Pathogenesis Analysis Of Type â…¢ Secretion System HRP Genes In Xanthomonas Campestris Pathovar Campestris

Xanthomonas campestris pathovar campestris (Xcc) causes black rot, one of the most serious diseases of cruciferous plants, almost in all cruciferous plants worldwide.Gram-negative plant pathogenic bacteria cause disease in host plants and trigger a HR (hypersensitive response) in non-hosts or resistant host plant through injecting type III secreted effectors (T3SEs) into host cells. T3SE is a class of protein secreted by the conservative type III secretion system (T3SS), which is encoded by hrp cluster. To investigate the function of hrp genes per se in hrp cluster, the deletion mutants of hrp genes were constructed one by one. The results showed that each of the nine hrc genes mutants abolished the virulence in Chinese radish and lost the HR induction in pepper ECW-10R. As for the nine hrp genes, only the knockout of hrpW triggered a tardy HR and decreased virulence, others lost virulence and HR induction completely. The virulence and the ability to trigger HR abolished in hpaA and hpaB mutants, while the deletion of hpal and hpaP reduced virulence and HR significantly. Pathogenicity studies revealed that hrp gene mutant are essential for pathogenicity in cabbage. The growth curve assay of bacterial in host plant indicated plasmids lost were present of generally even completely, which may result in not restoring to the wild-type phenotype in trans complementation. Furthermore, transcription analysis through RT-PCR demonstrated that all members of hrp cluster in Xcc8004are activated by hrpG and hrpXat different levels.