Expansion and Adaptive Evolution of the mTERF Gene Family in Plants

Mitochondrial transcription termination factor ( mTERF ) genes are encoded in the nucleus and bind to nucleic acids to regulate the replication, transcription and translation of mitochondrial genomes. Plants possess a large family of mTERF genes that play important roles in regulating organellar gene expression and stress response. However, their origin and expansion in land plants has not been examined. Here, we conducted a comprehensive molecular evolution analysis of 611 mTERF genes identified in 18 plant species, including algae, moss, fern, gymnosperm and flowering plants. Higher plants have more mTERF genes compared to lower plants, forming a huge higher plant-specific clade (M-class mTERF genes). M-class mTERF genes occur in clusters, suggesting that tandem duplication contributed to their expansion. Compared to other mTERF genes, M-class mTERF genes have undergone rapid evolution, and several significant positively selected sites were located in nucleic acid-binding sites. The strong correlation between the number of M-class mTERF genes and corresponding mitochondrial genome variation suggests that the rapid evolution of M-class mTERF genes might account for the changes in the complex machinery for expression regulation of plant mitochondrial genomes, providing molecular evidence for the host-parasite interaction hypothesis between the nucleus and mitochondria.