The synthesis and accumulation of stearidonic acid in transgenic plants: a novel source of ‘heart‐healthy’ omega‐3 fatty acids

Summary Dietary omega‐3 polyunsaturated fatty acids have a proven role in reducing the risk of cardiovascular disease and precursor disease states such as metabolic syndrome. Although most studies have focussed on the predominant omega‐3 fatty acids found in fish oils (eicosapentaenoic acid and docosahexaenoic acid), recent evidence suggests similar health benefits from their common precursor, stearidonic acid. Stearidonic acid is a Δ6‐unsaturated C18 omega‐3 fatty acid present in a few plant species (mainly the Boraginaceae and Primulaceae ) reflecting the general absence of Δ6‐desaturation from higher plants. Using a Δ6‐desaturase from Primula vialii , we generated transgenic Arabidopsis and linseed lines accumulating stearidonic acid in their seed lipids. Significantly, the P. vialii Δ6‐desaturase specifically only utilises α‐linolenic acid as a substrate, resulting in the accumulation of stearidonic acid but not omega‐6 γ‐linolenic acid. Detailed lipid analysis revealed the accumulation of stearidonic acid in neutral lipids such as triacylglycerol but an absence from the acyl‐CoA pool. In the case of linseed, the achieved levels of stearidonic acid (13.4% of triacylglycerols) are very similar to those found in the sole natural commercial plant source ( Echium spp.) or transgenic soybean oil. However, both those latter oils contain γ‐linolenic acid, which is not normally present in fish oils and considered undesirable for heart‐healthy applications. By contrast, the stearidonic acid‐enriched linseed oil is essentially devoid of this fatty acid. Moreover, the overall omega‐3/omega‐6 ratio for this modified linseed oil is also significantly higher. Thus, this nutritionally enhanced linseed oil may have superior health‐beneficial properties.