The Colletotrichum gloeosporioides RhoB regulates cAMP and stress response pathways and is required for pathogenesis.

Rho GTPases regulate morphology and multiple cellular functions such as asexual development, polarity establishment, and differentiation in fungi. To determine the roles of CgRhoB, a Rho GTPase protein, here we characterized CgRhoB in the poplar anthracnose fungus Colletotrichum gloeosporioides. First of all, we determined that conidial germination was inhibited and intracellular cyclic AMP (cAMP) level was increased in the CgRhoB deletion mutants. Loss of CgRhoB resulted in shorter germ tubes and enhanced appressoria formation after germination on the hydrophobic surface. Exogenous addition of cAMP to the wild type generated the similar phenotypes of ΔCgRhoB inoculated in CM liquid. Furthermore, deletion of CgRhoB had discernible effect upon the sensitivity of C. gloeosporioides to cell wall perturbing agents and altered the distribution of chitin on the cell wall. HO sensitivity assay showed the hypersensitive effect on the oxidative stress, and transcriptional analysis revealed that transcription of genes involved in peroxidase activities was altered in the mutants. Finally, virulence assay revealed that CgRhoB was required for pathogenicity. Taken together, our results showed that CgRhoB was associated with appressoria formation and pathogenicity, and affected cAMP level and stress pathways.