Identification of six type III effector genes with the PIP box in Xanthomonas campestris pv. campestris and five of them contribute individually to full pathogenicity.
Xanthomonas campestris pv. campestris is the pathogen of black rot of cruciferous plants. The pathogenicity of the pathogen depends on the type III secretion system (T3SS) that translocates directly effector proteins into plant cells, where they play important roles in the molecular interaction between the pathogen and its hosts. The T3SS of Xanthomonas spp. is encoded by a cluster of hypersensitive response and pathogenicity (hrp) genes. It has been demonstrated that the expression of hrp genes and some type III secreted (T3S)-effector genes is coactivated by the key hrp regulatory protein HrpX. The regulation by HrpX can be mediated by the binding of HrpX protein to a cis-regulatory element named the plant-inducible promoter (PIP) box present in the promoter region of HrpX-regulated genes. A genome screen revealed that X. campestris pv. campestris 8004 possesses 56 predicted genes with the PIP box. Nine of these genes have been shown to encode T3S effectors, Hrp, and Hrp-associated proteins. In this study, we employed an established T3S effector translocation assay with the hypersensitive-reaction-inducing domain of X. campestris pv. campestris AvrBs1 as a reporter to characterize the remaining 47 genes with the PIP box and showed that 6 of them, designated as XopXccE1, XopXccP, XopXccQ, XopXccR1, XopXccLR, and AvrXccB, harbor a functional translocation signal in their N-terminal regions, indicating that they are T3S effectors of X. campestris pv. campestris. We provided evidence to demonstrate that all these effectors are expressed in an HrpX-dependent manner and their translocation into plant cells relies on the translocon protein HrpF and the chaperone HpaB. Mutational analyses demonstrated that all these effectors, except AvrXccB, are individually required for full virulence and growth of X. campestris pv. campestris in the host plant Chinese radish.
Jiang
Wei
W
Guangxi Key Laboratory of Subtropical Bioresources Conservation and Utilization, The Key Laboratory of Ministry of Education for Microbial and Plant Genetic Engineering, and College of Life Science and Technology, Guangxi University, 100 Daxue Road, Nanning, Guangxi 530004, China.
Jiang
Bo-Le
BL
Xu
Rong-Qi
RQ
Huang
Jun-Ding
JD
Wei
Hong-Yu
HY
Jiang
Guo-Feng
GF
Cen
Wei-Jian
WJ
Liu
Jiao
J
Ge
Ying-Ying
YY
Li
Guang-Hua
GH
Su
Li-Li
LL
Hang
Xiao-Hong
XH
Tang
Dong-Jie
DJ
Lu
Guang-Tao
GT
Feng
Jia-Xun
JX
He
Yong-Qiang
YQ
Tang
Ji-Liang
JL
D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D002212:Capsicum / Q000382:microbiology; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology; D005798:Genes, Bacterial; D005801:Genes, Homeobox; D009154:Mutation; D010935:Plant Diseases / Q000382:microbiology; D014774:Virulence; D016959:Xanthomonas campestris / Q000235:genetics* / Q000378:metabolism* / Q000472:pathogenicity
D001426:Bacterial Proteins