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Regulation of the pehA gene encoding the major polygalacturonase of Xanthomonas campestris by Clp and RpfF

¹ Department of Medical Laboratory Science and Biotechnology, Central Taiwan University of Science and Technology, Taichung 406, Taiwan, ROC
² Institute of Biotechnology, Chaoyang University of Technology, Taichung 413, Taiwan, ROC
³ Department of Biotechnology and Bioinformatics, Asia University, Taichung 413, Taiwan, ROC
⁴ Department of Medical Laboratory Science and Biotechnology, China Medical University, Taichung 404, Taiwan, ROC
⁵ Institute of Medical Biotechnology, Central Taiwan University of Science and Technology, Taichung 406, Taiwan, ROC

Correspondence
Yi-Hsiung Tseng
yhtseng{at}ctust.edu.tw

Exopolysaccharide and several extracellular enzymes of Xanthomonas campestris pv. campestris (Xcc), the causative agent of black rot in crucifers, are virulence factors. In this study, sequence and mutational analysis has demonstrated that Xcc pehA encodes the major polygalacturonase, a member of family 28 of the glycosyl hydrolases. Using the 5' RACE (rapid amplification of cDNA ends) method, the pehA transcription initiation site was mapped at 102 nt downstream of a Clp (cAMP receptor protein-like protein)-binding site. Transcriptional fusion assays showed that pehA transcription is greatly induced by polygalacturonic acid, positively regulated by Clp and RpfF (an enoyl-CoA hydratase homologue which is required for the synthesis of cis-11-methyl-2-dodecenoic acid, a low-molecular-mass diffusible signal factor), subjected to catabolite repression, which is independent of Clp or RpfF, and repressed under conditions of oxygen limitation or nitrogen starvation. Our findings extend previous work on Clp and RpfF regulation to show that they both influence the expression of pehA in Xcc.