GRAIN SIZE ONCHROMOSOME 2 orchestrates phytohormone, sugar signaling and energy metabolism to confer thermal resistance in rice

Abstract GRAIN SIZE ON CHROMOSOME 2 ( GS2 ) has been reported to enhance rice grain yield and confer tolerance to cold, drought, and salt stress, but its function in heat tolerance of rice remains undocumented. This study aimed to investigate whether GS2 could enhance thermal tolerance by subjecting rice seedlings of Huazhan (HZ) and its near‐isogenic line (HZ − GS2 ) to heat stress. HZ − GS2 plants exhibited less damage compared to HZ plants under heat stress. Transcriptome revealed the involvement of phytohormones, sugar signaling, and energy metabolism in the mechanism by which GS2 influences heat tolerance. Under heat stress, HZ − GS2 plants showed higher increases or lower decreases in glucose, gibberellins (GAs), salicylic acid (SA), indoleacetic acid (IAA), adenosine triphosphate (ATP), energy charge, as well as the activities of hexokinase, NADH dehydrogenase, cytochrome oxidase, ATP synthase, and ATPase. Exogenous GA 3 enhanced heat tolerance in rice by increasing energy charge, ATPase, activities of complex V and hexokinase. Additionally, glucose, sucrose, 3‐aminobenzamide (3‐ab), and Na 2 SO 3 conferred heat tolerance in rice plants. Importantly, a significant increase in Fv/Fm was observed in plants treated with a combination of GA 3 , glucose, and 3‐ab, compared to those sprayed alone. Thus, GS2 coordinates GA 3 , hexokinase, and energy metabolism to improve energy status, thereby enhancing heat tolerance in rice plants.