OsPHR2 and OsMYC2 coordinate phosphate starvation-induced sakuranetin biosynthesis for enhanced rice blast resistance

How plants integrate nutrient availability with immune defense remains incompletely understood. This study reveals a molecular mechanism by which rice (Oryza sativa) enhances disease resistance under inorganic phosphate (Pi)-limited conditions through the regulation of sakuranetin biosynthesis. We observed that the Osnomt mutant exhibits reduced sakuranetin levels and compromised disease resistance under Pi deficiency. Further investigations revealed that the Pi signaling regulator OsPHR2 directly binds to the P1BS element in the OsNOMT promoter, activating its expression and promoting sakuranetin production and disease resistance. Genetic analyses demonstrated the synergistic regulatory roles of OsPHR2 and OsMYC2 in controlling OsNOMT expression. Notably, OsMYC2 and its target genes exhibited expression patterns consistent with OsNOMT across developmental stages, while OsPHR2 specifically responded to Pi deficiency, underscoring their unique functions in regulating sakuranetin-mediated resistance under diverse environmental conditions. Additionally, the Pi-sensing protein OsSPX1 negatively regulated sakuranetin biosynthesis and rice resistance by inhibiting OsPHR2-mediated transcriptional activation of OsNOMT. Consequently, under Pi-sufficient conditions, OsSPX1 synergizes with OsBZR1 to further modulate this process. In contrast, Pi-deficient conditions trigger the dissociation of OsPHR2 from the OsSPX1-OsPHR2 complex, thereby activating the biosynthetic pathway and leading to sakuranetin accumulation and enhanced disease resistance. This study elucidates a precise molecular network that coordinates nutrient signaling with immune defense, providing insights for improving crop resistance under nutrient-limited conditions.