Abstract
Exploring the evolutionary patterns of mitochondrial genomes is important for our understanding of the Saccharomyces sensu stricto (SSS) group, which is a model system for genomic evolution and ecological analysis. In this study, we first obtained the complete mitochondrial sequences of two important species, Saccharomyces mikatae and Saccharomyces kudriavzevii. We then compared the mitochondrial genomes in the SSS group with those of close relatives, and found that the non-coding regions evolved rapidly, including dramatic expansion of intergenic regions, fast evolution of introns and almost 20-fold higher rearrangement rates than those of the nuclear genomes. However, the coding regions, and especially the protein-coding genes, are more conserved than those in the nuclear genomes of the SSS group. The different evolutionary patterns of coding and non-coding regions in the mitochondrial and nuclear genomes may be related to the origin of the aerobic fermentation lifestyle in this group. Our analysis thus provides novel insights into the evolution of mitochondrial genomes.
Highlights
Mitochondria (MT) are one of the two endosymbiotic organelles with non-nuclear genetic materials found in eukaryotic cells [1]
Based on a phylogenetic tree of five sensu stricto (SSS) yeasts and ten yeasts from outside of the SSS group, we found that the MT genome sizes of the SSS group were visibly larger than those of most close relatives (Fig 1C and S2 Table), such as species in the Kazachstania/Naumovozyma (K/N), Candida/Nakaseomyces (C/N) and Lachancea lineages, except for N. bacillisporus in the C/N linage where the genome was enlarged by the invasion of palindromic GC clusters [22]
By comparing the MT genomes of the SSS group with their close relatives, we found that there was an expansion of the MT genome size
Summary
Mitochondria (MT) are one of the two endosymbiotic organelles with non-nuclear genetic materials found in eukaryotic cells [1]. Most of the genes from ancestral mitochondria have been transferred into the nuclear genome [2], mitochondrion are essential for cell respiration [3], biosynthesis of certain metabolites [4], ion homeostasis and apoptosis [5]. The Saccharomyces sensu stricto (SSS) group, which includes S. cerevisiae, has been used for a long time to study the evolutionary patterns of mitochondrial genomes [6]. The mitochondrial genome size in the SSS group has expanded two- to four-fold compared to close relatives [9,10,11], even though they diverged only ~10–20 million years ago (MYA) [12]. The wide diversity of mitochondrial genomes in the SSS group provides an excellent case for investigating the mechanisms of genome evolution among (closely-related) species [13,14,15,16]
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