The Complete Chloroplast Genome of Clematis tangutica (Maxim.) Korsh. and an Adaptive Evolutionary Analysis of the ycf2 Gene.

BACKGROUND: Clematis tangutica (Maxim.) Korsh. is a Tibetan medicinal plant, but its chloroplast genome and plastid gene evolution remain unexplored. Here, we assembled the complete chloroplast genome of C. tangutica and investigated the adaptive evolution of the ycf2 gene. METHODS: Chloroplast DNA was extracted from fresh leaves and sequenced on the Illumina HiSeq PE150 platform. We then performed comprehensive genomic analyses, including genome structure characterization, repeat and SSR identification, comparative genomics, and positive selection analysis of the ycf2 gene. RESULTS: The genome is 159,584 bp with a typical quadripartite structure, containing 134 genes and 23 SSRs. Comparative analyses revealed that ycf2 is the most variable gene among the 13 divergent loci identified. Positive selection analysis detected 12 significant sites in ycf2, all clustered in the middle region of the protein. CONCLUSIONS: This study provides the first complete chloroplast genome resource for C. tangutica, offers new insights into the adaptive evolution of ycf2 in Ranunculaceae, and yields molecular markers applicable to population genetics, phylogenetic studies, and conservation planning for this species of medicinal importance.