Assembly and comparative analysis of the complete multichromosomal mitochondrial genome of Cymbidium ensifolium, an orchid of high economic and ornamental value

Abstract

Background Orchidaceae is one of the largest groups of angiosperms, and most species have high economic value and scientific research value due to their ornamental and medicinal properties. In China, Chinese Cymbidium is a popular ornamental orchid with high economic value and a long history. However, to date, no detailed information on the mitochondrial genome of any species of Chinese Cymbidium has been published. Results Here, we present the complete assembly and annotation of the mitochondrial genome of Cymbidium ensifolium (L.) Sw. The mitogenome of C. ensifolium was 560,647 bp in length and consisted of 19 circular subgenomes ranging in size from 21,995 bp to 48,212 bp. The genome encoded 35 protein-coding genes, 36 tRNAs, 3 rRNAs, and 3405 ORFs. Repeat sequence analysis and prediction of RNA editing sites revealed a total of 915 dispersed repeats, 162 simple repeats, 45 tandem repeats, and 530 RNA editing sites. Analysis of codon usage showed a preference for codons ending in A/T. Interorganellar DNA transfer was identified in 13 of the 19 chromosomes, with plastid-derived DNA fragments representing 6.81% of the C. ensifolium mitochondrial genome. The homologous fragments of the mitochondrial genome and nuclear genome were also analysed. Comparative analysis showed that the GC content was conserved, but the size, structure, and gene content of the mitogenomes varied greatly among plants with multichromosomal mitogenome structure. Phylogenetic analysis based on the mitogenomes reflected the evolutionary and taxonomic statuses of C. ensifolium. Interestingly, compared with the mitogenomes of Cymbidium lancifolium Hook. and Cymbidium macrorhizon Lindl., the mitogenome of C. ensifolium lost 8 ribosomal protein-coding genes. Conclusion In this study, we assembled and annotated the mitogenome of C. ensifolium and compared it with the mitogenomes of other Liliidae and plants with multichromosomal mitogenome structures. Our findings enrich the mitochondrial genome database of orchid plants and reveal the rapid structural evolution of Cymbidium mitochondrial genomes, highlighting the potential for mitochondrial genes to help decipher plant evolutionary history.