Originally published as Genetics Published Articles Ahead of Print on January 12, 2009.

Genetics, Vol. 181, 1045-1056, March 2009, Copyright © 2009
doi:10.1534/genetics.108.093229

The Control Region of Maternally and Paternally Inherited Mitochondrial Genomes of Three Species of the Sea Mussel Genus Mytilus

Liqin Cao^*,1, Brian S. Ort^,2, Athanasia Mizi, Grant Pogson, Elen Kenchington^*,, Eleftherios Zouros^** and George C. Rodakis^,3

^* Department of Biology, Dalhousie University, Halifax, Nova Scotia B3H 4J1, Canada, Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, California 95064, Department of Biochemistry and Molecular Biology, National and Kapodistrian University of Athens, Panepistimioupolis, 15701 Athens, Greece, Department of Fisheries and Oceans, Dartmouth, Nova Scotia B2Y 4A2, Canada and ^** Department of Biology, University of Crete, 71409 Heraklion, Crete, Greece

³ Corresponding author: Department of Biochemistry and Molecular Biology, National and Kapodistrian University of Athens, Panepistimioupolis, 15701 Athens, Greece.
E-mail: grodakis{at}biol.uoa.gr

Species of the mussel genus Mytilus possess maternally and paternally transmitted mitochondrial genomes. In the interbreeding taxa Mytilus edulis and M. galloprovincialis, several genomes of both types have been fully sequenced. The genome consists of the coding part (which, in addition to protein and RNA genes, contains several small noncoding sequences) and the main control region (CR), which in turn consists of three distinct parts: the first variable (VD1), the conserved (CD), and the second variable (VD2) domain. The maternal and paternal genomes are very similar in gene content and organization, even though they differ by >20% in primary sequence. They differ even more at VD1 and VD2, yet they are remarkably similar at CD. The complete sequence of a genome from the closely related species M. trossulus was previously reported and found to consist of a maternal-like coding part and a paternal-like and a maternal-like CR. From this and from the fact that it was extracted from a male individual, it was inferred that this is a genome that switched from maternal to paternal transmission. Here we provide clear evidence that this genome is the maternal genome of M. trossulus. We have found that in this genome the tRNA^Gln in the coding region is apparently defective and that an intact copy of this tRNA occurs in the CR, that one of the two conserved domains is missing essential motifs, and that one of the two first variable domains has a high rate of divergence. These features may explain the large size and mosaic structure of the CR of the maternal genome of M. trossulus. We have also obtained CR sequences of the maternal and paternal genomes of M. californianus, a more distantly related species. We compare the control regions from all three species, focusing on the divergence among genomes of different species origin and among genomes of different transmission routes.

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Genetics 2009 181: NP. [Full Text]  

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