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J. Bacteriol. doi:10.1128/JB.01331-06
Copyright (c) 2006, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

hpaR, a putative marR family transcriptional regulator, is positively controlled by HrpG and HrpX and involved in the pathogenesis, hypersensitive response and extracellular protease production of Xanthomonas campestris pathovar campestrism

College of Agriculture and Biotechnology, Zhejiang University, Hangzhou 310029, China. 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

^* To whom correspondence should be addressed. Email: jltang{at}gxu.edu.cn.

	Abstract

The MarR family transcriptional regulators of bacteria are involved in the regulation of many cellular processes, including pathogenesis. In this work, we have demonstrated genetically that hpaR (hpa, hrp-associated), which encodes a putative MarR family regulator, is involved in the hypersensitive response (HR), pathogenicity and extracellular protease production of the phytopathogenic bacterium Xanthomonas campestris pathovar campestris. A mutation in hpaR resulted in complete loss of virulence in the host plant cabbage, a delayed and weakened HR in the non-host plant pepper ECW-10R and an increase in extracellular protease production. Detection of the GUS activity of a plasmid-drived hpaR promoter-gusA reporter revealed that the expression of hpaR is positively controlled by HrpG and HprX, and is suppressed in rich medium while being strongly induced in minimal and hrp-inducing media and inside the host. These findings indicate that hpaR belongs to the hrpG and hrpX regulon and HprX regulates the extracellular protease production via hpaR in X. campestris pv. campestris.

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