Study On Lipids Distribution In Brassica Napus L. Seeds And Establishment Of UPLC-TripleTOF Based Lipidomics Method

Lipid not only provides energy and nutrition for human,but also is the raw material for industrial production.Brassica napus L.is an important oil crop in China,and the rapeseed oil is one of the main sources of edible oil.Improving the oil content of rapeseed is important to ensure the balance between supply and demand of edible oil in China.In recent years,the consumption of oils and fats is increasing.Therefore,studying the spatial distribution of lipids in Brassica napus seeds will provide theoretical support for breeding of high-oil Brassica napus.In this study,ZS11(high oil content)and WH5557(low oil content)were selected from more than 500 Brassica napus and the accumulation of fatty acids in the developed seeds was determined by GC-MS.The results showed that the content and composition of fatty acids in seeds were significantly different,and the accumulation rate of ZS11 fatty acids was faster than that of WH5557.The spatial distribution of TAG and PC in different tissues of mature seeds(outer cotyledon,inner cotyledon,embryonic axis)was analyzed by MALDI-MSI.The results showed that there was a significant difference in the content and composition of TAG and PC among different tissues.At the same time,TAG and PC in seeds were analyzed by ESI-MS/MS,which was similar to the result of MALDI-MSI.It shows that the MALDI-MSI results are reliable.The mature seeds are separated into outer cotyledon,inner cotyledon and embryonic axis under the microscope.The lipids of seeds were extracted and detected by LC-ESI-MS/MS.The results showed that the content and composition of lipidome in different tissues were significantly different.This result is consistent with the MALDI-MSI results,and further validates the reliability of MALDI-MSI.The seeds of 34 days of development were collected in the field and RNA was extracted from each tissue for transcriptome analysis.Transcriptome analysis showed that the expression of the key genes of lipid metabolic pathways such as glycolytic,fatty acid biosynthesis,TAG assembly and lipid droplet packaging were different.The above results show that the expression level of key genes in lipid metabolism plays an important role in the spatial distribution of lipids.The difference of protein,soluble sugar and starch content between 2 seeds implied that carbon in WH5557 seeds tended to accumulate to carbohydrates,which may result in the low oil content.In addition,we have established a high-throughput lipidome analysis approach based on UPLC-TripleTOF to meet the need of lipidomics research.Compared with the traditional method of lipidome analysis,this approach has higher efficiency,faster speed,less sample requirement and higher accuracy.Based on this method,the lipid content and composition of the roots,stems,leaves,petioles and developing seeds of ZS11 were analyzed.The lipidome data showed that the lipidome analysis approach based on UPLC-TripleTOF have good reproducibility.It can accurately identify 13 lipid species including neutral lipids,phospholipids,glycolipids and lysophospholipids(total 146 lipids molecule).The determination of the lipidome of ZS11 different organs and different developmental stages in seeds provides a reference for lipidomics research.Therefore,the lipidome analysis approach based on UPLC-TripleTOF would be a high-throughput approach for lipidome analysis in the future.