Mitochondrial genome diversity and the specific evolutionary trends in mitochondrial genome organization within each lineage. The mechanisms involved in the evolution of the mitochondrial genome in general, we need more knowledge about the extent of To decipher the processes involved in the evolution of the green algal mitochondrial genome in particular, and to understand Green algal lineages are not known yet, although some suggestions have been made ( Nedelcu 1998 Nedelcu and Lee 1998a, b). The causes, factors, and mechanisms responsible for the extensive changes sustained by the mitochondrial genome in different (fast-evolving) sequences form a clade separate from both ancestral green algal and land plant homologs ( Turmel et al. Trees the ancestral mitochondrial sequences directly affiliate, as expected, with their land plant counterparts, the reduced–derived Furthermore, whereas in mitochondrial protein
1996) the above two types of mitochondrial genome fail to affiliate with each other. In phylogenetic analyses using mitochondrial rDNA sequences ( Denovan-Wright et al. Type (i.e., Chlamydomonas reinhardtii, Chlamydomonas eugametos, Chlorogonium elongatum, and Pedinomonas minor ), and two are members of the ancestral type (i.e., Prototheca wickerhamii and Nephroselmis olivacea ). Of these, four belong to the reduced–derived To date, six green algal mitochondrial genomes have been completely sequenced. The Prototheca-like type represents an ancestral form of green algal mitochondrial genome that features a larger size (45–55 kb), a moreĬomplex set of protein-coding genes (including ones for ribosomal proteins), a complete or almost complete set of tRNA genes,Īnd 5S rRNA as well as conventional continuous rRNA genes ( Nedelcu 1998 Gray et al. (no ribosomal protein or 5S rRNA genes and only a few respiratory protein and tRNA genes), and the presence of fragmentedĪnd scrambled rRNA coding regions. The Chlamydomonas-like type displays a reduced-derived organizational pattern characterized by small genome size (16–25 kb), limited gene content Two distinct mitochondrial genome types have been described among the green algal lineages investigated to date. Stage in the evolutionary process of mitochondrial genome streamlining in green algae. Presence of fragmented and scrambled rRNA genes are shared with the reduced–derived type of mitochondrial genome organization.įurthermore, the gene content and the fragmentation pattern of the rRNA genes suggest that this genome represents an intermediate TRNA genes is shared with the ancestral type, whereas the lack of 5S rRNA and ribosomal protein-coding genes as well as the The mitochondrial genome of Scenedesmus combines features of both green algal mitochondrial genome types: the presence of a more complex set of protein-coding and
The standard protein-coding genes feature a deviant genetic code characterized by the use of UAG (normally a stopĬodon) to specify leucine, and the unprecedented use of UCA (normally a serine codon) as a signal for termination of translation. No 5S rRNA or ribosomal protein-coding genes have been identified in Scenedesmus mtDNA. Reading frame with endonuclease/maturase similarity.
Respiratory protein-coding genes), four additional free-standing open reading frames with no known homologs, and an intronic This genome is 42,919 bp in size and encodes 42 conserved genes (i.e., large and small subunit rRNA genes, 27 tRNA and 13 In the evolution of the green algal mitochondrial genome, we sequenced and analyzed the mitochondrial DNA (mtDNA) of Scenedesmus obliquus. To determine if this unexpected dichotomy is real or is due to insufficient or biased sampling and to define trends Two distinct mitochondrial genome types have been described among the green algal lineages investigated to date: a reduced–derived, Chlamydomonas-like type and an ancestral, Prototheca-like type.