SRF6, a heat-inducible receptor-like kinase, regulates thermotolerance in Arabidopsis thaliana.

Abstract

Key message: SRF6 is a heat-inducible, non-RD receptor-like kinase that contributes to thermotolerance in Arabidopsis by modulating heat-, ER stress-, ABA-, and ROS-responsive pathways. Receptor-like kinases (RLKs) are central regulators of plant growth, development, and stress perception, yet their roles in heat stress (HS) responses remain largely unclear. Here, we identify STRUBBELIG-RECEPTOR-FAMILY 6 (SRF6) as a heat-inducible, plasma membrane-localized, non-arginine-aspartate (non-RD) RLK that contributes to thermotolerance in Arabidopsis thaliana. HS significantly induces SRF6 expression, and this induction is attenuated in hsfA1a/b/d/e quadruple knockout and hsfA7b mutants, suggesting that HSFA1s and HSFA7b influence its heat-induced expression. Although SRF6 lacks detectable kinase activity, its sustained expression after heat priming is consistent with a heat-memory-associated response. Functionally, the srf6-1 mutant exhibits impaired thermotolerance, whereas SRF6 overexpression in srf6-1 restores heat tolerance. Targeted gene expression analyses revealed that loss of SRF6 alters the expression of heat-, ER stress-, ABA-, and ROS-responsive genes, including HSP22/70/90/101, CaM3, bZIP28/60, BiP2, AREB1/2, RD29A/B, APX1/2, CAT1, and RBOHD, accompanied by enhanced ER stress and altered heat-memory-associated responses under HS. Together, these findings suggest that SRF6 contributes to cellular stress homeostasis and thermotolerance during HS and provide evidence for a role of the LRR-V/SRF family in plant HS responses.