Nucleic Acids Research Advance Access published online on June 23, 2009
Nucleic Acids Research, doi:10.1093/nar/gkp532
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A trans-splicing group I intron and tRNA-hyperediting in the mitochondrial genome of the lycophyte Isoetes engelmannii
1Institut für Zelluläre und Molekulare Botanik (IZMB), Universität Bonn, Kirschallee 1, 53115 Bonn and 2Institut für Genomforschung und Systembiologie (IGS), Universität Bielefeld, Universitätsstraße 25, 33594 Bielefeld, Germany
*To whom correspondence should be addressed. Tel: +49 228 73 6466; Fax: +49 228 73 6467; Email: volker.knoop{at}uni-bonn.de
Received March 19, 2009. Revised June 5, 2009. Accepted June 6, 2009.
Plant mitochondrial genomes show much more evolutionary plasticity than those of animals. We analysed the first mitochondrial DNA (mtDNA) of a lycophyte, the quillwort Isoetes engelmannii, which is separated from seed plants by more than 350 million years of evolution. The Isoetes mtDNA is particularly rich in recombination events, and chloroplast as well as nuclear DNA inserts document the incorporation of foreign sequences already in this most ancestral vascular plant lineage. On the other hand, particularly small group II introns and short intergenic regions reveal a tendency of evolution towards a compact mitochondrial genome. RNA editing reaches extreme levels exceeding 100 pyrimidine exchanges in individual mRNAs and, hitherto unobserved in such frequency, also in tRNAs with 18 C-to-U conversions in the tRNA for proline. In total, some 1500 sites of RNA editing can be expected for the Isoetes mitochondrial transcriptome. As a unique molecular novelty, the Isoetes cox1 gene requires trans-splicing via a discontinuous group I intron demonstrating disrupted, but functional, RNAs for yet another class of natural ribozymes.