Submitted to: CDFA Pierce's Disease Control Program Research Symposium
Publication Type: Proceedings
Publication Acceptance Date: 12/15/2013
Publication Date: 12/16/2013
Citation: Lin, H., Shi, X. 2013. Characterization of Xylella fastidiosa gcvR gene required for pathogenicity. CDFA Pierce's Disease Control Program Research Symposium, December 16-18, 2013, Sacramento, California. p.48-52. Interpretive Summary: Xylella fastidiosa (Xf) is a plant pathogenic bacterium that causes Pierce’s disease (PD) in grapevine. The virulence regulator, gvcR, is known to coordinate expression of virulence-related factors responsible for cellular aggregation and biofilm formation of Xf in host plants. To reveal the role of gcvR in PD, a mutant strain of Xf that lacks gcvR was constructed. Pathogenicity was evaluated by inoculation of the mutant strain into grapevines. The mutant strain exhibited reduced biofilm formation resulting in reduced pathogenicity. The characterization of the virulence regulator gcvR of Xf improves the understanding of how Xf causes PD.
Technical Abstract: The transcriptional regulator gcvR of Xylella fastidiosa (Xf) is a putative pathogenicity gene. To elucidate the role of gcvR in Pierce's disease (PD) development, mutant Xf'gcvR and complementary Xf'gcvR-C strains were constructed. The genetically modified strains and wild type Xf were inoculated into cabernet sauvignon grapevines. Three months after inoculation, grapevines inoculated with wild type or Xf'gcvR-C showed typical PD symptoms while plants inoculated with Xf'gcvR showed very mild symptoms. Quantitative PCR assays demonstrated that Xf titers in grapevines inoculated with wild type or Xf'gcvR-C strains were significantly higher than that of grapevines inoculated with Xf'gcvR. In vitro studies showed that while all Xf strains had similar growth curves, Xf'gcvR exhibited significant reduction in biofilm formation. The results suggest that the knockout of gcvR in Xf reduces colonization of grapevines, resulting in reduced pathogenicity.