GsmR, a response regulator with an HD‐related output domain in Xanthomonas campestris, is positively controlled by Clp and is involved in the expression of genes responsible for flagellum synthesis

Abstract

In prokaryotes, two-component signal transduction systems, consisting of a histidine kinase and a response regulator, play a critical role in regulating a range of cellular functions. A recent study suggests that XCC3315, a response regulator with a CheY-like receiver domain attached to an uncharacterized HD-related output domain (HDOD domain), plays a role in the general stress response of the Gram-negative bacterium Xanthomonas campestris pv. campestris (Xcc), the causal agent of black rot in cruciferous plants. Here, we demonstrated genetically that XCC3315, designated as gsmR (general stress and motility regulator), is involved in the expression of genes responsible for flagellum synthesis, including rpoN2, flhF, flhB, and fliC. Site-directed mutagenesis revealed that Glu9 and Arg100 in the receiver domain and Gly205, Asp263, His287, Trp298 and His311 in the HDOD are critical amino acids for GsmR function in cell motility regulation. The gsmR transcription initiation site was mapped. Promoter analysis and gel retardation assay revealed that the expression of gsmR is positively controlled by the global transcriptional regulator Clp in a direct manner, and is subject to catabolite repression. Our findings not only extend the previous work on Clp regulation to show that it influences the expression of gsmR in Xcc, but are also the first to characterize the expression of this response regulator gene in this phytopathogen. Furthermore, GsmR is the first HDOD-containing protein of bacteria in which key amino acids have been experimentally identified and characterized.

Identification and characterization of naturally occurring DSF‐family quorum sensing signal turnover system in the phytopathogen Xanthomonas

“…Clp has been well studied as a cyclic di‐GMP‐responsive transcriptional regulator that plays essential roles in virulence factor production and the DSF signalling network in Xcc (He et al ., ; Chin et al ., ; Tao et al ., ). In most cases, Clp acts a transcriptional activator in Xcc (He et al ., ; Liu et al ., ). The present study demonstrated that Clp acts as a repressor in the regulation of rpfB expression (Fig.…”

Genome-Wide Screening for Novel Candidate Virulence Related Response Regulator Genes in Xanthomonas oryzae pv. oryzicola

“…campestris ATCC 33913, four RR genes had been demonstrated in the full virulence for Xcc ( Qian et al, 2008b ). To date, 20 TCS proteins have been identified to be related to pathogenesis of Xanthomonas , including eight pairs of typical TCSs, RpfC-RpfG ( Tang et al, 1991 ), RaxH-RaxR ( Burdman et al, 2004 ), PhoQ-PhoP ( Lee et al, 2008 ), ColS-ColR (also named VgrS-VgrR) ( Qian et al, 2008b ; Zhang et al, 2008 ; Noh et al, 2014 ; Wang et al, 2016 ), RavS-RavR ( He et al, 2009 ), PdeK-PdeR (also named RavA-RavR) ( Yang et al, 2012 ; Tao et al, 2014 ), HpaR2-HpaS ( Li R.F et al, 2014 ), PcrK-PcrR ( Wang et al, 2017 ), four orphan RRs HrpG ( Wengelnik et al, 1996 ), VemR ( Tao and He, 2010 ), BfdR ( Huang et al, 2013 ), GsmR ( Liu et al, 2013 ), and XerR (also named XmbR and XibR) ( Wang et al, 2011 ; Yaryura et al, 2015 ; Pandey et al, 2016 ). The TCSs modulate the expression of several virulence factors through diverse molecular mechanisms such as interacting with DNA, protein-binding and involvement in second messenger metabolism, which generates a high level of regulatory versatility ( Qian et al, 2008a ; Wang et al, 2010 ).…”

Identification of a cyclic-di-GMP-modulating response regulator that impacts biofilm formation in a model sulfate reducing bacterium

“…An HDOD RR, GsmR, was recently characterized from Xanthomonas campestris , and found to regulate the expression of motility related genes. GsmR lacked the conserved His in the active site, and also lacked phosphatase or phosphodiesterase activity (Liu et al, 2013). DVU0330 has the conserved HD active site residues (Figure 1C), and here we showed that the isolated domain has weak PDE activity with bis- p NPP and none with c-di-GMP or any of the other substrates.…”