Abstract: Heat stress severely impairs plant growth and limits crop productivity. GSK3-like family proteins regulate diverse cellular processes, including plant responses to abiotic and biotic stresses. Nevertheless, their specific functions in heat stress responses remain poorly characterized. Here, we demonstrate that the expression of OsSK13 and the protein abundance of OsSK12/13 increase under heat stress in rice. Mutation in both OsSK12/13 compromises thermotolerance at both vegetative and reproductive stages, whereas overexpression of OsSK13 enhances seedling thermotolerance. We further identify that OsSK12/13 physically interact with and phosphorylate the APETALA2/ETHYLENE RESPONSIVE FACTOR (AP2/ERF) transcription factor OsERF60, and phosphorylation by OsSK12/13 enhances the stability of OsERF60. Consistent with its role in this regulatory module, OsERF60 loss-of-function mutants exhibit enhanced thermosensitivity at vegetative and reproductive stages. Expression profiling reveals that induction of heat stress-responsive genes, including OsHsfA2c, is reduced in both the OsSK12/13 double mutant and the OsERF60 mutant. OsERF60 directly binds to the OsHsfA2c promoter and activates its expression. Collectively, our findings uncover the OsSK12/13-OsERF60-OsHsfA2c regulatory module as a key component of the heat stress response in rice and provide mechanistic insights into thermotolerance in plants.

Key words: GSK3-like family protein, heat stress, OsERF60, OsSK12, OsSK13, phosphorylation, rice, thermotolerance