J Syst Evol ›› 2013, Vol. 51 ›› Issue (1): 1-12.DOI: 10.1111/j.1759-6831.2012.00228.x

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Plant mitochondrial genome peculiarities evolving in the earliest vascular plant lineages

Volker KNOOP*   

  1. (Abteilung Molekulare Evolution, Institut für Zelluläre und Molekulare Botanik, Universität Bonn, Kirschallee 1, 53115 Bonn, Germany)
  • Received:2012-05-02 Published:2012-11-15

Abstract: In plants, the mitochondrial DNA has evolved in peculiar ways. Simple circular mitochondrial genomes found in most other eukaryotic lineages have expanded tremendously in size. Mitochondrial DNAs in some flowering plants may in fact be larger than genomes of free-living bacteria. Introns, retrotransposons, pseudogene fragments, and promiscuous DNA copied from the chloroplast or nuclear genome contribute to the size expansion but most intergenic DNA remains unaccounted for so far. Additionally, frequent recombination results in heterogeneous pools of coexisting, subgenomic mtDNA molecules in angiosperms. In contrast, the mitochondrial DNAs of bryophytes, the extant representatives of very early splits in plant phylogeny, are more conservative in structural evolution and seem to be devoid of active recombination. However, whereas mitochondrial introns are highly conserved among seed plants (spermatophytes), not a single one of more than 80 different introns in bryophyte mtDNAs is conserved among the three divisions, liverworts, mosses, and hornworts. Lycophytes are now unequivocally identified as living representatives of the earliest vascular plant branch in a crucial phylogenetic position between bryophytes and later diversifying tracheophytes including spermatophytes. Very recently, mtDNAs have become available for the three orders of extant lycophytes—Isoetales, Selaginellales, and Lycopodiales. As I will discuss here, the lycophyte mtDNAs not only show a surprising diversity of features but also previously unseen novelties of plant mitochondrial DNA evolution. The transition from a gametophyte-dominated bryophyte lifestyle to a sporophyte-dominated vascular plant lifestyle apparently gave rise to several peculiar independent changes in plant chondrome evolution.

Key words: endosymbiotic gene transfer, group I and group II introns, organelle DNA recombination, RNA editing.