title: Conservation of the links between gene transcription and chromosomal organization in the highly reduced genome of Buchnera aphidicola.
abstract: BACKGROUND
  Genomic studies on bacteria have clearly shown the existence of chromosomal organization as regards, for example, to gene localization, order and orientation. Moreover, transcriptomic analyses have demonstrated that, in free-living bacteria, gene transcription levels and chromosomal organization are mutually influenced. We have explored the possible conservation of relationships between mRNA abundances and chromosomal organization in the highly reduced genome of Buchnera aphidicola, the primary endosymbiont of the aphids, and a close relative to Escherichia coli.
  
  
  RESULTS
  Using an oligonucleotide-based microarray, we normalized the transcriptomic data by genomic DNA signals in order to have access to inter-gene comparison data. Our analysis showed that mRNA abundances, gene organization (operon) and gene essentiality are correlated in Buchnera (i.e., the most expressed genes are essential genes organized in operons) whereas no link between mRNA abundances and gene strand bias was found. The effect of Buchnera genome evolution on gene expression levels has also been analysed in order to assess the constraints imposed by the obligate symbiosis with aphids, underlining the importance of some gene sets for the survival of the two partners. Finally, our results show the existence of spatial periodic transcriptional patterns in the genome of Buchnera.
  
  
  CONCLUSIONS
  Despite an important reduction in its genome size and an apparent decay of its capacity for regulating transcription, this work reveals a significant correlation between mRNA abundances and chromosomal organization of the aphid-symbiont Buchnera.
authors.affiliation: UMR 203 Biologie Fonctionnelle Insectes et Interactions, IFR41, INRA, INSA-Lyon, Villeurbanne, France. jose.vinuelas@insa-lyon.fr
authors.forename: José
authors.initials: J
authors.lastname: Viñuelas
authors.forename: Federica
authors.initials: F
authors.lastname: Calevro
authors.forename: Didier
authors.initials: D
authors.lastname: Remond
authors.forename: Jacques
authors.initials: J
authors.lastname: Bernillon
authors.forename: Yvan
authors.initials: Y
authors.lastname: Rahbé
authors.forename: Gérard
authors.initials: G
authors.lastname: Febvay
authors.forename: Jean-Michel
authors.initials: JM
authors.lastname: Fayard
authors.forename: Hubert
authors.initials: H
authors.lastname: Charles
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D001042:Aphids / Q000382:microbiology; D020635:Buchnera / Q000235:genetics*; D002876:Chromosomes, Bacterial / Q000235:genetics*; D004269:DNA, Bacterial; D019143:Evolution, Molecular; D005798:Genes, Bacterial; D016680:Genome, Bacterial / Q000235:genetics*; D020411:Oligonucleotide Array Sequence Analysis; D012333:RNA, Messenger / Q000235:genetics; D015203:Reproducibility of Results; D014158:Transcription, Genetic
chemical_list: D004269:DNA, Bacterial; D012333:RNA, Messenger