Exploring non-coding mitochondrial DNA sequences in bryophyte molecular evolution

Abstract

The thesis presented here focussed on the molecular evolution of non-coding mitochondrial DNA in liverworts and mosses.<br /> To address remaining questions in moss phylogeny, three mitochondrial gene regions were investigated and established as novel molecular markers: the <em>nad5-nad4</em> intergenic spacer region (Wahrmund <em>et al.</em> 2009) and the two group I introns in the <em>cob</em> gene and <em>cox1 </em>gene (cobi420, Wahrmund <em>et al.</em> 2010 and cox1i624, Volkmar and Knoop subm). Phylogenetic trees based on the single loci and concatenated data sets identified a placement of <em>Catoscopium, Drummondia </em>and<em> Timmiella </em>in the basal Dicranidae, proposed the exclusion of Gigaspermaceae from the Funariidae and a potential sister relationship of the nematodontous moss classes Tetraphidopsida and Polytrichopsida (Wahrmund <em>et al.</em> 2009, 2010). A different resolution of the basal-most moss taxa by chloroplast and mitochondrial markers was observed (Volkmar and Knoop subm) and its implications on molecular and morphological evolution in mosses discussed.<br /> The hitherto assumed slow evolution of the mitochondrial genome in liverworts was contrasted with the discovery of recombinational activity in the intergenic region of the <em>trnA-trnT-nad7 </em>cluster, an ancient gene arrangement that is also present in algae and mosses. During liverwort evolution, an inversion and at least three independent losses of the <em>trnT</em> and adjacent spacer regions resulted in independent size decreases (Wahrmund <em>et al.</em> 2008). The <em>nad7 </em>gene, part of this gene cluster, is a pseudogene in all jungermanniid and marchantiid liverworts investigated. An ancient gene transfer to the nuclear genome occurred probably in the common ancestor of both classes, more than 350 million years ago (Groth-Malonek <em>et al.</em> 2007b). The exceptionally long retention of the pseudogene indicates an underlying but yet unknown function. In the three haplomitriid liverwort genera <em>Haplomitrium, Apotreubia </em>and<em> Treubia</em>, however, the mitochondrial <em>nad7 </em>gene is intact and functional and experiences an extremely varying degree of C-to-U RNA editing, a modification of mRNAs in plant organelles to reconstitute conserved codon identities.