MaMsb2, a signaling mucin, is involved in conidiation, stress tolerances, and virulence in the entomopathogenic fungus <i>Metarhizium acridum</i>

Entomopathogenic fungi are pivotal microbial resources for crop protection in agriculture, offering a natural and environmentally friendly alternative to chemical pesticides. The signalling mucin gene <i>Msb2</i> contributes to the modulation of fungal development and virulence, yet its functions have remained unexplored in entomopathogenic fungi. In this study, we aimed to characterize the functions of <i>Msb2</i> in the model entomopathogenic fungus <i>Metarhizium acridum</i> using gene knockout and complementation strategies. The absence of <i>MaMsb2</i> led to a delay in conidial germination and an increase in conidial yield due to a shift in the conidiation pattern. Additionally, the <i>MaMsb2</i>-disruption bring about the significantly reduced tolerances to various adversities in <i>M. acridum</i>. Moreover, inactivation of <i>MaMsb2</i> resulted in the decreased virulence of <i>M. acridum</i> owing to the decrease in conidial hydrophobicity and adhesion, the impairment of appressorium formation, and the reduction of <i>M. acridum</i> growth in the locust haemolymph. To elucidate the molecular mechanisms by which <i>MaMsb2</i> exerts its influence, we conducted an RNA-seq analysis during appressorium formation. As a result, 880 differentially expressed genes (DEGs) regulated by MaMsb2 were identified. Our data indicated that MaMsb2 governs the appressorium formation of <i>M. acridum</i> by mediating the expression of genes associated with conidia adhesion, appressorium formation, and host cuticle penetration. These findings not only shed light on the multifaceted role of <i>MaMsb2</i> in the biology of entomopathogenic fungi but also lay the groundwork for future research aimed at unravelling the intricate mechanisms by which MaMsb2 regulates conidiation and pathogenesis.