title: Quorum-sensing system affects gall development incited by Pantoea agglomerans pv. gypsophilae.
abstract: The quorum-sensing (QS) regulatory system of the gall-forming Pantoea agglomerans pv. gypsophilae was identified. Mass spectral analysis, together with signal-specific biosensors, demonstrated that P. agglomerans pv. gypsophilae produced N-butanoyl-l-homoserine lactone (C4-HSL) as a major and N-hexanoyl-l-homoserine lactone (C6-HSL) as a minor QS signal. Homologs of luxI and luxR regulatory genes, pagI and pagR, were characterized in strain P. agglomerans pv. gypsophilae Pag824-1 and shown to be convergently transcribed and separated by 14 bp. The deduced PagI (23.8 kDa) and PagR (26.9 kDa) show high similarity with SmaI (41% identity) and SmaR (43% identity), respectively, of Serratia sp. American Type Culture Collection 39006. PagR possesses characteristic autoinducer binding and a helix-turn-helix DNA-binding domain. Gall formation by P. agglomerans pv. gypsophilae depends on a plasmid-borne hrp/hrc gene cluster, type III effectors, and phytohormones. Disruption of pagI, pagR, or both genes simultaneously in Pag824-1 reduced gall size in gypsophila cuttings by 50 to 55% when plants were inoculated with 10(6) CFU/ml. Higher reductions in gall size (70 to 90%) were achieved by overexpression of pagI or addition of exogenous C4-HSL. Expression of the hrp/hrc regulatory gene hrpL and the type III effector pthG in the pagI mutant, as measured with quantitative reverse-transcriptase polymerase chain reaction, was reduced by 5.8 and 6.6, respectively, compared with the wild type, suggesting an effect of the QS system on the Hrp regulon.
authors.affiliation: Department of Plant Pathology and Weed Research, ARO, The Volcani Center, Bet Dagan, Israel.
authors.forename: Laura
authors.initials: L
authors.lastname: Chalupowicz
authors.forename: Shulamit
authors.initials: S
authors.lastname: Manulis-Sasson
authors.forename: Maxim
authors.initials: M
authors.lastname: Itkin
authors.forename: Ayelet
authors.initials: A
authors.lastname: Sacher
authors.forename: Guido
authors.initials: G
authors.lastname: Sessa
authors.forename: Isaac
authors.initials: I
authors.lastname: Barash
mesh_terms: D015107:4-Butyrolactone / Q000031:analogs & derivatives / Q000096:biosynthesis; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D029748:Caryophyllaceae / Q000382:microbiology; D003001:Cloning, Molecular; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D020636:Pantoea / Q000235:genetics* / Q000472:pathogenicity*; D010941:Plant Tumors / Q000382:microbiology*; D053038:Quorum Sensing; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; C085427:LuxI protein, Bacteria; C092312:N-butyrylhomoserine lactone; C104908:N-hexanoyl-L-homoserine lactone; D012097:Repressor Proteins; D015534:Trans-Activators; D014157:Transcription Factors; C064778:LuxR autoinducer binding proteins; D015107:4-Butyrolactone