Open Access Research

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

Yong-Qiang He1, Liang Zhang2, Bo-Le Jiang1, Zheng-Chun Zhang1, Rong-Qi Xu1, Dong-Jie Tang1, Jing Qin1, Wei Jiang1, Xia Zhang1, Jie Liao1, Jin-Ru Cao1, Sui-Sheng Zhang1, Mei-Liang Wei1, Xiao-Xia Liang1, Guang-Tao Lu1, Jia-Xun Feng1, Baoshan Chen1, Jing Cheng2 and Ji-Liang Tang1*

Author Affiliations

1 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

2 CapitalBio Corporation, Life Science Parkway, Changping District, Beijing 102206, People's Republic of China

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Genome Biology 2007, 8:R218  doi:10.1186/gb-2007-8-10-r218

Published: 10 October 2007

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.

Conclusion

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.