Characterization and comparative analysis of the complete mitochondrial genome of Christia vespertilionis (Leguminosae: Desmodieae)

Christia vespertilionis , a legume species commonly known as “butterfly wings” or “aircraft grass”, holds considerable ornamental and medicinal values. It belongs to the taxonomically challenging tribe Desmodieae within the non-protein amino acid accumulating (NPAAA) clade of Fabaceae. Although its chloroplast genome has been documented, the mitochondrial genome remains uncharacterized, thereby hindering our comprehensive understanding of its genomic structure and evolutionary dynamics. In this study, we employed Oxford Nanopore Technologies (ONT) and Illumina sequencing data to assemble and annotate the complete mitochondrial genome of C. vespertilionis . The mitochondrial genome is circular, spanning 423,055 bp, and contains a total of 52 annotated genes, including 33 protein-coding genes (PCGs), 16 tRNA genes, and three rRNA genes. We detected 503 potential editing events across 32 of the 33 mitochondrial PCGs, with the nad4 and ccmB genes showing the highest editing frequencies. Comparative genomic analyses revealed that the mt genomes are conserved within tribe Desmodieae in terms of gene composition, codon preference and RNA editing patterns, suggesting functional evolutionary constraints. However, notable differences were observed in the patterns of repetitive sequences and mitochondrial plastid DNAs (MTPTs), indicating evolutionary dynamics. Specifically, C. vespertilionis contains 299 dispersed repeats (DRs) and 102 SSRs, whereas its relative Hylodesmum podocarpum harbors 472 DRs and 139 SSRs. Both species possess 18 MTPTs, with total lengths of 3450 bp in C. vespertilionis and 3154 bp in H. podocarpum . MTPTs shorter than 100 bp share the same tRNA flanking regions distribution, whereas those exceeding 100 bp exhibit distinct distribution patterns. Phylogenetic analyses based on concatenated datasets of shared mitochondrial and chloroplast PCGs generated an identical topology with high resolution at the tribe level. Within the NPAAA clade, 22 species from 10 tribes were resolved into two monophyletic subclades. The tribe Desmodieae, represented by C. vespertilionis and H. podocarpum , was well-supported as a monophyletic sister group to the tribe Phaseoleae. In this study, we sequenced, assembled, and annotated the mitochondrial genome of C. vespertilionis for the first time and conducted comparative genomic and phylogenetic analyses with species from the NPAAA clade. Our findings contribute to the mitochondrial genome database of legume plants and provide valuable insights into the exploitation and utilization of C. vespertilionis , as well as for taxonomic and evolutionary investigations within the taxonomically tribe Desmodieae.