An Asp f2-like protein negatively affects stress tolerance, conidiation and virulence in Metarhizium acridum.

Metarhizium acridum is a typical filamentous fungus that has been widely used to control grasshoppers, locusts, and crickets. Genetic engineering is a common strategy to enhance its virulence, conidiation, and stress tolerance. Here, we report that the M. acridum Asp f2-like protein (MaAL) plays key roles in virulence, conidiation, and stress tolerance. Disruption of MaAL (ΔMaAL) resulted in faster conidial germination and significantly increased conidial yield. The conidial yield of the ΔMaAL strain was 113.33 % higher than that of the wild-type (WT) strain. The ΔMaAL strain exhibited significantly enhanced tolerance to UV-B irradiation, heat shock, and high osmotic stress. Furthermore, both topical inoculation and intra-hemocoel injection demonstrated significantly increased virulence against Locusta migratoria. Specifically, the LT of ΔMaAL was reduced by 1.54 days for topical inoculation and 1.08 days for intra-hemocoel injection compare to WT. Further investigation revealed that the deletion of MaAL led to increased turgor pressure in appressoria, reduced immune responses in locusts, and faster hyphal growth in the hemolymph. This study explores the function of Asp f2-like proteins in entomopathogenic fungi, providing theoretical support and genetic resources for the development of high-virulence strains.