Independent activity of the homologous small regulatory RNAs AbcR1 and AbcR2 in the legume symbiont Sinorhizobium meliloti

PLoS One. 2013 Jul 15;8(7):e68147. doi: 10.1371/journal.pone.0068147. Print 2013.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • ATP-Binding Cassette Transporters / genetics
  • ATP-Binding Cassette Transporters / metabolism
  • Down-Regulation
  • Fabaceae / microbiology*
  • Gene Expression Regulation, Bacterial
  • Mutation
  • Nucleic Acid Conformation
  • RNA Stability
  • RNA, Bacterial / chemistry
  • RNA, Bacterial / genetics
  • RNA, Bacterial / physiology*
  • RNA, Small Untranslated / chemistry
  • RNA, Small Untranslated / genetics
  • RNA, Small Untranslated / physiology*
  • Sinorhizobium meliloti / genetics*
  • Sinorhizobium meliloti / metabolism
  • Symbiosis / genetics

Substances

  • ATP-Binding Cassette Transporters
  • RNA, Bacterial
  • RNA, Small Untranslated

Grants and funding

This work has been funded by ERDF-cofinanced grants AGL2009-07925 and CSD2009-00006 (Consolider-Ingenio Program) from the former Spanish Ministerio de Ciencia e Innovación, currently Ministerio de Economía y Competitividad, to JIJ-Z and NT, respectively. OT-Q was recipient of a FPI fellowship from the same Ministry. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.