Poster: Plant Pathogen/Symbiont Interactions

Abs # 753: Characterization of the virulence and avirulence functions of the Xanthomonas campestris pv. campestris avrBs1 locus

Presenter:	Tang, Xiaoyan , xtang@ksu.edu
Authors	Tang, Xiaoyan  (A)   Chen, Jianfu  (A)   Shan, Libo  (A)   White, Frank  (A)   He, Chao  (B)
Affiliations:	(A): Kansas State University (B): Institute of Microbiology, Chinese Academy of Sciences

Xanthomonas campestris pv. campestris (Xcc) causes black rot diseases on crucifer plants. Like many other Gram negative bacterial pathogens, Xcc injects an array of virulence proteins, referred to as type III effectors, into host cells through the type III secretion system. Here we report the characterization of the avrBs1 locus of Xcc. The Xcc avrBs1 locus contains two genes, ORF2099 and ORF2100, that appear to encode two type III effectors. ORF2099 encodes a functional phosphotyrosine phosphatase homologous to HopPtoD2, a type III effector of Pseudomonas syringae pv. tomato DC3000 strain. ORF2100 encodes a protein homologous to the C-terminus of the AvrA protein of P. s. pv. glycinia and accounts for the avirulence activity in X. c. pv. vesictoria on pepper plants carrying the Bs1 disease resistance gene. Insertional mutation of ORF2099, which also created a polar mutation on ORF2100, in Xcc 33913 strain clearly reduced the bacterial pathogenicity on cabbage and Arabidopsis plants. Disruption of ORF2100 alone in Xcc also reduced the bacterial pathogenicty. Expression of ORF2099 alone in Xcc slightly enhanced the bacterial pathogenicity. These results suggest that both ORFs contribute to bacterial pathogenicity. ORF2099 alone does not have avirulence activity on Bs1 pepper plants. However, mutation that truncates the ORF2099 gene reduced the avirulence activity of the avrBs1 locus, suggesting a functional interaction of the ORF2099/2100 proteins in avirulence function. The functional interaction of ORF2099/2100 proteins, the role of the tyrosine phosphatase activity of ORF2099 in virulence and avirulence, and the molecular functions of ORF2099/2100 in plant cells are being investigated.