title: Horizontal gene transfer and diverse functional constrains within a common replication-partitioning system in Alphaproteobacteria: the repABC operon.
abstract: BACKGROUND
  The repABC plasmid family, which is extensively present within Alphaproteobacteria, and some secondary chromosomes of the Rhizobiales have the particular feature that all the elements involved in replication and partitioning reside within one transcriptional unit, the repABC operon. Given the functional interactions among the elements of the repABC operon, and the fact that they all reside in the same operon, a common evolutionary history would be expected if the entire operon had been horizontally transferred. Here, we tested whether there is a common evolutionary history within the repABC operon. We further examined different incompatibility groups in terms of their differentiation and degree of adaptation to their host.
  
  
  RESULTS
  We did not find a single evolutionary history within the repABC operon. Each protein had a particular phylogeny, horizontal gene transfer events of the individual genes within the operon were detected, and different functional constraints were found within and between the Rep proteins. When different repABC operons coexisted in the same genome, they were well differentiated from one another. Finally, we found different levels of adaptation to the host genome within and between repABC operons coexisting in the same species.
  
  
  CONCLUSIONS
  Horizontal gene transfer with conservation of the repABC operon structure provides a highly dynamic operon in which each member of this operon has its own evolutionary dynamics. In addition, it seems that different incompatibility groups present in the same species have different degrees of adaptation to their host genomes, in proportion to the amount of time the incompatibility group has coexisted with the host genome.
authors.affiliation: Programa de Genómica Evolutiva, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, Mexico. iago@ccg.unam.mx
authors.forename: Santiago
authors.initials: S
authors.lastname: Castillo-Ramírez
authors.forename: Jorge F
authors.initials: JF
authors.lastname: Vázquez-Castellanos
authors.forename: Víctor
authors.initials: V
authors.lastname: González
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Cevallos
mesh_terms: D000222:Adaptation, Physiological; D020561:Alphaproteobacteria / Q000235:genetics*; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D001499:Bayes Theorem; D003062:Codon / Q000235:genetics; D004261:DNA Replication; D019143:Evolution, Molecular; D022761:Gene Transfer, Horizontal; D009876:Operon / Q000235:genetics*; D010802:Phylogeny; D010957:Plasmids / Q000235:genetics*; D013045:Species Specificity
chemical_list: D001426:Bacterial Proteins; D003062:Codon