The Type II secretion system mediates virulence for the xylem-limited pathogen, Xylella fastidiosa
B. INGEL (1), P. Wang (2) (1) University of California Riverside, U.S.A.; (2) University of California Riverside, U.S.A.

Xylella fastidiosa (Xf) is a gram-negative bacterium that inhabits the grapevine xylem and causes Pierce’s disease (PD), a lethal disease of grapevines. PD symptom progression is highly correlated with systemic colonization. Movement within the xylem is critical for achieving systemic colonization and relies on the degradation of pit membranes that separate adjacent xylem vessels. This is facilitated by Xf cell wall-degrading enzymes (CWDEs), three of which have been implicated as virulence factors: a polygalacturonase (PG), and two endoglucanases (EngXCA1 and EngXCA2). These CWDEs are predicted to be secreted by Xf into the xylem via the Type II secretion system (T2SS). A knockout mutation of the T2SS ATPase gene (ΔxpsE) resulted in a complete loss of pathogenicity similar to that displayed by the PG-deficient mutant strain. Furthermore, secretome analyses of both the Xf wild-type and ΔxpsE mutant strains had distinct differences in protein composition, and an antibody targeting EngXCA2 revealed that secretion of this endoglucanase is Type II-dependent. Xf lacks a Type III secretion system, a canonical mechanism of delivery of virulence-related effectors into host cells. Our study provides clear evidence that the Xf relies heavily on the T2SS during its interaction with its host and that Type II-dependent secretion of CWDEs are indispensible for systemic colonization of grapevines.

Abstract Number: P7-175
Session Type: Poster