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

Background: The signal transduction mucin Msb2 initiates the signal transduction response in the HOG pathway and participates in the infection and pathogenesis of fungal pathogens. Metarhizium acridum, an entomopathogenic fungus, is a promising biopesticide for agricultural, forestry, and urban pest control. This study focuses on the characterization of MaMsb2 in M. acridum.

Materials and Methods: Gene expression profiles of MaMsb2 in M. acridum were analyzed using RT-qPCR. Knockout strain of MaMsb2 was constructed via homologous recombination, and the ΔMaMsb2 complementation strain was constructed via ectopic insertion. Their phenotypic characteristics were examined. The conidial germination rates and conidial yield of different fungal strains were ascertained on 1/4 SDAY. The fungal tolerances to UV-B radiation and heat stress was evaluated. Fungal virulence was evaluated using the fifth instar nymphs of Locusta migratoria manilensis, and infection structures formation and penetration ability were assessed on locust hind wings. 

Results: Disruption of MaMsb2 resulted in the delayed conidial germination, the increased conidial yield owing to the changed conidiation pattern, the reduced tolerances to multiple stresses, the decreased virulence because of the impairments of appressorium formation and the growth of M. acridum in the hemolymph of locusts. RNA-seq showed that MaMsb2 governed the appressorium formation of M. acridum by mediating the expression of related genes such as conidial adhesion, appressorium formation, and host cuticle penetration.

Conclusion: MaMsb2 is crucial for fungal conidiation, stress tolerances, virulence in M. acridum, playing essential roles in infection structures formation, penetration. Understanding its functions provides insights into the pathogenic mechanisms of insect pathogenic fungi.