Cell-cell signal interference in Xylella fastidiosa and Xanthomonas campestris

• Published in: Phytopathology 2004-06, Vol.94 (6)
• Main Authors: Newman, K L, Lindow, SE
• Format: Article
• Language: English
• Subjects: Xanthomonas campestris; Xanthomonas fastidiosa
• ISSN: 0031-949X

Xylella fastidiosa (Xf) is a Gram-negative bacterium that causes Pierce's disease of grapevine and other plant diseases. Xf is restricted to the xylem, where it forms an aggregated biofilm. In other systems, biofilms are characterized by community behavior under the control of cell density-dependent gene expression, which requires cell-cell signaling. Xf has homologs of the rpf cell-cell signaling genes found in the plant pathogen Xanthomonas campestris pv. campestris (Xcc) and probably shares a similar means of coordinating gene expression in a community. In Xcc, cell-cell signaling controls the expression of genes required for virulence in plants. We investigated cell-cell signaling in Xf with the aim of developing cell-cell signaling disruption as a means of controlling Pierce's disease. We found that Xf produces a cell-cell signal (DSF) and that the rpfF gene is necessary and sufficient for synthesis of this signal. Xf rpfF mutants are hypervirulent suggesting that cell-cell signaling attenuates virulence in Xf. We screened collections of bacterial strains and identified strains that interfere with DSF-mediated signaling. We are testing how these strains interact with Xf and Xcc in infected plants, identifying to which species they belong and isolating the genes responsible for DSF-interference activity. DSF-interference genes can then be introduced into plants for potential disease control. However, since DSF appears to attenuate disease symptoms in plants infected by Xf, expressing DSF synthases in plants may also reduce disease. Therefore we are constructing transgenic plants that synthesize DSF to evaluate pathogenicity of Xf and Xcc in these plants.