The Complete Mitochondrial Genome of Ophioglossum vulgatum L. Is with Highly Repetitive Sequences: Intergenomic Fragment Transfer and Phylogenetic Analysis

Many plant mitochondrial (mt) genomes have been sequenced but few in ferns. Ophioglossum vulgatum represents a typical species of fern genus Ophioglossum with medicinal and scientific value. However, its mt genome structure remains to be characterized. This study assembled and annotated the complete O. vulgatum mt genome and presented its structural characters and repeat sequences firstly. Its mt and chloroplast (cp) transfer sequences were explored, and the phylogenetic significance of both mt and cp genomes was also evaluated at the family level. Our results showed that the complete mt genome of O. vulgatum is a single circular genome of 369,673 bp in length, containing 5000 dispersed repetitive sequences. Phylogenetic trees reconstructed from cp and mt genomes displayed similar topologies, but also showed subtle differences at certain nodes. There exist 4818 bp common gene fragments between cp and mt genomes, of which more than 70% are located in tRNA intergenic regions (in mt). In conclusion, we assembled the complete mt genome of O. vulgatum, identified its remarkable structural characters, and provided new insights on ferns. The complementary results derived from mt and cp phylogeny highlighted that some higher taxonomic-level phylogenetic relationships among ferns remain to be resolved.