title: Comparative and functional genomics reveals genetic diversity and determinants of host specificity among reference strains and a large collection of Chinese isolates of the phytopathogen Xanthomonas campestris pv. campestris.
abstract: BACKGROUND
  Xanthomonas campestris pathovar campestris (Xcc) is the causal agent of black rot disease of crucifers worldwide. The molecular genetic diversity and host specificity of Xcc are poorly understood.
  
  
  RESULTS
  We constructed a microarray based on the complete genome sequence of Xcc strain 8004 and investigated the genetic diversity and host specificity of Xcc by array-based comparative genome hybridization analyses of 18 virulent strains. The results demonstrate that a genetic core comprising 3,405 of the 4,186 coding sequences (CDSs) spotted on the array are conserved and a flexible gene pool with 730 CDSs is absent/highly divergent (AHD). The results also revealed that 258 of the 304 proved/presumed pathogenicity genes are conserved and 46 are AHD. The conserved pathogenicity genes include mainly the genes involved in type I, II and III secretion systems, the quorum sensing system, extracellular enzymes and polysaccharide production, as well as many other proved pathogenicity genes, while the AHD CDSs contain the genes encoding type IV secretion system (T4SS) and type III-effectors. A Xcc T4SS-deletion mutant displayed the same virulence as wild type. Furthermore, three avirulence genes (avrXccC, avrXccE1 and avrBs1) were identified. avrXccC and avrXccE1 conferred avirulence on the hosts mustard cultivar Guangtou and Chinese cabbage cultivar Zhongbai-83, respectively, and avrBs1 conferred hypersensitive response on the nonhost pepper ECW10R.
  
  
  CONCLUSIONS
  About 80% of the Xcc CDSs, including 258 proved/presumed pathogenicity genes, is conserved in different strains. Xcc T4SS is not involved in pathogenicity. An efficient strategy to identify avr genes determining host specificity from the AHD genes was developed.
authors.affiliation: Guangxi Key Laboratory of Subtropical Bioresources Conservation and Utilization, and College of Life Science and Technology, Guangxi University, Daxue Road, Nanning, Guangxi 530004, People's Republic of China. yqhe@gxu.edu.cn
authors.forename: Yong-Qiang
authors.initials: YQ
authors.lastname: He
authors.forename: Liang
authors.initials: L
authors.lastname: Zhang
authors.forename: Bo-Le
authors.initials: BL
authors.lastname: Jiang
authors.forename: Zheng-Chun
authors.initials: ZC
authors.lastname: Zhang
authors.forename: Rong-Qi
authors.initials: RQ
authors.lastname: Xu
authors.forename: Dong-Jie
authors.initials: DJ
authors.lastname: Tang
authors.forename: Jing
authors.initials: J
authors.lastname: Qin
authors.forename: Wei
authors.initials: W
authors.lastname: Jiang
authors.forename: Xia
authors.initials: X
authors.lastname: Zhang
authors.forename: Jie
authors.initials: J
authors.lastname: Liao
authors.forename: Jin-Ru
authors.initials: JR
authors.lastname: Cao
authors.forename: Sui-Sheng
authors.initials: SS
authors.lastname: Zhang
authors.forename: Mei-Liang
authors.initials: ML
authors.lastname: Wei
authors.forename: Xiao-Xia
authors.initials: XX
authors.lastname: Liang
authors.forename: Guang-Tao
authors.initials: GT
authors.lastname: Lu
authors.forename: Jia-Xun
authors.initials: JX
authors.lastname: Feng
authors.forename: Baoshan
authors.initials: B
authors.lastname: Chen
authors.forename: Jing
authors.initials: J
authors.lastname: Cheng
authors.forename: Ji-Liang
authors.initials: JL
authors.lastname: Tang
mesh_terms: D019607:Brassicaceae / Q000382:microbiology*; D002681:China; D019295:Computational Biology; D014644:Genetic Variation; D040481:Genome Components; D023281:Genomics / Q000379:methods; D046228:Microarray Analysis; D009693:Nucleic Acid Hybridization; D012680:Sensitivity and Specificity; D013045:Species Specificity; D014774:Virulence / Q000235:genetics; D016959:Xanthomonas campestris / Q000235:genetics* / Q000472:pathogenicity