Comparative analysis of the complete multi-chromosomal mitogenome of an antitussive herb Fritillaria unibracteata

A renowned antitussive herb, Fritillaria unibracteata P. K. Hsiao & K. C. Hsia, has long been used as the original source of many traditional Chinese medicines (TCM) prescriptions for its pharmacological effects. Currently, this species is at risk of extinction owing to overexploitation. Genomic data can provide a scientific basis for the effective protection of wild germplasm resources. Although the plastome of F. unibracteata has been released, its mitogenome remains unclear.

The mitogenome of F. unibracteata exhibited a sophisticated multi-chromosomal configuration containing one master circular chromosome (82,085 bp) and 21 submaster chromosomes (18,718 bp-54,256 bp). It contained 60 genes, including 44 PCGs, 13 tRNA and 3 rRNA genes. Repeat sequences, including 862 dispersed repeats, 142 simple repeats, and 23 tandem repeats, contributed more to the mitogenome size than coding genes and chloroplast-derived fragments. A total of 518 RNA editing sites were identified in 36 PCGs, with NADH dehydrogenase and cytochrome c biogenesis genes being the most prevalent. The codon usage bias is in accordance with the model for most terrestrial plants that use ATG as an initiator codon and shows an obvious A/T (U) bias in the third site of all PCGs. These results provide key insights into the F. unibracteata mitogenome.

The assembled and annotated F. unibracteata mitogenome advanced the features and organization of multi-chromosome genomes. This provides helpful information for further research on conservation, breeding, phylogenetic, and evolutionary studies of the genus Fritillaria.