The GTPase-Activating Protein FgGyp1 Is Important for Vegetative Growth, Conidiation, and Virulence and Negatively Regulates DON Biosynthesis in Fusarium graminearium.

Ypt1 is a small Rab GTPase in yeast, Gyp1 functions at the Golgi as a negative regulator of Ypt1. Gyp1 homologs are conserved in filamentous fungi. However, the roles of Gyp1 in phytopathogenic fungi are still unclear. Herein, we investigated the functions of FgGyp1 in the wheat pathogen Fusarium graminearum by live-cell imaging, genetic, and pathological analyses. Targeted gene replacement method was used to delete FgGYP1 in F. graminearum. Phenotypic analyses showed that FgGyp1 is critically important not only for the vegetative growth of F. graminearum but also its conidiation. The mutant's vegetative growth was significantly reduced by 70% compared to the wild type PH-1. The virulence of FgGYP1 deletion mutant was significantly decreased when compared with the wild type PH-1. We further found that FgGyp1 negatively regulates DON production of the fungus. Live-cell imaging clearly demonstrated that FgGyp1 mainly localizes to the Golgi apparatus. Moreover, the TBC domain, C-terminal, and N-terminal regions of FgGyp1 are found to be indispensable for its biological functions and normal localization. The Arg357 residue of FgGyp1 is essential for its functions but dispensable for the normal localization of the protein, while the Arg284 residue is not required for both the functions and normal localization of the protein. Furthermore, we showed that FgGyp1 essentially hydrolyzes the GTP-bound FgRab1 (activated form) to its corresponding GDP-bound (inactive) form in vitro, suggesting that FgGyp1 is a GTPase-activating protein (GAP) for FgRab1. Finally, FgGyp1 was found to be important for FgSnc1-mediated fusion of secretory vesicles from the Golgi with the plasma membrane in F. graminearum. Put together, these data demonstrate that FgGyp1 functions as a GAP for FgRab1 and is important for vegetative growth, conidiation and virulence, and negatively regulates DON biosynthesis in F. graminearum.