P-145 - Prediction and confirmation of type III effectors in Xylophilus ampelinus, the causal agent of the Oléron's disease of grapevine

Bacterial blight of grapevine, also known as "maladie d’Oléron" in France, is caused by the slow-growing bacterium Xylophilus ampelinus (Willems et al., 1987), formerly known as Bacillus vitivorus (Baccarini, 1893), Erwinia vitivora (Du Plessis, 1940) and Xanthomonas ampelina (Panagopoulos, 1969). Symptoms include discoloration of young shoots, necrotic spots on leaves, reddish-brown streaks on shoots, cracks, cankers, wilting and dieback. The bacterium is reported as vascular pathogen colonizing the xylem, forming biofilms. Later, also phloem and cambial tissues were found to be infected. To shed light into the biology of this pathogen, we scrutinized all available genomes of the genus for the presence of type III secretion systems, predicted >30 type III effectors using the machine-learning program Effectidor. Most of the predicted effectors have homologs in Ralstonia, Xanthomonas and/or Pseudomonas. Three less conserved effectors, belonging to the Ulp1 family of isopeptidases, were shown to contain a functional type III secretion signal using an AvrBs1 reporter approach. The presence of type III effectors suggests that effector-triggered immunity may exist in grapevine or non-host plants and that strategies targeting type III effectors for resistance engineering may contribute to suitable control measures.