Molecular characterization and functional analysis of a specific secreted protein from highly virulent defoliating Verticillium dahliae.

Verticillium dahliae Kleb. is a phytopathogenic fungus that causes wilt diseases in hundreds of dicotyledonous plant species. Previous research has demonstrated that the secretome plays an important role in the pathogenicity of V. dahliae. In this study, the specific secreted protein gene (VdSSP1) in highly virulent defoliating V. dahliae strain VDG1 was cloned, and considered to be a secreted protein by signal peptide activity assay. VdSSP1 deletion mutants in VDG1 significantly compromised virulence, and the fungal growth decreased in media with pectin and starch as carbon sources. Pathogenicity and carbon utilization were restored upon complementation of the VdSSP1 deletion strains or low virulence non-defoliating strain VDG2, which lacks VdSSP1. It is indicated that the virulence role of VdSSP1 is associated with plant cell wall degradation. In conclusion, our data suggested that VdSSP1 is a secreted protein that is engaged in the pathogenicity of the highly virulent defoliating V. dahliae.