title: Independent activity of the homologous small regulatory RNAs AbcR1 and AbcR2 in the legume symbiont Sinorhizobium meliloti.
abstract: The legume symbiont Sinorhizobium meliloti expresses a plethora of small noncoding RNAs (sRNAs) whose function is mostly unknown. Here, we have functionally characterized two tandemly encoded S. meliloti Rm1021 sRNAs that are similar in sequence and structure. Homologous sRNAs (designated AbcR1 and AbcR2) have been shown to regulate several ABC transporters in the related α-proteobacteria Agrobacterium tumefaciens and Brucella abortus. In Rm1021, AbcR1 and AbcR2 exhibit divergent unlinked regulation and are stabilized by the RNA chaperone Hfq. AbcR1 is transcribed in actively dividing bacteria, either in culture, rhizosphere or within the invasion zone of mature alfalfa nodules. Conversely, AbcR2 expression is induced upon entry into stationary phase and under abiotic stress. Only deletion of AbcR1 resulted into a discrete growth delay in rich medium, but both are dispensable for symbiosis. Periplasmic proteome profiling revealed down-regulation of the branched-chain amino acid binding protein LivK by AbcR1, but not by AbcR2. A double-plasmid reporter assay confirmed the predicted specific targeting of the 5'-untranslated region of the livK mRNA by AbcR1 in vivo. Our findings provide evidences of independent regulatory functions of these sRNAs, probably to fine-tune nutrient uptake in free-living and undifferentiated symbiotic rhizobia.
authors.affiliation: Grupo de Ecología Genética de la Rizosfera, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas (CSIC), Granada, Spain.
authors.forename: Omar
authors.initials: O
authors.lastname: Torres-Quesada
authors.forename: Vicenta
authors.initials: V
authors.lastname: Millán
authors.forename: Rafael
authors.initials: R
authors.lastname: Nisa-Martínez
authors.forename: Florian
authors.initials: F
authors.lastname: Bardou
authors.forename: Martín
authors.initials: M
authors.lastname: Crespi
authors.forename: Nicolás
authors.initials: N
authors.lastname: Toro
authors.forename: José I
authors.initials: JI
authors.lastname: Jiménez-Zurdo
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism; D015536:Down-Regulation; D007887:Fabaceae / Q000382:microbiology*; D015964:Gene Expression Regulation, Bacterial; D009154:Mutation; D009690:Nucleic Acid Conformation; D020871:RNA Stability; D012329:RNA, Bacterial / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D058727:RNA, Small Untranslated / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D016962:Sinorhizobium meliloti / Q000235:genetics* / Q000378:metabolism; D013559:Symbiosis / Q000235:genetics
chemical_list: D018528:ATP-Binding Cassette Transporters; D012329:RNA, Bacterial; D058727:RNA, Small Untranslated