Genetic Dissection Of Oil Content Based On Dynamic QTL And Time-series Transcriptome During Seed Development In Brassica Napus

There is a serious shortage of edible oil supply in China.As the largest oil crop in China,increasing rapeseed oil content(OC)is one of the main research directions.However,the basic research on the genetic mechanism of OC accumulation and the identification of excellent candidate genes is relatively insufficient.In this study,a high-density genetic linkage map was constructed based on genotyping 348 lines of KN DH population using a Brassica 60 K SNP array.The high-density genetic linkage map contained 3207 molecular markers(including 3106 SNP-bins and 101 non-SNP markers)and covered 3072.7 c M of B.napus genome(covering the length of A and C genomes is 1398.6 c M and 1674.1 c M,respectively).QTL mapping was performed for OC in 12 environments using the high-density genetic linkage map.Sixty-seven QTL for OC were obtained,of which five novel major QTL for OC.There is obvious competition between protein and oil synthesis.In order to analyze its genetic basis,QTL colocalization analysis of OC and protein content(PC)in 11 environments was carried out based on the high-density genetic linkage map.Eleven unique QTL which controlled OC and PC at the same time with opposite additive effects,and the hot-spots of OC and PC-QTL with opposite additive effects on C3 and C5,revealed that the genetic basis of competition mechanism between OC and PC contained both pleiotropy and close linkage.As yet,all most of studies on QTL mapping for OC in rapeseed are based on mature seeds,while there is different oil metabolism regulation in different stages during seed development.In order to locate the genes or transcription factors functioning in different stages of seed development and understand the regulation model of oil accumulation,dynamic QTL mapping for OC and 10 fatty acid components(FAs)during seed development and the transcriptome analysis for high and low oil materials were carried out simultaneously.A total of 448 unconditional QTL in five stages during seed development and 397 conditional QTL between adjacent stages were identified by dynamic QTL analysis for OC and 10 FAs.Among them,45 unconditional and 27 conditional QTL were for OC,of which 3 QTL detected in no less than two periods and 1 QTL in no less than two stages respectively,while most of which are period or stage specific.Through co-localization analysis,36 pairs of unconditional and conditional QTL were found to be co-localized;45 unconditional and 33 conditional QTL were co-localized with QTL for corresponding traits in mature seeds;32 unconditional and 20 conditional QTL for OC were detected to co-localize with unconditional and conditional QTL for FAs,respectively.The results provided new clues for dissecting oil accumulation patterns and identifying OC related candidate genes in B.napus.The RNA-Seq analysis for extreme lines with high and low OC from KN population in 6 stages during seed development revealed the time series characteristics of oil accumulation regulation during seed development.Comparison transcriptomic analysis showed that the genes related to energy metabolism and fatty acid synthesis had higher expression level in the middle stage during seed development and entered the mature stage later,which increased substance accumulation and formed high OC.The candidate genes located within mature seed OC-QTL and dynamic QTL during seed development were analyzed by comparative genome and homologous annotation,including metabolic pathway fitting and interaction network analysis,which provided more insights for genetic mechanism of oil metabolism and accumulation in B.napus.Finally,by integrating RNA-Seq,dynamic OC-QTL during seed development and OC-QTL were detected in mature seed,some key differentially expressed candidate genes were identified,including Bna C02g39140 D,Bna A08.SESA4,Bna A03g30740 D,Bna A03.FIB,Bna A06.LCR69,Bna C03.TT4,Bna A03.MFP2,Bna A09.CAC2 and Bna A02.KASI.