Moderate heat stress (HS) primes a plant to subsequently withstand high temperatures that are lethal to a plant in the naïve state. After returning to non-stress temperatures the primed state is maintained over several days, and this memory is genetically separable from the thermopriming itself. While the molecular events that lead to thermopriming are relatively well understood, little is known about the mechanism of thermomemory, i. e. the maintenance of the primed state after HS.
This project addresses the contribution of chromatin regulation to thermomemory in Arabidopsis thaliana. In the past funding period, we have identified thermomemory-related genes based on their sustained induction after a priming HS. We have used a subset of these genes to study chromatin dynamics during the memory phase. To this end, we have compared the chromatin at several memory-related loci in the naïve, primed and triggered states by analysing histone modifications, nucleosome distribution and DNA methylation. We identified a specific histone modification on thermomemory-related genes that increases during the later stages of thermomemory (when active transcription declines). Interestingly, this modification is defective in a thermomemory-deficient mutant. Thus, this modification may act as a mark of recent transcriptional activity and mediate a modified physiological response upon recurring HS. Building on these findings, in the second funding period we aim to determine the functional relevance of this thermomemory mark, and investigate its molecular regulation. Specifically, we will address the following questions: What is the role of the candidate memory mark in the transcriptional and physiological response to a triggering stimulus? How is the candidate memory mark established and maintained at individual genomic loci? Is the acquisition of the mark associated with higher-order chromatin structures? How is this affected in accessions with varying thermomemory? Why do some heat-induced genes show sustained expression through the memory phase and others do not? We will investigate these questions using an array of molecular and genetic approaches such as chromatin immunoprecipitation, gene expression analyses, reverse genetics, mutant and promoter analyses.
In summary, this project will elucidate the role of chromatin structure during thermomemory and provide insights into its regulation.