MANAGEMENT OF PIERCES DISEASE OF GRAPE BY INTERFERING WITH CELL-CELL COMMUNICATION IN XYLELLA FASTIDIOSA

• Author(s): Lindow, Steven; Almeida, Rodrigo; Newman, Karyn; Purcell, Alexander;
• Abstract: Xylella fastidiosa (Xf) is an endophyte that is restricted to the xylem, a network of vessels for water transport, in which it forms an aggregated biofilm. It is transmitted from plant to plant by xylem sap-feeding insects, and forms a polar biofilm in these insects foreguts. 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 cell-cell signaling genes found in the important plant pathogen Xanthomonas campestris pathovar campestris (Xcc) and probably shares a similar means of coordinating gene expression in a community (2, 7). Using the Xcc paradigm as a guide, we have investigated cell-cell signaling in Xf with the aim of developing cell-cell signaling disruption as a means of controlling Pierces disease. We have determined that Xf produces a cell-cell signal and that the rpfF gene is necessary and sufficient for signal synthesis. We compared rpfF mutants to the wild type and found they are hypervirulent and non-transmissible. Lack of transmissibility was linked to an inability of the rpfF mutant to form a biofilm in the insect foregut. We are in the process of investigating the mechanism of hypervirulence. To further elucidate the behavior of Xf in planta, we created a green fluorescent strain of Xf and used confocal laser scanning microscopy to observe this strain of Xf within the xylem of plants. We found that vessel plugging is the colonization feature most tightly correlated with disease symptom expression, providing strong evidence that vessel plugging causes disease. We screened several collections of bacterial strains isolated from plants and identified bacterial strains that can interfere with Xf signaling. We are in the process of testing how these strains interact with Xf in the xylem, identifying to which species they belong and isolating the genes responsible for signal interference activity.
• Publication Date: Aug 2003
• Journal: 2003 Pierce's Disease Research Symposium