Metabolic Engineering Plant Seeds with Fish Oil-Like Levels of DHA

James R Petrie,Qing Liu,Xue-Rong Zhou,Pushkar Shrestha,Srinivas Belide,Maged P Mansour,Surinder P Singh,Peter D Nichols,Els Jm Van Damme

doi:10.1371/journal.pone.0049165

James R Petrie, Qing Liu + Show 7 more

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https://doi.org/10.1371/journal.pone.0049165

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Abstract

BackgroundOmega-3 long-chain (≥C20) polyunsaturated fatty acids (ω3 LC-PUFA) have critical roles in human health and development with studies indicating that deficiencies in these fatty acids can increase the risk or severity of cardiovascular and inflammatory diseases in particular. These fatty acids are predominantly sourced from fish and algal oils, but it is widely recognised that there is an urgent need for an alternative and sustainable source of EPA and DHA. Since the earliest demonstrations of ω3 LC-PUFA engineering there has been good progress in engineering the C20 EPA with seed fatty acid levels similar to that observed in bulk fish oil (∼18%), although undesirable ω6 PUFA levels have also remained high.Methodology/Principal FindingsThe transgenic seed production of the particularly important C22 DHA has been problematic with many attempts resulting in the accumulation of EPA/DPA, but only a few percent of DHA. This study describes the production of up to 15% of the C22 fatty acid DHA in Arabidopsis thaliana seed oil with a high ω3/ω6 ratio. This was achieved using a transgenic pathway to increase the C18 ALA which was then converted to DHA by a microalgal Δ6-desaturase pathway.Conclusions/SignificanceThe amount of DHA described in this study exceeds the 12% level at which DHA is generally found in bulk fish oil. This is a breakthrough in the development of sustainable alternative sources of DHA as this technology should be applicable in oilseed crops. One hectare of a Brassica napus crop containing 12% DHA in seed oil would produce as much DHA as approximately 10,000 fish.

Highlights

Metabolic engineering of omega-3 long-chain ($C20) polyunsaturated fatty acids (v3 LC-PUFA, Figure 1) has been a key metabolic engineering target in recent years
In pJP3416_GA7, these genes were expressed by the Brassicaceae-active seed-specific promoters A. thaliana FAE1, Linum usitatissimum conlinin1 (Cnl1) and conlinin2 (Cnl2) and the truncated Brassica napus napin promoter (FP1) with the tobacco mosaic virus 59 untranslated enhancer leader sequence upstream of each fatty acid biosynthesis gene
The construct was transformed in the A. thaliana ecotype Columbia and a fad2 mutant

Summary

Introduction

Metabolic engineering of omega-3 long-chain ($C20) polyunsaturated fatty acids (v3 LC-PUFA, Figure 1) has been a key metabolic engineering target in recent years. The difficulties associated with achieving high levels of DHA accumulation have been described [10,11] with key challenges including the reduction of undesirable v6 fatty acid co-production, achieving a continuous flux of substrates throughout the entire pathway without large losses to metabolically inactive pools and improvement of the critical D5-elongase efficiency to convert EPA to DPA (Figure 1).

Results

Conclusion