Characterization of the Xylella fastidiosa PD1311 gene mutant and its suppression of Pierce's disease on grapevines
Xylella fastidiosa causes Pierce's disease (PD) on grapevines, leading to significant economic losses in grape and wine production. To further our understanding of X. fastidiosa virulence on grapevines, we examined the PD1311 gene, which encodes a putative acyl-coenzyme A (acyl-CoA) synthetase, and is highly conserved across Xylella species. It was determined that PD1311 is required for virulence, as the deletion mutant, DPD1311, was unable to cause disease on grapevines. The DPD1311 strain was impaired in behaviours known to be associated with PD development, including motility, aggregation and biofilm formation. DPD1311 also expressed enhanced sensitivity to H2O2 and polymyxin B, and showed reduced survival in grapevine sap, when compared with wild-type X. fastidiosa Temecula 1 (TM1). Following inoculation, DPD1311 could not be detected in grape shoots, which may be related to its altered growth and sensitivity phenotypes. Inoculation with DPD1311 2 weeks prior to TM1 prevented the development of PD in a significant fraction of vines and eliminated detectable levels of TM1. In contrast, vines inoculated simultaneously with TM1 and DPD1311 developed disease at the same level as TM1 alone. In these vines, TM1 populations were distributed similarly to populations in TM1-only inoculated plants. These findings suggest that, through an indirect mechanism, pretreatment of vines with DPD1311 suppresses pathogen population and disease.