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

• Published in: Molecular microbiology Vol. 38; no. 5; pp. 986 - 1003
• Main Authors: Slater, Holly, Alvarez‐Morales, Ariel, Barber, Christine E., Daniels, Michael J., Dow, J. Maxwell
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.12.2000
• Subjects: Amino Acid Sequence; Bacterial Proteins - biosynthesis; Bacterial Proteins - chemistry; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Base Sequence; DNA Primers; DNA Transposable Elements; DSF molecule; exopolysaccharides; extracellular polysaccharide; Molecular Sequence Data; Mutagenesis; Mutation; RNA, Messenger - genetics; rpfB gene; rpfC gene; RpfC protein; rpfE gene; rpfF gene; rpfG gene; RpfG protein; RpfH protein; Sequence Homology, Amino Acid; Signal Transduction; Virulence - genetics; Xanthomonas campestris; Xanthomonas campestris - genetics; Xanthomonas campestris - pathogenicity
• ISSN: 0950-382X; 1365-2958
• DOI: 10.1046/j.1365-2958.2000.02196.x

The 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.