Phylogeography Of Xanthopappus Subacaulis(Asteraceae),an Endemic Species From The Qinghaitibet Plateau

Xanthopappus subacaulis is a unique medicinal plant in alpine meadows,belongs to Xanthopappus(Asteraceae).X.subacaulis had many significant characteristics such as cold,drought,and salinity resistance,especially for maintaining the stability of alpine meadow ecosystem.So far,domestic and foreign researches on X.subacaulis mainly focus on the fields of biological characteristics,chemical constituents and pharmacological activities,stress tolerance physiology and system status.However,the study of population genetic structure and evolutionary history using molecular markers is still blank.In the present study,we constructed the phylogenetic study of 232 individuals from 44 populations of X.subacaulis,with the maternally inherited cpDNA(coding region rbc L and non-coding regions psb A-trn H,trn L-F,and psb I-psb K)and parental inherited nrITS markers.It is used to explore the genetic structure and genetic diversity of the X.subacaulis populations,to speculate on its glacial refuge and population history,and to clarify the impact of climate change on the Qinghai-Tibet Plateau(QTP)about the genetic variation distribution and modern geographical distribution pattern of X.subacaulis.These findings have important implications for understanding the evolutionary history of alpine medicinal plants.(1)A total of 13 haplotypes(H1-H13)and 29 genotypes(T1-T29)were detected by chloroplast DNA and nuclear ribosomal nrITS fragments,and X.subacaulis showed high genetic diversity(cpDNA:H_D=0.7010,?=0.0009,H_T=0.720;nrITS:H_D=0.8430,?=0.0094,H_T=0.853).The genetic variation mainly exists between populations(cpDNA:81.74%;nrITS:86.06%)of X.subacaulis,the populations genetic divergence was high(cpDNA:F_ST=0.81736;nrITS:F_ST=0.86059)and gene flow was infrequent(cpDNA:N_m=0.11;nrITS:N_m=0.08).(2)Population genetic structure analysis shows that X.subacaulis had a significant pedigree geographic structure(cpDNA:N_ST=0.809ST=0.737,P>0.05;nrITS:N_ST=0.861ST=0.366,P<0.01).Mantel test results showed that there was significant positive correlation between geographic distance and genetic distance,and the geographic distance was the main reason for genetic differentiation among populations(cpDNA:r=0.401,P=0.01;nrITS:r=0.401,P=0.01).(3)Phylogenetic analysis showed that the 44 populations of X.subacaulis were divided into two lineages,Northern(Group 1)and Southern(Group 2)lineages,with the Aemye Ma-chhen Range as the boundary,and the clustering results of the Median-joining network,Split tree and STRUCTURE consistent.Based on cpDNA and nrITS fragments to estimate of the time of haplotype divergence,it was found that the divergence time between the Northern and Southern lineage was estimated about 4.92 Ma(95%HPD:3.34-6.63 Ma).The onset of lineage diversification was estimated as 4.33 Ma in the Northern lineage(95%HPD:2.94-5.89 Ma)and3.13 Ma in the Southern lineage(95%HPD:1.81-4.47 Ma),so lineage differentiation was related to Miocene and Pliocene climate fluctuations.(4)The population of X.subacaulis did not experienced recent expansion,but only experienced population shrinkage during the Quaternary glacial period.Quaternary glacial climatic oscillations and the uplifting of the Qinghai-Tibet Plateau caused the area of the most suitable distribution area of X.subacaulis to shrink sharply after the Last Glacial Maximum,and the habitat was severely fragmented.Based on the results of cpDNA and nrITS,there may be multiple glacial micro-refugia in the Qinghai Lake basin,Aemye Ma-chhen Range and Hengduan Mountains.We thought that the main reason of forming the current geographical distribution pattern of haplotypes and genotypes of X.subacaulis may be the secondary contact of populations in the refuge.