Melatonin induces class A1 heat‐shock factors (HSFA1s) and their possible involvement of thermotolerance in Arabidopsis

Abstract Melatonin (N‐acetyl‐5‐methoxytryptamine) serves as an important signal molecule during plant developmental processes and multiple abiotic stress responses. However, the involvement of melatonin in thermotolerance and the underlying molecular mechanism in Arabidopsis were largely unknown. In this study, we found that the endogenous melatonin level in Arabidopsis leaves was significantly induced by heat stress treatment, and exogenous melatonin treatment conferred improved thermotolerance in Arabidopsis . The transcript levels of class A1 heat‐shock factors ( HSFA 1 s), which serve as the master regulators of heat stress responses, were significantly upregulated by heat stress and exogenous melatonin treatment in Arabidopsis . Notably, exogenous melatonin‐enhanced thermotolerance was largely alleviated in HSFA 1s quadruple knockout ( QK ) mutants, and HSFA 1s ‐activated transcripts of heat‐responsive genes ( HSFA 2 , heat stress‐associated 32 ( HSA 32 ), heat‐shock protein 90 ( HSP 90 ), and 101 ( HSP 101 )) might be contributed to melatonin‐mediated thermotolerance. Taken together, this study provided direct link between melatonin and thermotolerance and indicated the involvement of HSFA 1s ‐activated heat‐responsive genes in melatonin‐mediated thermotolerance in Arabidopsis .