title: Succinic semialdehyde couples stress response to quorum-sensing signal decay in Agrobacterium tumefaciens.
abstract: Quorum sensing (QS) signal decay in Agrobacterium tumefaciens occurs in response to starvation or host signals. We have demonstrated that the gamma-aminobutyric acid (GABA) shunt metabolite links stress response to QS signal decay. Mutation of the aldH gene encoding a succinic semialdehyde dehydrogenase (SSADH) that converts succinic semialdehyde (SSA) to succinic acid results in early expression of the signal degrading enzyme, AttM. Exogenous addition of SSA or its precursor GABA induces AttM expression and abolishes Ti plasmid conjugative transfer. SSA acts by binding to the repressor AttJ that regulates the attKLM operon. attK encodes another SSADH. The stress alarmone ppGpp and SSA modulates separately the expression of the two SSADH enzymes, which might control the intracellular SSA level and hence to switch on/off the QS signal decay system in response to environmental changes. These findings document for the first time a sophisticated signalling mechanism of the widely conserved GABA degradation pathway in prokaryotes.
authors.affiliation: Institute of Molecular and Cell Biology, 61 Biopolis Drive, Singapore 138673.
authors.forename: Chao
authors.initials: C
authors.lastname: Wang
authors.forename: Hai-Bao
authors.initials: HB
authors.lastname: Zhang
authors.forename: Lian-Hui
authors.initials: LH
authors.lastname: Wang
authors.forename: Lian-Hui
authors.initials: LH
authors.lastname: Zhang
mesh_terms: D016960:Agrobacterium tumefaciens / Q000235:genetics / Q000378:metabolism*; D000444:Aldehyde Dehydrogenase / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D002265:Carboxylic Ester Hydrolases / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial / Q000235:genetics; D008954:Models, Biological; D015394:Molecular Structure; D009876:Operon / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding; D017384:Sequence Deletion / Q000235:genetics; D015398:Signal Transduction / Q000502:physiology*; D050644:Succinate-Semialdehyde Dehydrogenase / Q000235:genetics / Q000378:metabolism; D005680:gamma-Aminobutyric Acid / Q000031:analogs & derivatives* / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D005680:gamma-Aminobutyric Acid; D050644:Succinate-Semialdehyde Dehydrogenase; D000444:Aldehyde Dehydrogenase; D002265:Carboxylic Ester Hydrolases; C432003:N-acyl homoserine lactonase; C009338:succinic semialdehyde