An apoplastic effector Uv7366 contributes to Ustilaginoidea virens virulence and elicits plant immunity.

Ustilaginoidea virens (Cook) Takahashi, the causal agent of rice false smut disease (RFS), causes severe losses in yield and grain quality worldwide. The ascomycete pathogen deploys a large arsenal of effectors to facilitate infection, but only a few have been functionally characterized. In this study, we characterized Uv7366, an apoplastic glycoside hydrolase family 12 (GH12) protein that was previously identified in the culture filtrate of U. virens. Purified Uv7366 triggered a reactive oxygen species (ROS) burst and strongly induced the transcription of multiple defense-associated genes, and pretreatment of rice (Oryza sativa L.) and Nicotiana benthamiana plants with Uv7366 enhanced their disease resistance. Uv7366 was strongly induced during host invasion and targeted deletion of this gene in U. virens substantially attenuated virulence on rice. Collectively, our findings demonstrate that Uv7366 facilitates U. virens infection while also being recognized by the plant innate immune system, providing new insights into the pathogenic mechanisms of U. virens and potential strategies for the biocontrol of RFS.