Methionine biosynthetic genes and methionine sulfoxide reductase A are required for Rhizoctonia solani AG1-IA to cause sheath blight disease in rice.

Rhizoctonia solani is a polyphagous necrotrophic fungal pathogen that causes sheath blight disease in rice. It deploys effector molecules as well as carbohydrate-active enzymes and enhances the production of reactive oxygen species for killing host tissues. Understanding R. solani ability to sustain growth under an oxidative-stress-enriched environment is important for developing disease control strategies. Here, we demonstrate that R. solani upregulates methionine biosynthetic genes, including Rs_MET13 during infection in rice, and double-stranded RNA-mediated silencing of these genes impairs the pathogen's ability to cause disease. Exogenous treatment with methionine restores the disease-causing ability of Rs_MET13-silenced R. solani and facilitates its growth on 10 mM HO-containing minimal-media. Notably, the Rs_MsrA gene that encodes methionine sulfoxide reductase A, an antioxidant enzyme involved in the repair of oxidative damage of methionine, is upregulated upon HO treatment and also during infection in rice. Rs_MsrA-silenced R. solani is unable to cause disease, suggesting that it is important for the repair of oxidative damage in methionine during host colonization. We propose that spray-induced gene silencing of Rs_MsrA and designing of antagonistic molecules that block MsrA activity can be exploited as a drug target for effective control of sheath blight disease in rice.