Poster: Plant-pathogen interactions

Abs # 536: The Xanthomonas campestris pv. vesicatoria effector protein XopX contributes to pathogen virulence and suppresses host defense in Nicotiana benthamiana

Presenter:	Morales, Christina Q, cmorales@uclink.berkeley.edu
Authors	Morales, Christina Q (A)   Metz, Matthew  (B)   Dahlbeck, Douglas  (A)   Al Sady, Bassem  (A)   Staskawicz, Brian  (A)
Affiliations:	(A): University of California, Berkeley (B): Bureau for Economic Growth, Agriculture & Trade

A genomic library of Xanthomonas campestris pv. vesicatoria (Xcv) was constructed in the wide host range cosmid pLAFR3 and conjugated into Xanthomonas campestris pv. campestris (Xcc) strain 8004. Transconjugants were inoculated into Nicotiana benthamiana leaves and screened for the production of a non-host necrotic reaction. Two overlapping cosmid clones were identified, both containing a novel gene, xopX, that encodes the 74kD effector protein. XopX contributes to the fitness of Xcv on pepper and tomato plants, as site-directed gene knock-outs in Xcv were less virulent in the normally susceptible pepper and tomato hosts. Unexpectedly, Agrobacterium-mediated transient expression of XopX in N. benthamiana produced detectable protein levels but no necrotic reaction was seen. However, the necrotic reaction was observed in Agrobacterium-mediated transient expression of XopX in N. benthamiana when co-inoculated with either Xcv∆XopX or Xcc, which lacks XopX. The necrotic reaction is Type III Secretion System (TTSS)-dependent. In addition, XopX is translocated from Xcv into the plant cell by measuring increased levels of cAMP that result from the translocation of a calmodulin-dependent xopX:adenyl cyclase translational fusion. Transgenic XopX-expressing N. benthamiana plants were also compromised in basal host defense as these plants were more susceptible to bacterial infection. These results suggest that XopX is an important bacterial effector protein that targets basic innate immunity in plants and contributes to pathogen virulence. Current work is to determining the in planta targets of XopX, identifying other bacterial effectors necessary for the causing the necrotic reaction, and determining the regions of xopX necessary for activity.