Function Analyses Of The Wxc Gene Cluster Of Xanthomonas Campestris Pv.Campestris

Xanthomonas campestris pv. campestris (Xcc) is the pathogenic agent of black rot disease of cruciferous plants. Lipopolysacchride (LPS) is one of the biochemical factors leading to pathogenicity of Xcc. It was shown that wxc gene cluster of Xcc B100 is involved in the biosynthesis of LPS core and LPS O-antigen. Analysis based on genomic sequencing revealed that wxc gene cluster of Xcc 8004 is not identical to that of Xcc BlOO. To identify the function of wxc cluster of Xcc 8004 strain, integration mutants of wxcN, rmd, wzt and XC3621 of this cluster were constructed to analysis their pathogenicity and phenotypes of LPS and EPS. SDS-PAGE analysis showed that LPS pattern of mutant NK3626 on gel differed significantly from wild-type strain 8004 and it is deduced that rmd is involved in the biosynthesis of the LPS core. Analysis of pathogenicit} on Chinese radish revealed that virulence of PK3620, NK3626 reduced by more than 50% compared with 8004 and could restored to 71.7% and 90.3% respectively after complemented in trans with the intact wxcN and rmd gene. LPS yields of PK3620, NK3626and NK3632 decreased significantly in contrast to 8004. After complemented with the intact wxcN,rmd and wzt gene, EPS yield of PK3620 restored to the level of 8004 and those of NK3626 and NK3632 surpassed 8004 by 35% and 28%. The combined data showed that wxcN as well as rmd are involved in both virulence and EPS biosynthesis of Xcc 8004, but wzt is only related to the biosynthesis of EPS. This study also showed that phenotypes of NK3621 did not change significantly and more research is needed to elucidate the function of ORF XC3621.