Abstract
Metabolic engineering of omega-3 long-chain (≥C20) polyunsaturated fatty acids (ω3 LC-PUFA) in oilseeds has been one of the key targets in recent years. By expressing a transgenic pathway for enhancing the synthesis of the ω3 LC-PUFA docosahexaenoic acid (DHA) from endogenous α-linolenic acid (ALA), we obtained the production of fish oil-like proportions of DHA in Arabidopsis seed oil. Liquid chromatography-mass spectrometry (LC-MS) was used to characterize the triacylglycerol (TAG), diacylglycerol (DAG) and phospholipid (PL) lipid classes in the transgenic and wild type Arabidopsis seeds at both developing and mature stages. The analysis identified the appearance of several abundant DHA-containing phosphatidylcholine (PC), DAG and TAG molecular species in mature seeds. The relative abundances of PL, DAG, and TAG species showed a preferred combination of LC-PUFA with ALA in the transgenic seeds, where LC-PUFA were esterified in positions usually occupied by 20:1ω9. Trace amounts of di-DHA PC and tri-DHA TAG were identified and confirmed by high resolution MS/MS. Studying the lipidome in transgenic seeds provided insights into where DHA accumulated and combined with other fatty acids of neutral and phospholipids from the developing and mature seeds.
Highlights
Metabolic engineering of omega-3 long-chain polyunsaturated fatty acids (ω3 LC-PUFA) in oilseed crops has been attempted by several groups in recent years due to the plateauing in global fishery stocks and the rise in demand for ω3 LC-PUFA containing fish oils (Haslam et al, 2013)
Fish oils which contain omega-3 LC-PUFA such as eicosapentaenoic acid (EPA, 20:5ω3) or docosahexaenoic acid (DHA, 22:6ω3) are well known to have anti-inflammatory properties it is not known if EPA and/or DHA are involved in the suppression of cytokine production (James et al, 2000)
MEMBRANE PHOSPHOLIPID CHARACTERIZATION: INCREASED PHOSPHOLIPIDS IN TRANSGENIC LINE We previously showed that expressing seven enzymes for DHA biosynthesis pathway in Arabidopsis resulted in the efficient accumulation of DHA in total seed lipids of transgenic line GA7 (Petrie et al, 2012)
Summary
Metabolic engineering of omega-3 long-chain polyunsaturated fatty acids (ω3 LC-PUFA) in oilseed crops has been attempted by several groups in recent years due to the plateauing in global fishery stocks and the rise in demand for ω3 LC-PUFA containing fish oils (Haslam et al, 2013). As it is proposed that the fatty acyl chains in the PC and DAG pools direct the flux of engineered LC-PUFA products onto TAG, a detailed analysis of the lipids in TAG, DAG and PL in control and transgenic Arabidopsis seeds during seed development was required.
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