A Novel Hexose Transporter ChHxt6 Is Required for Hexose Uptake and Virulence in Colletotrichum higginsianum.

Qinfeng Yuan,Lu Zheng,Junbin Huang,Hao Liu,Tom Hsiang,Muhammad Aamir Sohail,Yaqin Yan

doi:10.3390/ijms22115963

Abstract

Colletotrichum higginsianum is an important hemibiotrophic plant pathogen that causes crucifer anthracnose worldwide. To date, some hexose transporters have been identified in fungi. However, the functions of hexose transporters in virulence are not clear in hemibiotrophic phytopathogens. In this study, we identified and characterized a new hexose transporter gene named ChHxt6 from a T-DNA insertion pathogenicity-deficient mutant G256 in C. higginsianum. Expression profiling analysis revealed that six ChHxt genes, ChHxt1 to ChHxt6, exhibited specific expression patterns in different infection phases of C. higginsianum. The ChHxt1 to ChHxt6 were separately deleted using the principle of homologous recombination. ChHxt1 to ChHxt6 deletion mutants grew normally on PDA plates, but only the virulence of ChHxt4 and ChHxt6 deletion mutants was reduced. ChHxt4 was required for fungal infection in both biotrophic and necrotrophic stages, while ChHxt6 was important for formation of necrotrophic hyphae during infection. In addition, ChHxts were functional in uptake of different hexoses, but only ChHxt6-expressing cells could grow on all five hexoses, indicating that the ChHxt6 was a central hexose transporter and crucial for hexose uptake. Site-directed mutation of T169S and P221L positions revealed that these two positions were necessary for hexose transport, whereas only the mutation Thr169 caused reduced virulence and defect in formation of necrotrophic hyphae. Taken together, ChHxt6 might regulate fungal virulence by modulating the utilization of hexose.

Highlights

The hemibiotrophic ascomycete fungus Colletotrichum higginsianum is an important pathogen that causes anthracnose on various cruciferous plants and leads to serious economic losses worldwide [1]
To test the pathogenicity of the deletion mutants, conidial suspension of each mutant was sprayed onto Arabidopsis plants, and the results showed that virulence of ∆ChHxt4 and ∆ChHxt6 were significantly decreased and formed fewer necrotic lesions on leaves at 4 days post inoculation (Figure 3C)
This study demonstrated that ChHxt6 is a novel hexose transporter in hemibiotrophic fungi, and it affects the virulence of C. higginsianum through influencing the uptake of hexose in the necrotrophic stage

Summary

Introduction

The hemibiotrophic ascomycete fungus Colletotrichum higginsianum is an important pathogen that causes anthracnose on various cruciferous plants and leads to serious economic losses worldwide [1]. The conidia of C. higginsianum attach onto the host surfaces, germinate and produce dark appressoria. The fungus penetrates epidermal cells and generates large bulbous biotrophic hyphae in the first infected living cell. Thin necrotrophic hyphae are produced which grow to kill host tissues, resulting in formation of necrotic leaf lesions [2]. A few plasma membrane-localized carbohydrate transporters have been identified in other fungi including the biotrophic fungi Uromyces fabae (the causal agent of broad bean rust) [7,8], Ustilago maydis (the causal agent of corn smut) [9,10], and Puccinia striiformis (the causal agent of wheat stripe rust) [11,12], the symbiotic glomeromycotan

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