cold stress on wild type Col vs fcafpa plants, sequencing both polyA and non-polyA transcripts, strand-specific and both strands.The sequencing was carried out in 2012 and repeated in 2013.
P5 focused the research on the autonomous pathway, analyzing the role of proteins involved in this pathway and the role of antisense RNA production at the FLC locus. The fcafpa mutant was shown to inhibit proper polyadenylation of mRNAs, resulting in transcriptional read-through, longer transcripts and alternative polyA tails. At the FLC locus this means the production of long antisense RNA instead of short antisense - COOLAIR – RNA, hampering the downregulation of FLC expression and thereby flowering. Analyses of polyA and non-poly RNAs showed that in fcafpa mutant, cold treatment can substitute the function of FCA and FPA proteins; cold treatment of wildtype and fcafpa mutant gave rise to similar RNA profiles. The P5 lab also identified a homeodomain protein, AtNDX that represses expression of COOLAIR, delaying flowering. It appears to do so via stabilization of an R-loop at the COOLAIR promoter.
P5 have investigated whether higher-order chromatin structures are involved in the regulation of the Arabidopsis floral repressor gene FLC. They identified a gene loop involving the physical interaction of the 5’ and 3’ flanking regions of the FLC locus using chromosome conformation capture. The FLC loop is unaffected by mutations disrupting conserved chromatin regulatory pathways leading to very different expression states. However, the loop is disrupted during vernalization, the cold-induced, Polycomb-dependent epigenetic silencing of FLC. Loop disruption parallels tim-ing of the cold-induced FLC transcriptional shut-down and upregulation of FLC antisense transcripts, but does not need a cold-induced PHD protein required for the epigenetic silencing.
Pedro Crevillen, Cagla Sonmez, Zhe Wu and Caroline Dean (2013) A gene loop containing the floral repressor FLC is disrupted in the early phase of vernalization. The EMBO Journal (2013) 32, 140–148.
Sub-task 1.4: Transcriptional stress response of the FCA/FPA targets
In collaboration with the P6, P5 has analysed the small RNA profile of Col seedlings before and after 2 weeks cold and fcafpa double mutants. Size-fractionated small RNA from 2 week old seedlings (in the size range 20- 30) were cloned and sequenced using 454 technology. From 208k extractable reads there were 30,332 wt; 128,536 fcafpa; 49,908 2w cold. David Studholme (Sainsbury Laboratory) analyzed the samples and found a similar profile between Col and fcafpa. However, there was a large difference in small RNA size distribution when Col before and after 2 week cold was compared. A more detailed bioinformatic analysis on this dataset was generously performed by Alexis Sarazin in Vincent Colot’s group (IBENS Paris). In the cold-treated sample there was an overabundance of 21nt-long sRNAs (40% of total, 19 422 out of 48 002 sequences) compared 24nt-long sRNAs (10% of total, 11 214 out of 48 002 sequences). The distribution of matching reads was plotted for each chromosome, the density of reads was highest in the centromeric and pericentromeric regions. Those in the euchromatic arms correspond almost exclusively to miRNA sequences. An overrepresentation of the miRNA category in cold-treated seedlings explains most of the 21-mer overabundance observed in the Col0 cold-treated library. Inspection of the 21nt class indicates that most of the increase in miRNA abundance in cold-treated seedlings is due to miR169 or its priMiRNA stem loop (58,6%, or 10363 out of 14364 21nt reads; vs (0.3% or 7 out of 5131 21nt reads in our Col0 library).
In conclusion, the comparisons of genome-wide small RNA profiles in Arabidopsis mutants for autonomous, sRNA and DNA methylation pathways grown under cold stress conditions, showed that cold stress may affect transcriptional read-through, possibly through a different mechanism than fcafpa and other silencing mutants. JIC lab started a collaboration with P7 for RNA-seq of the following materials: Col-0, fcafpa, Col-0 2w cold; fcafpa 2w cold; Ler; fcafpa in Ler.
Task 2 Discovery of epigenetic mechanisms involved in stress mediated modulations of the small RNAs pathway (Lead participant P6; other participants: P4– P5– P7)
A variety of different stress assays (high temperature, low temperature, high salt, osmotic stress, drought, Cu++, Cd++) have been developed to determine the effect of stress on Arabidopsis seed germination and seedling growth. The nrpd1a mutant and the respective wild-type were compared in these assays. No phenotypic variation was observed between the nrpd1a mutant and wild-type under these conditions. Seed from the primary stressed plants and controls, both mutant and wild-type, has been harvested in order to test the effects of the same stresses on the progeny.
Heat, cold and high salt treatments were used to analyze the effects of stress on global small RNA levels. Stress treatments have been performed on the nrpd1a mutant and relevant wild-type seedlings. Shoot tissue from stressed and control plants were harvested and small RNA libraries were sequenced. Bioinformatic analysis (in collaboration with Tom Hardcastle) was undertaken to determine differentially expressed sRNAs in the different samples. Very few sRNAs were differentially expressed in response to high salt conditions (approximately 3%); it is likely that this result is due to the stress treatment and not to do with the construction and analysis of the sRNA cDNA libraries. In contrast, 34% of sRNA loci were differentially expressed in response to high temperature. Of the loci that were differentially expressed, 80% were up-regulated. The majority of the up-regulated genes were 24-nucleotide in length suggesting novel epigenetic marks could be established in response to heat. However, the majority of these differentially expressed loci have similar sRNA profiles to those of floral tissue and DNA methylation is associated with these sRNA populations. Molecular analysis of the heat stressed plants have shown that known markers for the transition from vegetative to reproductive phase where up-regulated in response to high temperature suggesting that the induced 24-nucleotide sRNAs are a result of this transition. A second round of bioinformatic analysis focussed on comparing differentially expressed sRNA loci in control, heat and floral samples. The analysis identified 21-nucleotide sRNAs that were induced in response to high temperature. Specifically, a set of sRNAs that map to VANDAL6 transposable elements were induced by heat and they persist following recovery after the stress. The VANDAL6 transposable elements are of the DNA/MuDR subfamily class and their transcription was also induced in response to heat stress. The 21-nucleotide sRNAs are likely the product of RNA silencing mechanisms that target the VANDAL6 transposable elements. Preliminary data suggests that the VANDAL6 sRNAs can also target endogenous genes that are repressed in response to high temperatures, suggesting a large heat stress network of gene regulation as a result of VANDAL6 transposable element expression. Current work is focussing on the RNA silencing components required for this response.P6 is also assembling sensor constructs in order to test transcriptional gene silencing and trans-generational inheritance of gene silencing induced by siRNAs. This construct involves a multiple cloning site placed upstream of a minimal 35s promoter driving the expression of the GFP reporter gene. Target regions of small RNAs will then be cloned into the multiple cloning site and the level of GFP expression will be used as an output for this small RNA target region – do small RNAs target genomic region in the reporter construct and cause stable silencing of GFP in progeny? The use of the sensor construct will allow us to detect low frequency events.
Initial constructs have been made that include cDNA fragments from the Tobacco Rattle Virus (TRV) genome. These constructs have been transformed into Arabidopsis and, once homozygous lines have been identified, they will be infected with TRV. Infections of wild-type Arabidopsis with TRV have been performed and optimised. that can direct heritable epigenetic modifications at an endogenous locus. Tobacco Rattle Virus (TRV) Virus Induced Gene Silencing (VIGS) has been used to target promoter regions of endogenous genes for silencing. No silencing of adjacent genes has been observed when VIGS was employed to target promoter regions that have never experienced silencing or DNA methylation. In contrast, VIGS was successful when the promoter of FWA was targeted in an FWA epi-mutant line. In wild-type plants, the promoter region of FWA is heavily methylated which causes the gene to be in a repressed state and as a result Arabidopsis wild-type (Col-0) plants flower early. In the FWA epi-mutant, methylation is lost at the FWA promoter which releases the repression of FWA so these plants flower late. TRV VIGS constructs containing a portion of the FWA promoter was successful in inducing methylation at the FWA promoter. This increase in methylation did not occur in the infected plants but in the progeny of plants that exhibit high levels of viral sRNAs as a result of the viral infection. The increase in methylation at the FWA promoter in the progeny plant causes an early flowering, wild-type phenotype. Various RNA silencing mutations were crossed into the FWA epi-mutant background in order to determine the factors required to establish DNA methylation.
An additional system to study the establishment DNA methylation was set-up using inverted repeat transgene constructs. The targets of these constructs were two novel epialleles in Arabidopsis: RITA and MRD1, two loci that exist in differentially methylated states within different inbred populations of Arabidopsis. Both of these loci comprise of two divergent transcripts that overlap at their 5’ regions – one is a protein coding RNA and the other is a proposed non-coding RNA. Where the two transcripts overlap is the site of the differential methylation – if the overlap region is methylated both transcripts are repressed, if the overlap region is unmethlyated both transcripts are expressed. In order to determine the factors required to establish DNA methylation at these loci, inverted repeat transgenes that target the overlap regions at RITA and MRD1 were transformed into various RNA silencing mutants where RITA and/or MRD1 exist in an unmethylated state.
Establishment of DNA methylation at the different endogenous loci, using VIGS or the inverted repeat transgene, required Pol V and the de novo methyltransferase gene DRM2. However, other components of the canonical RdDM pathway were not required. Surprisingly this included DCL3, the DICER-like enzyme responsible for the production of 24-nucleotide sRNAs from double stranded RNA precursors. This result suggested that other size classes of RNAs could be responsible for the establishment of DNA methylation at target loci. In support of this hypothesis, 21-nucleotide primary sRNAs are produced from the inverted repeat transgene and 21-nucleotide secondary sRNAs from the target loci (RITA or MRD1) in a dcl3 mutant. In addition, 21-nucleotide sRNAs are produced as a result of viral infection in the VIGS experiments that target the FWA epimutant. Current work is focussing on other RNA silencing factors, such as those involved in the trans-acting sRNA pathway, and their role in the establishment of DNA methylation.
These results have led us to produce a new working model for the establishment of DNA methylation at endogenous loci.
When sRNAs complementary to a target are supplied from an exogenous source (VIGS or an inverted repeat), the primary phase involves 21-nucleotide sRNAs that act to prime amplification of sRNAs at a target locus (a trans-acting like pathway). In order to establish methylation Pol V is required suggesting a Pol V transcript must be present at the target. The amplified 21-nucleotide sRNAs can bind to the complementary Pol V transcript which will recruit the de novo methyltransferase to methylate DNA at the target region. This will then recruit the canonical RdDM components to the locus (perhaps because Pol IV prefers methylated DNA as a template), which will lead to the production of 24-nucleotide sRNAs at the target. Maintenance of DNA methylation at target regions will depend on the context of methylation – symmetric methylation will be maintained independent of sRNAs whereas maintenance of symmetric methylation will depend on 24-nucleotide sRNAs. Final experiments for this project are being conducted to further support this model.
Task 3: Discovery of epigenetic mechanisms involved in stress mediated modulations of the CpG methylation pathway (Lead participant P4 other participants: P5 – P6– P7)
Background: Recently, P4 has established particular environmental “shock” conditions that release silencing of “constitutively” silent CpG methylated heterochromatic loci.
P4 described an experimental system designed to test the influence of various environmental challenges on transcriptional suppression in Arabidopsis heterochromatin. The system exploits the well-documented observation that multicopy transgenic inserts tend to acquire properties and epigenetic marks characteristic of constitutive heterochromatin. Such silent transgenic loci can be activated in mutants affecting epigenetic regulation of endogenous targets residing in heterochromatin. P4 applied a series of abiotic stresses to transgenic Arabidopsis plants and used the activation of an originally silent transgenic locus as readout for the destabilization of heterochromatic TGS. This approach allowed the definition of environmental stress conditions that not only destabilize transgene silencing but also result in genomewide
reactivation of endogenous heterochromatic loci. However, silencing release was mostly transient and was rapidly restored upon return to normal growth conditions. This transient activation of heterochromatic transcription occurred genome wide and was not associated with changes in DNA methylation or repressive histone modifications that were examined at a subset of reactivated loci. Intriguingly, mutations in common epigenetic gene silencing regulators, including those involved in de novo DNA methylation or H3K9me, did not prevent rapid resilencing after stress treatments.
M Tittel-Elmer, E Bucher, L Broger, O Mathieu, J Paszkowski and I Vaillant (2010) Stress-Induced Activation of Heterochromatic Transcription. Plos Genetics 6(10): e1001175.
P4 also analyzed the effect on genome destabilization in Arabidopsis seedlings subjected to heat stress and reported that a copia-type retrotransposon named ONSEN (Japanese ‘hot spring’) not only became transcriptionally active but also synthesized extrachromosomal DNA copies. Heat-induced ONSEN accumulation was stimulated in mutants impaired in the biogenesis of small interferingRNAs (siRNAs); however, there was no evidence of transposition occurring in vegetative tissues. After stress, both ONSEN transcripts and extrachromosomal DNAgradually decayed and were no longer detected after 20–30 days. Surprisingly, a high frequency of new ONSEN insertions was observed in the progeny of stressed plants deficient in siRNAs. Insertion patterns revealed that this transgenerational retrotransposition occurred during flower development and before gametogenesis. Therefore in plants with compromised siRNA biogenesis, memory of stress was maintained throughout development, priming ONSEN to transpose during differentiation of generative organs. Retrotransposition was not observed in the progeny of wild-type plants subjected to stress or in non-stressed mutant controls, pointing to a crucial role of the siRNApathway in restricting retrotransposition triggered by environmental stress. Finally, we found that natural and experimentally induced variants in ONSEN insertions confer heat responsiveness to nearby genes, and therefore mobility bursts may generate novel, stress-responsive regulatory gene networks.
H Ito, H Gaubert, E Bucher, M Mirouze, I Vaillant1 & Jerzy Paszkowski (2011) An siRNA pathway prevents transgenerational retrotransposition in plants subjected to stress. Nature 7 (472) 115-9.
P4 screened for mutants able to release gene silencing upon heat shock. As a model system they used a transcriptionally silenced luciferase gene in a mom1 mutant background. They found multiple mutants and selected four, two of which appeared to be ddm1 mutants. Further testing showed that ddm1 and mom1 mutants are sensitive to heat stress on their own, and the ddm1 and ddm1 mom1 double mutants prevent the luciferase gene from getting silenced again. The release of silencing was not associated with major changes in DNA methylation and they hypothesized the effect could act at the nucleosome occupancy level.
This is the current working model of P4 on DDM1 concerning the effect of stress on genome destabilization
P4 is also involved in isolation of retrotransposons activated by stress. To identify the activated transposons they focused on extrachromosomal DNA derived from retrotransposons and developed a SIRT assay (sequence-independent retro-element trapping) that can identify mobilized LTR transposons. They performed studies on both Arabidopsis and maize in collaboration with P2, using the SIRT assay. In Arabidopsis they observed ONSEN and EVD LTR element DNA upon heat stress. In maize (collaboration with P2) they are analyzing sequenced libraries produced from non-stressed and cold-stressed wild-type B73 and rmr6 mutant plants.
P4 also analyzed meiotic recombination in mutant plants with hypomethylated DNA and observed unexpected and counterintuitive effects of DNA methylation losses on cross-overs (CO) distribution. Recombination was further promoted in the hypomethylated chromosome arms while it was inhibited in heterochromatic regions encompassing pericentromeric DNA. Importantly, the total number of COs was not affected, implying that loss of DNA methylation led to a global redistribution of COs along chromosomes. To determine by which mechanisms altered levels of DNA methylation influence recombination—whether directly in cis or indirectly in trans by changing expression of genes encoding recombination components—we analyzed CO distribution in wild-type lines with randomly scattered and well-mapped hypomethylated chromosomal segments. The results of these experiments, supported by expression profiling data, suggest that DNA methylation affects meiotic recombination in cis.
Marie Mirouze, Michal Lieberman-Lazarovich, Riccardo Aversano, Etienne Bucher, Joël Nicolet, Jon Reinders and Jerzy Paszkowski (2012) Loss of DNA methylation affects the recombination landscape in Arabidopsis. PNAS, 2012 vol. 109 (1) 5880-5
Work package 2
Work package number 2 Start date or starting event: Month 1
Work package title Molecular and genetics tools for studies of epigenetic responses to environment in maize
Activity Type1 RTD
Participant number 1 2 3 7 8
Participant short name UNIPD CRAMAC
WP coordinator UNIWA MPG BIO
Objectives:
The main objective of WP2 is to generate the molecular and genetic tools in maize for the exploitation of the epigenetic regulation of gene expression in response to environmental stresses. This WP has three specific objectives:
1. The identification, through genome-wide analysis, of the target sequences (hereinafter named epi-targets) of selected stress and epi-regulator mutants of three key maize environmental epi-regulators homologues of their Arabidopsis counterparts (FVE, PolIVa, and MET1 genes) characterized in WP1. These environmental epi-regulators have already been characterized at a genetic level in maize, showing that they play a crucial role in the three epigenetic pathways investigated in this proposal: the autonomous pathway, the small RNA pathway (sRNA), and CpG methylation (mCpG) pathway.
2. The detailed characterization of the epigenetic and transcriptional profile of a selected number (up to 25) of the maize epi-targets.
3. The phenotypic characterization and identifications of differentially expressed sequences in new and not yet characterized maize mutants, which compromise function of epi-regulators for the three epigenetic pathways mentioned above.
Summary of progress towards objectives:
1. Development of cold, and heat stress protocols in maize and sequencing of mRNA, sRNAs, ChIP and Bisulfite libraries produced to identify maize epitargets. Application of temperature shift, drought and salinity stress protocols to maize B73 and mutants.
3. Characterization of the FVE (nfc102 RNAi and of three nfc102 AS) mutant. Introgression of new 5 maize mutants into B73 and production of new transgenic maize mutants of three pathways.
Task 1: Identification of maize targets of selected stress and environmental epi-regulators Lead participant: P2: other participants: P1, P3, P7)
P3 applied cold and heat stress treatments to B73 maize plants. Young plants (10 – 14 days corresponding at V6 developmental stage) were grown in glasshouse conditions during the day, followed by night time incubation at 4 ˚C for 7 consecutive nights. After a recovery period of 4 days (T4) and 7 days (T7), fresh material samples consisting of the inner growing leaf and the meristem (hereinafter named “meristematic area”: MA), from stressed and control populations were isolated and frozen at -80 ˚C for RNA and DNA preparation.
The RNA extracted from MA was employed by P3 for production and sequencing of small RNA (sRNA) and RNA-seq libraries (with polyadenylated RNA enrichment) using Illumina sequencing machine. UNIWA applied both cold and heat stresses in his lab. Both B73 and mutants from the three epigenetic pathways (rmr6; mop1; fve and dmt1) were grown and stressed at UNIWA; for each time point, five individual plants were pooled for material collection. Plant materials were used for preparing small RNA and DGEx libraries, which were sequenced. P1 received DNA from P3 and developed a protocol for preparing libraries to be employed in BS-seq; the first sample was paired end sequenced by P7. The protocol developed by P7 to prepare BS-seq libraries in Arabidopsis has been adapted by P1 to maize; a main point concerned the bisulphite conversion efficiency and the observation that maize chloroplastic DNA is methylated and cannot be used to evaluate conversion. Subsequently, BS-seq libraries were prepared and analysed by MPG before sequencing and data processing. P2 optimized chromatin preparation using plants grown at UNIWA and ChIP assays from MA and prepared libraries for ChIP-seq, for cold stressed B73 materials. Libraries of chromatin immunoprecipitated with anti-H3K4me3 and with H3K27me3 were sequenced by P7, Depending upon the antibody used for ChIP, the mappable sequenced ranged between 25% and 65%.
P3 data analysis showed that heat seemed to have bigger effects than cold. Furthermore, at early time points after the treatment, compared to control treatment, the changes in transcriptome, small RNAs and DNA methylation (5mC) are larger than at later time points, indicating reversal of stress-induced effects. Upon stress treatment, large amounts of ‘stress unlocked siRNAs (susiRNAs) derived from transposon and other repeat sequences were observed and most of these mapped to the gene-rich regions of the genome. Most of the changes in siRNAs are reset in time; some of them are still present at later time-points after the treatment. Intriguingly, part of the susiRNAs seem to direct de novo 5mC resulting in differentially methylated regions (DMRs). These changes are mostly reset again upon recovery of the temperature stress. It appears that about 10% of the DMRs retain the changed 5mC pattern. Together with the group of Detlef Weigel, they showed that in maize CpG and CHG methylation is mainly present at the centromeric region, while CHH methylation is enriched at the chromosome arms. Heat stress appears to primarily induce changes in 5mC at CHH, not at CG and CHG sites.
Task 2: Detailed molecular characterization of maize epi-targets (Lead participant P1, other participants: P2, P3)
Maize epitargets identification is the results of different stresses application to B73 inbred and selected maize epiregulator mutants followed both by the analyses of transcriptomes using RNA-seq andsmall RNAs-seq and epigenetic marks by ChIP-seq and Bi-seq. Consequently, the characterization of the epitargets has been postponed with respect to the original workplan and was performed during the final part of the project and in many cases is still ongoing. Indeed the number of epitargets that can be identified and characterized , analyzing the genome-wide data produced using the next generation sequencing technology (Illumina) is really high as consequences of the application of hightroughput technology. WP2 maintained the aim reported in Annex Ito produce results that could be then used in WP3 for comparative genomic between Arabidopsis and maize, but the comparison is mainly intended in genome wide terms and considering the emerging differences between the epiregulators function and the epigenetic pathways For this reason, the detailed description of the epi-targets derived both from the genome wide analysis of plants stressed with different treatments and mutants for epiregulators are reported describing the analysis of the data set obtained after stress applications (see the effect of cold and heat stress above and of the salinity stress below).
Task 3: Characterization of new maize mutants for environmental epi-regulators (Lead participantP8: other participants: P1, P2, P3)
P2 characterized the maize (Zea mays) nucleosome remodeling factor complex component101 (nfc101) and nfc102, putative paralogs encoding WD-repeat proteins with homology to plant and mammalian components of various chromatin modifying complexes. They generated transgenic lines with simultaneous nfc101 and nfc102 downregulation and analyzed phenotypic alterations, along with effects on RNA levels, the binding of NFC101/NFC102, and Rpd3-type histone deacetylases (HDACs), and histone modifications at selected targets. Direct NFC101/NFC102 binding and negative correlation with mRNA levels were observed for indeterminate1 (id1) and the florigen Zea mays CENTRORADIALIS8 (ZCN8), key activators of the floral transition. In addition, the abolition of NFC101/NFC102 association with repetitive sequences of different transposable elements (TEs) resulted in tissue-specific upregulation of nonpolyadenylated RNAs produced by these regions. All direct nfc101/nfc102 targets showed histone modification patterns linked to active chromatin in nfc101/nfc102 downregulation lines. However, different mechanisms may be involved because NFC101/NFC102 proteins mediate HDAC recruitment at id1 and TE repeats but not at ZCN8. These results, along with the pleiotropic effects observed in nfc101/nfc102 downregulation lines, suggest that NFC101 and NFC102 are components of distinct chromatin modifying complexes, which operate in different pathways and influence diverse aspects of maize development.
Iride Mascheretti, Raffaella Battaglia, Davide Mainieri, Andrea Altana, Massimiliano Lauria, and Vincenzo Rossi (2013) The WD40-Repeat Proteins NFC101 and NFC102 Regulate Different Aspects of Maize Development through Chromatin Modification. The Plant Cell, Vol. 25: 404–42
In comparison to Arabidopsis only some maize mutants affecting the function of environmental epi-regulators belonging to the autonomous, sRNAs, and mCpG pathways are available for scientific community and have been characterized. In the time course of this project we characterized additional maize mutants for environmental epi-regulators belonging to the three pathways. Lines for five epi-regulators were identified by P8 using MAG. The following mutants were sent to UNIPD for genotyping and introgression in B73 background.
P1 applied the following procedure for introgression in B73 background:
P1 characterized the following mutations:
dmt101 BC2S1 homozygous mutant plants obtained as intermediate checkpoint showed no gene down-regulation so the mutant line was abandoned; ago5 BC3S1 homozygous plants did not survive in greenhouse conditions, however P1 are growing the BC5 plants in the field. fpa BC2S1 homozygous plants showed variation in gene expression and abnormal splicing: P1 is investigating the mutation more deeply while introgression is going on. BC5S1 plants shows the complete silencing of CHR120 gene: no visible phenotype can be observed and the molecular characterization is underway. hda108 BC5S1 homozygous plants show a strong phenotype, with reduction of plant height, leaf blade and seed germination rate: further characterization is in progress.
P8 performed RNAi transgenesis and obtained the following mutants that werephenotypically characterized.
P3 started using the mutants generated by Biogemma to test the effect of the downregulation of epigenetic regulators on the activation of a silenced GFP reporter locus. They did already see reactivation in a number of RNAi lines targeting DRM2, AGO4 and DDM1.
Finally, P8 performed the transcritome analysis of selected lines and the results obtained are summarized in the following table.
The phenotypic characterization and genome-wide identification of target sequences are in progress for selected lines.
Work package 3
Work package number 3 Start date or starting event: Month 18
Work package title Epigenetic responses to environmental signals in maize and comparative genomics with Arabidopsis
Activity Type1 RTD
Participant number 1 2 3 7
Participant short name UNIPD CRAMAC UNIWA
WP coordinator MPG
Objectives:
After the changes agreed by the AENEAS Consortium in the work plan of WP2, the main objective of WP3 is to evaluate the potential of maize epi-regulators for generation and inheritance of newly formed epi-alleles in response to environmental stresses. In particular, WP3 has three specific objectives:
1. To analyze epi-targets behavior under different stress conditions.
2. To analyze the trans-generational inheritance of environmentally induced epialleles
3. To explore possible maize peculiarities in the formation of epialleles in response to environmental stresses
Summary of progress towards objectives:
Different stress protocols were developed and applied to maize plants and mutants in epiregulators and materials collected to analyze the effect of the stresses on previously identified epitargets and to eventually identified new stress-specific epitargets.
Different stress protocols were developed to identify the best combination of stress and epiregulator mutation inducing Transposable Elements (TEs) mobilization.
Seed were collected from B73 plants and rmr6 mutant plants grown under salinity and drought conditions to analyze the transgenerational effects on environmental epi-targets induced by environmental stress in maize.
Task 1: The molecular analysis of maize epi-targets under different environmental stresses
Sub-task 1: Analysis of selected epi-targets (from task 1 – WP2) under different stress conditions.
P1, P2, and P3 collaborate to identify the changes in transcription and epigenetic marks for a selected number of maize epi-targets in response to environmental stresses. These epi-targets were those under identification in WP2 and WP3, as the targets both of selected stresses (cold, heat, drought and salinity stress) and some maize epi-regulators belonging to one of three epi-regulatory pathways: autonomous, sRNA, and mCpG.
Sub-task 2: Development of protocols for different stress treatments in maize
The stress conditions to be applied for analysis of maize epitargets were selected among the most effectives for the induction of trans-generationally stable epigenetic changes in Arabidopsis mutants characterized in WP1. However, stress conditions showing prominent effects in Arabidopsis might be less effective in maize, due to the different genome evolution, structure and organization. Therefore, P1 and P3 have performed preliminary tests to assess the effect of stresses selected in WP1. On the basis of pilot experiments, P1 and P2 have selected different stress conditions (heat-shocks, cold, salinity and drought) which were applied to maize wild-type and mutants affecting the function of the maize homologues of FVE and PolIVa
More in detail, P1 has developed and applied a reproducible protocol of drought and salinity stress in maize. The effect of the application of these stress conditions were monitored using functional markers, some of which indicated by P8 that was agronomically interested on this type of stress. The maize plants (B73 wt and rmr6 mutant) were stressed (drought, salinity and a combination of the two stresses were applied) for 10 days and the plant material (last developed leaf) collected from a pool of four plants. Plant material was also collected after a period of recovery of four days (T4) and seven days (T7) from both B73 and rmr6. Finally, some stressed plants (S0) from both genotypes were self-pollinated and seed (S1) harvested from B73 and rmr6 mutants. Three replicates of the stress experiments were produced in two different years. To analyze the effect of the stress at genome wide level the following sequencings were done: two replicates of RNA-seq (total RNA was previously depleted from rRNA, one replicate was a simple pair-end sequencing while the second a directional one) three replicates of sRNA-seq and ChIP-seq for three histone modifications H3K27me3, H3K9 ac, H3k4me3). The total RNA-Seq strategy was used to analyze the transcriptome of wild type and mutant leaves after ten days of stress application and after 7 day of recovery period. Illumina sequenced reads weremapped to the maize reference genome (B73), to analyze the expression of annotated genes and to create a new annotation of the “stress-specific transcriptome” including TEs and long-non-coding RNAs (lncRNAs). Recent studies showed that many lncRNAs are potent cis- and trans-regulators of gene activity during development and in response to external stimuli and they can function as scaffolds for chromatin-modifying complex. Gene expression analysis revealed the modulation of many stress-related genes and the transcription of thousands of novel loci, many of these are encoding for non-annotated TEs. The characterization of these novel loci is underway and the transcriptomic data is being integrated at genome-wide level with the smallRNA dataset (sRNA-Seq) and with the distribution of chromatin marks exploring the whole epigenomic landscape of stress response and adaptation in maize. Analysis of sRNA sequencing data started from conserved miRNAs: differentially expressed miRNAs were identified employing a generalized linear model: salt and drought treatments caused slight up-regulation of five and one miRNAs, respectively, while the interaction between the two stresses did not provoke any additional effect. We are currently working on putative novel miRNAs identification and on the investigation of the relationship between microRNAs abundances and the expression levels of the corresponding targets, through the comparison with RNA sequencing data produced from the same samples.
Analysis of siRNA population confirmed previous results that siRNAs unique sequences have low expression levels and differ between samples. We are currently comparing siRNA loci abundances among samples, making distinction depending on the kind of genomic feature near to which they align: genes, transposons or other repetitive sequences, whose expression levels will be obtained from RNA sequencing data. The aim is to look for possible significant correlations between the expression levels of siRNA loci and the expression levels of their neighbouring elements.
The results obtained by combining these different approaches aim to identify a robust list of sequences targets of epigenetic regulation (epitargets) that will be further studied and analyzed in the progeny of stressed plants.
Sub-task 3 Epigenetic regulation of stress induced TEs: i) to identify the best combination of stress and epi-regulator mutation inducing TEs mobilization and ii) what are the most sensitive TEs.
P2 in collaboration with P4 investigated the epigenetic control of stress induced maize TEs, in B73, rmr6 (maize NRPD1 homolog) and nfc102 mutants. P2 has selected specific low copies TEs from a maize TE catalogue for B73 line. Plant material harvested after the different stress treatments was used to check for the presence of extrachromosomal DNA (intermediate of retrotrasposition) and analyze up-regulation of RNA transcripts. Materials and information will be shared with P4 and Marie Mirouze (AENEAS associate) to study the epi-genetic control of stress induced transposition in maize. P2 developed temperature stress protocols for maize and studied the occurrence of extrachromosomal DNA (collaboration with P4). They could not detect such DNA in wild type or rmr6 mutant lines in response to stress. They can, however, detect such DNA in other genotypes, but also other developmental stages of the maize plant, suggesting other features than stress are more important for the production of extrachromosomal DNA. To identify activated retrotransposons P2 and P4 used a SIRT assay (sequence-independent retro-element trapping) that can identify mobilized LTR transposons. They performed studies on both Arabidopsis and maize using the SIRT assay. In Arabidopsis they e.g. observed ONSEN and EVD LTR element DNA upon heat stress. For maize (collaboration with P2) they are in the process of analyzing sequenced libraries produced from non-stressed and cold-stressed wild-type B73 and rmr6 mutant plants.
Task 2: Trans-generational effects on environmental epi-targets induced by environmental stress in maize
Different environmental stresses impact greatly on the generation of rapidly-acquired traits in maize via the creation of epialleles. However, it is not yet known whether this epigenetically-acquired information is transmitted to the progenies. To overcome this caveat in our knowledge, we aimed to analyze the impact of environment on the trans-generational inheritance of newly acquired epialleles.
P1 sowed the seed and grown the stressed plant progenies of B73 inbred line. In the next years, these progenies will produce mutation accumulation lines following a single seed descent (SSD) procedure for 5 generations. The sequencing of the lines and their transcriptome and epigenomic analyses will be used to evaluate how much the genetic mutation background is important in determining the epigenetic variation that is to separate the genetic component of variation which induces epigenetic variability from the pure epigenetic components.
To assess the stress-induced epigenetic heritability P3 obtained the progeny of B73 WT, rmr6 mutant and mop1 muatant. In particular P3 analyzed the Inheritance of stress-induced DMRs (Differentially methylated Regions) in the unstressed progenies of stressed plants and obtained a genome-wide hereditability maps of stress-induced DMRs.
Considering the results obtained so far both by different stresses application and response in wt B73 and in mutants of epiregulators and the first evidences on epigenetic heritability of stress response, a working model for epiallele formation by exposure to abiotic stress in maize has been produced.
This model hypothesize that maize mutants impaired in RdDM may be sensitive to stress: further elaboration of dataset from stress applications on mutants such as AGO4 and rmr6 both involved in RdDM pathway will be used to confirm this model.
Work package 4
Work package number 4 Start date or starting event: Month 1
Work package title Genomics and bioinformatics platforms, website
Activity Type1 RTD
Participant number 1 2 3 4 5 6 7
Participant short name
UNIPD
CRAMAC
UNIWA
UNIGE JIC UCAM MPG
WP coordinator
Objectives:
The objective of WP4 is to provide a genomics and bioinformatics platform for the genome-wide analysis of the epigenome carried out in the WP1, WP2, and WP3. The genomics platform is based principally on the next-generation sequencing, and where warranted, tiling microarray analyses. The data generated on these instruments will be analyzed using bioinformatics tool that need to be developed or adapted for AENEAS purposes.
In particular, the specific objectives of WP4 are:
1. The employment of a common pipeline for the bioinformatics analysis of the genome-wide data arising from activities carried out in the others WPs, to present data in a unique and common format.
2. The application of a bioinformatics-based approach for a comparative analysis of the epigenomic environmental changes identified in two evolutionary distinct species such as Arabidopsis and maize, and their mode of inheritance.
3. The constitution and the management of a project database for collecting and for the dissemination of the project’s results.
Summary of progress towards objectives:
1. Development of a common pipeline for the analyses of Arabidopsis tiling arrays in the project.
2. Adoption of GenomeMapper in the context of SHORE for the analyses of bisulfite converted reads. GenomeMapper tools were adopted for mapping of reads from bisulfite converted DNA of Arabidopsis thaliana BS-seq material. Optimization for its application to maize BS-seq material is in progress Maize DNA from ChIP were analyzed by Illumina sequencing and mapped using SHOREpeak.
3. The constitution and the management of a project database for collecting and for dissemination of the project’s results.
Task 1: Adapting SHORE pipeline.
P7 has previously developed a pipeline for analysis of Arabidopsis tiling arrays, both for the detection of expression of annotated genes and of unannotated transcriptionally active regions (TARs). P7 receive RNA extracted from seedlings treated with different stresses from UNIGE, JIC, and UCAM. RNA was converted to tiling array probes and hybridizations carried out. 72 samples were processed during the period. AGRONOMICS1 array platform was used for the experiments in AENEAS.
P7 has developed the SHORE pipeline for mapping of short reads and a graph method, GenomeMapper, for effective mapping of variant sequences (Schneeberger et al., 2009).
Task 2: Develop statistical methods for small RNA and ChIP-seq.
A manuscript in which P7 inferred indirectly patterns of DNA methylation from small RNAs in A. thaliana and its relative A. lyrata has been published: the 24-nt siRNAs were mapped to the A. thaliana and A. lyrata reference genomes by using the SHORE pipeline
Hollister, J., Smith, L. M., Guo, Y.-L. Ott, F., Weigel, D., and Gaut, B. S. (2011) On the role of transposable elements and small RNAs in driving gene expression divergence between Arabidopsis thaliana and Arabidopsis lyrata. Proc. Natl. Acad. Sci. USA 108, 2322-2327.
In the context of AENEAS, P7 has developed a peak finder algorithm that is integrated into SHORE, SHORE peak. P7 has provided proof of concept for the ability of SHORE peak to detect genome-wide binding site of individual transcription factors in ChIP experiments with Arabidopsis. P7 have received from CRAMAC ChIP-seq libraries for two histone modifications (H3K4me3 and H3K27me3) from plants grown at UNIWA. Depending upon the antibody used for ChIP, the mappable sequenced ranged between 25% and 65%. using SHORE peak.
Task 3: Bioinformatics analysis of bisulphite sequencing in maize.
P7 has adopted its GenomeMapper tools for mapping of reads from bisulfite converted DNA in Arabidopsis.
A major question of AENEAS is the transgenerational stability of epigenetic marks. To provide baseline information, MPG has compared genome-wide DNA methylation among 10 Arabidopsis thaliana lines, derived 30 generations ago from a common ancestor. Epimutations at individual positions were easily detected, and close to 30,000 cytosines in each strain were differentially methylated. In contrast, larger regions of contiguous methylation were much more stable, and the frequency of changes was in the same low range as that of DNA mutations. Like individual positions, the same regions were often affected by differential methylation in independent lines, with evidence for recurrent cycles of forward and reverse mutations. Transposable elements and short interfering RNAs have been causally linked to DNA methylation8. In agreement, differentially methylated sites were farther from transposable elements and showed less association with short interfering RNA expression than invariant positions.
C Becker, J Hagmann, J Muller, D Koenig, O Stegle, K Borgwardt & D Weigel (2011) Spontaneous epigenetic variation in the Arabidopsis thaliana methylome. Nature published on line 20 Septmber 2011.
GenomeMapper tools for mapping of reads from bisulfite worked well for A. thaliana BS-seq material, and were optimized to maize BS-seq material in collaboration with P3.
P7 studied the dynamics of the DNA methylome in a natural environment. They focused on Arabidopsis populations from three different regions in the US. Arabidopsis has been introduced into the US relatively recently and these different populations therefore evolved relatively recently, providing an excellent population to study the rate by which epialleles are formed and their stability in a natural environment. The genomic mutation rate and epimutation rate appeared to occur at a similar speed in the wild as in laboratory conditions and also the genomic locations were similar. Furthermore, loci that showed to be hypervariable at the epigenomic level in the lab behaved similar in the wild, undergoing epimutations more often than other regions. A more recent study in the lab of P7 showed that the variation in DNA methylation is more pronounced between different tissues than between control and cold-treated tissues, suggesting that the induction of epigenetic changes by environmental cues may not be as wide-spread as suggested by some published papers.
Potential Impact:
AENEAS Final Report
Description of the potential impact (including the socio-economic impact and the wider societal implications of the project so far) and the main dissemination activities and the exploitation of results.
Impacts
The 20th century has seen a tremendous increase in crop yield, mainly due to changes in the genetic potential of the crop and advances in agricultural practices. Nevertheless, the challenge to feed a rapidly increasing world population, FAO estimated that the future food request will be 80-100% more than current needs by 2050 (FAO, 2009) is formidable, particularly since recent analyses suggest that the rate of increase in yields of several crops may have dropped over the last decade. In this context, it is important to point out that the increasing yield ability for crops obtained in the last century was due primarily to the use of genetic breeding to improve tolerance of abiotic and biotic stresses, coupled with maintenance of ability to maximize yield per plant under non-stressful growth conditions. Since global climate change will lead to more severe fluctuations in climate, exacerbate effects of low water availability, and enhance desertification it is evident that improving the ability of crops to grow in adverse environmental conditions remains a great challenge in the 21th century. Therefore, food security has not only moved to the forefront of agricultural research, but is now perceived as an important topic for more fundamental research (Nature Specials 8 July 2010; Science Special on-line Collection, 12 February 2010). Of particular interest, it is to identify mechanisms able to maintain high yield under not optimal stressing conditions.
Accordingly, the scope of the AENEAS proposal was to explore the environmentally-induced and epigenetically-related variation as a new, until now largely under-estimated, source of variability for crop improvement. In particular, we focused on the exploitation of this source of variability in maize, a crop of high agronomic relevance for Europe (11 Mha of land under maize cultivation) and worldwide (145 Mha).
It is well documented that environmental cues, particularly stresses and shocks, strongly affect gene and genome activity and that this occurs by the modulation of a short-term transient response related to changes in the epigenetic profile of the environmental targets (Lukens and Zhan, 2007). The complex responses of plants to environmental stresses go from stress perception to late acclimation. In both cases a complex network of hormonal and secondary messenger signals induces metabolic alterations aimed at controlling cellular homeostasis. Much molecular information has been produced on the response of plants to stress by analyzing the induction of regulatory and functional sets of genes and their downstream metabolic pathways (Bartels and Sunkar, 2005 Plant Sciences 24: 23-58). Instead, very little is known about the epigenetic events in the perception of stress signals. It is however evident that environment, in addition to inducing genetic variability due to mutation of the DNA nucleotide sequence, also provokes formation of stably inherited epialleles, with relevant effects on the phenotype: the precise mechanisms of the environmentally-induced epiallele formation and their maintenance throughout generations, needs further investigation, particularly for crops. Therefore, the first aim of the proposal was to clarify these phenomena at a mechanistic level in Arabidopsis and to use the combined effects of different epi-regulators and environmental stresses to set up Arabidopsis genetic system/s to generate new epiallelic variants. In parallel, the second aim was to use information from studies in Arabidopsis, together with pre-existing indications for maize suggesting that mechanisms common to Arabidopsis regulate the environmental-related epialleles formations, to constitute a so-called “maize environmental epigenetics” platform. This platform is a collections of tools (epi-regulators, epi-targets, and environmental conditions) that will allow the establishment of maize genetic systems, like those obtained and evaluated for Arabidopsis, which create and explore environmentally-related epigenetic variability for breeding programs.
Therefore, through the above mentioned steps and strategies, the main impacts of this proposal are two and are described below.
1. The first impact has been the increasing of the knowledge of the European scientific community, regarding the mechanisms regulating the environmentally-induced formation and stable inheritance of epialleles in a model plant such as Arabidopsis. Three important issues were faced by the AENEAS Participants working on Arabidopsis: i) Does the environment induce epigenetic changes? ii) if yes, how long do they persist? iii) What are the mechanisms for durable epigenetic changes? The results produced with the aim to answer to these questions are novel and interesting and were published on Scientific Journal of high impact. They mainly clarify the role of the environment in destabilizing the Arabidopsis genome dependently and /or independently by the epigenetic regulators. They also analyze the effects of these genome destabilization both in the parents and their progeny, considering the genome destabilization in the evolutionary context. The comparison of the research results between Arabidopsis and maize enabled analysis of similarities and divergences in environmentally-related epigenetic response that characterize two evolutionary diverse plants (a dicot compared to a monocot), with distinct genome size and organization, mainly due to differences in the number and distribution of repetitive sequences. This comparison was crucial to establish how and to what extent indications from model plants such as Arabidopsis can be applied to crops, which are the real targets for agronomic improvement. During the course of AENEAS it was clear that every protocol, both in the lab and in the greenhouse, needed to be adjusted from Arabidopsis to maize and this was done coupling the results coming from Arabidopsis research and experience developed in the labs working with maize. Many of the facilities available for Arabidopsis proved to be not as useful when developed in maize. Indeed, new specific strategies for maize were planned and developed.
2. The second impact of this proposal is the constitution of a platform that has start to collect maize tools (environmental epi-regulators and epi-targets and most effective environmental treatments with respect to effect on the epigenome) to transfer knowledge from the Arabidopsis model to an important European crop such as maize. This platform represents the starting step towards the generation of genetic systems in maize, which enhance and optimize the formation and the exploitation of the environmental-induced epialleles. The new challenges that starts during AENEAS and needs to be continued for the coming years, by means of the “maize environmental epigenetics” platform, is the translation of knowledge from basic research into novel strategies/methodologies to improve plant yield production and stability in adverse environmental conditions. A series of stress protocols and bioinformatics’ tools specific for maize and new mutants for epiregulators were produced in the course of the project. These materials were used to begin to analyze the epigenetic pathways that are responsible for the formation of epiallels in maize. The detailed characterization of these epiallels will be a future outcome of the maize platform. Establishing the epi-regulators responsible for modulating trans-generational inheritance of environmentally-induced epiallele formation remains a key goal, as this will help ensure the epigenetic variability vital to future breeding programmes.
Moreover, next-generation sequencing approaches were used for small RNA (sRNA-seq), RNA (RNA-seq) expression analyses, Chromatin Immuno Precipitation (ChIP-seq) and Bisulphite-treated DNA analyses (BS-seq). These approaches have been used on Arabidopsis over the last five years and are now being applied to crops such as rice, maize and tomato. Similarly during AENEAS, bioinformatics tools initially developed for handling Arabidopsis data had to be adjusted for processing maize data and this was not simply a transfer of knowledge. In the last year, AENEAS partners working on maize have been deeply involved in developing suitable tools for application of next-generation sequencing methods and data processing.
In correlation with this objective, several additional impacts of the AENEAS project are expected and are related to the relevance and benefits that maize cultivation has for the European Community. These additional impacts can be grouped into five areas.
• Science, Research, and Technology
The tools within the “maize environmental epigenetics” platform will represent the basis for new technologies and strategies to sustain competitiveness of the European Community in the production of superior maize hybrids, with enhanced agronomic performance when grown in adverse environments. In particular, we investigated the extent of stress-induced epigenetic variation in maize focusing mainly on the effect of transposable elements on epigenetic variation in the flanking regions, i.e. on the obligatory component of epigenetic variation. A future possible application of our platform would be to extend our analysis to estimate the spontaneous epigenetic variation and to distinguish between its obligatory and pure component. The discrimination between obligatory and pure epigenetic variation can be achieved using appropriate genetic materials, where genetic variation is either reduced as much as possible or extremely emphasized. To this end, it is possible to employ materials previously developed by our laboratories. Moreover, the industrial partner participating to the AENEAS Consortium is using the deliverables arising from this project to provide stakeholders with future generation of new hybrids, by using environmental-related epialleles formation as a new source to generate variability. It is already clear that the novel epigenetic mechanisms present in plants – including the various species-specific characteristics – present unique opportunities for research into the development of the crops of the future. However, the extent to which species-specific epigenetic marks are related to differences in genomic organisation, and how they are linked to distinct responses remains to be seen. Nonetheless, the comparisons that AENEAS has made of the behaviour of Arabidopsis and maize epi-targets in response to specific stress treatments will pave the way for further identification of the similarities and differences between two evolutionarily-distinct plant species, eventually allowing us to tailor more robust strains of maize – a vital component of our efforts to ensure adequate food production in the decades to come. It is the partners’ belief that the information and materials generated in this program might become the subject of patent applications. In order to disseminate and to more effectively exploit research results the Consortium of AENEAS will aim to translate results into new products and services. During AENEAS project, means to realise this included academia-industry collaborations. In order to effectively exploiting research results, the Consortium aimed to a proper management of intellectual property through the development of better communication and interaction between both the public and private sector. At academic level knowledge transfer is essential for attracting students, scientists and further research funding. Most AENEAS deliverables are very likely the subject of patent application. Given the presence of a strong industrial partner, P8: Biogemma, the commercial exploitation of the results by the participants is well covered. The presence of Biogemma in the project also guarantees an appropriate exploitation of the results produced in AENEAS.
• Economy and Employment
The relevance of maize to current and future European agriculture and economy is evident. Land under maize cultivation is approximately 142 Mha worldwide and 11 Mha in EC (http://www.fao.org). Simply considering the trends of annual improvement of 1.5 q/ha, reported for this crop (data from USDA), it is expected to increase the economic value of maize production by 24 M Euros/yr: at an economic return of 8-fold to the fund required for delivering on this proposal.
The negative effect of environmental stresses in maize productions is also evident, and encourages the exploitation of new strategies to improve yield stability in adverse environmental conditions. This negative effect occurs not only in countries located in the arid regions of the south of the world, but also in the territory of the EC. For example, data from USDA estimated that in 2005/06 the corn production in the European Community was of 46.9 million tons, down 6.4 million from previous year; USDA also identified a severe drought as the major factor affecting the corn production (http://www.fas.usda.gov/pecad/highlights/2005/12/europe_21dec2005/). Even more dramatic was the situation during the extreme dry and hot weather in 2003, which provoked a reduction of 8% of corn production in Central Europe (http://www.fas.usda.gov/pecad2/highlights/2003/08/Central_Europe/index.htm).
Finally, the effect of improving maize production and stability has also a relevant impact on the creation of job opportunities. Studies (Corn Refiners Association, a US based organization) indicate that if the European Community imported just 10% less maize based, finished agricultural products, then it could create 50,000 new jobs, increase personal income by more than 1 billion Euros, and increase gross output by an additional 2.5 billion Euros. Furthermore, the patenting of new tools, genes, and innovation in gene technologies will not only permit an increase of the community’s gross product, but also the creation of new qualified jobs and the maintenance of employment in a crucial economic area represented by the agribusiness and biotechnology sectors.
• Environment
For a sustainable increase of crop production, European Community must continually strive to efficiently and economically improve production capabilities without harming the environment and without creating an unmanageable surplus. The application of research progresses from the AENEAS project could hold the key to achieving this goal. Indeed, the future generation of maize genetic systems starting by the tools developed by this initiative is expected to improve maize production when plants are grown under stress conditions, reducing water consume and chemicals applications to the benefit of the environment.
• Energy
Achieving the European Community target of a 25% share of renewable energies in total energy consumption by 2030 will require a substantial raise in the use of biomasses. As one of the major crops, maize offer promises in this regard, for its productivity. Compared to other crops with bio-fuel potential, maize can provide both starch (seed) and cellulosic (stover) material for bioethanol production. In addition, maize is also seen as the most promising model plants to apply genomic approaches with the aim to better understand the mechanisms of cellulose formation and degradation: the main obstacle to improve utilization of whole plant biomass (Lawrence and Walbot, 2007). Nevertheless, the utilization of crops, including maize, for energy production must deal with its employment for food and feed and requires new advancements in quantitative improving of productivity. As all initiatives expected to improve the development of stress-tolerant maize varieties, representing the main constrain to further improve maize yield (Duvick et al., 1997; Bruce et al., 2002), AENEAS project is, therefore, expected to contribute also in advancement of the maize utilization for energy production.
• Health
In the near future, our ability to modify the crop plants could lead to the development of the much talked about ’nutriceuticals’, which combine the nutrient content of foods with the beneficial effects of pharmaceuticals. Like for energy production, also nutriceutical technologies require advance in yield potential and stability; accordingly, AENEAS initiative is expected to have an impact also in this field.
It is worth noting that the above listed objectives and expected impacts from AENEAS require integration of excellence in competence, technologies, and tools regarding different aspects of plant epigenetics and their application in two different systems such as Arabidopsis and maize. The AENEAS Consortium provided these requirements , thus ensuring the achievement of the listed impacts. Indeed, among the members of AENEAS Consortium there were: i) three Arabidopsis laboratories (P4, P5, P6), which are among the worldwide leaders in the area of plant epigenetics; ii) three maize laboratories (P1, P2, and P3), which are among the few in Europe devoted to studies on maize epigenetics; iii) one participant that coordinated high-throughput and bioinformatics analysis (P7); and iv) one industrial partner (P8). All these laboratories have produced researches related to the effect of environment on the plant epigenome. In addition, they provide complimentary competences, techniques, and tools required for a multidisciplinary investigation of different epigenetic regulatory pathways. It is, therefore, evident the European, trans-national, requirement of the AENEAS initiative, since a similar aggregation of competence, technologies, and tools cannot be obtained at national or local level., One of the outstanding features of AENEAS has been the formation of a consortium in which European groups and leaders in Arabidopsis research were combined with groups working on maize. This combination has allowed a fruitful collaboration, enabling the circulation of ideas between people and driving research in the right direction. In summary, AENEAS has succeeded in its transfer of knowledge from model to crop.
AENEAS proposal took into adequate account similar national and international initiatives and, when possible, a fruitful collaboration activity with such initiatives was established. This was ensured by the participation of many of the members of the AENEAS Consortium to national and European funded projects in the area of plant epigenetics. For example, participants P4 and P6 were member of the Epigenome Network of Excellence (http://www.epigenome-noe.net/) representing the focal point for the European Epigenetics research community. In addition, the participants P5, P6, and P7 were members of the SIROCCO European initiative (http://www.plantsci.cam.ac.uk/sirocco/) for a comprehensive analysis of the small RNA silencing. P1 and P2 are participating in the Italian Flagship Project (www.epigen.it) , in which P1 is coordinating a plant group working on crops. Epigen is also collaborating with the European Initiative Epigenesys (www.epigenesys.eu). The interaction with these initiatives, as well as others where AENEAS members participate, ensured a continuous exchange of information among various programs focused on epigenetics in plants and in other organisms.
In addition, the Advisory Board for the AENEAS project guaranteed contacts and collaborations with other plant epigenetics initiatives, not only from Europe but also from US and China. In this respect, it is important to point out that the AENEAS Consortium has established a link with the USreserchers working on maize in particular Dr. Jay Hollick at Cold Spring Harbor for MTA of rmr6 maize mutant .. Similarly, a crucial part of the research activity carried out in the AENEAS required the information arising from the US initiatives for maize genome sequencing projects (http://www.maizegenome.org). Many of the information from the two US initiatives are publically available; collaborations between AENEAS participants and US laboratories and the participation of P1, P2 and P3 to the “Annual Maize Conference” for dissemination of AENEAS results ensured the full exploitation of maize genomic resources generated from US projects.
Although contacts and collaboration with similar initiatives, focused on the investigation of plant epigenetics, were established, it is noteworthy that this proposal did not duplicate for specificity, integration and type of approach any other work being undertaken by either EU or US based academic scientists. In addition, probably the most relevant and specific characteristic of the AENEAS is that it coupled epigenetics research in two different plant species – Arabidopsis and maize - to transfer knowledge from a model to a crop plant. Together with the US Plant ChromDB initiative (http://www.chromdb.org) this project is the second initiative (the first in absolute for Europe) that will provide tools for crop improvement based on plant epigenetic research. The AENEAS initiative, however, did not overlap Plant ChromDB initiative and represented an advance with respect to the US program, because it focus specifically on the development and detailed characterization of maize tools (epi-regulator mutants and epi-targets) in response to environmental cues.
Dissemination
Several strategies for dissemination of AENEAS results were adopted.
1.The AENEAS web-site
To allow a world-wide and swift diffusion of the results of the project a dedicated Internet site was created and maintained by participant P4 in collaboration with P1. The AENEAS web-site contains: the project's work plan, the description of the participants involved (including links to corporate web-sites) a list of publications and an internal site (restricted to AENEAS Participants) where the results of the Consortium are available in form of presentation to the Project Annual Meetings.
2. Dissemination through the connection with the members of the Advisory Board
- A specific cross-talk was developed between Consortium members and members of the project Advisory Board with the aim of further facilitating exchange of information and possibly of tools and materials between AENEAS and related national and international initiatives, within and outside Europe. The members selected for the AENEAS Advisory Board were :
- Prof. Xiaofeng Cao – Chinese Academy of Science, China (representing plant epigenetics in China: the most populated country of the world, where maize production in adverse environmental conditions is of particular relevance).
- Dr. Alain Charcosset – INRA/INA-PG/UPS/CNRS, Station de Génétique Végétale, France (representing the academic European community of maize breeders).
- Professor Mike Stam University of Amsterdam (representing an European expert in maize molecular epigenetics).
- It is worth mentioning that the Advisory Board also provided a preferential channel to favor contacts and collaborations with others, EC and non-EC, projects related to plant epigenetics and to facilitate dissemination of results and deliverables. The AENEAS Annual Meetings were attended by at least two of the three members of Advisory Board. Unfortunately, AENEAS Consortium could not substitute Jonathan Crouch as CYMMIT representative.
- During the project, AENEAS Consortium agreed the association of Marie Mirouze to AENEAS project. She was a previous member of Jerzy Paszkowski’s lab and is currently Research Scientist in the Plant Epigenetic Regulation Group, IRD (Institute de Recherche pour le Développement, Montpellier, France). It was also agreed that the coordinator covered the costs of her participation to the AENEAS meeting with management fund and she actively participated in AENEAS results dissemination in her research Institute for the last two years of the project, collaborating with the labs working on maize particularly P2.
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- 3. Dissemination through national and international conferences and publication in dissemination journals
- All members of the AENEAS Consortium disseminated project’s results and discussed advances related to this research area by participating to national and international conferences, meetings and workshops. In some International Meetings the Coordinator had the opportunity to illustrate AENEAS Initiative: AENEAS research plan was presented at the XXIth International Congress Eucarpia “Maize and Sorghum Breeding in the Genomics Era, the title was ” AENEAS Consortium The AENEAS European Initiative for environmental epigenetics in arabidopsis and maize, Bergamo (Italy), 21-24 June 2009.
- At the 2nd International Symposium on Genomics of Plant genetic Resources Bologna (Italy): “Understanding epiallels formation and inheritance in response to environmental clues in plants”.
- A further dissemination effort was made by the Coordinator through the publications of three articles in three different years in International Innovation. The International Innovation series are open access publications which means that all content is freely available without charge to the user or institution. Readers are allowed to read, download, copy, distribute, print, search, or link to the full texts of the articles in this publication without asking prior permission from the publisher or the author. In the first article (2010 Food) “Picking apart Epigenetics“ a description and explanation of AENEAS initiative was reported. A second report was published in 2012 in the issue Farm to Fork, where the transfer of knowledge on epigenetics from Arabidopsis to maize was emphasized. Finally, in the third article (2013 Healthy Planet) an update concerning the results obtained in Arabidopsis and the genome-wide approach used in maize by AENEAS consortium was described.
- For six months between 2012 and 2013 a link to AENEAS website was present in http://www.paneuropeannetworks.com and a one page article “AENEAS - From Arabidopsis to maize” was published Pan European Networks Science and Technology in March 2013 issue 06. In this article was reported that project aims at investigating plant environmentally-induced epigenetic changes as the new frontiers of natural and artificial variability.
The AENEAS Consortium participated in European Industrial, Scientific, and Technological Platforms to disseminate results with potential application to the Agro-Tech industry. In particular, the connection with European industries was ensured by the industrial partner within AENEAS which is Biogemma P. This participant has frequent strategic and technical contacts with a number of cereal and vegetable breeding companies. This includes meetings at the management level on strategic, scientific and IP matters. This frequency of project meetings on technical and scientific progress at the research staff level is about 10/year. 2 or 3x a year there are bilateral visits by Biogemma scientists to individual breeding companies to discuss needs and give presentations. Breeding companies reached in this way are RAGT, Euralis, Vilmorin (the world’s fourth largest seed company) and all their associated breeding firms. In addition, P8 is in close contact with the French cereal and protein community via its partner Arvalis and its shareholders Softproteol and Unigrains. Biogemma and its shareholders have contacts with other major seed breeding companies, for example in France via PROMAIS which brings together maize breeders active in France (such as Syngenta, Pioneer, Monsanto and Vilmorin, RAGT and Pau Euralis).
5. Dissemination through publication in scientific journals and meetings with students.
The plan for the dissemination of results included the publication in peer-review journals of the highest quality and impact. The publication of results derived from a collaborative action between the scientists involved in the project, resulting in joint publications. In addition, we also focused on transmitting the excitement of science and knowledge of plant environmental epigenetics to students in Universities and Secondary Schools. In the University laboratories of the Consortium, the project was carried out by post-doctoral associates, PhD students and undergraduate students and thus it provided broad training in epigenetics and genomics within a comparative epigenomic context. In particular, the undergraduate students were drawn from programs which target training. Coordination of the molecular and epigenetic studies provided all participants with experience in cooperative teamwork, time management and interdisciplinary approaches that are essential for current day collaborative research. Furthermore, at University each year students from local high schools perform a short period of research in the lab of participants and have the opportunity to be informed of the new results produced by AENEAS Consortium on epigenetics.
AENEAS annual meeting were attended by many young members of the hosting groups, being an important occasion to establish contacts and collaborations. The following meeting were organized during the project:
• The kick off meeting of AENEAS was held in Cambridge on the 15th of July 2009.
• The first year meeting of AENEAS was held in Cartigny Geneva 2nd and 3rd June 2010; Xiaofeng Cao and Alain Charcosset were present as members of AENEAS Advisory Board.
• The mid-term meeting of AENEAS was held In Tuebingen the 12th and 13th July 2011. At the meeting Xiaofeng Cao and Mike Stam were present as members of AENEAS Advisory Board.
• The third year meeting was held in Norwich on the 26th June 2012. Alain Charcosset and Mike Stam were present as members of AENEAS Advisory Board
• A final international workshop was organized by the Coordinator of AENEAS at University of Padova, Palazzo Bo Aula Nievo on March 11th and 12th. The Final Meeting of AENEAS was a two-day’s meeting; the first day, AENEAS Participants presented the results of their research work. Two members of the Advisory Board were present: Mike Stam (University of Asterdam) and Xiaofeng Cao (Chinese National Academy of Science). The second day, a Workshop on “Plant Environmental Epigenetics” was organized with the following programs:
X. Cao (Chinese Academy of Sciences) “Histone methylation in higher plants”
M. Stam (University of Amsterdam) “Gene regulation by epigenetics and chromosomal interaction: b1 paramutation of maize.”
AENEAS WP1 (Baulcombe, Dean, Paszkowski, Weigel - Arabidopsis) Report
M. Mirouze (ICD Montpellier) “Stress and transposon activation in higher plants”.
M. Morgante (University of Udine) “Transposons and genetic variation in higher plants”.
AENEAS WP2 (Gutierrez-Marcos, Rossi Rouster Varotto - maize) Report
Round Table: A Plant Epigenetic roadmap towards Horizon 2020
The Workshop allowed further dissemination of the project results to a broad audience including representatives from Italian research institutes and academia. About 70 participants attended the workshop, comprising PhD students Post-doc , Researchers and University Professors. The workshop was also the occasion to discuss about plant epigenetics towards Horizons 2020, to identify the main open-questions in plant epigenetics and the transfer of knowledge from model to crops
List of Websites:
http://www.aeneas-a2m.eu/ Participant
number Participant short name Contacts
1 coordinator UNIPD serena.varotto@unipd.it
2 CRAMAC vincenzo.rossi@entecra.it
3 UNIWA J.F.Gutierrez-Marcos@warwick.ac.uk
4 UNIGE Jerzy.Paszkowski@unige.ch
5 JIC Caroline.Dean@bbsrc.ac.uk
6 UCAM dcb40@cam.ac.uk
7 MPG detlef.weigel@tuebingen.mpg.de
8 BIO jacques.rouster@biogemma.com
Interest in plant epigenetics is increasing both as an area of fundamental research and a source of new traits for breeding. DNA methylation, histone modifications and histone variants play a key role in regulating gene expression during the formation of epigenetic gene variants or epialleles, which can be propagated through mitosis and transmitted to the progeny, often remaining stable for several generations. Project AENEAS aimed to assess the impact of environmental conditions on epigenetic states and in the formation of epialles in the model plant Arabidopsis thaliana and then transfer the knowledge to maize (Zea mays) an important European crop.
The first general objective of AENEAS was to provide advances in understanding the detailed mechanisms of epialleles formation in response to environmental cues and their heritable maintenance in the model plant Arabidopsis, for which molecular and genetic tools were already available at the beginning of the project. Concomitantly, the constitution of an “environmental epigenetic platform” for maize has started with the development of tools indispensable for the shift of epigenetic research from Arabidopsis to maize, to achieve the second main objective of AENEAS: the transfer of knowledge from model to maize.
Both Arabidopsis and maize research has been sustained by application of genome wide technologies and bioinformatics analysis. The project focused on three epigenetic regulatory pathway: the autonomous, the small RNA and the CpG methylation pathway. These refer to how epiregulators perceive strong environmental change, by which environmentally-induced epialleles are formed and to what extent and how the newly formed epialleles are inherited trough generations.
Outstanding scientific article on Arabidopsis epigenetics were produced and published during the project aiming at: i) understanding the effect on destabilization of A. thaliana genome induced by environmental constrains; ii) elucidating the role of two RNA binding proteins FCA and FPA in Arabidopsis autonomous pathway; iii) producing a genome wide comparison of DNA methylation among ten A. thaliana lines, derived 30 generations ago from a common ancestors. Moreover, in Arabidopsis a new working model for the establishment of DNA methylation at endogenous loci were developed, characterizing different types of sRNAs and focussing on different RNA silencing factors.
In maize, a dataset on response to various environmental stresses previously tested in Arabidopsis was collected and analysed. Plants from both the B73 maize inbred line and maize mutants of epiregulators of the three epigenetic pathways under investigations in AENEAS were then used for preparing small RNAs , RNAs, ChIP-seq and BS-seq libraries. These were sequenced and the data was analysed in order to investigate, at genome-wide level, the effect of stress application on transcription, gene regulation and some epigenetic marks. Specific maize epitargets were identified and are currently under characterization.
In parallel a series of tools for maize were developed, protocols and mutants for epiregulators, some of which were characterized at molecular level in order to determine whether the three pathways are acting in the same way as in Arabidopsis. Indeed, the results indicated that some epiregulators belonging to these pathways have different targets in the maize genome and newly-produced mutants have been characterized and are now available at the Scientific Community.
It is already clear that the novel epigenetic mechanisms present in plants constitute unique opportunities for research into the development of the crops of the future. However, the extent to which species specific epigenetic marks are related to difference in genomic organization, and how they are linked to distinct responses remains to be seen. The comparison that AENEAS has made of the behaviour of Arabidopsis and maize epitargets in response to specific stress treatments will pave the way for further identifications of the similarities and differences between two evolutionarily distinct plant species.
AENEAS come to a close in March 2013 and the Final Meeting was held in Padova, where novel and important evidences produced during the project were discussed in view of new researches towards Horizon 2020.
Project Context and Objectives:
The project entitled AENEAS (Acquired Environmental Epigenetics Advances: from Arabidopsis to maize) aimed to investigate environmentally-induced epigenetic changes as the “new frontier” of natural and artificial variability. Epigenetics is defined as the study of heritable traits that are not encoded in the primary sequence of DNA and epigenetic mechanisms act through DNA and chromatin modifications. Environmental cues are thought to activate specific epigenetic mechanisms, which add epigenetic marks and in consequence alter spatial and temporal patterns of gene expression, destabilizes the plant genome and cause phenotypic changes that may be transmitted to the progeny, sometimes remaining stable for several generations.
The first general objective of AENEAS was to provide advances in understanding the detailed mechanisms of epiallele formation in response to environmental cues and their heritable maintenance in the model plant Arabidopsis. To this end, the project focuses on three epigenetic regulatory pathways, which have been well characterized for their interaction with environmental signals in mediating changes into the epigenome. They are the autonomous, the small RNA and the CpG methylation pathways. Cytosine methylation is one of the best characterised epigenetic mechanisms. Methylation occurs in CpG sequence context (mCpG) both in higher plants and animals, but plants differ from animals by significant levels of methylation at symmetric CpNpG (where N can be any nucleotide) and asymmetric CpHpH (where H is an A, C or T) sites. Two essential roles have been ascribed to DNA methylation: defending the genome against transposons and regulating gene expression. There is good evidence that siRNAs, which are generated by the sRNA pathway, can provide sequence specificity to guide cytosine methylation as well as other types of epigenetic modifications. In the Arabidopsis genome, there are thousands of loci for production of endogenous small RNAs that, in turn, can epigenetically modify the loci of origin. The epigenetic modifications involve DNA methylation, chromatin silencing or both. The autonomous pathway represents a good example of an interaction between environmental cues and the plant epigenome. This pathway was initially characterised because it regulates the switch from vegetative to reproductive development in Arabidopsis. However, more recent advances indicate that this pathway plays important, genome-wide roles and, in several cases, its function overlaps with other pathways mediating chromatin regulation.
Indeed, several bodies of evidence indicate that these three epigenetic regulatory pathways play a pivotal role in mediating epigenomic change in response to environmental cues. A large part of the information on the environmental-related epialleles formations is arising from studies carried out on the Arabidopsis model plant. In this model, it is well-documented that environmental cues, particularly stresses and shocks, strongly affect gene and genome activity. It is also evident that the environment, in addition to inducing genetic variability due to mutation of the DNA nucleotide sequence, also induces formation of stably inherited epialleles with relevant effects on the phenotype. Importantly, more preliminary results indicate that their function is also conserved in maize.
On the initial bases described above, AENEAS research activity has led to the generation of a genetic system(s) responding to a set(s) of environmental conditions, which affect the epigenome to favor adaptive selection of new epi-variants. This objective has been pursued through activity in work package 1 (WP1). Concomitantly, the constitution of an “Environmental Epigenetic platform” for maize has started with the development of tools indispensable for the shift of epigenetic research from Arabidopsis to maize and this has been directly followed by the second main objective of the AENEAS project: the transfer of knowledge from model plant to maize, an important European crop (WP2 and WP3 activity, respectively). Throughout the achievement of these two general objectives of the AENEAS project, we have started to make available for the scientific community a series of deliverables that can be the “progenitors” for the “next-generation” of breeding programs, based on the exploitation of the environmentally-induced epigenetic variability. For instance, it is thought that the ability to respond to abiotic stresses represents the main constraint on maize production. Thus the future release of maize varieties with high yield and stability will largely depend on the possibility to increase tolerance to environmental stresses. In plant improvement, breeders select for a consistent phenotype that is often conditioned by many genes with incremental effects, rather than single large effect mutations. Therefore, two important questions to address were: how much of this available variation exploited in breeding programs is caused by epigenetic processes, and how it is possible to increase epigenetic diversity from which advances in crop research and development can be drawn.
Furthermore, the main objectives of AENEAS research on Arabidopsis were the characterization of the epigenetic mechanisms involved in mitotically and meiotically heritable changes of epigenetic information in response to environmental cues and the development of reliable assays to efficiently monitor environmentally induced epigenomic alterations in this model plant. Each of the three WP1’s participants (P4, P5, and P6) focused their research activity on three selected pathways and applied different stress treatments, on the basis of their specific expertise and tools. They were interacting by using comparable developmental stages of plants for stress treatment and recovery, as well as comparable strategies for subsequent genomic analyses, which comprise RNA profiling, DNA methylation and siRNAs analyses. The research on Arabidopsis showed that the autonomous pathway has a general role on gene transcription termination and sRNA pathway is involved in controlling both genome stability and abiotic stress response. The next-generation sequencing of Arabidopsis and bioinformatics support for the AENEAS project were guaranteed by activity in WP4 coordinated by P7. P7 has previously developed the SHORE pipeline for mapping of short reads and a graph method, GenomeMapper, for effective mapping of variant sequences and adopted GenomeMapper in the context of SHORE for the analysis of reads that come from bisulfite conversion of Arabidopsis gDNA. P7 has compared genome wide. DNA methylation among 10 A. thaliana lines, derived 30 generations ago from a common ancestor, showing that CpG methylation marks is partially maintained across generations.
A further main objective of AENEAS research was to generate the molecular and genetic tools in a crop, maize, for the exploitation of the epigenetic regulation of gene expression in response to environmental stresses.. The objective of WP2 is to identify maize transcriptomic and epigenomic changes induced by stress treatments and analyze how the above mentioned epi-regulatory pathways (autonomous, small RNA and CpG methylation) will contribute to these changes. To achieve this objective, after preliminary investigations and considering the indications from Arabidopsis that provided some evidences on the effectiveness of specific treatment in the formation of trans-generationally stable epialleles, different stresses were applied to maize B73 and to maize mutants in epi-regulators by P1, P2 and P3. To address the role of stress-induced epigenetic gene and TE regulation P1 has analyzed the salt and drought stresses effects on transcriptional modulation (RNA-seq), transposon activity and on associated smallRNAs (sRNA-seq) and epigenetic marks (ChIP-seq for these histone modifications H3K4me3, H3K9ac and H3K27me3 in collaboration with P2), both in B73 inbred line and the epiregulator mutant rmr6. A collaboration between P3 and P7 was set to identify stress epi-targets, using a genome-wide approach. The meristematic area (MA) from cold and heat stressed and control populations at different time points was collected by P3 to produce Illumina libraries for sequencing: - P3 prepared and sequenced mRNA and small RNA (sRNA) libraries, P7 prepared libraries for BIS-seq form gDNA. In the time course of the project maize mutants for environmental epi-regulators were identified and characterized: insertional lines for five epi-regulators (one mutant for each pathway) were identified by P8 and introgressed by P1 in B73 background. P8 has also produced transgenic mutants of the three epigenetic pathways using a RNAi approach. Finally P2 has has deeply characterized an epiregulator mutant of the autonomous pathway and studied the effect of stress in maize genome destabilization.
While significant leaps in understanding of epigenetic phenomena had been made before AENEAS’ inception in 2009, several key questions remained, and the project has made solid progress towards finding workable answers. For instance, it has helped to clarify the interactions between the environment and epigenetic mechanisms and is already applying knowledge from its basic research to environmentally induced and epigenetic-related sources of variability. At the beginning of the project it was not clear whether different abiotic stresses and treatments cause distinct changes in the epigenome; since then, AENEAS has established protocols for the most effective stress treatments in epiallele formation in Arabidopsis and maize, where a genome-wide evaluation of their effects has produced interesting results.
Despite these successes, it is clear that there will be challenges ahead, as maize exhibits some characteristics not present in Arabidopsis, necessitating further characterizations and the development of unique tools. During the last part of AENEAS, the Consortium had the opportunity to start the comparison between the information produced on the model plant (Arabidopsis) and those coming from the crop (maize). This opened an interesting discussion both from an evolutionary and applicative point of view. The Consortium stressed the importance of crossing the data produced by the participants in order to depict a picture as much complete as possible on epialle formation in maize. A further effort is now needed for understanding the hereditability of epialles in maize, for their future exploitation in breeding programs. AENEAS research into the correlation between environment and epigenetics in maize is relatively young and only few epi-regulatory pathways have been characterised at a functional level, but the project has created a valuable collection of tools and information which together constitute the maize environmental-epigenetics platform.
The objectives of AENEAS WP5, the coordination WP, was to collect and coordinate all the activities related to the management of the project, the dissemination of the results, the staff exchange and the technology transfer among laboratories. P1, the Coordinator, was the responsible for maintaining the contact with the members of AENEAS Advisory Board, which was appositely constituted to guarantee the appropriate execution of the planned work within the project and to further exploit potential impacts from the project, throughout collaborations with non-EC Institutes of excellence. At the end of the project, it was a general opinion that one of the outstanding feature of AENEAS research project was the constitution of a consortium in which European groups, leaders in Arabidopsis research, were combined with groups working on maize. This combination has allowed a very fruitful collaboration making the ideas circulating among the people and driving the research on the right direction: AENEAS succeeded very well in the realization of the idea “ transfer of knowledge from model to crop”.
Project Results:
AENEAS Final Report
Description of the main S & T results/foregrounds
Participant
number Participant short name Beneficiary Name of Principle Investigator
1 coordinator UNIPD Università degli Studi di Padova Serena Varotto
2 CRAMAC CRA Unità di Ricerca per la maiscoltura Vincenzo Rossi
3 UNIWA University of Warwick Josè Gutierrez Marcos
4 UNIGE University of Geneva Jerzy Paszkowski
5 JIC John Innes Centre Caroline Dean
6 UCAM University of Cambridge David Baulcombe
7 MPG Max Planck Institute Tubingen Detlef Weigel
8 BIO BIOGEMMA Jacques Rouster
Work package 1
Work package number 1 Start date or starting event: Month 1
Work package title Epigenetic responses to environmental signals in Arabidopsis
Activity Type1 RTD
Participant number 4 5 6 7
Participant short name UNIGE
WP coordinator JIC UCAM MPG
General Objectives:
The objectives of WP1 are the characterization of epigenetic mechanisms involved in mitotically and meiotically heritable changes of epigenetic information in response to environmental and development of reliable assays to efficiently monitor environmentally induced epigenomic alterations.
Specific objectives of WP1 for the period are:
1. To characterize the global transcript changes in mutants affected in the autonomous, small RNA (sRNA) and CG methylation (mCpG) pathways – aiming to determine chromosomal targets affected by each of the pathways and thus the extent of their overlap. For certain mutants such as met1, and fca/fpa these data are available already, thus can be used directly for the comparative analysis.
2. To characterize the changes in RNA processing and in populations of small RNAs due to the deficiencies in each of the above mentioned pathways, allowing the overlaps between the pathways to be described in terms of RNA metabolism and RNA directed regulation. For certain mutants such as fca/fpa and nrpd1a small scale analysis have been completed and these data can be used directly for the comparative analysis.
3. To characterize genomic DNA methylation, chromatin properties and possibly direct targets of selected components of each of the pathways. For certain mutants (met1 at a genome-wide level and fca/fpa on a small number of selected targets) these data are available already, thus can be used directly in the comparative analysis.
4. To examine the influence of environmental cues/stresses/shocks of progressive severity on chromosomal targets regulated by a specific pathway, and targets controlled by multiple pathways (selected from objectives 1, 2 and 3). We aim to establish the most effective stress condition influencing each of the studied pathways (or several of them simultaneously). Plant material subjected to specific environmental triggers will be reassessed for genome-wide transcriptional responses, DNA methylation and chromatin analyses.
Summary of progress towards objectives:
1. Utilization of Affymetrix Whole Genome Tiling Array to investigate the genome-wide mis-expression profiles of the autonomous, mCpG and RNAi pathways. Comparative analysis of genome-wide differential expression profiles of mutants of the autonomous pathways (fcafpa double mutants), RNAi mutants ( dcl1, dcl23, hyl1, serrate and rdr6) and previously published data of the Arabidipsis DNA methylation mutants (drm1-1drm2-2cmt3-11ddc triple mutant).
2. Analyses of small RNA profiles in Arabidopsis wt and fcafpa double mutants (autonomous pathway) after cold stress application and comparison with previously published ddm1 mutant (mCpG pathway).
3. Studies on the destabilization of transcriptional gene silencing (TGS) in wt Arabidopsis and in mutants compromised in mCpG and siRNA pathways.
4. Development of a variety of different stress assays (high temperature, low temperature, high salt, osmotic stress, drought, Cu++, Cd++) to determine the effect of stress on Arabidopsis seed germination and seedling growth. The nrpd1a mutant and the respective wild-type were compared in these assays.
Task 1 Discovery of epigenetic mechanisms involved in stress mediated modulations of the autonomous pathway (P5 Lead participant; other participants P4– P6– P7)
Background:
FCA and FPA have been identified as RNA binding proteins that have important roles in vegetative to floral transition in Arabidopsis thaliana. It has been previously shown that FCA and FPA have widespread roles in silencing transgenes and transposons as well as single copy genes.
Sub-task 11 and 1.2: Transcriptome regulation by autonomous pathway and validation of the transcriptome data.
In order to investigate the extent of FCA and FPA targets in the Arabidopsis genome, P5 employed the Affymetrix Whole Genome Tiling Array Chip in collaboration with P7. Genome-wide transcript levels of Arabidopsis thaliana Columbia (Col-0) accession were compared to fcafpa double mutant seedlings from 7 and 17-day old plants, respectively. The results indicate a developmental difference in number of targets misregulated at two different time points. Performed analysis revealed that FCA and FPA have genome-wide targets not restricted to a certain class of genes or transcripts that belong to a single pathway/process. A number of upregulated segments from the fcafpa microarray analysis were selected for further verification.
Initially, P5 focused on unannotated segments that were novel transcripts in fcafpa double mutants. P5 selected a number of upregulated segments from the fcafpa microarray analysis for further verification. Out of 82 annotated segments, 27 were tested for verification via one-step RT-PCR and 18 were confirmed (~67%). Of these 18, 15 were further selected for analysis via quantitative RT-PCR. Particularly transcriptional changes were analyzed in the 15 selected targets in fcafpa double as well as fca and fpa single mutants compared to wild type Col-0. FCA and FPA show functional redundancy and they have differential interaction on different loci. P5 analyzed the 15 verified upregulated segments either using RT-PCR followed by sequencing or 5′ and 3′ rapid amplification of cDNA ends (RACE) analysis. This revealed a complex picture, with every misexpressed segment resulting from a slightly different event at each locus. Loss of FCA and FPA led to increased transcript read-through that continued several kilobases downstream to the adjacent gene, i) through an adjacent gene, ii) into an intergenic sequence, iii) into transposon rich regions, iv) or in convergently transcribed genes. Northern analysis of the misexpressed transcripts suggested that loss of FCA and FPA resulted mainly in increased transcriptional read-through. Northern blot also revealed accumulation of high molecular weight transcripts in fpa single and fcafpa double mutants, which was not detected by the RT-PCR or 3′ RACE analyses. In summary, P5 investigations showed that transcriptional read-through, alternative polyadenylation, and alternative splicing result in apparently unannotated genomic segments being misexpressed in the fcafpa double mutant. In some cases, the transcriptional read-through significantly reduced expression of the associated genes. Furthermore FCA/FPA dependent changes in DNA methylation were found at several loci, supporting previous associations of FCA/FPA function with chromatin modifications and suggesting that extensive read-through transcription because of defective 3′ processing is associated with chromatin changes and that FCA and FPA are involved in the interplay of these co-transcriptional mechanisms. Finally, data suggest that FCA and FPA play important roles in the A. thaliana genome in RNA 3′ processing and transcription termination, thus limiting intergenic transcription.
C Sonmez, I Bäurle, A Magusin, R Dreos, S Laubinger, D Weigel and C Dean (2011) RNA 3’ processing functions of Arabidopsis FCA and FPA limit intergenic transcription. PNAS 108 (20): 8508-13
In collaboration with P7, P5 employed the Affymetrix Whole Genome Tiling Array in order to do a comparative analysis of genome-wide differential expression profiles of mutants of the Autonomous pathway (i.e. fcafpa double mutants), RNAi mutants (i.e. dcl1, dcl234, hyl1, serrate and rdr6) and previously published data of the Arabidopsis DNA methylation mutants (drm1-1drm2-2cmt3-11 (ddc) triple mutants) (Kurihara et. al. Biochem Biophys Res Commun 2008 Nov 21;376(3):553-7).
P5 and P7 observed that the percentage of differentially expressed segments is quite similar between Autonomous, RNAi and DNA methylation pathways at 2 weeks. However, only ~9 % of the segments were misregulated in 1-week old fcafpa mutants. These results indicate a developmental bias in differential expression profiles of fcafpa mutants.
Of the total number of misregulated segments in fcafpa mutants, ~27% were in common with the RNAi and DNA methylation mutants irrespective of the time point. At 2-weeks, the autonomous pathway shared ~15 and 12% segments in common with the RNAi and DNA methylation pathways, respectively. When RNAi and DNA methylation pathways are compared alone, the percentage of the segments that were commonly misregulated was ~15%. These results show the extent of commonality between the Autonomous, RNAi and DNA Methylation pathways and suggest a genome-wide role of the autonomous pathway in gene silencing.
The tiling array analysis of the genome-wide targets of FCA and FPA with P7 in wild type Columbia and fcafpa mutants at two different time points identified a series of target sequences that comprised several unannotated segments (UAs). The detailed analysis of these targets showed that upregulation of UA segments/downregulation of genes in fcafpa can partly be explained by a “switch” in polyadenylation site.
The analysis of the antisense transcript of Helitron1 (AT1TE93275) that is upregulated in fcafpa mutants demonstrated a possible overlap of the Autonomous pathway with other silencing pathways, such as the DNA methylation and the sRNA pathway. This last observation was also confirmed by the analysis of several others UAs. Furthermore it was observed that DNA Methylation at the Helitron 1 locus is perturbed in fcafpa double mutant.
To better characterized the fcafpa double mutant In collaboration with P5 , P4 performed RNA-seq using Illumina technology for the genome-wide analysis of cold stress on wild type Col vs fcafpa plants, sequencing both polyA and non-polyA transcripts, strand-specific and both strands.The sequencing was carried out in 2012 and repeated in 2013.
P5 focused the research on the autonomous pathway, analyzing the role of proteins involved in this pathway and the role of antisense RNA production at the FLC locus. The fcafpa mutant was shown to inhibit proper polyadenylation of mRNAs, resulting in transcriptional read-through, longer transcripts and alternative polyA tails. At the FLC locus this means the production of long antisense RNA instead of short antisense - COOLAIR – RNA, hampering the downregulation of FLC expression and thereby flowering. Analyses of polyA and non-poly RNAs showed that in fcafpa mutant, cold treatment can substitute the function of FCA and FPA proteins; cold treatment of wildtype and fcafpa mutant gave rise to similar RNA profiles. The P5 lab also identified a homeodomain protein, AtNDX that represses expression of COOLAIR, delaying flowering. It appears to do so via stabilization of an R-loop at the COOLAIR promoter.
P5 have investigated whether higher-order chromatin structures are involved in the regulation of the Arabidopsis floral repressor gene FLC. They identified a gene loop involving the physical interaction of the 5’ and 3’ flanking regions of the FLC locus using chromosome conformation capture. The FLC loop is unaffected by mutations disrupting conserved chromatin regulatory pathways leading to very different expression states. However, the loop is disrupted during vernalization, the cold-induced, Polycomb-dependent epigenetic silencing of FLC. Loop disruption parallels tim-ing of the cold-induced FLC transcriptional shut-down and upregulation of FLC antisense transcripts, but does not need a cold-induced PHD protein required for the epigenetic silencing.
Pedro Crevillen, Cagla Sonmez, Zhe Wu and Caroline Dean (2013) A gene loop containing the floral repressor FLC is disrupted in the early phase of vernalization. The EMBO Journal (2013) 32, 140–148.
Sub-task 1.4: Transcriptional stress response of the FCA/FPA targets
In collaboration with the P6, P5 has analysed the small RNA profile of Col seedlings before and after 2 weeks cold and fcafpa double mutants. Size-fractionated small RNA from 2 week old seedlings (in the size range 20- 30) were cloned and sequenced using 454 technology. From 208k extractable reads there were 30,332 wt; 128,536 fcafpa; 49,908 2w cold. David Studholme (Sainsbury Laboratory) analyzed the samples and found a similar profile between Col and fcafpa. However, there was a large difference in small RNA size distribution when Col before and after 2 week cold was compared. A more detailed bioinformatic analysis on this dataset was generously performed by Alexis Sarazin in Vincent Colot’s group (IBENS Paris). In the cold-treated sample there was an overabundance of 21nt-long sRNAs (40% of total, 19 422 out of 48 002 sequences) compared 24nt-long sRNAs (10% of total, 11 214 out of 48 002 sequences). The distribution of matching reads was plotted for each chromosome, the density of reads was highest in the centromeric and pericentromeric regions. Those in the euchromatic arms correspond almost exclusively to miRNA sequences. An overrepresentation of the miRNA category in cold-treated seedlings explains most of the 21-mer overabundance observed in the Col0 cold-treated library. Inspection of the 21nt class indicates that most of the increase in miRNA abundance in cold-treated seedlings is due to miR169 or its priMiRNA stem loop (58,6%, or 10363 out of 14364 21nt reads; vs (0.3% or 7 out of 5131 21nt reads in our Col0 library).
In conclusion, the comparisons of genome-wide small RNA profiles in Arabidopsis mutants for autonomous, sRNA and DNA methylation pathways grown under cold stress conditions, showed that cold stress may affect transcriptional read-through, possibly through a different mechanism than fcafpa and other silencing mutants. JIC lab started a collaboration with P7 for RNA-seq of the following materials: Col-0, fcafpa, Col-0 2w cold; fcafpa 2w cold; Ler; fcafpa in Ler.
Task 2 Discovery of epigenetic mechanisms involved in stress mediated modulations of the small RNAs pathway (Lead participant P6; other participants: P4– P5– P7)
A variety of different stress assays (high temperature, low temperature, high salt, osmotic stress, drought, Cu++, Cd++) have been developed to determine the effect of stress on Arabidopsis seed germination and seedling growth. The nrpd1a mutant and the respective wild-type were compared in these assays. No phenotypic variation was observed between the nrpd1a mutant and wild-type under these conditions. Seed from the primary stressed plants and controls, both mutant and wild-type, has been harvested in order to test the effects of the same stresses on the progeny.
Heat, cold and high salt treatments were used to analyze the effects of stress on global small RNA levels. Stress treatments have been performed on the nrpd1a mutant and relevant wild-type seedlings. Shoot tissue from stressed and control plants were harvested and small RNA libraries were sequenced. Bioinformatic analysis (in collaboration with Tom Hardcastle) was undertaken to determine differentially expressed sRNAs in the different samples. Very few sRNAs were differentially expressed in response to high salt conditions (approximately 3%); it is likely that this result is due to the stress treatment and not to do with the construction and analysis of the sRNA cDNA libraries. In contrast, 34% of sRNA loci were differentially expressed in response to high temperature. Of the loci that were differentially expressed, 80% were up-regulated. The majority of the up-regulated genes were 24-nucleotide in length suggesting novel epigenetic marks could be established in response to heat. However, the majority of these differentially expressed loci have similar sRNA profiles to those of floral tissue and DNA methylation is associated with these sRNA populations. Molecular analysis of the heat stressed plants have shown that known markers for the transition from vegetative to reproductive phase where up-regulated in response to high temperature suggesting that the induced 24-nucleotide sRNAs are a result of this transition. A second round of bioinformatic analysis focussed on comparing differentially expressed sRNA loci in control, heat and floral samples. The analysis identified 21-nucleotide sRNAs that were induced in response to high temperature. Specifically, a set of sRNAs that map to VANDAL6 transposable elements were induced by heat and they persist following recovery after the stress. The VANDAL6 transposable elements are of the DNA/MuDR subfamily class and their transcription was also induced in response to heat stress. The 21-nucleotide sRNAs are likely the product of RNA silencing mechanisms that target the VANDAL6 transposable elements. Preliminary data suggests that the VANDAL6 sRNAs can also target endogenous genes that are repressed in response to high temperatures, suggesting a large heat stress network of gene regulation as a result of VANDAL6 transposable element expression. Current work is focussing on the RNA silencing components required for this response.P6 is also assembling sensor constructs in order to test transcriptional gene silencing and trans-generational inheritance of gene silencing induced by siRNAs. This construct involves a multiple cloning site placed upstream of a minimal 35s promoter driving the expression of the GFP reporter gene. Target regions of small RNAs will then be cloned into the multiple cloning site and the level of GFP expression will be used as an output for this small RNA target region – do small RNAs target genomic region in the reporter construct and cause stable silencing of GFP in progeny? The use of the sensor construct will allow us to detect low frequency events.
Initial constructs have been made that include cDNA fragments from the Tobacco Rattle Virus (TRV) genome. These constructs have been transformed into Arabidopsis and, once homozygous lines have been identified, they will be infected with TRV. Infections of wild-type Arabidopsis with TRV have been performed and optimised. that can direct heritable epigenetic modifications at an endogenous locus. Tobacco Rattle Virus (TRV) Virus Induced Gene Silencing (VIGS) has been used to target promoter regions of endogenous genes for silencing. No silencing of adjacent genes has been observed when VIGS was employed to target promoter regions that have never experienced silencing or DNA methylation. In contrast, VIGS was successful when the promoter of FWA was targeted in an FWA epi-mutant line. In wild-type plants, the promoter region of FWA is heavily methylated which causes the gene to be in a repressed state and as a result Arabidopsis wild-type (Col-0) plants flower early. In the FWA epi-mutant, methylation is lost at the FWA promoter which releases the repression of FWA so these plants flower late. TRV VIGS constructs containing a portion of the FWA promoter was successful in inducing methylation at the FWA promoter. This increase in methylation did not occur in the infected plants but in the progeny of plants that exhibit high levels of viral sRNAs as a result of the viral infection. The increase in methylation at the FWA promoter in the progeny plant causes an early flowering, wild-type phenotype. Various RNA silencing mutations were crossed into the FWA epi-mutant background in order to determine the factors required to establish DNA methylation.
An additional system to study the establishment DNA methylation was set-up using inverted repeat transgene constructs. The targets of these constructs were two novel epialleles in Arabidopsis: RITA and MRD1, two loci that exist in differentially methylated states within different inbred populations of Arabidopsis. Both of these loci comprise of two divergent transcripts that overlap at their 5’ regions – one is a protein coding RNA and the other is a proposed non-coding RNA. Where the two transcripts overlap is the site of the differential methylation – if the overlap region is methylated both transcripts are repressed, if the overlap region is unmethlyated both transcripts are expressed. In order to determine the factors required to establish DNA methylation at these loci, inverted repeat transgenes that target the overlap regions at RITA and MRD1 were transformed into various RNA silencing mutants where RITA and/or MRD1 exist in an unmethylated state.
Establishment of DNA methylation at the different endogenous loci, using VIGS or the inverted repeat transgene, required Pol V and the de novo methyltransferase gene DRM2. However, other components of the canonical RdDM pathway were not required. Surprisingly this included DCL3, the DICER-like enzyme responsible for the production of 24-nucleotide sRNAs from double stranded RNA precursors. This result suggested that other size classes of RNAs could be responsible for the establishment of DNA methylation at target loci. In support of this hypothesis, 21-nucleotide primary sRNAs are produced from the inverted repeat transgene and 21-nucleotide secondary sRNAs from the target loci (RITA or MRD1) in a dcl3 mutant. In addition, 21-nucleotide sRNAs are produced as a result of viral infection in the VIGS experiments that target the FWA epimutant. Current work is focussing on other RNA silencing factors, such as those involved in the trans-acting sRNA pathway, and their role in the establishment of DNA methylation.
These results have led us to produce a new working model for the establishment of DNA methylation at endogenous loci.
When sRNAs complementary to a target are supplied from an exogenous source (VIGS or an inverted repeat), the primary phase involves 21-nucleotide sRNAs that act to prime amplification of sRNAs at a target locus (a trans-acting like pathway). In order to establish methylation Pol V is required suggesting a Pol V transcript must be present at the target. The amplified 21-nucleotide sRNAs can bind to the complementary Pol V transcript which will recruit the de novo methyltransferase to methylate DNA at the target region. This will then recruit the canonical RdDM components to the locus (perhaps because Pol IV prefers methylated DNA as a template), which will lead to the production of 24-nucleotide sRNAs at the target. Maintenance of DNA methylation at target regions will depend on the context of methylation – symmetric methylation will be maintained independent of sRNAs whereas maintenance of symmetric methylation will depend on 24-nucleotide sRNAs. Final experiments for this project are being conducted to further support this model.
Task 3: Discovery of epigenetic mechanisms involved in stress mediated modulations of the CpG methylation pathway (Lead participant P4 other participants: P5 – P6– P7)
Background: Recently, P4 has established particular environmental “shock” conditions that release silencing of “constitutively” silent CpG methylated heterochromatic loci.
P4 described an experimental system designed to test the influence of various environmental challenges on transcriptional suppression in Arabidopsis heterochromatin. The system exploits the well-documented observation that multicopy transgenic inserts tend to acquire properties and epigenetic marks characteristic of constitutive heterochromatin. Such silent transgenic loci can be activated in mutants affecting epigenetic regulation of endogenous targets residing in heterochromatin. P4 applied a series of abiotic stresses to transgenic Arabidopsis plants and used the activation of an originally silent transgenic locus as readout for the destabilization of heterochromatic TGS. This approach allowed the definition of environmental stress conditions that not only destabilize transgene silencing but also result in genomewide
reactivation of endogenous heterochromatic loci. However, silencing release was mostly transient and was rapidly restored upon return to normal growth conditions. This transient activation of heterochromatic transcription occurred genome wide and was not associated with changes in DNA methylation or repressive histone modifications that were examined at a subset of reactivated loci. Intriguingly, mutations in common epigenetic gene silencing regulators, including those involved in de novo DNA methylation or H3K9me, did not prevent rapid resilencing after stress treatments.
M Tittel-Elmer, E Bucher, L Broger, O Mathieu, J Paszkowski and I Vaillant (2010) Stress-Induced Activation of Heterochromatic Transcription. Plos Genetics 6(10): e1001175.
P4 also analyzed the effect on genome destabilization in Arabidopsis seedlings subjected to heat stress and reported that a copia-type retrotransposon named ONSEN (Japanese ‘hot spring’) not only became transcriptionally active but also synthesized extrachromosomal DNA copies. Heat-induced ONSEN accumulation was stimulated in mutants impaired in the biogenesis of small interferingRNAs (siRNAs); however, there was no evidence of transposition occurring in vegetative tissues. After stress, both ONSEN transcripts and extrachromosomal DNAgradually decayed and were no longer detected after 20–30 days. Surprisingly, a high frequency of new ONSEN insertions was observed in the progeny of stressed plants deficient in siRNAs. Insertion patterns revealed that this transgenerational retrotransposition occurred during flower development and before gametogenesis. Therefore in plants with compromised siRNA biogenesis, memory of stress was maintained throughout development, priming ONSEN to transpose during differentiation of generative organs. Retrotransposition was not observed in the progeny of wild-type plants subjected to stress or in non-stressed mutant controls, pointing to a crucial role of the siRNApathway in restricting retrotransposition triggered by environmental stress. Finally, we found that natural and experimentally induced variants in ONSEN insertions confer heat responsiveness to nearby genes, and therefore mobility bursts may generate novel, stress-responsive regulatory gene networks.
H Ito, H Gaubert, E Bucher, M Mirouze, I Vaillant1 & Jerzy Paszkowski (2011) An siRNA pathway prevents transgenerational retrotransposition in plants subjected to stress. Nature 7 (472) 115-9.
P4 screened for mutants able to release gene silencing upon heat shock. As a model system they used a transcriptionally silenced luciferase gene in a mom1 mutant background. They found multiple mutants and selected four, two of which appeared to be ddm1 mutants. Further testing showed that ddm1 and mom1 mutants are sensitive to heat stress on their own, and the ddm1 and ddm1 mom1 double mutants prevent the luciferase gene from getting silenced again. The release of silencing was not associated with major changes in DNA methylation and they hypothesized the effect could act at the nucleosome occupancy level.
This is the current working model of P4 on DDM1 concerning the effect of stress on genome destabilization
P4 is also involved in isolation of retrotransposons activated by stress. To identify the activated transposons they focused on extrachromosomal DNA derived from retrotransposons and developed a SIRT assay (sequence-independent retro-element trapping) that can identify mobilized LTR transposons. They performed studies on both Arabidopsis and maize in collaboration with P2, using the SIRT assay. In Arabidopsis they observed ONSEN and EVD LTR element DNA upon heat stress. In maize (collaboration with P2) they are analyzing sequenced libraries produced from non-stressed and cold-stressed wild-type B73 and rmr6 mutant plants.
P4 also analyzed meiotic recombination in mutant plants with hypomethylated DNA and observed unexpected and counterintuitive effects of DNA methylation losses on cross-overs (CO) distribution. Recombination was further promoted in the hypomethylated chromosome arms while it was inhibited in heterochromatic regions encompassing pericentromeric DNA. Importantly, the total number of COs was not affected, implying that loss of DNA methylation led to a global redistribution of COs along chromosomes. To determine by which mechanisms altered levels of DNA methylation influence recombination—whether directly in cis or indirectly in trans by changing expression of genes encoding recombination components—we analyzed CO distribution in wild-type lines with randomly scattered and well-mapped hypomethylated chromosomal segments. The results of these experiments, supported by expression profiling data, suggest that DNA methylation affects meiotic recombination in cis.
Marie Mirouze, Michal Lieberman-Lazarovich, Riccardo Aversano, Etienne Bucher, Joël Nicolet, Jon Reinders and Jerzy Paszkowski (2012) Loss of DNA methylation affects the recombination landscape in Arabidopsis. PNAS, 2012 vol. 109 (1) 5880-5
Work package 2
Work package number 2 Start date or starting event: Month 1
Work package title Molecular and genetics tools for studies of epigenetic responses to environment in maize
Activity Type1 RTD
Participant number 1 2 3 7 8
Participant short name UNIPD CRAMAC
WP coordinator UNIWA MPG BIO
Objectives:
The main objective of WP2 is to generate the molecular and genetic tools in maize for the exploitation of the epigenetic regulation of gene expression in response to environmental stresses. This WP has three specific objectives:
1. The identification, through genome-wide analysis, of the target sequences (hereinafter named epi-targets) of selected stress and epi-regulator mutants of three key maize environmental epi-regulators homologues of their Arabidopsis counterparts (FVE, PolIVa, and MET1 genes) characterized in WP1. These environmental epi-regulators have already been characterized at a genetic level in maize, showing that they play a crucial role in the three epigenetic pathways investigated in this proposal: the autonomous pathway, the small RNA pathway (sRNA), and CpG methylation (mCpG) pathway.
2. The detailed characterization of the epigenetic and transcriptional profile of a selected number (up to 25) of the maize epi-targets.
3. The phenotypic characterization and identifications of differentially expressed sequences in new and not yet characterized maize mutants, which compromise function of epi-regulators for the three epigenetic pathways mentioned above.
Summary of progress towards objectives:
1. Development of cold, and heat stress protocols in maize and sequencing of mRNA, sRNAs, ChIP and Bisulfite libraries produced to identify maize epitargets. Application of temperature shift, drought and salinity stress protocols to maize B73 and mutants.
3. Characterization of the FVE (nfc102 RNAi and of three nfc102 AS) mutant. Introgression of new 5 maize mutants into B73 and production of new transgenic maize mutants of three pathways.
Task 1: Identification of maize targets of selected stress and environmental epi-regulators Lead participant: P2: other participants: P1, P3, P7)
P3 applied cold and heat stress treatments to B73 maize plants. Young plants (10 – 14 days corresponding at V6 developmental stage) were grown in glasshouse conditions during the day, followed by night time incubation at 4 ˚C for 7 consecutive nights. After a recovery period of 4 days (T4) and 7 days (T7), fresh material samples consisting of the inner growing leaf and the meristem (hereinafter named “meristematic area”: MA), from stressed and control populations were isolated and frozen at -80 ˚C for RNA and DNA preparation.
The RNA extracted from MA was employed by P3 for production and sequencing of small RNA (sRNA) and RNA-seq libraries (with polyadenylated RNA enrichment) using Illumina sequencing machine. UNIWA applied both cold and heat stresses in his lab. Both B73 and mutants from the three epigenetic pathways (rmr6; mop1; fve and dmt1) were grown and stressed at UNIWA; for each time point, five individual plants were pooled for material collection. Plant materials were used for preparing small RNA and DGEx libraries, which were sequenced. P1 received DNA from P3 and developed a protocol for preparing libraries to be employed in BS-seq; the first sample was paired end sequenced by P7. The protocol developed by P7 to prepare BS-seq libraries in Arabidopsis has been adapted by P1 to maize; a main point concerned the bisulphite conversion efficiency and the observation that maize chloroplastic DNA is methylated and cannot be used to evaluate conversion. Subsequently, BS-seq libraries were prepared and analysed by MPG before sequencing and data processing. P2 optimized chromatin preparation using plants grown at UNIWA and ChIP assays from MA and prepared libraries for ChIP-seq, for cold stressed B73 materials. Libraries of chromatin immunoprecipitated with anti-H3K4me3 and with H3K27me3 were sequenced by P7, Depending upon the antibody used for ChIP, the mappable sequenced ranged between 25% and 65%.
P3 data analysis showed that heat seemed to have bigger effects than cold. Furthermore, at early time points after the treatment, compared to control treatment, the changes in transcriptome, small RNAs and DNA methylation (5mC) are larger than at later time points, indicating reversal of stress-induced effects. Upon stress treatment, large amounts of ‘stress unlocked siRNAs (susiRNAs) derived from transposon and other repeat sequences were observed and most of these mapped to the gene-rich regions of the genome. Most of the changes in siRNAs are reset in time; some of them are still present at later time-points after the treatment. Intriguingly, part of the susiRNAs seem to direct de novo 5mC resulting in differentially methylated regions (DMRs). These changes are mostly reset again upon recovery of the temperature stress. It appears that about 10% of the DMRs retain the changed 5mC pattern. Together with the group of Detlef Weigel, they showed that in maize CpG and CHG methylation is mainly present at the centromeric region, while CHH methylation is enriched at the chromosome arms. Heat stress appears to primarily induce changes in 5mC at CHH, not at CG and CHG sites.
Task 2: Detailed molecular characterization of maize epi-targets (Lead participant P1, other participants: P2, P3)
Maize epitargets identification is the results of different stresses application to B73 inbred and selected maize epiregulator mutants followed both by the analyses of transcriptomes using RNA-seq andsmall RNAs-seq and epigenetic marks by ChIP-seq and Bi-seq. Consequently, the characterization of the epitargets has been postponed with respect to the original workplan and was performed during the final part of the project and in many cases is still ongoing. Indeed the number of epitargets that can be identified and characterized , analyzing the genome-wide data produced using the next generation sequencing technology (Illumina) is really high as consequences of the application of hightroughput technology. WP2 maintained the aim reported in Annex Ito produce results that could be then used in WP3 for comparative genomic between Arabidopsis and maize, but the comparison is mainly intended in genome wide terms and considering the emerging differences between the epiregulators function and the epigenetic pathways For this reason, the detailed description of the epi-targets derived both from the genome wide analysis of plants stressed with different treatments and mutants for epiregulators are reported describing the analysis of the data set obtained after stress applications (see the effect of cold and heat stress above and of the salinity stress below).
Task 3: Characterization of new maize mutants for environmental epi-regulators (Lead participantP8: other participants: P1, P2, P3)
P2 characterized the maize (Zea mays) nucleosome remodeling factor complex component101 (nfc101) and nfc102, putative paralogs encoding WD-repeat proteins with homology to plant and mammalian components of various chromatin modifying complexes. They generated transgenic lines with simultaneous nfc101 and nfc102 downregulation and analyzed phenotypic alterations, along with effects on RNA levels, the binding of NFC101/NFC102, and Rpd3-type histone deacetylases (HDACs), and histone modifications at selected targets. Direct NFC101/NFC102 binding and negative correlation with mRNA levels were observed for indeterminate1 (id1) and the florigen Zea mays CENTRORADIALIS8 (ZCN8), key activators of the floral transition. In addition, the abolition of NFC101/NFC102 association with repetitive sequences of different transposable elements (TEs) resulted in tissue-specific upregulation of nonpolyadenylated RNAs produced by these regions. All direct nfc101/nfc102 targets showed histone modification patterns linked to active chromatin in nfc101/nfc102 downregulation lines. However, different mechanisms may be involved because NFC101/NFC102 proteins mediate HDAC recruitment at id1 and TE repeats but not at ZCN8. These results, along with the pleiotropic effects observed in nfc101/nfc102 downregulation lines, suggest that NFC101 and NFC102 are components of distinct chromatin modifying complexes, which operate in different pathways and influence diverse aspects of maize development.
Iride Mascheretti, Raffaella Battaglia, Davide Mainieri, Andrea Altana, Massimiliano Lauria, and Vincenzo Rossi (2013) The WD40-Repeat Proteins NFC101 and NFC102 Regulate Different Aspects of Maize Development through Chromatin Modification. The Plant Cell, Vol. 25: 404–42
In comparison to Arabidopsis only some maize mutants affecting the function of environmental epi-regulators belonging to the autonomous, sRNAs, and mCpG pathways are available for scientific community and have been characterized. In the time course of this project we characterized additional maize mutants for environmental epi-regulators belonging to the three pathways. Lines for five epi-regulators were identified by P8 using MAG. The following mutants were sent to UNIPD for genotyping and introgression in B73 background.
P1 applied the following procedure for introgression in B73 background:
P1 characterized the following mutations:
dmt101 BC2S1 homozygous mutant plants obtained as intermediate checkpoint showed no gene down-regulation so the mutant line was abandoned; ago5 BC3S1 homozygous plants did not survive in greenhouse conditions, however P1 are growing the BC5 plants in the field. fpa BC2S1 homozygous plants showed variation in gene expression and abnormal splicing: P1 is investigating the mutation more deeply while introgression is going on. BC5S1 plants shows the complete silencing of CHR120 gene: no visible phenotype can be observed and the molecular characterization is underway. hda108 BC5S1 homozygous plants show a strong phenotype, with reduction of plant height, leaf blade and seed germination rate: further characterization is in progress.
P8 performed RNAi transgenesis and obtained the following mutants that werephenotypically characterized.
P3 started using the mutants generated by Biogemma to test the effect of the downregulation of epigenetic regulators on the activation of a silenced GFP reporter locus. They did already see reactivation in a number of RNAi lines targeting DRM2, AGO4 and DDM1.
Finally, P8 performed the transcritome analysis of selected lines and the results obtained are summarized in the following table.
The phenotypic characterization and genome-wide identification of target sequences are in progress for selected lines.
Work package 3
Work package number 3 Start date or starting event: Month 18
Work package title Epigenetic responses to environmental signals in maize and comparative genomics with Arabidopsis
Activity Type1 RTD
Participant number 1 2 3 7
Participant short name UNIPD CRAMAC UNIWA
WP coordinator MPG
Objectives:
After the changes agreed by the AENEAS Consortium in the work plan of WP2, the main objective of WP3 is to evaluate the potential of maize epi-regulators for generation and inheritance of newly formed epi-alleles in response to environmental stresses. In particular, WP3 has three specific objectives:
1. To analyze epi-targets behavior under different stress conditions.
2. To analyze the trans-generational inheritance of environmentally induced epialleles
3. To explore possible maize peculiarities in the formation of epialleles in response to environmental stresses
Summary of progress towards objectives:
Different stress protocols were developed and applied to maize plants and mutants in epiregulators and materials collected to analyze the effect of the stresses on previously identified epitargets and to eventually identified new stress-specific epitargets.
Different stress protocols were developed to identify the best combination of stress and epiregulator mutation inducing Transposable Elements (TEs) mobilization.
Seed were collected from B73 plants and rmr6 mutant plants grown under salinity and drought conditions to analyze the transgenerational effects on environmental epi-targets induced by environmental stress in maize.
Task 1: The molecular analysis of maize epi-targets under different environmental stresses
Sub-task 1: Analysis of selected epi-targets (from task 1 – WP2) under different stress conditions.
P1, P2, and P3 collaborate to identify the changes in transcription and epigenetic marks for a selected number of maize epi-targets in response to environmental stresses. These epi-targets were those under identification in WP2 and WP3, as the targets both of selected stresses (cold, heat, drought and salinity stress) and some maize epi-regulators belonging to one of three epi-regulatory pathways: autonomous, sRNA, and mCpG.
Sub-task 2: Development of protocols for different stress treatments in maize
The stress conditions to be applied for analysis of maize epitargets were selected among the most effectives for the induction of trans-generationally stable epigenetic changes in Arabidopsis mutants characterized in WP1. However, stress conditions showing prominent effects in Arabidopsis might be less effective in maize, due to the different genome evolution, structure and organization. Therefore, P1 and P3 have performed preliminary tests to assess the effect of stresses selected in WP1. On the basis of pilot experiments, P1 and P2 have selected different stress conditions (heat-shocks, cold, salinity and drought) which were applied to maize wild-type and mutants affecting the function of the maize homologues of FVE and PolIVa
More in detail, P1 has developed and applied a reproducible protocol of drought and salinity stress in maize. The effect of the application of these stress conditions were monitored using functional markers, some of which indicated by P8 that was agronomically interested on this type of stress. The maize plants (B73 wt and rmr6 mutant) were stressed (drought, salinity and a combination of the two stresses were applied) for 10 days and the plant material (last developed leaf) collected from a pool of four plants. Plant material was also collected after a period of recovery of four days (T4) and seven days (T7) from both B73 and rmr6. Finally, some stressed plants (S0) from both genotypes were self-pollinated and seed (S1) harvested from B73 and rmr6 mutants. Three replicates of the stress experiments were produced in two different years. To analyze the effect of the stress at genome wide level the following sequencings were done: two replicates of RNA-seq (total RNA was previously depleted from rRNA, one replicate was a simple pair-end sequencing while the second a directional one) three replicates of sRNA-seq and ChIP-seq for three histone modifications H3K27me3, H3K9 ac, H3k4me3). The total RNA-Seq strategy was used to analyze the transcriptome of wild type and mutant leaves after ten days of stress application and after 7 day of recovery period. Illumina sequenced reads weremapped to the maize reference genome (B73), to analyze the expression of annotated genes and to create a new annotation of the “stress-specific transcriptome” including TEs and long-non-coding RNAs (lncRNAs). Recent studies showed that many lncRNAs are potent cis- and trans-regulators of gene activity during development and in response to external stimuli and they can function as scaffolds for chromatin-modifying complex. Gene expression analysis revealed the modulation of many stress-related genes and the transcription of thousands of novel loci, many of these are encoding for non-annotated TEs. The characterization of these novel loci is underway and the transcriptomic data is being integrated at genome-wide level with the smallRNA dataset (sRNA-Seq) and with the distribution of chromatin marks exploring the whole epigenomic landscape of stress response and adaptation in maize. Analysis of sRNA sequencing data started from conserved miRNAs: differentially expressed miRNAs were identified employing a generalized linear model: salt and drought treatments caused slight up-regulation of five and one miRNAs, respectively, while the interaction between the two stresses did not provoke any additional effect. We are currently working on putative novel miRNAs identification and on the investigation of the relationship between microRNAs abundances and the expression levels of the corresponding targets, through the comparison with RNA sequencing data produced from the same samples.
Analysis of siRNA population confirmed previous results that siRNAs unique sequences have low expression levels and differ between samples. We are currently comparing siRNA loci abundances among samples, making distinction depending on the kind of genomic feature near to which they align: genes, transposons or other repetitive sequences, whose expression levels will be obtained from RNA sequencing data. The aim is to look for possible significant correlations between the expression levels of siRNA loci and the expression levels of their neighbouring elements.
The results obtained by combining these different approaches aim to identify a robust list of sequences targets of epigenetic regulation (epitargets) that will be further studied and analyzed in the progeny of stressed plants.
Sub-task 3 Epigenetic regulation of stress induced TEs: i) to identify the best combination of stress and epi-regulator mutation inducing TEs mobilization and ii) what are the most sensitive TEs.
P2 in collaboration with P4 investigated the epigenetic control of stress induced maize TEs, in B73, rmr6 (maize NRPD1 homolog) and nfc102 mutants. P2 has selected specific low copies TEs from a maize TE catalogue for B73 line. Plant material harvested after the different stress treatments was used to check for the presence of extrachromosomal DNA (intermediate of retrotrasposition) and analyze up-regulation of RNA transcripts. Materials and information will be shared with P4 and Marie Mirouze (AENEAS associate) to study the epi-genetic control of stress induced transposition in maize. P2 developed temperature stress protocols for maize and studied the occurrence of extrachromosomal DNA (collaboration with P4). They could not detect such DNA in wild type or rmr6 mutant lines in response to stress. They can, however, detect such DNA in other genotypes, but also other developmental stages of the maize plant, suggesting other features than stress are more important for the production of extrachromosomal DNA. To identify activated retrotransposons P2 and P4 used a SIRT assay (sequence-independent retro-element trapping) that can identify mobilized LTR transposons. They performed studies on both Arabidopsis and maize using the SIRT assay. In Arabidopsis they e.g. observed ONSEN and EVD LTR element DNA upon heat stress. For maize (collaboration with P2) they are in the process of analyzing sequenced libraries produced from non-stressed and cold-stressed wild-type B73 and rmr6 mutant plants.
Task 2: Trans-generational effects on environmental epi-targets induced by environmental stress in maize
Different environmental stresses impact greatly on the generation of rapidly-acquired traits in maize via the creation of epialleles. However, it is not yet known whether this epigenetically-acquired information is transmitted to the progenies. To overcome this caveat in our knowledge, we aimed to analyze the impact of environment on the trans-generational inheritance of newly acquired epialleles.
P1 sowed the seed and grown the stressed plant progenies of B73 inbred line. In the next years, these progenies will produce mutation accumulation lines following a single seed descent (SSD) procedure for 5 generations. The sequencing of the lines and their transcriptome and epigenomic analyses will be used to evaluate how much the genetic mutation background is important in determining the epigenetic variation that is to separate the genetic component of variation which induces epigenetic variability from the pure epigenetic components.
To assess the stress-induced epigenetic heritability P3 obtained the progeny of B73 WT, rmr6 mutant and mop1 muatant. In particular P3 analyzed the Inheritance of stress-induced DMRs (Differentially methylated Regions) in the unstressed progenies of stressed plants and obtained a genome-wide hereditability maps of stress-induced DMRs.
Considering the results obtained so far both by different stresses application and response in wt B73 and in mutants of epiregulators and the first evidences on epigenetic heritability of stress response, a working model for epiallele formation by exposure to abiotic stress in maize has been produced.
This model hypothesize that maize mutants impaired in RdDM may be sensitive to stress: further elaboration of dataset from stress applications on mutants such as AGO4 and rmr6 both involved in RdDM pathway will be used to confirm this model.
Work package 4
Work package number 4 Start date or starting event: Month 1
Work package title Genomics and bioinformatics platforms, website
Activity Type1 RTD
Participant number 1 2 3 4 5 6 7
Participant short name
UNIPD
CRAMAC
UNIWA
UNIGE JIC UCAM MPG
WP coordinator
Objectives:
The objective of WP4 is to provide a genomics and bioinformatics platform for the genome-wide analysis of the epigenome carried out in the WP1, WP2, and WP3. The genomics platform is based principally on the next-generation sequencing, and where warranted, tiling microarray analyses. The data generated on these instruments will be analyzed using bioinformatics tool that need to be developed or adapted for AENEAS purposes.
In particular, the specific objectives of WP4 are:
1. The employment of a common pipeline for the bioinformatics analysis of the genome-wide data arising from activities carried out in the others WPs, to present data in a unique and common format.
2. The application of a bioinformatics-based approach for a comparative analysis of the epigenomic environmental changes identified in two evolutionary distinct species such as Arabidopsis and maize, and their mode of inheritance.
3. The constitution and the management of a project database for collecting and for the dissemination of the project’s results.
Summary of progress towards objectives:
1. Development of a common pipeline for the analyses of Arabidopsis tiling arrays in the project.
2. Adoption of GenomeMapper in the context of SHORE for the analyses of bisulfite converted reads. GenomeMapper tools were adopted for mapping of reads from bisulfite converted DNA of Arabidopsis thaliana BS-seq material. Optimization for its application to maize BS-seq material is in progress Maize DNA from ChIP were analyzed by Illumina sequencing and mapped using SHOREpeak.
3. The constitution and the management of a project database for collecting and for dissemination of the project’s results.
Task 1: Adapting SHORE pipeline.
P7 has previously developed a pipeline for analysis of Arabidopsis tiling arrays, both for the detection of expression of annotated genes and of unannotated transcriptionally active regions (TARs). P7 receive RNA extracted from seedlings treated with different stresses from UNIGE, JIC, and UCAM. RNA was converted to tiling array probes and hybridizations carried out. 72 samples were processed during the period. AGRONOMICS1 array platform was used for the experiments in AENEAS.
P7 has developed the SHORE pipeline for mapping of short reads and a graph method, GenomeMapper, for effective mapping of variant sequences (Schneeberger et al., 2009).
Task 2: Develop statistical methods for small RNA and ChIP-seq.
A manuscript in which P7 inferred indirectly patterns of DNA methylation from small RNAs in A. thaliana and its relative A. lyrata has been published: the 24-nt siRNAs were mapped to the A. thaliana and A. lyrata reference genomes by using the SHORE pipeline
Hollister, J., Smith, L. M., Guo, Y.-L. Ott, F., Weigel, D., and Gaut, B. S. (2011) On the role of transposable elements and small RNAs in driving gene expression divergence between Arabidopsis thaliana and Arabidopsis lyrata. Proc. Natl. Acad. Sci. USA 108, 2322-2327.
In the context of AENEAS, P7 has developed a peak finder algorithm that is integrated into SHORE, SHORE peak. P7 has provided proof of concept for the ability of SHORE peak to detect genome-wide binding site of individual transcription factors in ChIP experiments with Arabidopsis. P7 have received from CRAMAC ChIP-seq libraries for two histone modifications (H3K4me3 and H3K27me3) from plants grown at UNIWA. Depending upon the antibody used for ChIP, the mappable sequenced ranged between 25% and 65%. using SHORE peak.
Task 3: Bioinformatics analysis of bisulphite sequencing in maize.
P7 has adopted its GenomeMapper tools for mapping of reads from bisulfite converted DNA in Arabidopsis.
A major question of AENEAS is the transgenerational stability of epigenetic marks. To provide baseline information, MPG has compared genome-wide DNA methylation among 10 Arabidopsis thaliana lines, derived 30 generations ago from a common ancestor. Epimutations at individual positions were easily detected, and close to 30,000 cytosines in each strain were differentially methylated. In contrast, larger regions of contiguous methylation were much more stable, and the frequency of changes was in the same low range as that of DNA mutations. Like individual positions, the same regions were often affected by differential methylation in independent lines, with evidence for recurrent cycles of forward and reverse mutations. Transposable elements and short interfering RNAs have been causally linked to DNA methylation8. In agreement, differentially methylated sites were farther from transposable elements and showed less association with short interfering RNA expression than invariant positions.
C Becker, J Hagmann, J Muller, D Koenig, O Stegle, K Borgwardt & D Weigel (2011) Spontaneous epigenetic variation in the Arabidopsis thaliana methylome. Nature published on line 20 Septmber 2011.
GenomeMapper tools for mapping of reads from bisulfite worked well for A. thaliana BS-seq material, and were optimized to maize BS-seq material in collaboration with P3.
P7 studied the dynamics of the DNA methylome in a natural environment. They focused on Arabidopsis populations from three different regions in the US. Arabidopsis has been introduced into the US relatively recently and these different populations therefore evolved relatively recently, providing an excellent population to study the rate by which epialleles are formed and their stability in a natural environment. The genomic mutation rate and epimutation rate appeared to occur at a similar speed in the wild as in laboratory conditions and also the genomic locations were similar. Furthermore, loci that showed to be hypervariable at the epigenomic level in the lab behaved similar in the wild, undergoing epimutations more often than other regions. A more recent study in the lab of P7 showed that the variation in DNA methylation is more pronounced between different tissues than between control and cold-treated tissues, suggesting that the induction of epigenetic changes by environmental cues may not be as wide-spread as suggested by some published papers.
Potential Impact:
AENEAS Final Report
Description of the potential impact (including the socio-economic impact and the wider societal implications of the project so far) and the main dissemination activities and the exploitation of results.
Impacts
The 20th century has seen a tremendous increase in crop yield, mainly due to changes in the genetic potential of the crop and advances in agricultural practices. Nevertheless, the challenge to feed a rapidly increasing world population, FAO estimated that the future food request will be 80-100% more than current needs by 2050 (FAO, 2009) is formidable, particularly since recent analyses suggest that the rate of increase in yields of several crops may have dropped over the last decade. In this context, it is important to point out that the increasing yield ability for crops obtained in the last century was due primarily to the use of genetic breeding to improve tolerance of abiotic and biotic stresses, coupled with maintenance of ability to maximize yield per plant under non-stressful growth conditions. Since global climate change will lead to more severe fluctuations in climate, exacerbate effects of low water availability, and enhance desertification it is evident that improving the ability of crops to grow in adverse environmental conditions remains a great challenge in the 21th century. Therefore, food security has not only moved to the forefront of agricultural research, but is now perceived as an important topic for more fundamental research (Nature Specials 8 July 2010; Science Special on-line Collection, 12 February 2010). Of particular interest, it is to identify mechanisms able to maintain high yield under not optimal stressing conditions.
Accordingly, the scope of the AENEAS proposal was to explore the environmentally-induced and epigenetically-related variation as a new, until now largely under-estimated, source of variability for crop improvement. In particular, we focused on the exploitation of this source of variability in maize, a crop of high agronomic relevance for Europe (11 Mha of land under maize cultivation) and worldwide (145 Mha).
It is well documented that environmental cues, particularly stresses and shocks, strongly affect gene and genome activity and that this occurs by the modulation of a short-term transient response related to changes in the epigenetic profile of the environmental targets (Lukens and Zhan, 2007). The complex responses of plants to environmental stresses go from stress perception to late acclimation. In both cases a complex network of hormonal and secondary messenger signals induces metabolic alterations aimed at controlling cellular homeostasis. Much molecular information has been produced on the response of plants to stress by analyzing the induction of regulatory and functional sets of genes and their downstream metabolic pathways (Bartels and Sunkar, 2005 Plant Sciences 24: 23-58). Instead, very little is known about the epigenetic events in the perception of stress signals. It is however evident that environment, in addition to inducing genetic variability due to mutation of the DNA nucleotide sequence, also provokes formation of stably inherited epialleles, with relevant effects on the phenotype: the precise mechanisms of the environmentally-induced epiallele formation and their maintenance throughout generations, needs further investigation, particularly for crops. Therefore, the first aim of the proposal was to clarify these phenomena at a mechanistic level in Arabidopsis and to use the combined effects of different epi-regulators and environmental stresses to set up Arabidopsis genetic system/s to generate new epiallelic variants. In parallel, the second aim was to use information from studies in Arabidopsis, together with pre-existing indications for maize suggesting that mechanisms common to Arabidopsis regulate the environmental-related epialleles formations, to constitute a so-called “maize environmental epigenetics” platform. This platform is a collections of tools (epi-regulators, epi-targets, and environmental conditions) that will allow the establishment of maize genetic systems, like those obtained and evaluated for Arabidopsis, which create and explore environmentally-related epigenetic variability for breeding programs.
Therefore, through the above mentioned steps and strategies, the main impacts of this proposal are two and are described below.
1. The first impact has been the increasing of the knowledge of the European scientific community, regarding the mechanisms regulating the environmentally-induced formation and stable inheritance of epialleles in a model plant such as Arabidopsis. Three important issues were faced by the AENEAS Participants working on Arabidopsis: i) Does the environment induce epigenetic changes? ii) if yes, how long do they persist? iii) What are the mechanisms for durable epigenetic changes? The results produced with the aim to answer to these questions are novel and interesting and were published on Scientific Journal of high impact. They mainly clarify the role of the environment in destabilizing the Arabidopsis genome dependently and /or independently by the epigenetic regulators. They also analyze the effects of these genome destabilization both in the parents and their progeny, considering the genome destabilization in the evolutionary context. The comparison of the research results between Arabidopsis and maize enabled analysis of similarities and divergences in environmentally-related epigenetic response that characterize two evolutionary diverse plants (a dicot compared to a monocot), with distinct genome size and organization, mainly due to differences in the number and distribution of repetitive sequences. This comparison was crucial to establish how and to what extent indications from model plants such as Arabidopsis can be applied to crops, which are the real targets for agronomic improvement. During the course of AENEAS it was clear that every protocol, both in the lab and in the greenhouse, needed to be adjusted from Arabidopsis to maize and this was done coupling the results coming from Arabidopsis research and experience developed in the labs working with maize. Many of the facilities available for Arabidopsis proved to be not as useful when developed in maize. Indeed, new specific strategies for maize were planned and developed.
2. The second impact of this proposal is the constitution of a platform that has start to collect maize tools (environmental epi-regulators and epi-targets and most effective environmental treatments with respect to effect on the epigenome) to transfer knowledge from the Arabidopsis model to an important European crop such as maize. This platform represents the starting step towards the generation of genetic systems in maize, which enhance and optimize the formation and the exploitation of the environmental-induced epialleles. The new challenges that starts during AENEAS and needs to be continued for the coming years, by means of the “maize environmental epigenetics” platform, is the translation of knowledge from basic research into novel strategies/methodologies to improve plant yield production and stability in adverse environmental conditions. A series of stress protocols and bioinformatics’ tools specific for maize and new mutants for epiregulators were produced in the course of the project. These materials were used to begin to analyze the epigenetic pathways that are responsible for the formation of epiallels in maize. The detailed characterization of these epiallels will be a future outcome of the maize platform. Establishing the epi-regulators responsible for modulating trans-generational inheritance of environmentally-induced epiallele formation remains a key goal, as this will help ensure the epigenetic variability vital to future breeding programmes.
Moreover, next-generation sequencing approaches were used for small RNA (sRNA-seq), RNA (RNA-seq) expression analyses, Chromatin Immuno Precipitation (ChIP-seq) and Bisulphite-treated DNA analyses (BS-seq). These approaches have been used on Arabidopsis over the last five years and are now being applied to crops such as rice, maize and tomato. Similarly during AENEAS, bioinformatics tools initially developed for handling Arabidopsis data had to be adjusted for processing maize data and this was not simply a transfer of knowledge. In the last year, AENEAS partners working on maize have been deeply involved in developing suitable tools for application of next-generation sequencing methods and data processing.
In correlation with this objective, several additional impacts of the AENEAS project are expected and are related to the relevance and benefits that maize cultivation has for the European Community. These additional impacts can be grouped into five areas.
• Science, Research, and Technology
The tools within the “maize environmental epigenetics” platform will represent the basis for new technologies and strategies to sustain competitiveness of the European Community in the production of superior maize hybrids, with enhanced agronomic performance when grown in adverse environments. In particular, we investigated the extent of stress-induced epigenetic variation in maize focusing mainly on the effect of transposable elements on epigenetic variation in the flanking regions, i.e. on the obligatory component of epigenetic variation. A future possible application of our platform would be to extend our analysis to estimate the spontaneous epigenetic variation and to distinguish between its obligatory and pure component. The discrimination between obligatory and pure epigenetic variation can be achieved using appropriate genetic materials, where genetic variation is either reduced as much as possible or extremely emphasized. To this end, it is possible to employ materials previously developed by our laboratories. Moreover, the industrial partner participating to the AENEAS Consortium is using the deliverables arising from this project to provide stakeholders with future generation of new hybrids, by using environmental-related epialleles formation as a new source to generate variability. It is already clear that the novel epigenetic mechanisms present in plants – including the various species-specific characteristics – present unique opportunities for research into the development of the crops of the future. However, the extent to which species-specific epigenetic marks are related to differences in genomic organisation, and how they are linked to distinct responses remains to be seen. Nonetheless, the comparisons that AENEAS has made of the behaviour of Arabidopsis and maize epi-targets in response to specific stress treatments will pave the way for further identification of the similarities and differences between two evolutionarily-distinct plant species, eventually allowing us to tailor more robust strains of maize – a vital component of our efforts to ensure adequate food production in the decades to come. It is the partners’ belief that the information and materials generated in this program might become the subject of patent applications. In order to disseminate and to more effectively exploit research results the Consortium of AENEAS will aim to translate results into new products and services. During AENEAS project, means to realise this included academia-industry collaborations. In order to effectively exploiting research results, the Consortium aimed to a proper management of intellectual property through the development of better communication and interaction between both the public and private sector. At academic level knowledge transfer is essential for attracting students, scientists and further research funding. Most AENEAS deliverables are very likely the subject of patent application. Given the presence of a strong industrial partner, P8: Biogemma, the commercial exploitation of the results by the participants is well covered. The presence of Biogemma in the project also guarantees an appropriate exploitation of the results produced in AENEAS.
• Economy and Employment
The relevance of maize to current and future European agriculture and economy is evident. Land under maize cultivation is approximately 142 Mha worldwide and 11 Mha in EC (http://www.fao.org). Simply considering the trends of annual improvement of 1.5 q/ha, reported for this crop (data from USDA), it is expected to increase the economic value of maize production by 24 M Euros/yr: at an economic return of 8-fold to the fund required for delivering on this proposal.
The negative effect of environmental stresses in maize productions is also evident, and encourages the exploitation of new strategies to improve yield stability in adverse environmental conditions. This negative effect occurs not only in countries located in the arid regions of the south of the world, but also in the territory of the EC. For example, data from USDA estimated that in 2005/06 the corn production in the European Community was of 46.9 million tons, down 6.4 million from previous year; USDA also identified a severe drought as the major factor affecting the corn production (http://www.fas.usda.gov/pecad/highlights/2005/12/europe_21dec2005/). Even more dramatic was the situation during the extreme dry and hot weather in 2003, which provoked a reduction of 8% of corn production in Central Europe (http://www.fas.usda.gov/pecad2/highlights/2003/08/Central_Europe/index.htm).
Finally, the effect of improving maize production and stability has also a relevant impact on the creation of job opportunities. Studies (Corn Refiners Association, a US based organization) indicate that if the European Community imported just 10% less maize based, finished agricultural products, then it could create 50,000 new jobs, increase personal income by more than 1 billion Euros, and increase gross output by an additional 2.5 billion Euros. Furthermore, the patenting of new tools, genes, and innovation in gene technologies will not only permit an increase of the community’s gross product, but also the creation of new qualified jobs and the maintenance of employment in a crucial economic area represented by the agribusiness and biotechnology sectors.
• Environment
For a sustainable increase of crop production, European Community must continually strive to efficiently and economically improve production capabilities without harming the environment and without creating an unmanageable surplus. The application of research progresses from the AENEAS project could hold the key to achieving this goal. Indeed, the future generation of maize genetic systems starting by the tools developed by this initiative is expected to improve maize production when plants are grown under stress conditions, reducing water consume and chemicals applications to the benefit of the environment.
• Energy
Achieving the European Community target of a 25% share of renewable energies in total energy consumption by 2030 will require a substantial raise in the use of biomasses. As one of the major crops, maize offer promises in this regard, for its productivity. Compared to other crops with bio-fuel potential, maize can provide both starch (seed) and cellulosic (stover) material for bioethanol production. In addition, maize is also seen as the most promising model plants to apply genomic approaches with the aim to better understand the mechanisms of cellulose formation and degradation: the main obstacle to improve utilization of whole plant biomass (Lawrence and Walbot, 2007). Nevertheless, the utilization of crops, including maize, for energy production must deal with its employment for food and feed and requires new advancements in quantitative improving of productivity. As all initiatives expected to improve the development of stress-tolerant maize varieties, representing the main constrain to further improve maize yield (Duvick et al., 1997; Bruce et al., 2002), AENEAS project is, therefore, expected to contribute also in advancement of the maize utilization for energy production.
• Health
In the near future, our ability to modify the crop plants could lead to the development of the much talked about ’nutriceuticals’, which combine the nutrient content of foods with the beneficial effects of pharmaceuticals. Like for energy production, also nutriceutical technologies require advance in yield potential and stability; accordingly, AENEAS initiative is expected to have an impact also in this field.
It is worth noting that the above listed objectives and expected impacts from AENEAS require integration of excellence in competence, technologies, and tools regarding different aspects of plant epigenetics and their application in two different systems such as Arabidopsis and maize. The AENEAS Consortium provided these requirements , thus ensuring the achievement of the listed impacts. Indeed, among the members of AENEAS Consortium there were: i) three Arabidopsis laboratories (P4, P5, P6), which are among the worldwide leaders in the area of plant epigenetics; ii) three maize laboratories (P1, P2, and P3), which are among the few in Europe devoted to studies on maize epigenetics; iii) one participant that coordinated high-throughput and bioinformatics analysis (P7); and iv) one industrial partner (P8). All these laboratories have produced researches related to the effect of environment on the plant epigenome. In addition, they provide complimentary competences, techniques, and tools required for a multidisciplinary investigation of different epigenetic regulatory pathways. It is, therefore, evident the European, trans-national, requirement of the AENEAS initiative, since a similar aggregation of competence, technologies, and tools cannot be obtained at national or local level., One of the outstanding features of AENEAS has been the formation of a consortium in which European groups and leaders in Arabidopsis research were combined with groups working on maize. This combination has allowed a fruitful collaboration, enabling the circulation of ideas between people and driving research in the right direction. In summary, AENEAS has succeeded in its transfer of knowledge from model to crop.
AENEAS proposal took into adequate account similar national and international initiatives and, when possible, a fruitful collaboration activity with such initiatives was established. This was ensured by the participation of many of the members of the AENEAS Consortium to national and European funded projects in the area of plant epigenetics. For example, participants P4 and P6 were member of the Epigenome Network of Excellence (http://www.epigenome-noe.net/) representing the focal point for the European Epigenetics research community. In addition, the participants P5, P6, and P7 were members of the SIROCCO European initiative (http://www.plantsci.cam.ac.uk/sirocco/) for a comprehensive analysis of the small RNA silencing. P1 and P2 are participating in the Italian Flagship Project (www.epigen.it) , in which P1 is coordinating a plant group working on crops. Epigen is also collaborating with the European Initiative Epigenesys (www.epigenesys.eu). The interaction with these initiatives, as well as others where AENEAS members participate, ensured a continuous exchange of information among various programs focused on epigenetics in plants and in other organisms.
In addition, the Advisory Board for the AENEAS project guaranteed contacts and collaborations with other plant epigenetics initiatives, not only from Europe but also from US and China. In this respect, it is important to point out that the AENEAS Consortium has established a link with the USreserchers working on maize in particular Dr. Jay Hollick at Cold Spring Harbor for MTA of rmr6 maize mutant .. Similarly, a crucial part of the research activity carried out in the AENEAS required the information arising from the US initiatives for maize genome sequencing projects (http://www.maizegenome.org). Many of the information from the two US initiatives are publically available; collaborations between AENEAS participants and US laboratories and the participation of P1, P2 and P3 to the “Annual Maize Conference” for dissemination of AENEAS results ensured the full exploitation of maize genomic resources generated from US projects.
Although contacts and collaboration with similar initiatives, focused on the investigation of plant epigenetics, were established, it is noteworthy that this proposal did not duplicate for specificity, integration and type of approach any other work being undertaken by either EU or US based academic scientists. In addition, probably the most relevant and specific characteristic of the AENEAS is that it coupled epigenetics research in two different plant species – Arabidopsis and maize - to transfer knowledge from a model to a crop plant. Together with the US Plant ChromDB initiative (http://www.chromdb.org) this project is the second initiative (the first in absolute for Europe) that will provide tools for crop improvement based on plant epigenetic research. The AENEAS initiative, however, did not overlap Plant ChromDB initiative and represented an advance with respect to the US program, because it focus specifically on the development and detailed characterization of maize tools (epi-regulator mutants and epi-targets) in response to environmental cues.
Dissemination
Several strategies for dissemination of AENEAS results were adopted.
1.The AENEAS web-site
To allow a world-wide and swift diffusion of the results of the project a dedicated Internet site was created and maintained by participant P4 in collaboration with P1. The AENEAS web-site contains: the project's work plan, the description of the participants involved (including links to corporate web-sites) a list of publications and an internal site (restricted to AENEAS Participants) where the results of the Consortium are available in form of presentation to the Project Annual Meetings.
2. Dissemination through the connection with the members of the Advisory Board
- A specific cross-talk was developed between Consortium members and members of the project Advisory Board with the aim of further facilitating exchange of information and possibly of tools and materials between AENEAS and related national and international initiatives, within and outside Europe. The members selected for the AENEAS Advisory Board were :
- Prof. Xiaofeng Cao – Chinese Academy of Science, China (representing plant epigenetics in China: the most populated country of the world, where maize production in adverse environmental conditions is of particular relevance).
- Dr. Alain Charcosset – INRA/INA-PG/UPS/CNRS, Station de Génétique Végétale, France (representing the academic European community of maize breeders).
- Professor Mike Stam University of Amsterdam (representing an European expert in maize molecular epigenetics).
- It is worth mentioning that the Advisory Board also provided a preferential channel to favor contacts and collaborations with others, EC and non-EC, projects related to plant epigenetics and to facilitate dissemination of results and deliverables. The AENEAS Annual Meetings were attended by at least two of the three members of Advisory Board. Unfortunately, AENEAS Consortium could not substitute Jonathan Crouch as CYMMIT representative.
- During the project, AENEAS Consortium agreed the association of Marie Mirouze to AENEAS project. She was a previous member of Jerzy Paszkowski’s lab and is currently Research Scientist in the Plant Epigenetic Regulation Group, IRD (Institute de Recherche pour le Développement, Montpellier, France). It was also agreed that the coordinator covered the costs of her participation to the AENEAS meeting with management fund and she actively participated in AENEAS results dissemination in her research Institute for the last two years of the project, collaborating with the labs working on maize particularly P2.
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- 3. Dissemination through national and international conferences and publication in dissemination journals
- All members of the AENEAS Consortium disseminated project’s results and discussed advances related to this research area by participating to national and international conferences, meetings and workshops. In some International Meetings the Coordinator had the opportunity to illustrate AENEAS Initiative: AENEAS research plan was presented at the XXIth International Congress Eucarpia “Maize and Sorghum Breeding in the Genomics Era, the title was ” AENEAS Consortium The AENEAS European Initiative for environmental epigenetics in arabidopsis and maize, Bergamo (Italy), 21-24 June 2009.
- At the 2nd International Symposium on Genomics of Plant genetic Resources Bologna (Italy): “Understanding epiallels formation and inheritance in response to environmental clues in plants”.
- A further dissemination effort was made by the Coordinator through the publications of three articles in three different years in International Innovation. The International Innovation series are open access publications which means that all content is freely available without charge to the user or institution. Readers are allowed to read, download, copy, distribute, print, search, or link to the full texts of the articles in this publication without asking prior permission from the publisher or the author. In the first article (2010 Food) “Picking apart Epigenetics“ a description and explanation of AENEAS initiative was reported. A second report was published in 2012 in the issue Farm to Fork, where the transfer of knowledge on epigenetics from Arabidopsis to maize was emphasized. Finally, in the third article (2013 Healthy Planet) an update concerning the results obtained in Arabidopsis and the genome-wide approach used in maize by AENEAS consortium was described.
- For six months between 2012 and 2013 a link to AENEAS website was present in http://www.paneuropeannetworks.com and a one page article “AENEAS - From Arabidopsis to maize” was published Pan European Networks Science and Technology in March 2013 issue 06. In this article was reported that project aims at investigating plant environmentally-induced epigenetic changes as the new frontiers of natural and artificial variability.
The AENEAS Consortium participated in European Industrial, Scientific, and Technological Platforms to disseminate results with potential application to the Agro-Tech industry. In particular, the connection with European industries was ensured by the industrial partner within AENEAS which is Biogemma P. This participant has frequent strategic and technical contacts with a number of cereal and vegetable breeding companies. This includes meetings at the management level on strategic, scientific and IP matters. This frequency of project meetings on technical and scientific progress at the research staff level is about 10/year. 2 or 3x a year there are bilateral visits by Biogemma scientists to individual breeding companies to discuss needs and give presentations. Breeding companies reached in this way are RAGT, Euralis, Vilmorin (the world’s fourth largest seed company) and all their associated breeding firms. In addition, P8 is in close contact with the French cereal and protein community via its partner Arvalis and its shareholders Softproteol and Unigrains. Biogemma and its shareholders have contacts with other major seed breeding companies, for example in France via PROMAIS which brings together maize breeders active in France (such as Syngenta, Pioneer, Monsanto and Vilmorin, RAGT and Pau Euralis).
5. Dissemination through publication in scientific journals and meetings with students.
The plan for the dissemination of results included the publication in peer-review journals of the highest quality and impact. The publication of results derived from a collaborative action between the scientists involved in the project, resulting in joint publications. In addition, we also focused on transmitting the excitement of science and knowledge of plant environmental epigenetics to students in Universities and Secondary Schools. In the University laboratories of the Consortium, the project was carried out by post-doctoral associates, PhD students and undergraduate students and thus it provided broad training in epigenetics and genomics within a comparative epigenomic context. In particular, the undergraduate students were drawn from programs which target training. Coordination of the molecular and epigenetic studies provided all participants with experience in cooperative teamwork, time management and interdisciplinary approaches that are essential for current day collaborative research. Furthermore, at University each year students from local high schools perform a short period of research in the lab of participants and have the opportunity to be informed of the new results produced by AENEAS Consortium on epigenetics.
AENEAS annual meeting were attended by many young members of the hosting groups, being an important occasion to establish contacts and collaborations. The following meeting were organized during the project:
• The kick off meeting of AENEAS was held in Cambridge on the 15th of July 2009.
• The first year meeting of AENEAS was held in Cartigny Geneva 2nd and 3rd June 2010; Xiaofeng Cao and Alain Charcosset were present as members of AENEAS Advisory Board.
• The mid-term meeting of AENEAS was held In Tuebingen the 12th and 13th July 2011. At the meeting Xiaofeng Cao and Mike Stam were present as members of AENEAS Advisory Board.
• The third year meeting was held in Norwich on the 26th June 2012. Alain Charcosset and Mike Stam were present as members of AENEAS Advisory Board
• A final international workshop was organized by the Coordinator of AENEAS at University of Padova, Palazzo Bo Aula Nievo on March 11th and 12th. The Final Meeting of AENEAS was a two-day’s meeting; the first day, AENEAS Participants presented the results of their research work. Two members of the Advisory Board were present: Mike Stam (University of Asterdam) and Xiaofeng Cao (Chinese National Academy of Science). The second day, a Workshop on “Plant Environmental Epigenetics” was organized with the following programs:
X. Cao (Chinese Academy of Sciences) “Histone methylation in higher plants”
M. Stam (University of Amsterdam) “Gene regulation by epigenetics and chromosomal interaction: b1 paramutation of maize.”
AENEAS WP1 (Baulcombe, Dean, Paszkowski, Weigel - Arabidopsis) Report
M. Mirouze (ICD Montpellier) “Stress and transposon activation in higher plants”.
M. Morgante (University of Udine) “Transposons and genetic variation in higher plants”.
AENEAS WP2 (Gutierrez-Marcos, Rossi Rouster Varotto - maize) Report
Round Table: A Plant Epigenetic roadmap towards Horizon 2020
The Workshop allowed further dissemination of the project results to a broad audience including representatives from Italian research institutes and academia. About 70 participants attended the workshop, comprising PhD students Post-doc , Researchers and University Professors. The workshop was also the occasion to discuss about plant epigenetics towards Horizons 2020, to identify the main open-questions in plant epigenetics and the transfer of knowledge from model to crops
List of Websites:
http://www.aeneas-a2m.eu/ Participant
number Participant short name Contacts
1 coordinator UNIPD serena.varotto@unipd.it
2 CRAMAC vincenzo.rossi@entecra.it
3 UNIWA J.F.Gutierrez-Marcos@warwick.ac.uk
4 UNIGE Jerzy.Paszkowski@unige.ch
5 JIC Caroline.Dean@bbsrc.ac.uk
6 UCAM dcb40@cam.ac.uk
7 MPG detlef.weigel@tuebingen.mpg.de
8 BIO jacques.rouster@biogemma.com
