A Glycosyl Hydrolase 5 Family Protein Is Essential for Virulence of Necrotrophic Fungi and Can Suppress Plant Immunity

Phytopathogenic fungi normally secrete large amounts of CWDEs to enhance infection of plants. In this study, we identified and characterized a secreted glycosyl hydrolase 5 family member inSclerotinia sclerotiorum(SsGH5,Sclerotinia sclerotiorumGlycosyl Hydrolase 5).SsGH5was significantly upregulated during the early stages of infection. Knocking outSsGH5did not affect the growth and acid production ofS. sclerotiorumbut resulted in decreased glucan utilization and significantly reduced virulence. In addition,Arabidopsis thalianaexpressing SsGH5 became more susceptible to necrotrophic pathogens and basal immune responses were inhibited in these plants. Remarkably, the lost virulence of theΔSsGH5mutants was restored after inoculating ontoSsGH5transgenicArabidopsis. In summary, these results highlight thatS. sclerotiorumsuppresses the immune responses ofArabidopsisthrough secreting SsGH5, and thus exerts full virulence for successful infection.