| Quercus species with a wide variety of species comprise the major genera in the family Fagaceae and they are widely distributed in the Northern Hemisphere.Many Quercus species are common dominant species and constructive species in forests,which have important economic and social values.Quercus species have complex morphological characteristics and overlapping distribution area.The interspecies hybridization among Quercus species is common.It is difficult to define the specific boundary,and there are many problems in the research on the determination of species and the relationship between the oaks species.However,China as one of the origins of Quercus plants,and many Quercus species are endemic in China,compared with a large number of studies on Quercus in Europe and America,there are relatively few studies on Quercus species in China,the research of Quercus in China is also of great importance.In this study,the comparative transcriptome analysis of Quercus liaotungensis Koidz.and Quercus mongolica Fisch.ex Ledeb.in the northernmost of Quercus in China was firstly conducted,and universal EST-SSR primers which were suitable for Quercus research were developed.On this basis,the population genetics research of 11 species of Quercus was carried out,so as to investigate the genetic structure and inter-species relationship of Section Quercus.The main research results are summarized as follows:(1)Comparative transcriptomes and development of expressed sequence tag-simple sequence repeat markers for two closely related oak speciesIn this study,we compared and analysed Q.liaotungensis and Q.mongolica by comparative transcriptome analysis.We used Illumina paired-end sequencing to obtain the transcriptomes of two oak species comprising Q.liaotungensis and Q.mongolica.Approximately 24 million Reads were generated and then a total of 103,618 Unigenes were obtained after assembly for both species.Comparative transcriptome analyses of both species identified a total of 12,981 orthologous contigs.The Ka/Ks estimation and enrichment analysis indicated that 1,179(9.08%)orthologs exhibited rapid evolution,and most of these orthologs were related to functions comprising “DNA repair”,“response to cold”,and “response to drought”.This findings may provide some insights into how these two closely related Quercus species adapted to extreme environments characterized by aridity and cold.The divergence time(approximately 4.27-5.93 Mya)between the two Quercus species was estimated according to the Ks distribution.Moreover,16,608 simple sequence repeat(SSR)loci were detected and 12,363 primer pairs were designed.Subsequently,158 of the 12,363 primer pairs were randomly selected to test the polymorphisms and 77 of the primer pairs were successfully amplified in the two oak species.(2)The research on population genetic in Section QuercusBased on 1700 individuals including 1672 individuals of 92 populations in 11 oaks species and 28 individuals of 2 outgroups,19 primer pairs with high polymorphism were selected from 77 primer pairs through the transcriptome research to analyze the population genetic of Section Quercus.The results based on EST-SSR markers showed that the genetic diversity of Section Quercus was lower(Hs=0.401,Ht=0.501).The results of AMOVA analysis showed that the variation mainly occurred within the population(88.55%).The genetic differentiation of the population of Section Quercus was insignificant(Fst=0.11),which indicated that gene flow was the main factor of genetic differentiation of Section Quercus.The results of STRUCTURE cluster analysis showed that the hybridization of Section Quercus was serious,none of them could be differentiated.As for the fact that Quercus yunnanensis Franch.and Quercus dentata Thunb.are divided into the same group,this supports the previous view that both of them are the same species. |
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