Fus3/Kss1-MAP kinase and Ste12-like control distinct biocontrol-traits besides regulation of insect cuticle penetration via phosphorylation cascade in a filamentous fungal pathogen.

BACKGROUND

Homolog of the yeast Fus3/Kss1 mitogen-activated protein kinase (MAPK) pathway and its target transcription factor, Ste12-like, are involved in penetration of host cuticle/pathogenicity in many ascomycete pathogens. However, details of their interaction during fungal infection, as well as their controlled other virulence-associated traits, are unclear.

RESULTS

Ste12-like (BbSte12) and Fus3/Kss1 MAPK homolog (Bbmpk1) interacted in nucleus, and phosphorylation of BbSte12 by Bbmpk1 was essential for penetration of insect cuticle in an insect fungal pathogen, Beauveria bassiana. However, some distinct biocontrol-traits were found to be mediated by Ste12 and Bbmpk1. In contrast to ΔBbmpk1 colony that grew more rapid than wild-type strain, inactivation of BbSte12 resulted in the opposite phenotype, which was consistent with their different proliferation rates in insect hemocoel after direct injection of conidia bypass the cuticle. Reduced conidial yield with decreased hydrophobicity was examined in both mutants, however they displayed distinct conidiogenesis, accompanying with differently altered cell cycle, distinct hyphal branching and septum formation. Moreover, ΔBbmpk1 showed increased tolerance to oxidative agent, whereas the opposite phenotype was seen for ΔBbSte12 strain. RNA sequencing analysis revealed that Bbmpk1 controlled 356 genes depending on BbSte12 during cuticle penetration, but 1077 and 584 genes were independently controlled by Bbmpk1 and BbSte12.

CONCLUSION

BbSte12 and Bbmpk1 separately participate in additional pathways for control of conidiation, growth and hyphal differentiation, as well as oxidative stress response besides regulating cuticle penetration via phosphorylation cascade. © 2023 Society of Chemical Industry.