A mitochondrial perspective on early land plants

Abstract

Mitochondrial DNA in land plants is characterised by very slowly evolving gene sequences in contrast to a very variable genome structure displaying frequent gene relocations and transfers. Studies in this thesis address different aspects of chondriome evolution with a focus on early land plants. The mitochondrial nad4 gene was established as a novel phylogenetic marker for liverworts, including an analysis of the secondary structure of the group II intron nad4i548 conserved in these plants. A review of the already well known mitochondrial nad5 gene is accompanied by a revision of the folding structure of the included group I intron nad5i753, revealing peculiarities unique for the liverwort genus Pellia. A phylogenetic study on liverworts is reported, which combines the novel nad4 sequences with nad5 data from several labs, and the chloroplast genes rbcL and rps4, resulting in a well supported topology. The gene continuities of the gene clusters nad5 nad4-nad2 and trnA-trnT-nad7 were of special interest regarding the variability of the mitochondrial genome in the earliest diverging land plant lineages, and revealed very different patterns of evolution in the analysed spacers and among different plant groups. Loss and potential regain of the trnT gene was found in liverworts. Finally, studies on the degeneration of nad7 into a pseudogene in liverworts identified different modes of sequence degeneration in the major liverwort subclades.