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HrpG and HrpX Play Global Roles in Coordinating Different Virulence Traits of Xanthomonas axonopodis pv. citri

June 2011 , Volume 24 , Number  6
Pages  649 - 661

Yinping Guo,1 Francisco Figueiredo,2 Jeffery Jones,2 and Nian Wang1

1Citrus Research and Education Center, Department of Microbiology and Cell Sciences, University of Florida, 700 Experiment Station Road, Lake Alfred 33850, U.S.A.; 2Department of Plant Pathology, University of Florida, Gainesville 32611, U.S.A.

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Accepted 21 January 2011.

Xanthomonas axonopodis pv. citri is the causal agent of citrus canker, which is one of the most serious diseases of citrus. To understand the virulence mechanisms of X. axonopodis pv. citri, we designed and conducted genome-wide microarray analyses to characterize the HrpG and HrpX regulons, which are critical for the pathogenicity of X. axonopodis pv. citri. Our analyses revealed that 232 and 181 genes belonged to the HrpG and HrpX regulons, respectively. In total, 123 genes were overlapped in the two regulons at any of the three selected timepoints representing three growth stages of X. axonopodis pv. citri in XVM2 medium. Our results showed that HrpG and HrpX regulated all 24 type III secretion system genes, 23 type III secretion system effector genes, and 29 type II secretion system substrate genes. Our data revealed that X. axonopodis pv. citri regulates multiple cellular activities responding to the host environment, such as amino acid biosynthesis; oxidative phosphorylation; pentose-phosphate pathway; transport of sugar, iron, and potassium; and phenolic catabolism, through HrpX and HrpG. We found that 124 and 90 unknown genes were controlled by HrpG and HrpX, respectively. Our results suggest that HrpG and HrpX interplay with a global signaling network and co-ordinate the expression of multiple virulence factors for modification and adaption of host environment during X. axonopodis pv. citri infection.

© 2011 The American Phytopathological Society