OsNOMT Contributes to Rice Blast Resistance and Viral Defense and Is Associated with Altered Jasmonate Homeostasis

Abstract

Sakuranetin (SAK), a flavonoid phytoalexin synthesized by naringenin 7-O-methyltransferase (NOMT), contributes to rice immunity. However, the relationship between OsNOMT-dependent SAK accumulation, resistance to fungal and viral pathogens, and jasmonate (JA) homeostasis remains unclear. Here, we combined genetic, metabolite and transcriptomic analyses of OsNOMT-overexpression (OsNOMT-OE) and knockout (osnomt) lines. Loss of OsNOMT abolished SAK accumulation and was associated with increased susceptibility to Magnaporthe oryzae and Southern rice black-streaked dwarf virus, whereas OsNOMT-OE lines accumulated high levels of SAK and exhibited enhanced resistance to both pathogens. Co-expression network analysis identified a susceptibility-associated module containing OsWRKY62, OsFBX148, and a putative ACC oxidase as candidate hub nodes. OsNOMT-OE plants exhibited increased expression of JA-related genes and higher JA levels but lower basal levels of JA-Ile than wild-type ZH11 plants. In osnomt mutants, basal JA-Ile levels were reduced, whereas JA-Ile levels after M. oryzae infection were comparable to those in ZH11 plants, indicating that OsNOMT-dependent SAK accumulation is linked to a reconfiguration of JA homeostasis rather than a uniform increase in all JA metabolites. In addition, short-term exogenous SAK application promoted JA and JA-Ile accumulation. Collectively, these findings associate OsNOMT-mediated SAK biosynthesis with rice resistance to fungal and viral diseases and altered JA homeostasis.