title: The autoregulatory role of EsaR, a quorum-sensing regulator in Pantoea stewartii ssp. stewartii: evidence for a repressor function.
abstract: Capsular polysaccharide synthesis and virulence in the plant pathogenic bacterium Pantoea stewartii ssp. stewartii requires the quorum-sensing regulatory proteins, EsaR and EsaI, and the diffusible inducer N-(3-oxo-hexanoyl)-L-homoserine lactone. Prior mutational studies suggested that EsaR might function as a repressor of quorum sensing in the control of capsular polysaccharide synthesis. Further, a lux box-like palindromic sequence coinciding with the putative -10 element of the esaR promoter suggested a possible negative autoregulatory role for EsaR. This report presents genetic evidence that EsaR represses the esaR gene under inducer-limiting conditions, and that addition of inducer promotes rapid, dose-dependent derepression. DNA mobility-shift assays and analyses by surface plasmon resonance refractometry show that EsaR binds target DNAs in a ligand-free state, and that inducer alters the binding characteristics of EsaR. Physical measurements indicate that the EsaR protein binds N-(3-oxo-hexanoyl)-L-homoserine lactone, in a 1:1 protein:ligand ratio, and that inducer binding enhances the thermal stability of the EsaR protein. These combined genetic and biochemical data establish that EsaR regulates its own expression by signal-independent repression and signal-dependent derepression. Additionally, we provide evidence that EsaR does not govern the expression of the linked esaI gene, thus EsaR has no role in controlling coinducer synthesis.
authors.affiliation: Department of Plant Science University of Connecticut, 302B AG Biotech, Storrs, CT 06269, USA.
authors.forename: Timothy D
authors.initials: TD
authors.lastname: Minogue
authors.forename: Markus
authors.initials: M
authors.lastname: Wehland-von Trebra
authors.forename: Frank
authors.initials: F
authors.lastname: Bernhard
authors.forename: Susanne B
authors.initials: SB
authors.lastname: von Bodman
mesh_terms: D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000302:isolation & purification; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D005809:Genes, Regulator / Q000235:genetics; D006706:Homeostasis; D020636:Pantoea / Q000235:genetics*; D011401:Promoter Regions, Genetic; D014157:Transcription Factors / Q000235:genetics* / Q000302:isolation & purification
chemical_list: D001426:Bacterial Proteins; C095458:EsaI protein, Erwinia stewartii; C095459:EsaR protein, Pantoea stewartii; D014157:Transcription Factors