Comparative and phylogenetic analyses of Swertia L. (Gentianaceae) medicinal plants (from Qinghai, China) based on complete chloroplast genomes

Abstract

Swertia L. is a large genus in Swertiinae (Gentianaceae). In China, many Swertia species are used as traditional Tibetan medicines, known as “Zangyinchen” or “Dida”. However, the phylogenetic relationships among Swertia medicinal plants and their wild relatives have remained unclear. In this study, we sequenced and assembled 16 complete chloroplast (cp) genomes of 10 Swertia species, mainly distributed in Qinghai Province, China. The results showed that these species have typical structures and characteristics of plant cp genomes. The sizes of Swertia cp genomes are ranging from 149,488 bp to 154,097 bp. Most Swertia cp genomes presented 134 genes, including 85 protein coding genes, eight rRNA genes, 37 tRNA genes, and four pseudogenes. Furthermore, the GC contents and boundaries of cp genomes are similar among Swertia species. The phylogenetic analyses indicated that Swertia is a complex polyphyletic group. In addition, positive selection was found in psaI and petL genes, indicating the possible adaptation of Qinghai Swertia species to the light environment of the Qinghai-Tibet plateau. These new cp genome data could be further investigated to develop DNA barcodes for Swertia medicinal plants and for additional systematic studies of Swertia and Swertiinae species.

Comparative chloroplast genomics of 34 species in subtribe Swertiinae (Gentianaceae) with implications for its phylogeny

“…Thus, nectaries at the base of the ovary may be ancestral characteristics of subtribe Swertiinae. However, the position of V. baillonii is still unresolved because the results of this study were inconsistent with those of previous studies [ 25 , 26 , 28 ] . C. falcatum and C. pulmonstium formed a clade, which showed that Comastoma was as one monophyletic group.…”

“…A plastome phylogenomics approach has been successfully used to solve many enigmatic relationships within angiosperms and across all green plants [ 18 – 24 ]. Some studies have also revealed that chloroplast genome resources could offer helpful data for inferring the evolutionary relationships of Gentianaceae plants, thus reflecting vital evidence for a well-supported hypothesis of classification [ 25 , 26 ]. To date, 34 complete chloroplast genomes of subtribe Swertiinae species have been sequenced, and some studies have been conducted based on these chloroplast genomes [ 25 – 28 ].…”

“…Meanwhile, the phylogenetic relationships of subtribe Swertiinae were also examined. However, the phylogenetic relationships of subtribe Swertiinae obtained from the same chloroplast genome were inconsistent [ 25 , 26 ]. Moreover, the structural patterns among genera within subtribe Swertiinae are still unknown.…”