title: Identification of Xenologs and Their Characteristic Low Expression Levels in the Cyanobacterium Synechococcus elongatus.
abstract: Horizontal gene transfer (HGT) is a central process in prokaryotic evolution. Once a gene is introduced into a genome by HGT, its contribution to the fitness of the recipient cell depends in part on its expression level. Here we show that in Synechococcus elongatus PCC 7942, xenologs derived from non-cyanobacterial sources exhibited lower expression levels than native genes in the genome. In accord with our observation, xenolog codon adaptation indexes also displayed relatively low expression values. These results are in agreement with previous reports that suggested the relative neutrality of most xenologs. However, we also demonstrated that some of the xenologs detected participated in cellular functions, including iron starvation acclimation and nitrate reduction, which corroborate the role of HGT in bacterial adaptation. For example, the expression levels of some of the xenologs detected are known to increase under iron-limiting conditions. We interpreted the overall pattern as an indication that there is a selection pressure against high expression levels of xenologs. However, when a xenolog protein product confers a selective advantage, natural selection can further modulate its expression level to meet the requirements of the recipient cell. In addition, we show that ORFans did not exhibit significantly lower expression levels than native genes in the genome, which suggested an origin other than xenology.
authors.affiliation: Departamento de Ingeniería Genética, CINVESTAV-Irapuato, Km. 9.6 Libramiento Norte, Carretera Irapuato-León, 36821, Irapuato, Guanajuato, Mexico.
authors.forename: Gilberto
authors.initials: G
authors.lastname: Álvarez-Canales
authors.forename: Guadalupe
authors.initials: G
authors.lastname: Arellano-Álvarez
authors.forename: Carmen M
authors.initials: CM
authors.lastname: González-Domenech
authors.forename: Fernando
authors.initials: F
authors.lastname: de la Cruz
authors.forename: Andrés
authors.initials: A
authors.lastname: Moya
authors.forename: Luis
authors.initials: L
authors.lastname: Delaye
mesh_terms: D000222:Adaptation, Physiological / Q000235:genetics; D000465:Algorithms; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D002874:Chromosome Mapping; D003062:Codon; D015964:Gene Expression Regulation, Bacterial; D022761:Gene Transfer, Horizontal; D056084:Genetic Fitness; D016680:Genome, Bacterial; D007501:Iron / Q000378:metabolism; D058977:Molecular Sequence Annotation; D009566:Nitrates / Q000378:metabolism; D016366:Open Reading Frames; D010084:Oxidation-Reduction; D046940:Synechococcus / Q000235:genetics* / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D003062:Codon; D009566:Nitrates; D007501:Iron