Lipidomics has been widely applied to the study of oilseed crops, including rapeseed. Lipidomic analysis allows researchers to investigate changes in lipid metabolism in rapeseed at different developmental stages, as well as reveal tissue-specific distributions of different lipid classes. This information can be used to better understand the mechanisms of oil biosynthesis in canola, which is critical for improving the productivity of the canola crop. In addition, lipidomics can provide insights into potential key enzymes and metabolic pathways involved in oil biosynthesis that can be targets for genetic engineering to further improve the yield and quality of rapeseed oil.
Case 1. Lipidomics reveals lipid changes during rape seed development (1)
Oilseed rape, which produces about 12% of the vegetable oil market. With the decrease in agricultural land, the demand for vegetable oil is increasing, so it is of great relevance to increase the production capacity of oilseed crops. The authors hoped to solve this problem by regulating the accumulation of oil in rapeseed seeds.
The authors chose three time points after flowering of rape, representing the early (20 DAF), middle (27 DAF) and late (35 DAF) stages of rape seed development.
The authors analyzed the composition of mid-stage rape seeds. And the changes of lipids during the development of rapeseed seeds were analyzed and discussed. From the test results, the distribution of lipid molecules under TAG, DAG, PA, PC and PE subclasses changed during the development. The results are shown in the following figure.
The authors analyzed and discussed the changes in Acyl-CoA (acyl-coenzyme A), an active metabolic intermediate in fatty acid synthesis and catabolism, during rape seed development, total Acyl-CoA gradually increased, almost 2-fold from 20 to 35 DAF.
The authors used lipidomic data to speculate on the key enzyme activities for the TAG synthesis process. DGAT (diacylglycerol acyltransferase) and phospholipid: diglyceride acyltransferase (PDAT) are key enzymes for the TAG synthesis process. The theoretical values calculated for DGAT enzyme differed less from the actual values, suggesting that DGAT enzyme contributes more to TAG synthesis.
Through lipidomic studies, the authors observed changes in the distribution of lipid molecules during the development of rape seeds, especially during the early to middle stages. Compared to PDAT, DGAT enzyme has a more important effect on TAG synthesis.
Case 2. Revealing the tissue specificity of lipid metabolism in rape seeds (2)
Despite the importance of oilseeds for human nutrition worldwide, as well as for biodiesel fuel production, the understanding of the detailed mechanisms regulating seed oil biosynthesis is relatively limited, especially from a tissue-specific perspective. In this study, combined results based on matrix-assisted laser desorption/ionization mass spectrometry in situ imaging (MALDI-MSI), lipid profiling of seed tissue extracts, and tissue-specific transcriptome analysis revealed complex spatial distribution patterns of liposomes and transcripts in high and low oil germplasm of oilseed rape.
The authors started with a comparative analysis of the material composition of two different oil content rape seeds. To investigate the in situ lipid distribution of TAG and its metabolic precursor PC, seeds from both germplasm were frozen sectioned and then analyzed by MALDI-MSI. For TAG, differences were mainly found between cotyledons (OC and IC) and EA tissue, while only minor differences were observed between OC and IC. For PC distribution, PC-34C (16:0/18:X) was preferentially enriched in EA of both materials. The total mol% of seed sections analyzed by MALDI-MSI was compared with the total mol% in the whole seeds determined by conventional quantitative methods, and they were essentially identical for TAG and PC.
To identify and quantify spatial differences in PC and TAG and other lipid classes in different types of seed tissues, seed tissues were manually dissected and total lipids were extracted and analyzed by LC-ESI-MS. Eleven lipid classes and their molecular species were analyzed. The content of different lipid classes showed significant differences between OC, IC and EA tissues, as shown in the figure below.
In addition to TAG and its major precursor metabolites, PE, PG, PS, PI, LPC, MGDG, and DGDG were also analyzed. the results indicate that many lipid species are differentially abundant in different types of seed tissues. In conclusion, these data suggest that differences in glycerolipid content and composition are prevalent in seed tissues of both germplasm, and that the metabolism of storage lipids and membrane lipids in seed tissues may be more complex than recognized from a spatial perspective.
References
- Woodfield, Helen K., et al. "Using lipidomics to reveal details of lipid accumulation in developing seeds from oilseed rape (Brassica napus L.)." Biochimica et Biophysica Acta (BBA)-Molecular and Cell Biology of Lipids 1863.3 (2018): 339-348.
- Lu, Shaoping, et al. "Spatial analysis of lipid metabolites and expressed genes reveals tissue‐specific heterogeneity of lipid metabolism in high‐and low‐oil Brassica napus L. seeds." The Plant Journal 94.6 (2018): 915-932.
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