FgBud3, a Rho4-Interacting Guanine Nucleotide Exchange Factor, Is Involved in Polarity Growth, Cell Division and Pathogenicity of Fusarium graminearum.

Chengkang Zhang,Hong Liu,Christopher Rensing,Hui Yin,Zenghong Luo,Dongdong He,Zonghua Wang,Guo Wang,Li Su

doi:10.3389/fmicb.2018.01209

Abstract

Rho GTPases are signaling macromolecules that are associated with developmental progression and pathogenesis of Fusarium graminearum. Generally, enzymatic activities of Rho GTPases are regulated by Rho GTPase guanine nucleotide exchange factors (RhoGEFs). In this study, we identified a putative RhoGEF encoding gene (FgBUD3) in F. graminearum database and proceeded further by using a functional genetic approach to generate FgBUD3 targeted gene deletion mutant. Phenotypic analysis results showed that the deletion of FgBUD3 caused severe reduction in growth of FgBUD3 mutant generated during this study. We also observed that the deletion of FgBUD3 completely abolished sexual reproduction and triggered the production of abnormal asexual spores with nearly no septum in ΔFgbud3 strain. Further results obtained from infection assays conducted during this research revealed that the FgBUD3 defective mutant lost its pathogenicity on wheat and hence, suggests FgBud3 plays an essential role in the pathogenicity of F. graminearum. Additional, results derived from yeast two-hybrid assays revealed that FgBud3 strongly interacted with FgRho4 compared to the interaction with FgRho2, FgRho3, and FgCdc42. Moreover, we found that FgBud3 interacted with both GTP-bound and GDP-bound form of FgRho4. From these results, we subsequently concluded that, the Rho4-interacting GEF protein FgBud3 crucially promotes vegetative growth, asexual and sexual development, cell division and pathogenicity in F. graminearum.

Highlights

Fusarium head blight (FHB), a disease of wheat and barley is mainly caused by the filamentous ascomycete Fusarium graminearum (Goswami and Kistler, 2004)
We identified six putative Rho GTPase guanine nucleotide exchange factors (RhoGEFs) proteins in F. graminearum by homology alignment
Domain alignment results showed that seven residues in two of the motifs identified are only conserved in the RhoGEF domain sequences of the six proteins (Figure 1B)

Summary

Introduction

Fusarium head blight (FHB), a disease of wheat and barley is mainly caused by the filamentous ascomycete Fusarium graminearum (teleomorph Gibberella zeae) (Goswami and Kistler, 2004). Rho GTPases are a small group of GTPases in the Ras GTPase superfamily They switch between active and inactive form by binding to GTP and GDP respectively. Rho GTPases including Rho and Cdc and their corresponding GEF activators have been well studied in budding yeast. Insights gained from studies conducted in yeast and filamentous fungi showed that some of these Rho GTPases, i.e., Rho in the budding yeast, could be activated by more than one GEF (Justa-Schuch et al, 2010; Krause et al, 2012; Kang et al, 2014). FgRac interacted with downstream targets including FgCla and FgNoxR to regulate asexual and sexual development in F. graminearum, respectively (Zhang et al, 2013, 2016). It is important to identify their roles in fungal development and pathogenesis process in plant pathogens

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