title: The complete mitochondrial DNA sequence of the green alga Oltmannsiellopsis viridis: evolutionary trends of the mitochondrial genome in the Ulvophyceae.
abstract: The mitochondrial genome displays a highly plastic architecture in the green algal division comprising the classes Prasinophyceae, Trebouxiophyceae, Ulvophyceae, and Chlorophyceae (Chlorophyta). The compact mitochondrial DNAs (mtDNAs) of Nephroselmis (Prasinophyceae) and Prototheca (Trebouxiophyceae) encode about 60 genes and have been ascribed an 'ancestral' pattern of evolution, whereas those of chlorophycean green algae are much more reduced in gene content and size. Although the mtDNA of the early-diverging ulvophyte Pseudendoclonium contains 57 conserved genes, it differs from 'ancestral' chlorophyte mtDNAs by its unusually large size (96 kb) and long intergenic spacers. To gain insights into the evolutionary trends of mtDNA in the Ulvophyceae, we have determined the complete mtDNA sequence of Oltmannsiellopsis viridis, an ulvophyte belonging to a distinct, early-diverging lineage. This 56,761 bp genome harbours 54 conserved genes, numerous repeated sequences, and only three introns. From our comparative analyses with Pseudendoclonium mtDNA, we infer that the mitochondrial genome of the last common ancestor of the two ulvophytes closely resembled that of the trebouxiophyte Prototheca in terms of gene content and gene density. Our results also provide strong evidence for the intracellular, interorganellar transfer of a group I intron and for two distinct events of intercellular, horizontal DNA transfer.
authors.affiliation: Département de biochimie et de microbiologie, Pavillon Charles-Eugène Marchand, Université Laval, Québec, Canada.
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Pombert
authors.forename: Philippe
authors.initials: P
authors.lastname: Beauchamp
authors.forename: Christian
authors.initials: C
authors.lastname: Otis
authors.forename: Claude
authors.initials: C
authors.lastname: Lemieux
authors.forename: Monique
authors.initials: M
authors.lastname: Turmel
mesh_terms: D020029:Base Pairing; D001483:Base Sequence; D000460:Chlorophyta / Q000235:genetics*; D004272:DNA, Mitochondrial / Q000235:genetics*; D019143:Evolution, Molecular; D023061:Gene Order / Q000235:genetics; D016013:Likelihood Functions; D008957:Models, Genetic; D008969:Molecular Sequence Data; D010802:Phylogeny; D017422:Sequence Analysis, DNA; D013045:Species Specificity
chemical_list: D004272:DNA, Mitochondrial