SNARE-Encoding Genes VdSec22 and VdSsol Mediate Protein Secretion Required for Full Virulence in Verticillium dahliae

摘要

Proteins that mediate cellular and subcellular membrane fusion are key factors in vesicular trafficking in all eukaryotic cells, including the secretion and transport of plant pathogen virulence factors. In this study, we identified vesicle-fusion components that included 22 soluble N-ethyhnaleimide-sensitive factor attachment protein receptors (SNAREs), four Secl/Muncl8 (SM) family proteins, and 10 Rab GTPases encoded in the genome of the vascular wilt pathogen Verticillium dahliae Vd991. Targeted deletion of two SNARE-encoding genes in V. dahliae, VdSec22 and VdSsol, significantly reduced virulence of both mutants on cotton, relative to the wild-type Vd991 strain. Comparative analyses of the secreted protein content (exoproteome) revealed that many enzymes involved in carbohydrate hydrolysis were regulated by VdSec22 or VdSsol. Consistent with a role of these enzymes in plant cell-wall degradation, pectin, cellulose, and xylan utilization were reduced in the VdSec22 or VdSsol mutant strains along with a loss of exoproteome cytotoxic activity on cotton leaves. Comparisons with a pathogenicity-related exoproteome revealed that several known virulence factors were not regulated by VdSec22 or VdSsol, but some of the proteins regulated by VdSec22 or VdSsol displayed different characteristics, including the lack of a typical signal peptide, suggesting that V. dahliae employs more than one secretory route to transport proteins to extracellular sites during infection.