MBE Advance Access published online on January 12, 2008
Molecular Biology and Evolution, doi:10.1093/molbev/msn009
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Research Article |
The Mitochondrial Genome of the Gymnosperm Cycas taitungensis Contains a Novel Family of Short Interspersed Elements, Bpu sequences, and Abundant RNA Editing Sites
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* Research Center for Biodiversity, Academia Sinica, Taipei 115, Taiwan
Institute of Information Science, Academia Sinica, Taipei 115, Taiwan
¶ Department of Informatics, Indiana University, 107 S. Indiana Ave. Bloomington, IN 47405-7000, USA
Institute of Medical Biotechnology, Central Taiwan University of Science and Technology, 11 Buzih Lane, Beitun District, Taichung City 406, Taiwan
Corresponding authors: Email: smchaw{at}sinica.edu.tw; dywang{at}gate.sinica.edu.tw, Phone: (886)227892887; (886)227890159
Received for publication November 12, 2007. Revision received December 27, 2007. Accepted for publication January 6, 2008.
The mtDNA of Cycas taitungensis is a circular molecule of 414,903 bp, making it 2-6 fold larger than the known mtDNAs of charophytes and bryophytes, but similar to the average of seven elucidated angiosperm mtDNAs. It is characterized by abundant RNA editing sites (1,084), more than twice the number found in the angiosperm mtDNAs. The A+T content of Cycas mtDNA is 53.1%, the lowest among known land plants. About 5% of the Cycas mtDNA is composed of a novel family of mobile elements, which we designated as ‘Bpu sequences’. They share a consensus sequence of 36 bp with two terminal direct repeats (AAGG) and a recognition site for the Bpu 10I restriction endonuclease (CCTGAAGC). Comparison of the Cycas mtDNA with other plant mtDNAs revealed many new insights into the biology and evolution of land plant mtDNAs. For example, the non-coding sequences in mtDNAs have drastically expanded as land plants have evolved, with abrupt increases appearing in the bryophytes, and then in the seed plants. As a result, the genomic organizations of seed plant mtDNAs are much less compact than in other plants. Also, the Cycas mtDNA appears to have been exempted from the frequent gene loss observed in angiosperm mtDNAs. Similar to the angiosperms, the three Cycas genes nad1, nad2, and nad5 are disrupted by five group II intron squences, which have brought the genes into trans-splicing arrangements. The evolutionary origin and invasion/duplication mechanism of the Bpu sequences in Cycas mtDNA are hypothesized and discussed.
Key Words: mitochondrial genome • Cycas • RNA editing sites • repeats • mobile elements
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