OsLOX9 confers thermotolerance in rice via JA-mediated enhancement of antioxidant defense

• Mutation of the jasmonic acid (JA) biosynthetic gene OsLOX9 increases heat sensitivity in rice. • Exogenous methyl jasmonate restores thermotolerance in lox9 mutants. • Mutation of OsLOX9 alters the expression of heat-responsive genes. • OsLOX9 positively regulates peroxidase activity under heat stress. With global warming threatening rice production, heat stress significantly reduces yields. Although jasmonic acid (JA) is known to mediate thermotolerance, the specific roles of JA biosynthesis genes, particularly lipoxygenases (LOXs), remain poorly characterized. Here, we explored the function of rice lipoxygenase gene OsLOX9 under heat stress. OsLOX9 expression was strongly induced by high temperatures. Mutants of OsLOX9 showed increased heat sensitivity, with lower survival rates, higher malondialdehyde, and reduced JA and jasmonyl-isoleucine levels. Exogenous application of methyl jasmonate restored thermotolerance in the mutants. Transcriptome indicated that OsLOX9 modulates the expression of peroxidase-related genes and enhances peroxidase activity, thereby reducing reactive oxygen species accumulation under heat stress. Collectively, our results demonstrated that OsLOX9 is essential for JA-mediated thermotolerance, highlighting its role in regulating antioxidant defense mechanisms. These findings provide new insights into the molecular mechanisms of heat response and suggest potential strategies for improving thermotolerance in rice through engineering the JA pathway.