Cooperators:

Xylella fastidiosa (Xf) has homologs of the cell-cell signaling genes found in the important plant pathogen Xanthomonas campestris pathovar campestris (Xcc) and produces a similar alpha,beta unsaturated fatty acid signal molecule called DSF that coordinates gene expression. We have investigated DSF-mediated cell-cell signaling in Xf with the aim of developing cell-cell signaling disruption as a means of controlling Pierce’s disease (PD). The rpfF gene is necessary and sufficient for DSF signal synthesis and rpfF mutants of Xf 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; while taken up by insects, the mutant strain is not retained. Xf strains that overproduce DSF produce disease symptoms in grape, but only at the site of inoculation and the cells do not move within the plant as do wild-type strains. Thus elevating DSF levels in plants should reduce movement of Xf in the plant and also reduce the likelihood of transmission by sharpshooters. We identified bacterial strains that can interfere with Xf signaling both by producing large amounts of DSF, by degrading DSF, or by in some way interfering with recognition of DSF. When co-inoculated into grape with Xf, both DSF-producing strains and DSF-degrading strains greatly reduced the incidence and severity of disease in grape; DSF-producing strains consistently were the most effective in reducing disease. Disease was also reduced when some of these strains were simply sprayed onto grape before inoculation with Xf, indicating that they can alter behavior of the pathogen even when not co-inoculated. To verify that disease control i