The mitochondrial genome of the moss Physcomitrella patens sheds new light on mitochondrial evolution in land plants

The phylogenetic positions of bryophytes and charophytes, together with their genome features, are important for understanding early land plant evolution. Here we report the complete nucleotide sequence (105,340 bp) of the circular-mapping mitochondrial DNA of the moss Physcomitrella patens. Available evidence suggests that the multipartite structure of the mitochondrial genome in flowering plants does not occur in Physcomitrella. It contains genes for 3 rRNAs (rnl, rns, and rrn5), 24 tRNAs, and 42 conserved mitochondrial proteins (14 ribosomal proteins, 4 ccm proteins, 9 nicotinamide adenine dinucleotide dehydrogenase subunits, 5 ATPase subunits, 2 succinate dehydrogenase subunits, apocytochrome b, 3 cytochrome oxidase subunits, and 4 other proteins). We estimate that 5 tRNA genes are missing that might be encoded by the nuclear genome. The overall mitochondrial genome structure is similar in Physcomitrella, Chara vulgaris, Chaetosphaeridium globosum, and Marchantia polymorpha, with easily identifiable inversions and translocations. Significant synteny with angiosperm and chlorophyte mitochondrial genomes was not detected. Phylogenetic analysis of 18 conserved proteins suggests that the moss-liverwort clade is sister to angiosperms, which is consistent with a previous analysis of chloroplast genes but is not consistent with some analyses using mitochondrial sequences. In Physcomitrella, 27 introns are present within 16 genes. Nine of its intron positions are shared with angiosperms and 4 with Marchantia, which in turn shares only one intron position with angiosperms. The phylogenetic analysis as well as the syntenic structure suggest that the mitochondrial genomes of Physcomitrella and Marchantia retain prototype features among land plant mitochondrial genomes.