Study On Ecological Genetics And Species Divergence Of Quercus Species In Qinlin Mountain

The interspecies hybridization and introgression among Quercus species is common.The study of introgression will help to reveal the mechanism of evolutionary events such as speciation and local adaptation of Quercus.Different oak species distributed vicariously across altitude ranges of Qinling Mountain.In this study five oak species were sampled,including Quercus wutaishansea Mary,Quercus aliena Blume var.acutiserrata Maximowicz ex Wenzig,Quercus serrata Thunb.var.brevipetiolata A.DC.Nakai,Quercus variabilis Bl.,and Quercus acutissima Carruth.,along the East-West transect designed in Qinling Mountain.The transect comprised,from east to west,Henan Baotianman National Nature Reserve,Taibai Mountain National Nature Reserve,and Xiaolong Mountain National Nature Reserve.Through 2b-RAD reduced-representation genome sequencing,the correlations between population genetic structure of all species studied and the altitudinal gradient were investigated.By comparative genomics,nuclear and plasmid genes were screened to identify positive selection to explore the molecular mechanisms of adaptive evolution in oak species by gene functions.The main results as follows:1.Through 2b-RAD reduced-representation genome sequencing,genome-wide SNPs of220 samples were developed for Structure analysis,species trees and PCA(principal component analysis)to reveal population genetic Structure for the five species.The level of genetic diversity is generally low,and The genetic diversity level of Quercus species(Q.wutaishansea,Q,aliena var.acutiserrata and Q.serrata var.brevipetiolata)at higher altitudes was less than lower ones(Q.variabilis and Q.acutissima).The proportion of Interspecific introgression was great and 103 samples of introgression were detected among them,two samples(R-3 and R-23)were assumed to be hybrid F1.A bidirectional hybridization was found among white oaks,while unidirectional introgression from Q.variabilis to white oaks was detected.A good linear correlation between the degree of introgression and the altitude was found,espescially in Taibai Mountain(R~2=0.8653 and 0.8691).2.Comparative analysis of the complete chloroplast genomes of five oak species were performed including Quercus wutaishansea Mary,Quercus aliena Blume var.acutiserrata Maximowicz ex Wenzig,Quercus serrata Thunb.var.brevipetiolata A.DC.Nakai,Quercus variabilis Bl.,and Quercus acutissima Carruth,as well as another eight Fagaceae species(Quercus mongolica Fischer ex Ledebour,Quercus aliena Blume,Quercus dentata Thunb.,Quercus rubra L.,Quercus bawanglingensis Huang Li et Xing,Quercus aquifolioides Rehd.et Wils.,Fagus engleriana Seem.and Castanea henryi Skan Rehd.et Wils.).The complete cp genomes of three white oak species(Q.serrata var.brevipetiolata,Q.wutaishansea and Q.mongolica)were sequenced to get the whole cp genomes(161,254 bp,161,229 bp and 161,254bp in size,respectively).Thirteen highly divergent regions including four(ndh F,rpl32-t RNA-UAG,ndh D,ycf1)in SSC and nine in LSC(mat K-rps16,trn S-GCU-trn G-GCC,trn G-GCC-trn R-UCU,trn T-GGU-psb D,ycf3-t RNA-GGA,trn F-GAA-ndh J,trn M-CAU-atp E,ndh J,atp E)were detected through comparative analyses,which have potentials to be used as molecular markers.The?ratio of the rps12,pet A,ndh A,ndh B,ycf1 genes was greater than 1in several comparison groups between Q.wutaishansea,Q.aliena var.acutiserrata,Q.serrata var.brevipetiolata,Q.variabilis and the pet A gene was subjected to significant positive selection between the comparision of white oaks and Q.variabilis,which provided a conceivable explanation for different adapativity in Quercus populations of different altitudes.3.Comparative transcriptome analysis of the complete chloroplast genomes of five oak species was conduct.After quality control,clean reads 62,588,802(Q.wutaishansea,)-96,373,990(Q.serrata var.brevipetiolata)were obtained.After the assembly and the clustering 35,527(Q.wutaishansea)-72,737(Q.serrata var.brevipetiolata)unigenes were obtained.62.73%(Q.variabilis)-72.60%(Q.wutaishansea)of unigenes were annotated.Then,selection pressure and phylogenetic tree constructed was performed based on single copy orthologs screened.A total of 86 positive selection genes with?>1 were detected.The KEGG and GO annotation inferred that one of these candidate genes could be gene RBCS in carbon metabolism.RBCS was a small subunit gene for ribulose 1,5-bisphosphate carboxylase,which was involved in photosynthetic protection mechanism against low temperature.The gene may further clarify the reasons for the occurrence of oak species among climatic zones or different niche genetic differentiation between oak species,and improve our understandings of oak species'adaptability to the environment.Furthermore,this analysis complement and improve the Quercus genetic database resources by providing basic data for the future research related to genetics and genomics.In summary,the present study revealed that interspecific introgression occured more commonly among oak species in the same group,and had linear correlations with the altitude based on the analysis of population genetic Structure.Under positive selection,genes necessary for photosynthesis such as pet A and RBCS genes related to carbon metabolism were detected,which was presumably associated with environment adaptive evolution in oak species.Our results could improve our understanding on the adaptative strategy of oak species to environmental changes.