01790nas a2200169   4500008004100000245012300041210006900164260001200233300001600245490000700261520117100268100001401439700001801453700001801471700001401489856011701503       2009                        eng d00aA trans-splicing group I intron and tRNA-hyperediting in the mitochondrial genome of the lycophyte Isoetes engelmannii0 atranssplicing group I intron and tRNAhyperediting in the mitocho  c2009///  a5093 - 51040 v373 aPlant 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 cox 1 gene requires trans-splicing via a discontinuous group I intron demonstrating disrupted, but functional, RNAs for yet another class of natural ribozymes. © 2009 The Author(s).1 aGrewe, F.1 aViehoever, P.1 aWeisshaar, B.1 aKnoop, V.  uhttp://www.scopus.com/inward/record.url?eid=2-s2.0-69849093397&partnerID=40&md5=b046c2a9f2f25d1f22409335cffd8762