Abstract
The ability to manipulate expression of key biosynthetic enzymes has allowed the development of genetically modified plants that synthesise unusual lipids that are useful for biofuel and industrial applications. By taking advantage of the unique activities of enzymes from different species, tailored lipids with a targeted structure can be conceived. In this study we demonstrate the successful implementation of such an approach by metabolically engineering the oilseed crop Camelina sativa to produce 3-acetyl-1,2-diacyl-sn-glycerols (acetyl-TAGs) with medium-chain fatty acids (MCFAs). Different transgenic camelina lines that had been genetically modified to produce MCFAs through the expression of MCFA-specific thioesterases and acyltransferases were retransformed with the Euonymus alatus gene for diacylglycerol acetyltransferase (EaDAcT) that synthesises acetyl-TAGs. Concomitant RNAi suppression of acyl-CoA:diacylglycerol acyltransferase increased the levels of acetyl-TAG, with up to 77 mole percent in the best lines. However, the total oil content was reduced. Analysis of the composition of the acetyl-TAG molecular species using electrospray ionisation mass spectrometry demonstrated the successful synthesis of acetyl-TAG containing MCFAs. Field growth of high-yielding plants generated enough oil for quantification of viscosity. As part of an ongoing design-test-learn cycle, these results, which include not only the synthesis of 'designer' lipids but also their functional analysis, will lead to the future production of such molecules tailored for specific applications.
Highlights
Seed oils are comprised mostly of triacylglycerols (TAGs), energy-dense molecules that consist of three fatty acids esterified to a glycerol backbone (Fig. 1A)
By combining the expression of enzymes resulting in the production of medium-chain fatty acids (MCFAs) with those resulting in high levels of acetyl-TAGs, we demonstrate the synthesis of MCFA-containing acetyl-TAGs that have not been found in nature (Fig. 1)
We combined the expression of Euonymus alatus gene for diacylglycerol acetyltransferase (EaDAcT) with DGAT1-RNAi and PDAT1-RNAi constructs targeting the assembly of lcTAGs, which have previously been shown to increase the accumulation of acetyl-TAGs (Liu et al, 2015a, 2015b)
Summary
Seed oils are comprised mostly of triacylglycerols (TAGs), energy-dense molecules that consist of three fatty acids esterified to a glycerol backbone (Fig. 1A). The fatty acid composition of the TAG molecular species determines the physical properties of a particular vegetable oil. TAGs from commercially grown oilseed crops typically contain mainly five fatty acids: palmitic, stearic, oleic, linoleic, and linolenic. Medium-chain fatty acids (MCFAs) with chain lengths of 8–14. Acetyl-TAGs produced in a camelina high-oleic background possess a higher viscosity than acetyl-TAGs containing more PUFAs from a wild-type background (Liu et al, 2015b)
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