Rab GTPases serve as master regulators of membrane trafficking. They can be activated by guanine nucleotide exchange factors (GEF) and be inactivated by GTPase-activating proteins (GAPs). The roles of some GAPs have been explored in Saccharomyces cerevisiae, but are largely unknown in filamentous fungi. Here, we investigated the role of GAP Gyp3 gene, an ortholog of S. cerevisiae Gyp3, in an entomopathogenic fungus, Metarhizium acridum. We found that MaGyp3 is mainly localized to the endoplasmic reticulum (ER) of vegetative hyphae, nuclei of mature conidia, and both ER and nuclei in invasive hyphae. Lack of MaGyp3 caused a decreased tolerance to hyperosmotic stress, heat-shock and UV-B radiation. Moreover, the ΔMaGyp3 mutant showed a significantly decreased pathogenicity owing to delayed germination, reduced appressorium-mediated penetration and impaired invasive growth. Loss of MaGyp3 also caused impaired fungal growth, advanced conidiation and defects in utilization of carbon and nitrogen sources, while overexpression of MaGyp3 exhibited delayed conidiation on nutrient-rich medium and conidiation pattern shift from microcycle conidiation to normal conidiation on nutrient-limited medium. Mavib-1, a tanscription factor invloved in conidiation by affecting nutrient utilizaiton, can directly bind to the promoter of MaGyp3. ΔMaGyp3 and ΔMavib-1 mutants shared similar phenotypes, and overexpression mutants of MaGyp3 and Mavib-1 (Mavib-1-OE) exhibited similar phenotypes in growth, conidiation and pathogenicity. Reintroduction of the Magyp3 driven by strong promoter gpd in ΔMavib-1 mutant recovered the defects in growth and conidiation for dysfunction of Mavib1. Taken together, our findings uncovered the role of GAP3 in a filamentous pathogenic fungus and and illustrated the upstream regulatory mechanism by direct interaction with Mavib-1.请用nature杂志的风格润色成学术论文的形式。

Metarhizium acridum GTPase-activating protein 3 (MaGyp3) is a GTPase-activating protein (GAP) ortholog of Saccharomyces cerevisiae Gyp3. Here, we investigated the role of MaGyp3 in an entomopathogenic fungus. We found that MaGyp3 is mainly localized to the endoplasmic reticulum (ER) of vegetative hyphae, nuclei of mature conidia, and both ER and nuclei in invasive hyphae. Loss of MaGyp3 caused decreased tolerance to hyperosmotic stress, heat-shock, and UV-B radiation, and significantly decreased pathogenicity owing to delayed germination, reduced appressorium-mediated penetration and impaired invasive growth. Additionally, MaGyp3 was found to be involved in fungal growth, conidiation, and utilization of carbon and nitrogen sources. Mavib-1, a transcription factor involved in conidiation, was identified as a direct upstream regulator of MaGyp3. Our findings uncover the role of GAP3 in a filamentous pathogenic fungus and illustrate the upstream regulatory mechanism by direct interaction with Mavib-1.