Population Adaptability And Associated Loci For Growth And Wood Properties In Eucalyptus Cloeziana

The long-term primary breeding task of Eucalyptus was pulpwood,however,there are few studies on large-size timber.Because of excellent wood properties and rapid growth,it is one of the most promising Eucalyptus species for high-value solid wood production and a large-size timber breeding objective has been developed for southern China.Eucalyptus cloeziana is native to the coastal and inland regions of northern and middle Queensland in Australia,and its habitats are characterized with remarkable variation in climatic and edaphic conditions,thereby enabling the identification of popul ation genetic diversity and adaptability.Adaptability is composed of three factors:environment,phenotype and genotype.Phenotype is the result of the interaction of environment and genotype.The phenotyp es of growth and wood properties are important economic traits,Thus,identification of genomic loci and candidate genes associated with growth?wood properties and adaptability will enrich our understanding of the genetic structure of these traits and provide valuable genomic resources for molecular breeding.In this dissertation,based on a provennce/family trial of E.cloeziana,used simple sequence repeats(SSR)markers to analyze the population genetic diversity,structureand adaptability of E.cloeziana.Also,genomic loci associated with 9.5-year-old growth and wood properties were identified,and candidate genes were mined throughtranscriptome sequencing(RNA-seq)and alignment with the E.grandis genome sequence.The main results are as follows:(1)A high level of genetic diversity was observed within E.cloeziana population,,and the population differentiation mainly existed between the southern and northern subgroupsThe number of alleles(N_a),the number of private alleles(N_pa),observed heterozygosity(H_o)and expected heterozygosity(H_e)were averaged at 6.88,4.5,0.749 and 0.780,respectively,demonstrating high levels of genetic diversity.Mean fixation index(F)was 0.040,indicating a very low degree of inbreeding.Overall F_st was 0.120 and analysis of molecular variance(AMOVA)showed that among-population variance took only 3.1%of the total variance,suggesting moderate to relatively low levels of population differentiation.Principal coordinate analysis,cluster analysis and structure analysis resulted consistently in obvious separation of the seven northern populations from the seven southern populations from Queensland,Australia.These results indicate that the population differentiation mainly existed between the southern and northern subgroups.(2)Climate factors driving population differentiation,and adaptability loci not only ensure survival but also participate in growth and developmentUsing Mantel test,isolation by distance(IBD)was revealed between the northern and southern populations of E.cloeziana,and the clustering analysis based on 19 climatic variables also resulted in division of the northern and southern populations into independent groups,suggesting the climatic effect on driving the population divergence.Six alleles from five outlier loci were identified with logistic regression,each associated significantly with one or more climatic factors(P<0.001)and showed dramatic difference in allelic frequency between the northern and southern populations.There are three alleles find the function annotation,Embra6-118 bp?Embra20-121 bp and EUCe SSR676-168 bp.These alleles are involved in plant growth and resistance to external factors affecting growth stability to varying degrees.This suggests that adaptive loci are important for the maintenance of plant survival and growth.(3)11 SSR loci which were significantly associated with growth and wood properties were identifiedA total of 38 SSR loci related to the growth and wood properties of E.cloeziana.were developed.6 traits of 339 E.cloeziana.samples were analyzed.Using general linear model(GLM)and mixed linear model(MLM),we found 11 loci significantly associated with growth and wood properties.The number of markers significantly associated with the diameter at breast height(D)?basic density(BD)?green density(GD)and the modulus of rupture(MOR)were 2,4,6 and 3 respectively(P<0.05).The explanatory rate of phenotypic variability was2.2-29.7%.Two marker was associated with two traits at the same time.There were 3 marker did not alignment annotations but another 8 markers alignment their functional annotations that were mainly focus on growth and development,stress response and cellulose metabolism.(3)The function of DEG are major related to synthesis of chemical in plant cell wallAnalysis of differentially expressed genes by transcriptome analysis in E.cloeziana.by RNA-Seq.The results showed that the difference of gene expression of D_H-D_L?BD_H-BD_L???_H-??_L?MOE_H-MOE_Land MOR_H-MOR_L were 866,32,58,53 and 104.The GO-enriched annotations of D_H-D_L?BD_H-BD_L???_H-??_L?MOE_H-MOE_L and MOR_H-MOR_L were 117,5,11,3 and 15.KEGG enriched pathways of D_H-D_L?BD_H-BD_L???_H-??_L?MOE_H-MOE_L and MOR_H-MOR_L were were 89,14,15,6 and 19.The results of GO and KEGG enrichment results are all related to the synthesis of three major chemical substances in plant cell wall:cellulose,hemicellulose and lignin.(5)Six groups of marker-differentially expressed genome combinations were selected,2 were related to climate adaptability,and 4 were related to growth and wood propertiesSix groups of marker-differentially expressed genome combinations with a distance of 10Kb were aligned.Embra20-Eucgr.F04138.v2.0 and EUCe SSR298-Eucgr.H00722.v2.0 were related to climate adaptability.The other groups were related to growth and wood properties:EUCe SSR0508-Eucgr.C03709.v2.0,EUCe SSR06-Eucgr.C00653.v2.0,Embra8.0.A8-Eucgr.F01859.v2.0 and EUCe SSR0542-Eucgr.G02727.v2.0.