Phylogeography Of Medicinal Plant Species Polygala Tenuifolia Willd

Polygala tenuifolia Willd (Polygalaceae) is a perennially medicinal plant species. Due to slowly-growing characteristics and sharply reducing of wild resources of P. tenuifolia. this plant species has been listed in the "protection and management regulations of Wild herbs resources". In this project, we will investigate the phylogeography of32natural populations of P. tenuifolia based on the sequence variations of three chloroplast DNA (trnL intron, psbA-trnH,psbB-psbF) fragments and nrDNA ITS intergenic spacer. Then, we will detect the effects of climatic oscillations on genetic structure of P. tenuifolia during the Quaternary glacial periods, and then reveal the formation reasons of patterns of geographic distribution combined with Paleobotany and biogeography, finally to further infer its potential glacial refuges, diversity center and the possible migration routes. Our findings will provide a scientific basis to develop strategies of protection of P. tenuifolia. The main conclusions are as follows:(1) The sequence lengths of three chloroplast DNA (cpDNA)(trnL intron, psbA-trnH, psbB-psbF) were523bp,362bp,282bp, respectively. And12,2and7haplotypes were examined in the trnL intron,psbB-psbF, and psbA-trnH regions, respectively. After the combination of three sequences,16haplotypes (H1-H16) were recovered. Among them, the haplotypes H1and H4were widespread distributions, which were shared by most populations in northern China. We speculated that H4was an ancient haplotype, with its neutral position in network of haplotypes. Our study suggested that there were three diversity centers of P. tenuifolia, one was located in the eastern part of the Tibetan Plateau, including Qinghai, Gansu (XH, LZ); the second one was northwestern regions of China, included Shaanxi and Shanxi (HY, XJ); the third one was located in Southern China, including Zhejiang, Jiangxi (GC, and ZKH). In addition, GC Population included in the most haplotypes in all the populations, and four different haplotypes were identified. We concluded that the diversity centers were the glacial refuges of P. tenuifolia in Quaternary periods. In addition, H8only distributed in two populations (JZ and BP in Liaoning province, which was not found in other regions of Northern China, so we speculated that these areas also might be glacial refuges of P. tenuifolia, and the other possibly explanation was that this population might be migrated from other nearby refuges after glacial periods, and subsequently genetic drift resulted in the haplotype H16was retained.(2) A total of15ITS haplotypes were identified in155individuals of32natural populations of P. tenuifolia. And haplotype â…¡ was widely distributed in the northern populations. In addition, the eastern edge of the Tibetan Plateau and the west Qinling mountains with high haplotype diversity (Hd) and much more private haplotypes than other regions. For the southern populations, almost every population had different ITS haplotypes except for113was shared by two populations in the south part, and population GC was also detected to have private haplotypes(I15). These results were consistently with ones of the cpDNA, and we concluded that those areas were possible refuges of P. tenuifolia in the Quaternary glacial periods.(3) The phylogenetic relationships of cpDNA haplotypes was consistent with that of ITS haplotypes, which devided into two distinct braches, one corresponding to populations of northern China, and the other matched along with the southern populations. AMOVA revealed that genetic variation occurred mainly between groups (90.12%of variation partitioned between the northern and southern group, while8.56%among populations within group). These results indicated that genetic differentiation within P. tenuifolia. We found that total genetic diversity of P. tenuifolia was higher (HT=0.828), the average genetic diversity within populations was lower (Hs=0.162). Total NST (0.881) was significantly larger than GST (0.804; P<0.05) demonstrated that clear geographically structure across the distribution range of P. tenuifolia.Finally, we proposed some conservation and management strategies according to the results of phylogeography of P. tenuifolia. And we advised that in situ conservation of P. tenuifolia populations should be enhanced. Especially, the neutral populations (e.g., LZ, HY, XJ, GC, and ZKH) of genetic diversity of P. tenuifolia should be more concerned. In addition, those areas that contained private haplotypes should be taken extra care to avoid lose of rare genetic resources of P. tenuifolia.