Functional analysis of avrBs2 from Taiwan-isolated Xanthomonas vesicatoria Xvt147

• Main Authors: You-Jen Chen, 陳宥溱
• Other Authors: 鄧文玲
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/07022958051610024959

碩士 === 國立中興大學 === 植物病理學系所 === 97 === Bacterial spot disease of pepper and tomato caused by Xanthomonas campestris pv. vesicatoria (Xcv) is a major problem where high temperatures and high humidity occur simultaneously. The pathogenicity of Xanthomonas spp. depends on a functional Type III secretion system (T3SS) and an array of effectors translocating through the T3SS. One effector of interest found in nearly all examined Xanthomonas spp. is AvrBs2. AvrBs2 is readily recognized by the R protein of Bs2 in resistant plants and is involved in promoting virulence in susceptible plants by unknown mechanisms. Sequence analysis reveals the amino acid residues 271-422 of Xv AvrBs2 are homologous to the catalytic domain residing in agrocinopine synthase (encoded by acs) of Agrobacterium tumefaciens and glycerophosphoryl diester phosphodiesterase (GDPD, encoded by ugpQ) of E. coli. In addition, diverse avrBs2 alleles identified in other Xanthomonas spp. are highly conserved in the catalytic domain, suggesting it is important for AvrBs2 activities in planta. Genetic studies of AvrBs2 function are done using gain-of-function and loss-of-function strategies in X. vesicatoria Taiwan strain Xvt147 and Xanthomonas campestris pv. raphani (cxsp3) Taiwan strain cxsp3, respectively. Xvt147 avrBs2 is mutated by marker exchange and the resultant mutant phenotypes are assayed in tomato. The degrees of symptom development and bacterial multiplication of Xvt147 avrBs2 mutant are comparable to the wild type strain. Nevertheless, overexpression of AvrBs2 in Xvt147 elicits severe symptoms on tomato when infected plants are subjected to short-term water deficiency. Heterologous expression of AvrBs2 in cxsp3 lacking the avrBs2 gene slightly increases bacterial growth at 1 dpi and delays the onset of symptom development in cabbage, indicating Xvt147 AvrBs2 might affect plant biochemical activities for symptom production. Interestingly, the expression of AvrBs2 in cxsp3 31 prevents the formation of bacterial aggregates that are usually seen in the stationary phase-grown bacteria, suggesting the functions of AvrBs2 might be important for bacterial adaptation in vitro and in planta.