350 My of Mitochondrial Genome Stasis in Mosses, an Early Land Plant Lineage

Among land plants, angiosperms have the structurally most labile mitochondrial (mt) genomes. In contrast, the so-called early land plants (e.g., mosses) seem to have completely static mt chromosomes. We assembled the complete mt genomes from 12 mosses spanning the moss tree of life, to assess 1) the phylogenetic depth of the conserved mt gene content and order and 2) the correlation between scattered sequence repeats and gene order lability in land plants. The mt genome of most mosses is approximately 100 kb in size, and thereby the smallest among land plants. Based on divergence time estimates, moss mt genome structure has remained virtually frozen for 350 My, with only two independent gene losses and a single gene relocation detected across the macroevolutionary tree. This is the longest period of mt genome stasis demonstrated to date in a plant lineage. The complete lack of intergenic repeat sequences, considered to be essential for intragenomic recombinations, likely accounts for the evolutionary stability of moss mt genomes.