The C-terminal MIR-containing region in the Pmt1 O-mannosyltransferase restrains sporulation and is dispensable for virulence in Beauveria bassiana

Protein O -mannosyltransferases (Pmts) belong to a highly conserved protein family responsible for the initiation of O -glycosylation of many proteins. Pmts contain one dolichyl-phosphate-mannose-protein mannosyltransferases (PMT) domain and three MIR motifs (mannosyltransferase, inositol triphosphate, and ryanodine receptor) that are essential for activity in yeast. We report that in the insect fungal pathogen, Beauveria bassiana , deletion of the C-terminal Pmt1 MIR-containing region (Pmt1 ∆ 311–902 ) does not alter O -mannosyltransferase activity, but does increase total cell wall protein O -mannosylation levels and results in phenotypic changes in fungal development and cell wall stability. B. bassiana mutants harboring the Pmt1 ∆ 311–902 mutation displayed a significant increase in conidiation with up-regulation of conidiation-associated genes and an increase in biomass accumulation as compared to the wild-type parent. However, decreased vegetative growth and blastospore production was noted, and Pmt1 ∆ 311–902 mutants were altered in cell wall composition and cell surface features. Insect bioassays revealed little effect on virulence for the Pmt1 ∆ 311–902 strain via cuticle infection or intrahemocoel injection assays, although differences in hyphal body differentiation in the host hemolymph and up-regulation of virulence-associated genes were noted. These data suggest novel roles for Pmt1 in negatively regulating conidiation and demonstrate that the C-terminal Pmt1 MIR-containing region is dispensable for enzymatic activity and organismal virulence.