Δ6 Fatty Acid Elongase is Involved in Eicosapentaenoic Acid Biosynthesis Via the ω6 Pathway in the Marine Alga Nannochloropsis oceanica

Nannochloropsis oceanica represents a promising sunlight-driven alga for producing eicosapentaenoic acid (EPA, 20:5Δ5,8,11,14,17), a value-added very long-chain polyunsaturated fatty acid (VLC-PUFA). Here, we unraveled the function and roles of a Δ6 fatty acid elongase (NoΔ6-FAE) in N. oceanica. Heterologous expression of NoΔ6-FAE in yeast confirmed its function in elongating C18 Δ6-PUFAs rather than others. Subcellular localization experiments suggested that NoΔ6-FAE resides in the chloroplast endoplasmic reticulum. NoΔ6-FAE knockdown attenuated C20:3Δ8,11,14, C20:4Δ5,8,11,14, and EPA yet enhanced C18:3Δ6,9,12, leading to overall decreases in total fatty acids, triacylglycerol, diacylglycerol, free fatty acids, and polar membrane lipids. In contrast, NoΔ6-FAE overexpression in N. oceanica caused nearly opposite phenotypes. Moreover, N. oceanica lacked detectable C18:3Δ9,12,15, C18:4Δ6,9,12,15, and C20:4Δ8,11,14,17 even under NoΔ6-FAE knockdown or overexpression. Our results reveal the involvement of NoΔ6-FAE in EPA biosynthesis via the ω6 pathway in N. oceanica and highlight the potential of manipulating NoΔ6-FAE for improved lipid production