UvWhi2 Is Required for Stress Response and Pathogenicity in Ustilaginoidea virens

Some stress response-related genes have been identified in Ustilaginoidea virens, but it is not clear whether and how defects of stress responses affect the pathogenesis processes of U. virens. In this study, we identified a general stress response factor UvWHI2 as a homolog of Saccharomyces cerevisiae Whi2 in U. virens. The relative expression level of UvWhi2 was significantly up-regulated during infection, suggesting that UvWHI2 may be involved in pathogenesis. Furthermore, knockout of UvWhi2 showed decreased mycelial growth, increased conidiation in the potato sucrose medium and a defect in pathogenicity. In addition, the RNA-Seq and phenotypic analysis showed that UvWHI2 was involved in response to oxidative, hyperosmotic, cell wall stress and nutrient limitation. Further studies revealed that the defects of stress responses of the ΔUvwhi2 mutant affected the formation of secondary spores on the nutrient limited surface and the rice surface, resulting in a significant reduction of pathogenicity of U. virens. Our results suggest that UvWHI2 is necessary for fungal growth, stress responses and the formation of secondary spores in U. virens. In addition, the defects of stress responses can affect the formation of secondary spores on the rice surface, and then compromise the pathogenicity of U. virens.