Comparative Transcriptome Analysis Of Developing Seeds And Silique Wall In Brassica Napus With Different Oil Content

Vegetable oil is an essential constituent of human diet and renewable raw materials for industrial applications.Enhancement of oil production by increasing seed oil content in oil crops is the most viable,environment-friendly and sustainable approach to meet the continuous demand for global vegetable oil supply.Rapeseed(Brassica napus)is one of the most important oil crop cultivated on multiple continents,contributing more than 15%in world edible oil supply.The in-depth understanding of gene networks involved in oil biosynthesis during seed development is the prerequisite for breeding of high oil content varieties.The RNA-Seq is considered as an advanced technique to detect expression of less abundant transcripts and identify genetic variations.To fathom the phasic nature of oil biosynthesis and the dynamic regulation of critical pathways for effective oil accumulation in B.napus,a comparative transcriptomic profiling was performed with developing seeds and silique wall(SW)tissues of two contrasting inbred lines with ~13%seed oil content difference.We detected 62524 genes with expression FPKM > 1 in seed and SW tissues of both lines collectively.MapMan analysis of these genes revealed that the photosynthesis,carbohydrate metabolism,lipid metabolism,and transport are up-regulated at most of the developmental stages of seed and SW in high oil content line(HOCL),while,degradation,amino acid metabolism,protein,and secondary metabolism were up-regulated in low oil content line(LOCL)at most of the developmental stages of seed and SW.In total,3288 of differentially expressed genes(DEGs)between HOCL and LOCL were identified across six key developmental stages of seeds and the SW.Gene enrichment analyses shown that genes related to photosynthesis,metabolism,carbohydrates,lipid,phytohormones,transporter and triacylglycerol and fatty acid synthesis were intending to be up-regulated in HOCL.Differentially regulated DEGs patterns were uncovered for the control of metabolites and photosynthates production in the SW and oil biosynthesis and accumulation in seeds.The DEGs also includes 75 acyl lipid metabolism(ALM)genes,42 transcription factors(TFs)and 56 hormones related genes.Further,DEGs were mapped to QTLs and out of 3288 DEGs,1098 were mapped to QTLs including 31 ALM genes and 9 TFs.In addition,16 ALM DEGs were characterized by qRT-PCR by using the seed tissues from multiple contrasting sets ofnear isogeneic lines(NILs)vary in seed oil content.Results validate the RNA-Seq data and reassure the candidacy of these genes.Moreover,4884 of relatively differentially expressed genes(RDEGs)in both tissues of each line were identified and most of the RDEGs were enriched in the pathways of metabolism,carbohydrate metabolism,transporters,and transcription factors.Additionally,to integrate the gene expression data and phenotypic variation,we also measure the oil,carbohydrates(Glucose,sucrose and starch)and hormones(jasmonic acid,abscisic acid and auxin)at all developmental stages,which revealed their fundamental effects on effective oil accumulations and thus provide insights on the molecular basis of high oil content(SOC)and new direction for developing high SOC rapeseed and other oil crops.Finally,on the basis of transcriptome results,we select nine ALM genes and TFs for further characterization by using Arabidopsis mutants.Seed oil content of all these mutants except one was significantly higher as compared to wild type.Taken together,these results establish that 11 to 44 DAP is the major oil biosynthesis phase in seed but 11 to 23 DAP is a critical period,while degradation predominantly happens after 44 DAP.The discrepancy of DEGs expression profile between seed and SW suggests that preliminary metabolites and photosynthates produced in SW as a result of photosynthesis and oil biosynthesis and accumulation majorly occur in the seed.The SW plays a crucial role in oil biosynthesis at the initial stage and also has contribution at later stages.Carbohydrates pathways and hormones singling have a fundamental effect on oil accumulations in Brassica napus.These findings majorly identify the oil biosynthesis and accumulation pathways in seed and SW,and potential new targets for high oil varietal development.Our study offers a deeper understanding of the regulatory gene network for oil biosynthesis dynamics in seed and SW.