The bHlhzip-type transcription factor, MaHpa3 , regulates conidial rodlet formation and cell surface hydrophobicity in the insect fungal pathogen me tar hizium acr idum

Fungal conidial hydrophobicity plays critical roles in spore dispersal, host invasion, and environmental adaptation. However, the regulatory mechanisms underlying this phenomenon remain poorly understood. Here, we identified MaHpa3, an uncharacterized bHLHzip-type transcription factor in the insect pathogenic fungus Metarhizium acridum, and demonstrated its role in regulating conidial hydrophobicity along with other cellular processes. Deletion of MaHpa3 resulted in reduced conidial yield, altered pigmentation, impaired stress tolerance, attenuated virulence, and decreased conidial hydrophobicity. Scanning electron microscopy revealed structural defects and surface alterations in ΔMaHpa3 mutant conidia, including the reduction of the rodlet layer. Additionally, six hydrophobin encoding genes (MaHyd1-6) were identified in the M. acridum genome, and MaHpa3 was shown to act as a positive regulator of the expression of MaHyd2. Targeted deletion of MaHyd2 phenocopied the hydrophobicity defect observed in the ΔMaHpa3 mutant. Our findings establish MaHpa3 as a key regulator of conidial surface hydrophobicity and rodlet layer formation in M. acridum.