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

Abstract

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 59 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.

Transcriptional analysis and functional characterization of XCC1294 gene encoding a GGDEF domain protein in Xanthomonas campestris pv. campestris

“…Glycerol or glucose was supplemented (2%) as required. The stress conditions have been described previously (Loprasert et al 1999;Hsiao et al 2008). BrieXy, for high osmolarity, 0.3 M NaCl was added.…”

“…The virulence of Xcc in cabbage (Brassica oleracea) was estimated after bacteria were introduced into the leaves by leaf clipping method (Hsiao et al 2008). The lesion length was measured 14 days post-inoculation.…”

“…It has been shown that motility is required for the full virulence of Xcc (McCarthy et al 2008). The expression of these virulence determinants is upregulated by Clp (cAMP receptor protein-like protein, Crp-like protein) (de CrecyLagard et al 1990;Chan and Goodwin 1999;Hsiao and Tseng 2002;Hsiao et al 2005Hsiao et al , 2008Hsiao et al , 2009Hsiao et al , 2010He et al 2007;Chen et al 2010). Deletion of clp causes reduced production of these pathogenic factors with a concomitant loss of pathogenicity (de Crecy-Lagard et al 1990;Tseng et al 1999;He et al 2007).…”

“…It exerts transcriptional activation by binding to the promoter of the target gene gum operon (involved in xanthan synthesis), as well as engA, pelA1, and pehA (coding for extracellular endogulcanase, pectate lyase, and polygalacturonase) in Xcc strain Xc17 (Hsiao et al 2005(Hsiao et al , 2008(Hsiao et al , 2009Chen et al 2010) and type II secretion structural gene xpsE in strain 8004 (Ge and He 2008). Recent Wndings have indicated that Clp binds with cyclic di-GMP and that this interaction abolishes the ability of Clp to bind to its target gene promoter (Tao et al 2010).…”

Expressional Regulation of the Virulence Gene eglXoA Encoding Endoglucanase, Dependent on HrpXo and Cyclic AMP Receptor-Like Protein (Clp) in Xanthomonas oryzae pv. oryza

“…It has been reported that the Clp protein directly binds to the promoter regions of the endoglucanase (engA) and polygalacturonase (pheA) genes of X. campestris, presumably enhancing transcriptional expression [26,28]. Therefore, it is reasonable to assume that ClpXo can also bind to the promoter region of eglXoA.…”