Periodic Reporting for period 1 - ACQUIRE (The mechanism of acquired thermotolerance in potato)
Berichtszeitraum: 2016-05-01 bis 2018-04-30
Potato is the third most important food crop in the world after rice and wheat. More than a billion people worldwide eat potato, and global crop production exceeds 300 MT. Yet this crop is particularly vulnerable to increased temperature, considered to be the most important uncontrollable factor affecting growth and yield. For many commercial potato cultivars, tuber yield is optimal at average day time temperatures in the range of 14-22˚C. Further rises in ambient temperature can reduce or completely inhibit potato tuber production, with damaging consequences for both producer and consumer.
As the EU exports seed to countries where temperature stress is a growing problem, yield at higher temperature is an issue of increasing magnitude to the EU potato industry. Furthermore, the implementation of measures to mitigate the effects of rising temperatures in the EU is vital to protect food self-sufficiency.Thus the objectives of the ACQUIRE project were: to develop a robust screen to assay for acquired thermotolerance in potato; to test potato genotypes and transgenic lines for variation in the acquired thermotolerance response; to determine traits associated with acquired thermotolerance; to introgress beneficial alleles of a potato heat tolerance gene (StHot1) and develop new genotypes with improved acquired thermotolerance characteristics; to assess the impact of acquired thermotolerance on tuber yield in a range of genotypes.
As the EU exports seed to countries where temperature stress is a growing problem, yield at higher temperature is an issue of increasing magnitude to the EU potato industry. Furthermore, the implementation of measures to mitigate the effects of rising temperatures in the EU is vital to protect food self-sufficiency.Thus the objectives of the ACQUIRE project were: to develop a robust screen to assay for acquired thermotolerance in potato; to test potato genotypes and transgenic lines for variation in the acquired thermotolerance response; to determine traits associated with acquired thermotolerance; to introgress beneficial alleles of a potato heat tolerance gene (StHot1) and develop new genotypes with improved acquired thermotolerance characteristics; to assess the impact of acquired thermotolerance on tuber yield in a range of genotypes.
WP1. Development of an acquired thermotolerance assay in potato
We demonstrated and characterized in detail a robust screen for acquired thermotolerance in potato, showing the time course required for tolerance, the reversibility of the process and the requirement for light. In addition, we also investigated effects of acclimation to high temperature on photosynthetic performance and oxidative stress.
WP2. Assessment of acquired thermotolerance in potato genotypes and transgenic lines
We tested for variation in the acquired thermotolerance response of several potato genotypes and transgenic lines. In all commercial tetraploid cultivars that were tested, acquisition of thermotolerance by priming was required for tolerance at elevated temperature. However, accessions from several wild type species and diploid genotypes as well as StHot1 transgenic lines did not require priming for heat tolerance under the test conditions employed, suggesting that useful variation for this trait exists.
WP3. Detailed molecular and biochemical analysis of genotypes with contrasting acquired thermotolerance characteristics
Physiological, transcriptomic and metabolomic approaches were employed to elucidate potential mechanisms that underpin the acquisition of heat tolerance. This analysis indicated a role for cell wall modification, auxin and ethylene signalling, and chromatin remodelling in acclimatory priming resulting in reduced metabolic perturbation and delayed stress responses in acclimated plants following transfer to 40⁰C.
WP4. Generation of hybrid cultivars with increased heat tolerance originating from S. tuberosum Group Phureja. Secondment at Solynta .
The first step towards developing new genotypes with improved acquired thermotolerance characteristics has been accomplished by introgressing a heat tolerant donor containing the beneficial StHot1 allele with an elite inbred line without the beneficial allele and generating a segregating population that will be used for further genetic studies. The Solynta parental line was unexpectedly highly heat tolerant and so further rounds of back crossing will be required to fully assess the impact of the StHot1 gene.
A marker assisted backcrossing programme will be used to develop Nearly Isogenic Lines (NILs) that will be assayed using the established (WP1) acquired thermotolerance assay.
WP5. Yield experiments using genotypes with contrasting acquired thermotolerance characteristics.
We aimed to establish a link between acquired thermotolerance characteristics and tuber yield. The impact of acquired thermotolerance on tuber yield was investigated in growth room experiments using single stem plants or a model nodal cuttings assay. Genotypes with contrasting acquired thermotolerance characteristics including extremes from a diploid potato collection, and transgenic lines were compared. The presence of the beneficial StHot1 allele results in enhanced yield at elevated temperature. In transgenic lines, the yield was up to two fold greater than in wildtype plants at 28 °C but with no significant effect on yield at 20 °C. We propose the rapid response of the StHot1 allele to temperature perturbation underlies the yield effect. Further work was initiated to investigate yield in heat tolerant and sensitive wild species. Initial experiments were confounded by experimental difficulties due to growth cabinet failure. Nevertheless the experimental set up has been repeated and results will be available in the next stage of research, post ACQUIRE.
The results obtained within the project have been published in a high-ranking open-access scientific journal (“Planta”). The ER presented a poster and gave a talk at The 13th Solanaceae Conference –Solgenomics: From Advances to Applications held in Davis, California (2016) and presented a poster at the New Phytologist Next Generation Scientists Symposium (2017). A poster and a presentation relevant to the ACQUIRE project have been presented as well at the Hutton Annual Research Symposium (2017).
It was also important that ACQUIRE engaged with the plant breeding and end-user communities. Hence the ER attended the “Potatoes in Practice” day (2016) the UK's biggest potato field event aimed at farmers, agronomists, industry and scientists, where a poster relevant to the project has been also presented. JHI staff members also contribute to “Fascination of Plants Days”. This Global event is aimed at raising the awareness of plant and crop science and targets the general public. The ER spend one day per year on this activity. Feedback from these events was gathered each year and used to adjust content to maximise impact.
We demonstrated and characterized in detail a robust screen for acquired thermotolerance in potato, showing the time course required for tolerance, the reversibility of the process and the requirement for light. In addition, we also investigated effects of acclimation to high temperature on photosynthetic performance and oxidative stress.
WP2. Assessment of acquired thermotolerance in potato genotypes and transgenic lines
We tested for variation in the acquired thermotolerance response of several potato genotypes and transgenic lines. In all commercial tetraploid cultivars that were tested, acquisition of thermotolerance by priming was required for tolerance at elevated temperature. However, accessions from several wild type species and diploid genotypes as well as StHot1 transgenic lines did not require priming for heat tolerance under the test conditions employed, suggesting that useful variation for this trait exists.
WP3. Detailed molecular and biochemical analysis of genotypes with contrasting acquired thermotolerance characteristics
Physiological, transcriptomic and metabolomic approaches were employed to elucidate potential mechanisms that underpin the acquisition of heat tolerance. This analysis indicated a role for cell wall modification, auxin and ethylene signalling, and chromatin remodelling in acclimatory priming resulting in reduced metabolic perturbation and delayed stress responses in acclimated plants following transfer to 40⁰C.
WP4. Generation of hybrid cultivars with increased heat tolerance originating from S. tuberosum Group Phureja. Secondment at Solynta .
The first step towards developing new genotypes with improved acquired thermotolerance characteristics has been accomplished by introgressing a heat tolerant donor containing the beneficial StHot1 allele with an elite inbred line without the beneficial allele and generating a segregating population that will be used for further genetic studies. The Solynta parental line was unexpectedly highly heat tolerant and so further rounds of back crossing will be required to fully assess the impact of the StHot1 gene.
A marker assisted backcrossing programme will be used to develop Nearly Isogenic Lines (NILs) that will be assayed using the established (WP1) acquired thermotolerance assay.
WP5. Yield experiments using genotypes with contrasting acquired thermotolerance characteristics.
We aimed to establish a link between acquired thermotolerance characteristics and tuber yield. The impact of acquired thermotolerance on tuber yield was investigated in growth room experiments using single stem plants or a model nodal cuttings assay. Genotypes with contrasting acquired thermotolerance characteristics including extremes from a diploid potato collection, and transgenic lines were compared. The presence of the beneficial StHot1 allele results in enhanced yield at elevated temperature. In transgenic lines, the yield was up to two fold greater than in wildtype plants at 28 °C but with no significant effect on yield at 20 °C. We propose the rapid response of the StHot1 allele to temperature perturbation underlies the yield effect. Further work was initiated to investigate yield in heat tolerant and sensitive wild species. Initial experiments were confounded by experimental difficulties due to growth cabinet failure. Nevertheless the experimental set up has been repeated and results will be available in the next stage of research, post ACQUIRE.
The results obtained within the project have been published in a high-ranking open-access scientific journal (“Planta”). The ER presented a poster and gave a talk at The 13th Solanaceae Conference –Solgenomics: From Advances to Applications held in Davis, California (2016) and presented a poster at the New Phytologist Next Generation Scientists Symposium (2017). A poster and a presentation relevant to the ACQUIRE project have been presented as well at the Hutton Annual Research Symposium (2017).
It was also important that ACQUIRE engaged with the plant breeding and end-user communities. Hence the ER attended the “Potatoes in Practice” day (2016) the UK's biggest potato field event aimed at farmers, agronomists, industry and scientists, where a poster relevant to the project has been also presented. JHI staff members also contribute to “Fascination of Plants Days”. This Global event is aimed at raising the awareness of plant and crop science and targets the general public. The ER spend one day per year on this activity. Feedback from these events was gathered each year and used to adjust content to maximise impact.
A promoter motif in the HSC70 (StHot1) gene has been previously correlated with increased HSC70 expression levels and heat stress tolerance in a diploid biparental potato population (Trapero-Mozos et al. 2017). We further investigated the occurrence of the promoter motif in other potato tetraploid genotypes and diploid wild species and were able to link heat stress tolerance to the presence of the promoter motif.
New avenues in heat stress research and hybrid breeding are envisaged through the extension of the present collaboration with Solynta that will allow investigations into the diploid population containing the StHot1 allele and development of direct commercial applications based on Solynta material.
Outputs of ACQUIRE have contributed to knowledge about heat tolerance in potato, findings that could impact on food security in Europe and globally. As the EU exports seed to countries where temperature stress is a growing problem, yield at higher temperature is an issue of increasing magnitude to the EU potato industry. Furthermore, the implementation of measures to mitigate the effects of rising temperatures in the EU is vital to protect food self-sufficiency.
New avenues in heat stress research and hybrid breeding are envisaged through the extension of the present collaboration with Solynta that will allow investigations into the diploid population containing the StHot1 allele and development of direct commercial applications based on Solynta material.
Outputs of ACQUIRE have contributed to knowledge about heat tolerance in potato, findings that could impact on food security in Europe and globally. As the EU exports seed to countries where temperature stress is a growing problem, yield at higher temperature is an issue of increasing magnitude to the EU potato industry. Furthermore, the implementation of measures to mitigate the effects of rising temperatures in the EU is vital to protect food self-sufficiency.