The Verticillium dahliae SnodProt1-Like Protein VdCP1 Contributes to Virulence and Triggers the Plant Immune System

Abstract

During pathogenic infection, hundreds of proteins that play vital roles in the <i>Verticillium dahliae</i>-host interaction are secreted. In this study, an integrated proteomic analysis of secreted <i>V</i>. <i>dahliae</i> proteins was performed, and a conserved secretory protein, designated VdCP1, was identified as a member of the SnodProt1 phytotoxin family. An expression analysis of the <i>vdcp1</i> gene revealed that the transcript is present in every condition studied and displays elevated expression throughout the infection process. To investigate the natural role of VdCP1 in <i>V. dahliae</i>, two <i>vdcp1</i> knockout mutants and their complementation strains were generated. Bioassays of these mutants revealed no obvious phenotypic differences from the wild-type (WT) in terms of mycelial growth, conidial production or mycelial/spore morphology. However, compared with the WT, the <i>vdcp1</i> knockout mutants displayed attenuated pathogenicity in cotton plants. Furthermore, treating plants with purified recombinant VdCP1 protein expressed in <i>Pichia pastoris</i> induced the accumulation of reactive oxygen species (ROS), expression of several defense-related genes, leakage of ion electrolytes, enhancement of defense-related enzyme activity and production of salicylic acid. Moreover, VdCP1 conferred resistance to <i>Botrytis cinerea</i> and <i>Pseudomonas syringae</i> pv. tabaci in tobacco and to <i>V. dahliae</i> in cotton. Further research revealed that VdCP1 possesses chitin-binding properties and that the growth of <i>vdcp1</i> knockout mutants was more affected by treatments with chitinase, indicating that VdCP1 could protect <i>V. dahliae</i> cell wall from enzymatic degradation, which suggests an effector role of VdCP1 in infecting hosts.