Phylogeny And Geographical Pattern Of Population Genetic Differentiation In Camellia Oleifera

Camellia oleifera is the first major woody oil crop in China.Its wild relative species are valuable genetic resources for breeding.However,the phylogeny of C.oleifera and its wild relative species is still under debate,limiting the effective exploration and utilization of the genetic resources.Camellia oleifera is widely distributed in the East Asian subtropics,and it is a typical plant in subtropical evergreen broad-leaved forest.Study the geographical pattern of population genetic differentiation in C.oleifera can provide scientific basis for exploration and utilization of genetic resources,and such researches can also help to understand the genetic diversity patterns and formation mechanisms of plant species in East Asia subtropical evergreen broad-leaved forests.This study used the distribution data of C.oleifera relative species to analyze the geographical distribution patterns and species diversity of C.oleifera relative species.Comparative transcriptome analyses were performed to screen orthologous genes among C.oleifera and its relative species.Phylogenetic trees were constructed using the orthologous genes to resolve the phylogenetic relationships among C.oleifera and relative species.MaxEnt ecological niche model was used to estimate the potential distribution of C.oleifera in Last Glacial Maximum(LGM).Based on35 highly polymorphic simple sequence repeat(SSR)markers,the population genetic diversity and structure were analyzed for 17 C.oleifera wild populations and65 major cultivated varieties in China.The main results and conclusions are as following:1.Regions with high species diversity of C.oleifera relative species are Nan mountain,Miao mountain,Wuyi mountain,Wuling mountain and the surrounding areas.Those areas may be potential interspecific hybridization zones with high genetic diversity.Exploring genetic resources should focus on areas of high species diversity.The level of species diversity decreased from Nan mountain to Wuling mountain,from Nan mountain to Luoxiao mountain and from Nan mountain to Wuyi mountain.2.With comparative transcriptome analyses,we screened 450 orthologous genes from 22 species in Sect.Oleifera,Sect.Paracamellia,Sect.Camellia and Sect.Thea.The maximum likelihood and Bayesian phylogenetic trees constructed with the genes showed almost identical topology.The results showed that Sect.Oleifera was an isolated branch including C.lanceoleosa,C.meiocarpa,C.oleifera,C.vietnamensis,C.gauchowensis,and C.sasanqua,and some species of Sect.Paracamellia should be merged into Sect.Oleifera(i.e.C.fluviatilis,C.kissi,and C.brevistyla).The remaining species in Sect.Paracamellia cannot be grouped into an isolated branch,and therefore cannot be grouped into an independent section.3.According to the simulation by the Max Ent model,the highly suitable distribution areas of C.oleifera in LGM were also in Nan mountain,Wuyi mountain,Luoxiao mountain,and Wuling mountain.However,the distribution areas of C.oleifera in LGM were more fragmented than today.Part of the highly suitable distribution areas shrank to the south in LGM,but there were still some highly suitable distribution areas in the north.At the same time,small isolated refuges might exist in the north in LGM,such as Mount Lu.4.The levels of genetic diversity among the C.oleifera populations were similar,and there was no obvious downward trend from south to north.It is suggested that there may be many refuges both in the north and in the south in LGM.There was no significant difference in genetic diversity between main cultivars and wild C.oleifera.We found obvious genetic structure among natural populations of C.oleifera.First of all,Lu mountain and Mao'er mountain have obviously genetic differentiation with other populations.Secondly,populations in the east(Nan mountain in Guangdong Province,Wuyi mountain,Luoxiao mountain,and Huang mountain)were similar,and the populations in the west(Wuling mountain and Miao mountain etc.)were similar,and the eastern populations were obviously genetically differentiated from the western populations.The modern cultivars were similar to the eastern populations suggesting that the modern cultivars were mainly originated from eastern populations.