Abstract
BACKGROUND
Basic helix-loop-helix (bHLH) transcription factors are critical regulators of differentiation, metabolism, and environmental response in eukaryotes. However, their functions in entomopathogenic fungus remain largely unexplored.
RESULTS
In this study, we identified and characterized the bHLH transcription factor MrBHLH1 in the model entomopathogenic fungus Metarhizium robertsii. Localization studies revealed that MrBHLH1 is predominantly found in the nuclei of both conidia and hyphae. The ΔMrbHLH1 mutant exhibited significant impairments in vegetative growth and conidial production, showing reductions of 63.01% and 63.95%, respectively, compared to the wild-type (WT) strain on potato dextrose agar. Interestingly, ΔMrbHLH1 demonstrated increased resistance to various abiotic stresses, including ultraviolet (UV) irradiation, thermal, oxidative, osmotic, and cell wall integrity stresses, relative to WT. Furthermore, ΔMrbHLH1 displayed enhanced virulence, evidenced by a 19.3% reduction in median lethal time (LT50, in days) compared to WT, which was associated with accelerated appressoria formation, increased conidial adhesion and hydrophobicity, and improved cuticle penetration ability. Chromatin immunoprecipitation sequencing analysis revealed that MrBHLH1 regulates a set of target genes significantly enriched in the MAPK signaling pathway and autophagy processes.
CONCLUSION
This study establishes MrBHLH1 as a pivotal regulator in M. robertsii, orchestrating a balance between growth, stress adaptation, and pathogenicity. These findings enhance our understanding of the functional roles of bHLH transcription factors in entomopathogenic fungi and provide novel targets for the engineering of entomopathogens with improved biocontrol characteristics. © 2025 Society of Chemical Industry.
