The transcriptional co‐activator multiprotein bridging factor 1 from the fungal insect pathogen, B eauveria bassiana , mediates regulation of hyphal morphogenesis, stress tolerance and virulence

Abstract

Summary Multiprotein bridging factors ( MBF s) are evolutionarily highly conserved cofactors that link TATA ‐binding protein and the associated basal transcription machinery to transcription factors. The filamentous fungus, B eauveria bassiana , has a multipotential lifestyle capable of growing as a saprophyte, plant endophyte and insect pathogen. Deletion of the single B . bassiana MBF homologue ( BbMBF 1 ) affected fungal growth and hyphal morphogenesis, stress response and virulence. Compared with wild type, the Δ BbMBF 1 strain displayed increased sensitivity to UV ‐irradiation and to oxidative, osmotic and heat stress, and decreased virulence in both topical and intrahaemocoel injection bioassays using the greater wax moth, G alleria mellonella larvae. Although only minor radial growth effects were seen for the Δ BbMBF 1 strain, aberrant hyphal morphogenesis was observed, which could be rescued by growth in rich broth media. Transcriptional analysis during stress response showed altered gene expression in Δ BbMBF 1 during growth under osmotic, oxidative and thermal stress conditions. Genome‐wide expression analyses during growth under unstressed and thermal stress conditions revealed global gene expression changes and a set of putative targets for MBF 1 mediated gene expression control. Our data indicate that BbMBF 1 acts as a key regulatory cofactor controlling stress responses and virulence and that MBF 1 dependent and independent pathways control proper hyphal morphogenesis.

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