Community Research and Development Information Service - CORDIS

Periodic Report Summary 1 - POLYMEIO (The Role of ASY1 in Promoting Meiotic Stability in Polyploid Arabidopsis)

Polyploidy is a major contributor to plant evolution but requires meiotic adaptation to be successful. Recently, ASY1 and REC8, two meiotic genes involved in chromosome synapsis and cohesion, were proposed as playing an important role in this “adaptation” of meiosis in autotetraploid Arabidopsis arenosa. In this project, I interrogate the working hypothesis that the tetraploid ASY1/REC8 variant promotes meiotic adaption in autotetraploid A. arenosa through a reduction in cross-over frequency, perhaps mediated through increased cross-over interference strength.

For this, I have begun to:
Aim 1: Compare crossover (CO) frequency and distribution in natural diploids, natural tetraploids and neo-tetraploids (colchicine-induced) in A. arenosa.
Aim 2: Determine how allelic variation in ASY1 and REC8 alters meiotic chromosome behavior
Aim 3: Determine whether A. arenosa tetraploid gene variants promote meiotic stability (e.g. bivalent/multivalent formation) in allotetraploid A. suecica (an A. thaliana x A. arenosa hybrid).
Aim 4: Determine the effect of temperature, another important driver of meiotic adaptation in A. arenosa, on recombination in Arabidopsis

Work performed so far
Although they are closely related to A. thaliana, A. arenosa and A. suecica are different species and thus, production of plant material is a major component of the project: segregating populations (Aims 1), transgenic complementation lines for ASY1 and REC8 (Aims 2), crosses with fluorescent reporter lines (FTLs) which enables meiotic recombination to be assessed (see below), A. suecica lines generated from both natural tetraploid and neo-tetraploid A. arenosa and containing FTL fluorescent reporter loci (Aims 3). All plant material has now been delivered. Final analyses are ongoing and on schedule.
Likewise, a series of genetic assays has been set up to determine recombination frequencies and interference strength. These include: genetically mapping of markers generated by restriction site-associated DNA sequencing (RADSeq), a high-throughput genotyping technology (Aims 1); scoring pollen grains for recombination between transgenic marker constructs encoding pollen-expressed fluorescent proteins of different colors (Aims 2 and 3). Analysis of a small pilot RADSeq data set was used to develop an analysis pipeline and to generate preliminary results. The analysis pipeline is now being implemented with the complete datasets. In the meantime, analysis of FTL lines has begun and is now over half-way complete.
In addition, recent research in the Bomblies lab has shown that in addition to polyploidy, temperature is an important driver of meiotic adaptation in A. arenosa. This has the potential to confound the results of this project as diploids and tetraploids may be optimally adapted to different temperatures. To address this issue I have determined recombination rates in Arabidopsis across a wide range of temperatures, analysis is almost complete (Aims 4).

Results to date
Aim 1) I have validated the approach for scoring recombination in tetraploids using a pilot dataset. The initial analysis (chromosome 8; 20 markers; n = 117) indicates each chromosome has a single CO. This suggests complete interference (leading to a single CO per chromosome) and is the likely cause of the meiotic adaptation (a single CO per chromosome results in strict bivalent formation). In addition, partner choice is random, with a chromosome equally likely to recombine with each of the other three homologous chromosomes. These preliminary results will be confirmed with the new data set i.e. genome wide, > 50 markers per chromosome, n ~ 400.
Aim 2) I have determined that both diploid and tetraploid A. arenosa alleles of ASY1 and SYN1 complement ASY1 and SYN1 A. thaliana mutants respectively (restoration of fertility). Thus both A. arenosa versions of these proteins are functional in A. thaliana.
Aim 3) I have developed and validated new A. suecica lines that can be used for high-throughput scoring of homeologous recombination. I have also determined that the A. arenosa parent of A. suecica is ancestral to the diploid/tetraploid A. arenosa divergence. This refutes the current paradigm that the A. arenosa parent of A. suecica was from one of the tetraploid A. arenosa populations that currently overlap with the geographic range of A. suecica.
Aim 4) I have determined that there is a U-shaped relationship between temperature and recombination frequency in Arabidopsis.
One paper resulting from this project has currently been published. The paper: Lloyd & Bomblies, “Meiosis in autopolyploid and allopolyploid Arabidopsis.” was published in Current Opinion in Plant Biology (2016, 30:116–122).

Expected Results and impacts
Aim 1) I expect to validate the preliminary results which indicate that there is strong CO interference in A. arenosa with only one CO per bivalent, and that partner choice is random. I also expect to determine whether aneuploidy is correlated with factors such as CO frequency or chromosome size. This will provide insights into a key determinant of the formation of new polyploid species.
Aim 2) I expect to determine whether A. arenosa diploid and tetraploid versions of ASY1 and SYN1 have different effects on recombination frequency and interference. This may lead to the identification of the first gene variant that increases interference strength, and thereby provide key insights into this fundamental, yet poorly understood biological phenomenon.
Aim 3) I expect to determine whether tetraploid alleles of meiotic genes from autotetraploid A. arenosa also contribute to meiotic stability in allopolyploid A. suecica. This will help reveal whether there is any overlap in the mechanisms by which auto and allo-polyploids adapt meiosis.
Aim 4) Revealing the relationship between temperature and recombination rates may impact plant breeding programs as a non-GMO based method to manipulate recombination rates / distribution.


Magali Nawrocki-Serin, (Directrice adjointe)
Tel.: +33 1 30833282
Fax: +33 1 30833319


Life Sciences
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