The Velvet Protein VeA Functions in Asexual Cycle, Stress Tolerance and Transcriptional Regulation of Beauveria Bassiana.

VeA is a key velvet protein that regulates sexual/asexual development and secondary metabolism in filamentous fungi, particularly Aspergilli, but has not been explored yet in asexual insect mycopathogens, such as Beauveria bassiana. Here, we report a localization of B. bassiana VeA in the cytoplasm of hyphal cells exposed to either light or dark cue and its migration to the nucleus only in darkness. Deletion of veA resulted in facilitated hyphal growth and decreased cell length on rich media, light growth defects on scant media, and increased sensitivities to oxidation, high osmolarity and prolonged heat shock during colony growth. Compared to wild-type, the deletion mutant was much more triggered in conidiation at optimal 25 °C in darkness than in a light/dark (L:D) cycle of 12:12, indicating the role of VeA acting as a negative regulator of conidiation in a light-dependent manner. The mutant conidia produced at L:D 12:12 showed defects in germination, thermotolerance and UVB resistance but no change in virulence, contrasting to attenuated virulence for the mutant conidia produced in darkness. Intriguingly, fungal outgrowth and conidiation were markedly suppressed on the surfaces of the mutant-mummified insect cadavers, suggesting a significant role of VeA in fungal survival, dispersal and prevalence in host habitats. Transcriptomic analysis revealed 1248 and 1183 differentially expressed genes in the deletion mutant versus wild-type grown at L:D 0:24 and 12:12 respectively, including those involved in central developmental pathway and secondary metabolism. Altogether, VeA is functionally involved in asexual cycle, stress tolerance and transcriptional regulation of B. bassiana.