A two‐component system involving an HD‐GYP domain protein links cell–cell signalling to pathogenicity gene expression in Xanthomonas campestris

Abstract

SummaryThe synthesis of extracellular enzymes and extracellular polysaccharide (EPS) in Xanthomonas campestris pv. campestris (Xcc) is regulated by a cluster of genes called rpf (for regulation of pathogenicity factors). Two of the genes, rpfF and rpfB, have previously been implicated in the synthesis of a diffusible regulatory molecule, DSF. Here, we describe a screen of transposon insertion mutants of Xcc that identified two DSF-overproducing strains. In each mutant, the gene disrupted is rpfC, which encodes a hybrid two-component regulatory protein in which the sensor and regulator domains are fused and which contains an additional C-terminal phosphorelay (HPt) domain. We show that rpfC is in an operon with rpfH and rpfG. The predicted protein RpfG has a regulatory input domain attached to a specialized version of an HD domain, previously suggested to function in signal transduction. The predicted protein RpfH is structurally related to the sensory input domain of RpfC. We show that RpfC and RpfG act positively to regulate the synthesis of extracellular enzymes and EPS, but that RpfC acts negatively to regulate the synthesis of DSF. We propose that RpfGHC is a signal transduction system that couples the synthesis of pathogenicity factors to sensing of environmental signals that may include DSF itself.

RETRACTED: Cell–cell signaling in Xanthomonas campestris involves an HD-GYP domain protein that functions in cyclic di-GMP turnover

“…campestris (Xcc), the causal agent of black rot, an agronomically important disease of crucifers (15). In Xcc the synthesis of extracellular enzyme and extracellular polysaccharide (EPS) virulence factors and the dispersal of biofilms are positively controlled by a two-component signal transduction system comprising the HD-GYP domain regulatory protein RpfG and cognate sensor RpfC (16,17). The genes encoding these proteins are organized as the rpfGHC operon (16).…”

“…In Xcc the synthesis of extracellular enzyme and extracellular polysaccharide (EPS) virulence factors and the dispersal of biofilms are positively controlled by a two-component signal transduction system comprising the HD-GYP domain regulatory protein RpfG and cognate sensor RpfC (16,17). The genes encoding these proteins are organized as the rpfGHC operon (16). Mutation of rpfG and rpfC either alone or in combination leads to a coordinate reduction in the synthesis of the extracellular enzymes protease, endoglucanase, and endomannanase and the EPS xanthan (16,17) and to the formation of biofilms (17).…”

Genetic and physiological characterization of the Borrelia burgdorferi ORF BB0374-pfs-metK-luxS operon

“…1) , 2006;Ryan et al, 2006a Ryan et al, , b, 2007Slater et al, 2000). A response regulator protein of B. burgdorferi, Rrp1, synthesizes cyclic di-GMP (Ryjenkov et al, 2005), but the phosphohydrolase responsible for degrading cyclic di-GMP has yet to be identified.…”

“…For example, HD-GYP domain proteins of Xanthomonas spp. degrade the small signalling molecule cyclic di-GMP and are linked to both intercellular signalling and pathogenicity (Andrade et al, 2006;Ryan et al, 2006aRyan et al, , b, 2007Slater et al, 2000). A response regulator protein of B. burgdorferi, Rrp1, synthesizes cyclic di-GMP (Ryjenkov et al, 2005), but the phosphohydrolase responsible for degrading cyclic di-GMP has yet to be identified.…”

Regulation of the Type II Secretion Structural Gene xpsE in Xanthomonas campestris Pathovar campestris by the Global Transcription Regulator Clp

“…Xcc has evolved different regulatory mechanisms governing the expression of virulence-related genes. A cluster of genes, composed of rpfA-G and designated the rpf (regulation of pathogenicity factors) gene cluster, regulate the synthesis but not the secretion of extracellular enzymes and polysaccharides [23,26]. The cyclic AMP receptor protein-like protein (Clp) as a global transcription regulator is involved in regulation of several virulence factors.…”