Conserved heat shock factors control barley heat stress memory through diverged mechanisms - extended replicate

Climate change requires optimizing stress responses in crops. Priming and memory of heat stress (HS) allow plants to improve their tolerance against high temperatures. Here, we investigate HS memory in cultivated barley (Hordeum vulgare) to assess whether the mechanisms underlying priming by and memory of HS are conserved between dicots and monocots. Mutation of the barley orthologs of two key transcriptional regulators of HS memory, HvHSFA2 and HvHSFA3, reduced HS memory. This correlated with altered transcriptional responses of heat-induced genes in the mutants after recurrent HS. Conversely, overexpression of HvHSFA2 increases HS tolerance with no penalty on productivity. While the biological role of HSFA2 and HSFA3 is conserved, their mechanistic functions appear to have diverged, as we did not find evidence that HvHSFA2 is involved in H3K4me-mediated priming. Instead, both factors are globally required to boost induction of HS-responsive genes after recurrent HS. In summary, while barley HS memory depends on the highly conserved HvHSFA2 and HvHSFA3, the underlying transcriptional wiring is different. Our findings provide a tangible route to improve HS tolerance in temperate cereals. Overall design: Gene expression analysis for Barley wild-type, hsfa2 and hsfa3 mutants with and without heat priming and heat treatment.