FgVps9, a Rab5 GEF, Is Critical for DON Biosynthesis and Pathogenicity in Fusarium graminearum.

Chengdong Yang,Yingzi Yun,Jie Zhou,Danhua Liao,Jingjing Li,Yakubu Saddeeq Abubakar,Zonghua Wang,Guangpu Li,Xingzhi Zhang,Xin Chen,Wenhui Zheng

doi:10.3389/fmicb.2020.01714

Abstract

Rab GTPases play an important role in vesicle-mediated membrane trafficking in eukaryotes. Previous studies have demonstrated that deletion of RAB5/VPS21 reduces endocytosis and virulence of fungal phytopathogens in their host plants. However, Rab5 GTPase cycle regulators have not been characterized in Fusarium graminearum, the causal agent of Fusarium head blight (FHB) or head scab disease in cereal crops. In this study, we have identified and characterized a Rab5 guanine nucleotide exchange factor (GEF), the Vps9 homolog FgVps9, in F. graminearum. Yeast two hybrid (Y2H) assays have shown that FgVps9 specifically interacts with the guanosine diphosphate (GDP)-bound (inactive) forms of FgRab51 and FgRab52, the Rab5 isoforms in F. graminearum. Deletion of FgVPS9 shows impaired fungal growth and conidiation. Pathogenicity assays indicate that deletion of FgVPS9 can significantly decrease the virulence of F. graminearum in wheat. Cytological analyses have indicated that FgVps9 colocalizes with FgRab51 and FgRab52 on early endosomes and regulates endocytosis and autophagy processes. Gene expression and cytological examination have shown that FgVps9 and FgRab51 or FgRab52 function in concert to control deoxynivalenol (DON) biosynthesis by regulating the expression of trichothecene biosynthesis-related genes and toxisome biogenesis. Taken together, FgVps9 functions as a GEF for FgRab51 and FgRab52 to regulate endocytosis, which, as a basic cellular function, has significant impact on the vegetative growth, asexual development, autophagy, DON production, and plant infection in F. graminearum.

Highlights

Rab proteins are small (21–25 kDa) monomeric GTPases/guanosine triphosphate (GTP)-binding proteins and constitute the largest subfamily of Ras-like GTPases (Mizuno-Yamasaki et al, 2012; Li and Marlin, 2015; Pfeffer, 2017)
Rabs exert their functions by alternating between active GTP-bound and inactive guanosine diphosphate (GDP)-bound states, and this cycle is regulated by cognate guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs) (Barr and Lambright, 2010)
Phylogenetic analysis of Vps9 proteins in S. cerevisiae, P. oryzae, F. graminearum, and Fol indicates that FgVps9 is most closely related to the Vps9 proteins of Fol with 86.1% identity, followed by P. oryzae with 68.71% identity, and S. cerevisiae with 40.42% identity (Supplementary Figure S1B), suggesting that the Vps9 proteins may show similar biological functions in filamentous fungi

Summary

Introduction

Rab proteins are small (21–25 kDa) monomeric GTPases/guanosine triphosphate (GTP)-binding proteins and constitute the largest subfamily of Ras-like GTPases (Mizuno-Yamasaki et al, 2012; Li and Marlin, 2015; Pfeffer, 2017). Rab is the best documented Rab protein involved in the early endocytic pathway, which promotes the fusion of early endosomes by interacting with its effectors (Ohya et al, 2009). Rabs exert their functions by alternating between active GTP-bound and inactive guanosine diphosphate (GDP)-bound states, and this cycle is regulated by cognate guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs) (Barr and Lambright, 2010). GAPs accelerate the intrinsic Rab GTPase activity, converting GTP-bound active state to its GDP-bound inactivate state (Mizuno-Yamasaki et al, 2012; Li and Marlin, 2015; Pfeffer, 2017)

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Conclusion