Adaption to stress via Pbs2 during Metarhizium rileyi conidia and microsclerotia development.

The high osmolarity glycerol (HOG) pathway plays important role in Metarhizium rileyi microsclerotia (MS) development. To investigate how M. rileyi transduce growth stress and regulate MS development via mitogen-activated protein kinase kinase (MAPKK) Pbs2, phenotypic characterization of the yeast Pbs2 homolog were performed. Expression of pbs2 peaked when MS formation occurred day 3 in liquid amended medium. Compared with wild-type and complemented strains, deletion mutant of pbs2 (Δpbs2) delayed dimorphic switch and vegetative growth, displayed sensitivities to various stress, and significantly reduced conidial (98%) and MS (40%) yields. Furthermore, transcription analysis showed that other genes of HOG signaling pathway were down-regulated in Δpbs2 mutants. Insect bioassays revealed that Δpbs2 mutants had decreased virulence levels in topical (24%) and injection (53%) bioassays. This study confirmed that Pbs2 play important roles in colony morphology, conidiation, stresses response and MS development in M. rileyi.