High Density Genetic Map Construction Of Populus Deltoides 'Danhong' × P.simonii 'Tongliao1' And QTLs Analysis Of Important Economic Traits

As one of the main afforestation tree species in China,Populus has very important economic and ecological values.A great number of poplar cultiavrs have been widely cultivated in different poplar suitable regions in China.Accurate identification of different poplar cultivars and dissection of genetic basis of important poplar traits are the key target of poplar production and genetic improvement.Based on poplar cultivars that were collected from domestic and abroad by our research group in the early stage,we analyzed the fingerprint and ploidy of 91 poplar cultivars.Among them,P.deltoides‘Danhong'and P.simonii‘Tongliao1'were selected as cross parents to construct F₁ population.A high density genetic map of P.deltoides‘Danhong'×P.simonii‘Tongliao1'was established based on whole genome re-sequencing.The leaf,adventitious root,and drought resistant traits of P.deltoides‘Danhong'×P.simonii‘Tongliao1'F₁ population were measured to revealed genetic basis and screen candidate genes.In this study,we constructed fingerprint of main poplar cultivars in China and established genetic map of P.deltoides‘Danhong'×P.simonii‘Tongliao1'.Besides,the genetic bases of important economic traits were also revealed through QTL analysis.All this results provide a theoretical basis of differentiation of poplar cultivars in production practice,and have great significance on poplar molecular assisted breeding and genetic improvement of important traits.The main conclusions were listed as following:1.Fingerprint of 91 poplar cultivars belonging to four sections[Aigeiros(57),Tacamahaca(11),Populus(5),Turanga(2)and inter/intra-section hybrids(16)]was constructed using 18 polymorphic simple sequence repeat(SSR)markers.In total,222diversity alleles were amplified with an average of 12.3 diversity alleles per marker,and the mean value of the polymorphic information content and power of discrimination were 0.706and 0.813,respectively.Five SSR markers(ORPM?103,ORPM?247,GCPM?1048,GCPM?1255 and LG?X?19)constituted a core fingerprint for all the tested cultivars.Flow cytometry indicated that 11 poplar cultivars were triploid.Among these cultivars,seven cultivars had three alleles at some loci,suggesting that SSR markers could assist ploidy level detection.2.P.deltoides‘Danhong'(maternal parent)originating from North America and a native tree species P.simonii‘Tongliao1'(paternal parent)in northern China were used to establish F₁population by artificial control pollination.The maternal,paternal,and integrated genetic maps were constructed using single nucleotide polymorphism(SNPs)developed by whole genome re-sequence.The maternal map contained 3 474 SNPs distributed on 19 linkage groups(LGs),spanning 2 686.63 centimorgans(c M)of genetic length,with an average density of 0.77 c M.The paternal map contained 2 831 SNPs distributed on 19 LGs,spanning 2 388.21 c M of genetic length,with an average density of 0.84 c M.The integrated map contained 5 796 SNPs distributed on 19 LGs,spanning 2 683.80 c M of genetic length,with an average density of 0.46c M.Collinearity and heatmap analysis suggested that the genetic map was high quality.3.Thirteen-three leaf morphological and physiological traits(leaf area,leaf perimeter,net photosynthetic rate and so on)of P.deltoides‘Danhong'×P.simonii‘Tongliao1'F₁ population were measured,and exhibited significant difference between parents.Correlations between traits within the same leaf trait categories were stronger than those in different categories in F₁population.We identified 109 QTLs on 18 LGs for leaf morphological traits and 55 QTLs on14 LGs for leaf physiological traits.A total of 208 putative candidate genes were identified within the candidate genomic region.Co-expression network and gene ontology enrichment analyses suggested that these candidate genes were involved in the photosynthetic process.The differential expression patterns of the CYCLIN(Potri.015G112200)and RED CHLOROPHYLL REDUCTASE(Potri.007G043600)genes between two parents indicated their potential roles in leaf development.4.The P.deltoides‘Danhong'×P.simonii‘Tongliao1'F₁ population was performed to hydroponic culture to determine 12 adventitious root and shoot related traits(total adventitious root number,maximum root length,leaf senescence and so on).Extensive segregation,high repeatability,and significant correlation relationship were detected for the investigated traits.A total of 150 QTLs were associated with adventitious root traits,explaining 3.1-6.1%of phenotypic variation(PVE);while 83 QTLs were associated with shoot traits,explaining3.1-19.8%of PVE.Twenty-five QTL clusters and 40 QTL hotspots were identified for the investigated traits.Ten QTL clusters were overlapped in both adventitious root traits and related shoot traits.Transcriptome analysis identified 10 172 differentially expressed genes(DEGs)among two parents,three fine rooting and three poor-rooting genotypes,143 of which were physically located within the QTL intervals.K-means cluster and weighted gene co-expression network analysis showed that Pt AAAP19(Potri.004G111400)encoding amino acid transport protein was tightly associated with adventitious roots and highly expressed in fine-rooting genotypes.Compare with‘Danhong',153 bp deletion in the coding sequence of Pt AAAP19 in‘Tongliao1'gave rise to lack one transmembrane domain,which might cause the variation of adventitious roots.5.Five drought-resistant traits(relative height growth,relative diameter growth,leaf senescence and so on)of P.deltoides‘Danhong'×P.simonii‘Tongliao1'F₁ population were measured under normal and moderate drought stress experiment.These traits exhibited normal distribution in F₁ population and under different degree of hereditary control.Significant block and treatment interactive effect were existed in relative height growth and specific leaf area.There were 208 QTLs were identified for drought resisting traits with 26 common QTLs,182specific QTLs,and two QTL clusters.Among them,92,63,and 53 QTLs were identified under control,moderate drought stress,and drought treatment index condition.A drought resistant molecular molecular(np2841)related to leaf relative water content common QTL q DLRWC-LG10-1 was developed preliminary.We identified 187 candidate genes within specific QTLs region and found two candidate genes(Potri.003G171300 and Potri.012G123900)interfered in drought response by functional annotation analysis.The fingerprint of main poplar cultivars adopted in China was constructed,and P.deltoides‘Danhong'×P.simonii‘Tongliao1'F₁ population were constructed high density genetic map.The genetic basis of important traits and key candidate genes were also dissected.These results formed the foundation for distinguishing different poplar cultivars and understanding the genetic basis of poplar important traits.Besides,it also had important theoretical significance and application value for new poplar variety protection,molecular marker assisted breeding,and genetic improvement breeding.