title: Regulation of AHL production and its contribution to epiphytic fitness in Pseudomonas syringae.
abstract: Pseudomonas syringae forms large cell aggregates that are more stress tolerant than solitary cells during epiphytic growth on plants. The differential survival of aggregates on leaves suggests that epiphytic fitness traits may be controlled in a density-dependent manner via cell-cell signaling. We investigated this hypothesis in P. syringae B728a. Synthesis of N-acyl-homoserine lactone (AHL), 3-oxo-hexanoyl homoserine lactone, and the expression of the gene encoding AHL synthase ahlI were maximal at high cell concentrations. The expression of the AHL regulator ahlR, in contrast, was similar at all cell concentrations. A screen of Tn5 mutants revealed that P. syringae B728a requires a novel transcriptional activator for AHL production. This regulator, which belongs to the TetR family, was also required for epiphytic fitness and has been designated AefR (for AHL and epiphytic fitness regulator). The expression of ahlI was greatly reduced in both aefR- and gacA- mutants and was completely restored in either mutant after addition of exogenous AHL. In contrast, the expression of aefR was not reduced in either gacS- or gacA- mutants. Thus, AefR appears to positively regulate AHL production independently of the regulators GacS/GacA and also controls traits in P. syringae B728a that are required for epiphytic colonization.
authors.affiliation: Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720-3102, USA.
authors.forename: Beatriz
authors.initials: B
authors.lastname: Quiñones
authors.forename: Catherine J
authors.initials: CJ
authors.lastname: Pujol
authors.forename: Steven E
authors.initials: SE
authors.lastname: Lindow
mesh_terms: D015107:4-Butyrolactone / Q000031:analogs & derivatives* / Q000096:biosynthesis*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D015964:Gene Expression Regulation, Bacterial; D008025:Ligases / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D010935:Plant Diseases / Q000382:microbiology; D044224:Pseudomonas syringae / Q000235:genetics / Q000378:metabolism* / Q000472:pathogenicity; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; C085427:LuxI protein, Bacteria; D012097:Repressor Proteins; D015534:Trans-Activators; D014157:Transcription Factors; C064778:LuxR autoinducer binding proteins; C088386:homoserine lactone; C030654:N-(3-oxohexanoyl)-3-aminodihydro-2(3H)-furanone; D008025:Ligases; C449816:N-acylhomoserine lactone synthase; D015107:4-Butyrolactone