title: Cooperation of two distinct ExpR regulators controls quorum sensing specificity and virulence in the plant pathogen Erwinia carotovora.
abstract: Quorum sensing, the population density-dependent regulation mediated by N-acylhomoserine lactones (AHSL), is essential for the control of virulence in the plant pathogen Erwinia carotovora ssp. carotovora (Ecc). In Erwinia carotovora ssp. the AHSL signal with an acyl chain of either 6 or 8 carbons is generated by an AHSL synthase, the expI gene product. This work demonstrates that the AHSL receptor, ExpR1, of Ecc strain SCC3193 has strict specificity for the cognate AHSL 3-oxo-C8-HSL. We have also identified a second AHSL receptor (ExpR2) and demonstrate a novel quorum sensing mechanism, where ExpR2 acts synergistically with the previously described ExpR1 to repress virulence gene expression in Ecc. We show that this repression is released by addition of AHSLs and appears to be largely mediated via the negative regulator RsmA. Additionally we show that ExpR2 has the novel property to sense AHSLs with different acyl chain lengths. The expI expR1 double mutant is able to act in response to a number of different AHSLs, while the expI expR2 double mutant can only respond to the cognate signal of Ecc strain SCC3193. These results suggest that Ecc is able to react both to the cognate AHSL signal and the signals produced by other bacterial species.
authors.affiliation: Viikki Biocenter, Faculty of Biosciences, Department of Biological and Environmental Sciences, Division of Genetics, University of Helsinki, P.O.B. 56, FIN-00014, Helsinki, Finland.
authors.forename: Solveig
authors.initials: S
authors.lastname: Sjöblom
authors.forename: Günter
authors.initials: G
authors.lastname: Brader
authors.forename: Gudrun
authors.initials: G
authors.lastname: Koch
authors.forename: E Tapio
authors.initials: ET
authors.lastname: Palva
mesh_terms: D015107:4-Butyrolactone / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000502:physiology*; D002473:Cell Wall / Q000201:enzymology; D002480:Cellulase / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects; D006714:Homoserine / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D008969:Molecular Sequence Data; D016973:Pectobacterium carotovorum / Q000235:genetics / Q000472:pathogenicity*; D010641:Phenotype; D010935:Plant Diseases / Q000382:microbiology*; D010940:Plant Proteins / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000235:genetics; D012097:Repressor Proteins / Q000235:genetics / Q000502:physiology*; D015398:Signal Transduction / Q000235:genetics; D014774:Virulence / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; C109860:N-(3-oxododecanoyl)homoserine lactone; D010940:Plant Proteins; D016601:RNA-Binding Proteins; D012097:Repressor Proteins; C095468:RsmA protein, Erwinia carotovora; D006714:Homoserine; D002480:Cellulase; D015107:4-Butyrolactone