Background: Ustilaginoidea virens causes rice false smut disease, which emerges as a worldwide disease of rice. At present, some stress response related genes have been identified in U. virens , but it is not clear whether and how defects of stress responses affect the pathogenesis processes of U. virens . To answer this question, the function of a general stress response factor Whi2 was analyzed in U. virens .
Results: In this study, we identified 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 the mycelial growth, increased in conidiation in the PS (potato sucrose) medium and a defect in pathogenicity. In addition, the RNA-Seq and phenotypic analysis showed that UvWHI2 is involved in response to oxidative, hyperosmotic, cell wall stresses, and nutrient limitation. Further studies revealed that the defects of stress responses of the ∆ Uvwhi2 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 .
Conclusions: 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 could affect the formation of secondary spores on the rice surface, and then compromise the pathogenicity of U. virens .