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, 20:5 Delta(5),8(11,14,17)) , a value-added very long-chain polyunsaturated fatty acid (VLC-PUFA). Here, we unraveled the function and roles of a Delta 6 fatty acid elongase (No Delta 6-FAE) in N. oceanica. Heterologous expression of No Delta 6-FAE in yeast confirmed its function in elongating C18 Delta 6-PUFAs rather than others. Subcellular localization experimehts 14 ggested that No Delta 6-FAE resides in the chloroplast endoplasmic reticulum. No Delta 6-FAE knockdown attenuated C20:3 Delta(8,11,14), C20:4 Delta(5,811,14), and EPA yet enhanced C18:3 Delta(6,9,12), leading to overall decreases in total fatty acids, triacylglycerol, diacylglycerol, free fatty acids, and polar membrane lipids. In contrast, No Delta 6-FAE overexpression in N. oceanica caused nearly opposite phenotypes. Moreover, N. oceanica lacked detectable C18:3 Delta(9,12,15), C18:4 Delta(6,9,12,15), and C20:4 Delta(8,11,14,17) even under No Delta 6-FAE knockdown or overexpression. Our results reveal the involvement of No Delta 6-FAE in EPA biosynthesis via the omega 6 pathway in N. oceanica and highlight the potential of manipulating No Delta 6-FAE for improved lipid production.