The Biosynthesis And Decomposition Of Seed Lipids At Maturation And Germination Stages Of Oilseed Rape(Brassica Napus L.) And The Associated Molecular Mechanism

Rapeseed is one of the major oil crops in the world and is an important source for vegetable oils and proteins.Currently,the gap between edible oil supply and demand on national level is increasing that led to increase in oil import.Therefore,it is important to bridge the gap between the supply and demand of edible oil.To meet the objectives,deeply understanding the molecular mechanism(s)involved in rapeseed oil biosynthesis and application of cutting edge technologies to increase the seed oil content and total oil production per unit area,is inevitable.At present,data on brassica(s)whole genome(s)sequencing and reference sequences have made the studies on biosynthesis and catabolism of the seed lipids more comprehensive and validated.In this study,the transcriptome sequencing(RNA-seq)technique was used to investigate the molecular mechanism(s)involved in the biosynthesis and catabolism of seed lipids in "Zhongyou 511" genotype during various stages of maturation and germination.Moreover,the correlations between biosynthesis and catabolism of seed lipids and seed-dormancy were also analyzed.The major findings are as follows:1.The changes in oil accumulation were determined in the mid-later stage of seed development of eight rapeseed genotypes,including five high oil varieties("Zhongshuang 11","Zhongyou 511","Zhongyou 036","Gaoyou 605","Zbeyou 50")and three low oil varieties("huyouqing","Gan 75-1","92-13xi").Significant decrease of 4.37%and 9.93%was observed in the seed oil content of "Zhongyou 511”and "Gan 75-1",respectively,at the later stage of seed maturity.2.Analyses of germination rate and dormancy status of seeds collected from maturing pods of eigh genotypes at 40 days after pollination(M40DAP)and 60 days after pollination(M60DAP).In general,we found that these genotypes produced either lightly dormant or nondormant seeds."Zhongyou 511" and "Gan 75-1" genotypes have lightly dormant seeds,whereas "Zhongzhuang 11" seeds have prolonged dormancy.Based on fatty acid data of the seeds during different stages of pods maturity,it is presumed that the abatement of seed fatty acids of "Zhongyou511' and "Gan 75-1" at late maturity stage might be due to the release of dormancy.3.The transcripts of "Zhongyou 511" seeds germinated 20 h after sowing(G20HAS)were sequenced,and the results were compared with those of 16DAP and 40 DAP seeds.Compared with 16 DAP,a total of 25938 differentially expressed genes(DEGs)were detected,of which 11022 genes were up-regulated and 14916 genes were down-regulated.Compared with 40 DAP,24974 DEGs were detected,including 10870 up-regulated genes and 14104 down-regulated genes.The results of KEGG enrichment analysis showed that the genes related to the metabolism of fatty acids were significantly up-regulated in germination phase compared with the maturity stage of "Zhongyou511" seed.Moreover,these genes correlated with the genes involved in the metabolism of carbon,nitrogen and chlorophyll in light and organs was significantly down-regulated.Furthermore,LACS7,ACX2,ACX3,MFP2 and KAT2 genes were significantly up-regulated during ?-oxidation,whereas in glyoxylic acid cycling the genes that control the expression of malate synthase and isocitrate lyase were significantly up-regulated.4.The expression levels of DOG1 and ABA signaling pathways gene of ABI3 during seed maturation stage i.e.M40DAP of "Zhongyou 511",were significantly higher compared with M16DAP(P<0.05).The transcription factor FUS3 associated with dormancy was significantly up-regulated,whereas down-regulation were observed in the expression patterns of the LEC1 and LEC2.In comparison to seed maturation stage(M40DAP),ABI3,SnRK2.6,HAB1 and AHG3 were significantly down-regulated in seed germination stage G20HAS,while SNF1-related protein kinase subfamily 2(SnRK2.2),and SnRK2.3 genes were up-regulated.Moreover,the expression of transcription factors(LEC1 and FUS3)and dormancy releasing factors namely SPATULA(SPT),PHYTOCHROME INTERACTING FACTOR 3-LIKE 5(PIL5),PROTEOLYSIS 6(PRT6)and arginyl-tRNA:protein arginyltransferase(ATE)were also significantly up-regulated during G20HAS stage.5.Our findings suggest that a series of dormancy-related genes are involved in the induction and release of seed dormancy at different stages of rapeseed ripening and germination.At maturation stage,seed dormancy can be induced by regulating the expression of DOG1 and ABA signaling pathway genes(ABI3 and FUS3),and at germination stage,mainly through the regulation of dormancy releasing factors such as SPT,PIL5,PRT6 and ATE.