title: RNA-Seq analysis of the multipartite genome of Rhizobium etli CE3 shows different replicon contributions under heat and saline shock.
abstract: BACKGROUND
  Regulation of transcription is essential for any organism and Rhizobium etli (a multi-replicon, nitrogen-fixing symbiotic bacterium) is no exception. This bacterium is commonly found in the rhizosphere (free-living) or inside of root-nodules of the common bean (Phaseolus vulgaris) in a symbiotic relationship. Abiotic stresses, such as high soil temperatures and salinity, compromise the genetic stability of R. etli and therefore its symbiotic interaction with P. vulgaris. However, it is still unclear which genes are up- or down-regulated to cope with these stress conditions. The aim of this study was to identify the genes and non-coding RNAs (ncRNAs) that are differentially expressed under heat and saline shock, as well as the promoter regions of the up-regulated loci.
  
  
  RESULTS
  Analysing the heat and saline shock responses of R. etli CE3 through RNA-Seq, we identified 756 and 392 differentially expressed genes, respectively, and 106 were up-regulated under both conditions. Notably, the set of genes over-expressed under either condition was preferentially encoded on plasmids, although this observation was more significant for the heat shock response. In contrast, during either saline shock or heat shock, the down-regulated genes were principally chromosomally encoded. Our functional analysis shows that genes encoding chaperone proteins were up-regulated during the heat shock response, whereas genes involved in the metabolism of compatible solutes were up-regulated following saline shock. Furthermore, we identified thirteen and nine ncRNAs that were differentially expressed under heat and saline shock, respectively, as well as eleven ncRNAs that had not been previously identified. Finally, using an in silico analysis, we studied the promoter motifs in all of the non-coding regions associated with the genes and ncRNAs up-regulated under both conditions.
  
  
  CONCLUSIONS
  Our data suggest that the replicon contribution is different for different stress responses and that the heat shock response is more complex than the saline shock response. In general, this work exemplifies how strategies that not only consider differentially regulated genes but also regulatory elements of the stress response provide a more comprehensive view of bacterial gene regulation.
authors.affiliation: Programa de Genómica Evolutiva, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Apartado Postal 565-A, Cuernavaca, Morelos C,P 62210, México. gamlopez@ccg.unam.mx.
authors.forename: Gamaliel
authors.initials: G
authors.lastname: López-Leal
authors.forename: Maria Luisa
authors.initials: ML
authors.lastname: Tabche
authors.forename: Santiago
authors.initials: S
authors.lastname: Castillo-Ramírez
authors.forename: Alfredo
authors.initials: A
authors.lastname: Mendoza-Vargas
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Ramírez-Romero
authors.forename: Guillermo
authors.initials: G
authors.lastname: Dávila
mesh_terms: D001665:Binding Sites; D015870:Gene Expression; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D016680:Genome, Bacterial; D018869:Heat-Shock Response / Q000235:genetics; D006358:Hot Temperature; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism; D059372:Nucleotide Motifs; D010957:Plasmids / Q000235:genetics; D056510:Position-Specific Scoring Matrices; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D022661:RNA, Untranslated / Q000235:genetics; D012093:Replicon; D042163:Rhizobium etli / Q000235:genetics* / Q000378:metabolism; D054712:Salinity; D064210:Secondary Metabolism / Q000235:genetics; D017423:Sequence Analysis, RNA; D013312:Stress, Physiological / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D026901:Membrane Transport Proteins; D022661:RNA, Untranslated; D014157:Transcription Factors