title: The fixM flavoprotein modulates inhibition by AICAR or 5'AMP of respiratory and nitrogen fixation gene expression in Sinorhizobium meliloti.
abstract: AICAR, a purine-related metabolite, was recently shown to inhibit respiratory and nifA gene expression in Sino-rhizobium meliloti. Here, we demonstrate that AICAR has essentially no or little effect in a wild-type S. meliloti strain and inhibits respiratory and nitrogen fixation gene expression only in specific mutant backgrounds. We have analyzed in detail a mutant in which addition of AICAR inhibited fixK,fixN,fixT and nifA expression. The corresponding gene,fixM, is located just downstream of fixK1 on pSymA megaplasmid and encodes a flavoprotein oxidoreductase. 5'AMP, a structural analogue of AICAR, mimicked AICAR effect as well as the nucleoside precursors AICAriboside and adenosine. The mode of action of AICAR and 5'AMP in vivo was investigated. We demonstrate that AICAR does not affect FixK transcriptional activity and instead regulates fixK and nifA gene expression. We hypothesize that AICAR and 5'AMP may modulate, possibly indirectly, the activity of the FixLJ two-component regulatory system. The possible physiological roles of AICAR, 5'AMP, and fixM in the context of symbiosis are discussed.
authors.affiliation: Laboratoire de Biologie Moléculaire des Relations Plantes Microorganismes, UMR215, CNRS-INRA, Castanet-Tolosan, France.
authors.forename: Céline
authors.initials: C
authors.lastname: Cosseau
authors.forename: Anne Marie
authors.initials: AM
authors.lastname: Garnerone
authors.forename: Jacques
authors.initials: J
authors.lastname: Batut
mesh_terms: D000249:Adenosine Monophosphate / Q000494:pharmacology*; D000595:Amino Acid Sequence; D000620:Aminoimidazole Carboxamide / Q000031:analogs & derivatives* / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D005420:Flavoproteins / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D009586:Nitrogen Fixation / Q000235:genetics; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D010101:Oxygen Consumption / Q000235:genetics*; D010641:Phenotype; D012265:Ribonucleotides / Q000494:pharmacology*; D017386:Sequence Homology, Amino Acid; D016962:Sinorhizobium meliloti / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D013559:Symbiosis / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; C087009:FixN protein, bacteria; D005420:Flavoproteins; D008565:Membrane Proteins; D012265:Ribonucleotides; C066628:FixK protein, Bacteria; D000620:Aminoimidazole Carboxamide; D000249:Adenosine Monophosphate; D010088:Oxidoreductases; C031143:AICA ribonucleotide