Management of Pierce’s disease of grape by interfering with cell-cell communication in Xylella fastidiosa. Pages 20-22

Xylella fastidiosa (Xf) produces an unsaturated fatty acid signal molecule called diffusible signal factor (DSF) that changes its gene expression in cells as they reach high numbers in plants. 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. We have investigated both the role of DSF-production by Xf on its behavior within plants, the manner in which other bacterial strains affect such cell signaling, the extent to which other endophytes could modulate density-dependent behaviors and virulence in Xf by interfering with cell-cell signaling, performed genetic transformation of grape to express DSF, and explored other means to alter DSF abundance in plants to achieve PD control. Xf mutant strains that overproduce DSF cause 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 or by degrading DSF. We have identified the genes needed to degrade DSF and when they were transferred to and over-expressed in other strains they conferred the ability of these strains to degrade 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. Given that DSF overabundance appears to mediate an attenuation of virulence in Xf we have transformed grape with the rpfF gen