A lipoxygenase gene modulates jasmonate biosynthesis to enhance blast resistance in rice

Inhibition of jasmonic acid (JA) signaling renders plants more susceptible to biotic stresses. Pathogen infection can induce an increase in JA levels. However, our understanding of the mechanisms mediating pathogen-induced JA accumulation in rice (Oryza sativa) remains limited. We characterized OsLOX9, a lipoxygenase gene of the 13-LOX subfamily involved in JA biosynthesis, which is induced upon infection by the rice blast fungus Magnaporthe oryzae. Two independent lox9 mutants exhibited increased susceptibility to M. oryzae infection, a phenotype that was fully restored by methyl jasmonate treatment, and showed reduced pathogen-induced accumulation of 12-oxo-phytodienoic acid, JA, and its bioactive form JA-Ile. RNA sequencing-based expression analysis in response to M. oryzae infection revealed an essential role of OsLOX9-produced jasmonates in up-regulating terpenoid phytoalexin pathway genes. Furthermore, we found that the JA core transcription factor, OsMYC2, can bind to the promoter of OsLOX9 and activate its expression, creating a positive feedback loop during pathogenesis. This study reveals that OsLOX9 is a key blast fungus-induced JA biosynthesis gene and contributes to resistance to blast disease in rice.