| dc.description | The present study points out that, in contrast to those of land plants, the mitochondrial and chloroplast genomes in chlamydomonadalean green algae seem to exhibit concerted modes and tempos of evolution. Limited data on mitochondrial genome structure and organization in other green algal lineages suggest, however, contrasting evolutionary patterns among green algae. This work (i) indicates that the observed dichotomy in the organization of mitochondrial ribosomal RNA genes among green algae, i.e., continuous conventional ribosomal RNA genes in Prototheca wickerhamii, but highly fragmented and scrambled counterparts in Chlamydomonas reinhardtii and Chlamydomonas eugametos, is not limited to these lineages but, rather, extends to at least three green algal classes, the Prasinophyceae and Trebouxiophyceae (sensu Friedl 1995) on the one hand, and the Chlorophyceae on the other, (ii) suggests that the divergent evolutionary changes undergone by the mitochondrial lineages among green algae could be the result of both distinct genetic potentials as well as changes in the habitat and life history of their green flagellate ancestors, and (iii) proposes factors, mechanisms, and potential evolutionary scenarios to explain the distinct evolutionary patterns and apparent phylogenetic affiliations of the chlamydomonadalean mitochondrial lineages relative to other green algal and land plant counterparts. Potential factors that could be responsible for the distinct evolutionary series of changes undergone by the chlamydomonadalean mitochondrial genome include: (i) accumulation of short inverted and direct GC-rich repetitive sequences with recombinogenic properties, (ii) light strand DNA replication occurring at multiple sites, and (iii) acquisition of specific group I and II introns as well as intronic open reading frames. In addition, this study proposes models and evolutionary scenarios to explain the fragmentation and scrambling of the mitochondrial ribosomal RNA genes, the high level of gene rearrangement, the reduction in gene content, and the genome linearization that occurred in the chlorophycean mitochondrial lineage. | en_US |
