ECOTHERM – Exploring the natural variation of the heat shock response in Arabidopsis thaliana to understand the molecular mechanism of heat perception

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Exposure to moderately elevated temperatures elicits a genetically encoded heat shock response (HSR) resulting in short-term acquired thermotolerance, which enables plants to withstand a subsequent temperature extreme that is lethal to non-acclimated plants. The HSR is characterised by a substantial transcriptional and metabolic reprogramming that is tightly regulated by a complex network of transcription factors. Central to this regulatory network is the activation of HEAT SHOCK TRANSCRIPTION FACTORs belonging to the A1 subfamily (HSFA1s). Despite the fact that the HSR has been relatively well characterised at the molecular level in Arabidopsis thaliana it is still unclear how an increase in temperature is sensed by the plant and how this initial signal translates into HSFA1 activation. In addition, knowledge on the natural variation of A. thaliana’s temperature responsiveness and the underlying mechanisms is limited. In our preliminary work we observed a significant variation in the ability to acquire thermotolerance across ten Arabidopsis accessions. In addition, plant survival correlated with the accumulation of raffinose, a trisaccharide whose temperature-dependent synthesis is positively regulated by HSFA1, making it a promising marker trait for the onset of the HSR. Based on these observations we propose to exploit the temperature-dependent raffinose accumulation to (I) gain insights into the genetic architecture of HSFA1-dependent signalling and the mechanisms underlying its intraspecific variation and (II) to identify candidate genes that are involved in temperature perception as well as yet unknown components of the HSFA1 signalling cascade in a genome-wide association study (GWAS). We will follow a two-step approach with an initial characterisation of HSR-related marker traits in 100 A. thaliana accessions that will result in the identification of extreme accessions and also allow for fine-tuning of the experimental conditions for the large-scale phenotyping at the second step. The identified extreme accessions will be characterised in detail at the metabolic and transcriptomic level using lipidomics and RNAseq. Transcription rates of selected differentially expressed genes will then be profiled across the 100 accessions and the data used for the generation of transcriptional networks resulting in the identification of the central regulatory elements underlying the observed intraspecific variation. At the second step, we will screen the temperature responsiveness of 1135 A. thaliana accessions whose genomes have been published recently thereby providing an excellent resource for GWA studies. The most significant candidate genes will be characterised and their exact role in temperature perception and acquired thermotolerance determined.Taken together, the proposed project will provide valuable insights into the molecular mechanism of temperature sensing as well as mechanisms of local adaptation to extreme temperatures.