Implication of a regulator of G protein signalling (BbRGS1) in conidiation and conidial thermotolerance of the insect pathogenic fungus Beauveria bassiana.

Beauveria bassiana is an insect pathogenic fungus widely used as a biocontrol agent to infect and control insect pests. The conidium initiates pathogenesis and mediates disease transmission, however, little is known about genetic elements that control conidiation. Here, the cloning and characterization of a regulatory G protein-signalling (RGS) gene Bbrgs1 from B. bassiana is reported. Phylogenetic analysis showed that BbRGS1 was orthologous to the RGS protein, FlbA from Aspergillus nidulans. The disruption of Bbrgs1 resulted in significantly reduced conidial production on agar plates or from infected insects. The DeltaBbrgs1 conidia also demonstrated reduced thermotolerance and conidial viability but germinated significantly faster than the wild type. Although hydrophobins have been implicated in conidial thermal sensitivity, the amount of hydrophobin on the conidial surface and the level of transcription of the hydrophobin-like protein gene hl were unaltered. Virulence toward insects was similar to that of the wild-type or reverse complementation transformants, and the mRNA levels of virulence factor genes for chitinase (Bbchit) and subtilisin-like protease (cdep1), were unchanged in DeltaBbrgs1. Characterization of a single RGS gene Bbrgs1 of B. bassiana suggests that it functions differently than RGS proteins in other fungi. However, there may be additional RGS proteins and signalling pathways that control colony development in B. bassiana.