| Rapeseed is one of the main sources of vegetable oil in China,and plays an important role in the edible oil supply of our country.In some years when there is with too much rainfalls at the maturation stage of rapeseed,some cultuivars will exhibit an abnormal phenomenon that seeds are able to germinatein the siliques of a living mother plant before full saturation.This kind of premature seed germination is largely due to the weak seed dormancy of certain cultivar,and will lead to a drastic reduction of seed oil content(SOC),downgrade of seed nutritional quality,as well as a negative effect on sowing for next generation.In this study,we analyzed the correlation between dormancy and SOC in rapeseed,compared the transcriptomes of different dormant types,and explored the molecular mechanism by which seed dormancy affactes SOC.Moreover,we compared the color and thickness of seed coats between different dormant types,and invested their effect on germination.Further,we simulated the effect of adverse storage conditions such as high temperature and high humidity on seed vigor,and identified some genes that were responsible for sensitivity or tolerance to the adverse condition.The main results of the research are as follows:1.According to the germination rate of the seeds 40 days after pollination(40 DAP),the cultivars could be classified into non-dormancy(ND),deep-dormancy(DD)and mild-dormancy(MD)groups.The typical ND,DD and MD seeds demonstrated an obviously different treads of seed oil accumulation,i.e.there was no obvious SOC peak in development of the DD seeds,but a continuous upward curve instead.In contrast,there was a sharp SOC peak in development of the ND seeds.The treand of seed oil accumulation in the MD seeds was somewhere in between.2.It was discovered that the ratio of gibberellin to abscisic acid content(GA:ABA)in the developing DD seeds showed an obvious downward trend after 45 DAP.On the contrary,the GA:ABA value in the developing ND seeds were increasing after 45 DAP.The GA:ABA value of the MD seeds decreased to a certain level after 45 DAP.The degree of the decline in the MD seeds is,however,much less significant than that in the DD seeds.Generally speaking,the seed coats of the DD seeds are thicker and darker than those of the ND seeds,indicating that the difference in germination rate among the three doemancy types might be attributed to a combined effect of the physiological,physical and chemical factors.3.RNA-seq analysis was performed to identify the differently expressed genes(DEGs)between the DD and ND seeds.It was shown that the ND seeds exhibited higher transcriptional levels of the genes that regulate seed lipid catabolism,and lower transcriptional levels of the genes that promote lipid biosynthesis,than the DD seeds.In particular,the ND seeds had significantly higher transcriptional levels of the genes in the ?-oxidation pathway than the DD seeds,indicating there was more accumulation of lipids than degradation of lipids in the ND seeds.Notably,a considerable proportion of the DEGs were expressed on the cell wall of seed coats,which might give rise to the different cell wall structure,eventually resulting in different dormancy types.4.Mature seeds were harvested and treated with high temperature and humidity.The seeds were then tested for their vigor reflected by germinatioin rate.There was an obvious genotypic difference among the cultivars in terms of germination rate after the treatment.Overall,the tested cultivars can be classified into sensitive-and tolerant-groups.Cross-analysis of GWAS RNA-seq results discovered 5 genes,namely BnaA01g14520D,BnaC02g40820D,BnaC02g40840D,BnaA01g14570D,BnaA01g14560D,that are likely responsible for the sensitive-or tolerant-responses.Taken together,we recommend a gene pool with moderate size,for selecting or manipulating the genes favouring the acquisition of seed dormancy,shedding light on the elevation of SOC and extension of seed-storage period,by manipulating these genes or by molecular-breeding approaches. |
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