Camelina cytosol-localized diacylglycerol acyltransferase 3 contributes to the accumulation of seed storage oils

In plants, triacylglycerol (TAG) is a form of seed storage oil that can provide a source of carbon and energy for seed germination and seedling development. Among three diacylglycerol acyltransferases (DGAT1, DGAT2, and DGAT3) that synthesize TAG, DGAT3 is involved in TAG synthesis in the cytosol, however, its biological function is still unclear. In this study, three CsDGAT3 homoeologs (CsDGAT3-1, CsDGAT3-2, and CsDGAT3-3) showed higher expression levels than CsDGAT1 in developing seeds of camelina (Camelina sativa). These were predominantly expressed in developing seeds, and the CsDGAT3 proteins were localized to the cytosol in the epidermal cells of Nicotiana benthamiana leaves. Seed weight and total seed fatty acid levels of transgenic Arabidopsis (Arabidopsis thaliana) seeds overexpressing CsDGAT3-2 or CsDGAT3-3 were approximately 13% and 11% higher, respectively, than those of nontransgenic seeds. In particular, the levels of C18:3 and C20:1 increased, while levels of C18:1 and C18:2 decreased. In CsDGAT3-knockout camelina, as compared to wild type, the seed weights and total fatty acid levels were about 7% and 19% lower, and the C18:3 and C20:1 levels, specifically, were reduced. We detected no significant differences in total seed fatty acid levels or composition between the Arabidopsis dgat1 mutant and the dgat1 mutant overexpressing CsDGAT3-3. Taken together, cytosol-localized DGAT3 contributes to the accumulation of seed storage oil and prefers the acylation of C18:3, which is the most abundant fatty acid in camelina seed oils. This finding can be applied to the development of oilseed plants with enhanced seed storage oils containing high levels of omega-3 fatty acids.

Automated summary

In this study, DGAT3 was found to contribute to the accumulation of seed storage oil and preferred the acylation of C18:3. Overexpression of CsDGAT3-2 or CsDGAT3-3 led to increased seed weight and total fatty acid levels in transgenic Arabidopsis seeds, especially in C18:3 and C20:1 levels. Knockout of DGAT3 in camelina resulted in reduced seed weight and fatty acid levels, particularly in C18:3 and C20:1. There were no significant differences in total seed fatty acid levels or composition between the Arabidopsis dgat1 mutant and the dgat1 mutant overexpressing CsDGAT3-3.