| Rapeseed(Brassica napus)is one of the most important oil crops worldwide,conducting the genetic improvement study of oil content and quality of rapeseed oil is of practical significance.Various agronomic traits of crops are the quantitative traits,quantitative traits are controlled by multi genes and easily influenced by the environment.QTL(Quantitative Trait Loci,QTL)mapping is the classical method for studying quantative trait,basing on the SNP-largely-based high density genetic linkage map that constructed previously by our group,this study took the KN DH population(the male parent of which is “Ken-C8” with the character of low erucic acid and high sulfur content and its female parent “N53-2” is opposite,the oil content of the parents differs by about10%)as the study project,focused on fatty acid compositions trait QTL mapping of rapeseed that planted in multi breeding sites and years and obtained environmental stable,environmental specific and some novel QTLs of fatty acid compositions,these QTLs provide direct facilitation for the molecular marker assisted breeding.Through the comparative genomics analysis,candidates associated with fatty acid metabolism were screened in the confidence interval of the mapped QTLs,and study also discussed the metabolic process of fatty acid in rapeseed on the overall level.The major content of this study as follows:(1)Phenotype measurement and the correlation analysis of fatty acid compositions.The content of oleic acid(C18:1,OA),linoleic acid(C18:2,LA)and erucic acid(C22:1,EA)are most abundant,the mean was 34.05%,15.53% and 26.48%,respectively.The distribution of the content of the three monounsaturated fatty acids of C18:1,eicosenoic acid(C20:1,EIA)and C22:1 showed apparent bimodal pattern,five compositons of palmitic acid(C16:0,PA),stearic acid(C18:0,SA),C18:2,linolenic acid(C18:3,ALA)and FAS all displayed normal or near normal distribution rule in the population.The correlation analysis result showed that C20:1 and C22:1 displayed high-positive correlation,and the two compositions showed negative correlation with other six ones,which displayed positive correlation with each other.(2)73 unconditional environmental stable QTLs,22 environmental specific QTLs and 25 novel QTLs mapping of fatty acid compositon.A total of 406 unconditional identified QTLs were detected,the maximum phenotypic variance(PV)of the single QTL that could explain is 45.05%.These QTLs were further intergrated into204 unconditional consensus QTLs,which including 81 major QTLs,74 environmental stable QTLs and 22 envrionmental specific QTLs.These unconditional consensus QTLs were further intergrated into 127 unconditional unique QTLs,the maximum PV of the single unique QTL could explain is 45.05%.Compareing with the previous findings,25 novel QTLs of fatty acid compositions were detected.(3)Obtaining of 69 epistatic pairs,2081 conditional identified QTLs and 1667 conditional consensus QTLs.A total of 69 pairs of Additive ? Additive(A?A)type QTL epistatic interaction were found,71% located in A8 and C3 linkage groups.A total of2081 conditional identified QTLs were detected and explained the PV range of1.32%-39.75%,the mean PV of these conditional QTLs reduced to 7.59% when compared with the unconditional mean of 17.99%.2081 conditional identified QTLs were further intergrated into 1667 conditional consensus QTLs.(4)The screening,the enrichment and interaction analysis of the 7802 candidates and construction of the metabolic pathway of fatty acid.There were 7802 homologous genes,which located in the confidence interval of 127 unconditional unique QTLs,of Arabidopsis screened out,and these candidates corresponded to 13599 rapeseed genes.Amonge these candidates,there were 278 relevant to acyl lipid metabolism only.7787 of the 7802 candidates participated into the GO enrichment analysis,and 1547 candidates were enriched into 16 different pathways of KEGG.In addition,the interaction analysis was also performed for the total candidates.The interaction analysis showed that acyl lipid metabolism correlated candidates extensively interacted with the biological processes,including cell transcription and regulation,plant stress resistance and energy metabolism etc.By further analysing of the54 candidates that participated in the interaction of five major lipid metabolism branch processes of TAG synthesis and degradation,fatty acid elongation,plastid fatty acid synthesis and ?-oxidation,it furtherreveales that the close interaction also existing among the acyl lipid metabolism related candidates.For the purpose of further intuitively understand how the candidates participate in the process of lipid metabolism,a fatty acid metabolic network were constructed,which included the pathways of plastid fatty acid synthesis,fatty acid elongation,TAG synthesis and degradation,synthesis of phospholipid and thiolipid,?-oxidation,lipid trafficking and the formation of oil body.To sum up,this study conducted the conditional and unconditional QTL mapping with fatty acid compositions of Brassica napus,and obtained large number of conditional and unconditional QTLs,including some multi environmental stable,environmental specific expressed QTLs and some novel QTLs.QTL epistasis analysis displayed the genetic complexity of fatty acid composition,candidates screening,enrichment and interaction analysis further revealled the complex precess of acyl lipid metabolism on genomic level.Construction of the network pathway more clearly exhibited the molecular mechanism of acyl lipid metabolism at the whole level.The outcomes above provided the QTL fine mapping of fatty acid compositions and molecular assisted breeding in rapeseed with assistance as well as supplied more theoretical basis for plant fatty acid metabolism. |
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