Genetic Diversity Of Paeonia Jishanensis And The Origin Of Cultivated Tree Peonies

Tree peony is a perennial woody flower plant native to China.Paeonia jishanensis is an important wild resource for tree peony breeding.China is also the geographic origin and developmental centre of the cultivated tree peonies.However,the geographic distribution and genetic diversity of P.jishanensis remain unresolved,and the domestication history of cultivated tree peonies has not got a consistent conclusion.Here,we assessed the genetic diversity of P.jishanensis and elucidated the origin and domestication history of cultivated tree peonies by combing nuclear SSRs with maternally inherited chloroplast DNA sequences,and revealed the suitable habitats for P.jishanensis using ecological niche models.The main results were as follows:1.Genetic diversity and structure of P.jishanensis based on nuclear SSR markersA total of 236 individuals of P.jishanensis from 10 extant populations were analysed using 21 EST-SSR markers to assess their genetic diversity and population structure.Moderate genetic diversity levels(HE=0.340)and high genetic differentiation among populations(FST=0.335)were revealed.Combining the results of STRUCTURE,PCA and neighbour-joining analyses,the 10 populations were divided into four genetic groups that were significantly related to their geographical origins,which were further supported by hierarchical AMOVA showing the highest variation of 17.9%among groups.The Mantel test(r=0.873,P<0.0001)showed a significant positive correlation between genetic distance and geographic distance among populations.The genetic structure of P.jishanensis may be due to limited gene flow hindered by vicariance.2.Genetic diversity and phylogeographic structure of P.jishanensis based on cpDNATen populations were analyzed using three cpDNA accD-psal,psbE-petL and petB-petD sequences.A total of 3 cpDNA haplotypes were detected based on 10 variation sites.Haplotype diversity(Hd)and nucleotide diversity(?)were 0.473 and 2.5610'3,respectively,indicating low level of genetic diversity.AMOVA revealed that most of the variation occurred among populations(FST=0.993).IBD showed significant relationship between genetic distance and geographic distance of populations.Phylogeographic structure of P.jishanensis was related to geographic isolation.The divergence time of the two cpDNA lineages began about 0.188Mya.Mismatch distribution indicated population expansion in the northern region.3.Prediction of the potential introduction habitats of P.jishanensisBased on data of 12 bioclimatic variables and 21 geographic distribution records,the potential geographic distribution of P.jishanensis in current and the 2070s were predicted by MaxEnt software.Our results showed that the main environmental factors influencing the potential distribution were UVB4(26.4%),Bio12(21.1%),Bio4(20.2%)and UVB2(15.2%).The model revealed the suitable habitats were mainly located in Qinling-Daba Mountains and the forests of the Loess Plateaus in Shaanxi and Gansu.The suitable habitats of P.jishanensis would decrease by 2070s and have a tendency of migrating northward and westward.4.Domestication history of cultivated tree peoniesUsing 34 nuclear SSR loci and 3 chloroplast DNA sequences,we genotyped a comprehensive sample set across China including cultivated tree peonies and the putative wild ancestors,P.jishanensis,P.rockii,P.ostii,P.qiui and P.decomposita of the subsection Vaginatae to elucidate the domestication history of cultivated tree peonies.Our result revealed that cultivated tree peony has maintained high levels of genetic diversity during domestication.The combined evidence from nuclear and chloroplast DNA revealed that multiple wild peony species including P.ostii,P.rockii and P.qiui involved in the origin of cultivated tree peonies.In addition,cultivated tree peonies were first domesticated from P.ostii in Qinling Mountains,and were subsequently developed from hybridization with P.rockii and P.qiui.