Comprehensive analysis of the first complete mitogenome and plastome of a traditional Chinese medicine Viola diffusa

Viola diffusa is used in the formulation of various Traditional Chinese Medicines (TCMs), including antiviral, antimicrobial, antitussive, and anti-inflammatory drugs, due to its richness in flavonoids and triterpenoids. The biosynthesis of these compounds is largely mediated by cytochrome P450 enzymes, which are primarily located in the membranes of mitochondria and the endoplasmic reticulum.

This study presents the complete assembly of the mitogenome and plastome of Viola diffusa. The circular mitogenome spans 474,721 bp with a GC content of 44.17% and encodes 36 unique protein-coding genes, 21 tRNA, and 3 rRNA. Except for the RSCU values of 1 observed for the start codon (AUG) and tryptophan (UGG), the mitochondrial protein-coding genes exhibited a codon usage bias, with most estimates deviating from 1, similar to patterns observed in closely related species. Analysis of repetitive sequences in the mitogenome demonstrated potential homologous recombination mediated by these repeats. Sequence transfer analysis revealed 24 homologous sequences shared between the mitogenome and plastome, including nine full-length genes. Collinearity was observed among Viola diffusa species within the other members of Malpighiales order, indicated by the presence of homologous fragments. The length and arrangement of collinear blocks varied, and the mitogenome exhibited a high frequency of gene rearrangement.

We present the first complete assembly of the mitogenome and plastome of Viola diffusa, highlighting its implications for pharmacological, evolutionary, and taxonomic studies. Our research underscores the multifaceted importance of comprehensive mitogenome analysis.