BbSNF1 contributes to cell differentiation, extracellular acidification, and virulence in Beauveria bassiana, a filamentous entomopathogenic fungus.

Abstract

SNF1/AMPK protein kinase plays important roles in fungal development and activation of catabolite-repressed genes. In this study, we characterized the role of the Beauveria bassiana SNF1 ortholog. The vegetative growth of the ΔBbSNF1 mutant was reduced by 16 to 50 % on diverse carbon/nitrogen sources. Transcriptional analysis revealed a collection of proteases and chitinases that were not induced when the mutant was grown on complex carbon/nitrogen sources. BbSNF1 also contributes to extracellular acidification. The ΔBbSNF1 mutant had enhanced production of lactic, pyruvic, and citric acid, but oxalic acid production was partially repressed. Transcriptional analysis showed that a set of genes involved in acid biosynthesis and secretion was changed in the disruption mutant, indicating that BbSNF1 controls the production of different organic acids with different mechanisms. Deletion of BbSNF1 resulted in a significant reduction in conidiation (57-75 %) and blastospore yield (80-95 %) in the mutant. Additionally, BbSNF1 regulates the morphology of blastospore-forming structures and the in vitro blastospore size. Insect bioassays revealed that the ΔBbSNF1 strain exhibited an approximately doubled median lethal time in topical bioassays, but the decreased virulence in intrahemocoel assays (~20 % change) was not as great as in the topical bioassays. These data suggest that BbSNF1 is important in penetration through the host cuticle. Moreover, a series of genes regulated by BbSNF1 and associated with blastospore formation were primarily involved in metabolism, cell cycle, and transportation. In conclusion, the SNF1/AMPK kinase contributes to the biocontrol potential of B. bassiana by mediating cellular differentiation and utilization of carbon/nitrogen sources.