A secreted protein UvWSC1 from Ustilaginoidea virens elicits plant immunity in an OsCPK13-dependent manner.

During infection, plant pathogens secrete a large number of proteins that may either function as virulence factors to facilitate infection or be recognized by the host plant to trigger immune responses. The secretome of Ustilaginoidea virens contains numerous functionally uncharacterized proteins. Which of these secreted proteins possess functions in both pathogenicity and immune activation remains largely unknown. Here, we show that UvWSC1, a water-soluble carbohydrate-containing protein from U. virens that localizes to the cell wall, induces cell death in Nicotiana benthamiana. UvWSC1(1-113) functions as a minimal immunogenic epitope that triggers cell death across multiple plant species. Both knockout and overexpression of UvWSC1 attenuate fungal pathogenicity, revealing its role as both a virulence factor and an immune elicitor recognized by plants. Heterologous expression of UvWSC1 in rice confers broad-spectrum resistance against diverse pathogens without compromising agronomic traits, while simultaneously activating plant basal immunity. Mechanistically, UvWSC1(1-113)-triggered cell death depends on the calcium-dependent protein kinase OsCPK13 and the co-receptor SOBIR1. UvWSC1 does not directly interact with OsCPK13 or SOBIR1; however, UvWSC1(1-113) enhances the interaction between OsCPK13 and OsSOBIR1. Our results suggest that UvWSC1(1-113) may act as an activating signal that promotes the recruitment of the SOBIR1-OsCPK13 complex. Overexpression of OsCPK13 in rice enhances the immune response triggered by UvWSC1(1-113), whereas knockout of OsCPK13 attenuates this response, confirming that OsCPK13 is required for UvWSC1(1-113)-triggered immune responses. The broad-spectrum resistance conferred by UvWSC1 highlights its potential as a molecular tool for breeding disease-resistant crops and for developing environmentally friendly green pesticides.