, 1991; Barber et al., 1997; Slater et al., 2000; Dow et al., 2003; Fouhy et al., 2006; Ryan et al., 2006). RavS/RavR affect cell motility, exopolysaccharide synthesis, extracellular enzyme secretion and biofilm production
selleck kinase inhibitor by regulating the expression of the corresponding genes by cyclic-di-GMP synthesis or hydrolysis and activation of RavR (He et al., 2009 and our unpublished data). XCC3107 was identified by genome-scale mutagenesis and was found to be involved in protease production and virulence (Qian et al., 2008). HrpG is an important regulator that controls the expression of the type III secretion system by interacting with the downstream AraC-family transcription factor, HrpX (Noel et al., 2001). However, HrpG is an orphan RR whose cognate histidine kinase has not been identified to date. In this study, we have identified an orphan RR (VemR)
that is required for virulence and adaptation of Xcc. The vemR gene resides in an operon that consists of the rpoN2, vemR and fleQ genes (Fig. 1a). The NVP-BEZ235 rpoN2 gene encodes a sigma 54 factor that is involved in nitrogen assimilation, nitrogen fixation, utilization of carbon sources, motility, alginate biosynthesis and virulence (Reitzer & Schneider, 2001; Yang et al., 2009). The fleQ gene encodes a sigma 54 factor cognate activator that is essential for normal flagellation and transcription of the promoters of the fliE, fliL, fliQ, flgB, flgG, flhF and flhBA genes in Xcc strain XC17 (Hu et al., 2005; Yang et al., 2009). It was observed that insertional inactivation of the fleQ gene resulted in impaired motility and virulence in Xcc strain XC17 (Yang et al., 2009). However, insertional inactivation of the vemR gene, which probably affects the expression of the fleQ gene, has no significant effect on virulence in Xcc ATCC 33913 (Qian et al., 2008). To avoid
unwanted polar effects, ΔvemR and ΔfleQ mutants were generated by in-frame deletion of the vemR and fleQ genes, respectively. Phenotyping demonstrated that mutation of the vemR gene severely affected Xcc virulence, exopolysaccharide production and motility (Fig. 1b, c and 2), whereas mutation of the fleQ gene showed less phenotypic effects in Xcc strain 8004 ADP ribosylation factor (Fig. 4). Similar phenotypes were observed on deletion of the vemR gene in Xcc ATCC 33913 (data not shown). Moreover, the double-deletion mutant ΔvemR/ΔfleQ had a phenotype similar to the single mutant ΔfleQ (Fig. 4 and data not shown), suggesting that insertion inactivation of the vemR gene in Xcc ATCC 33913 might inactivate both vemR and fleQ genes simultaneously. Previous studies have shown that FleQ is an important regulator of the expression of flagella and exopolysaccharide biosynthesis genes in Pseudomonas aeruginosa (Dasgupta et al.