Identification of Primula fatty acid delta6-desaturases with n-3 substrate preferences

Fatty acid Δ6‐desaturation, the first committed step in C20 polyunsaturated fatty acid biosynthesis, is generally considered not to discriminate between n‐3 and n‐6 substrates. We previously identified higher plant species that showed preferential Δ6‐desaturation of n‐3 C18 fatty acid substrates. A polymerase chain reaction‐based approach was used to isolate ‘front‐end’ cytochrome b 5 fusion desaturases from Primula vialii Franchet and Primula farinosa L. Functional analysis in Saccharomyces cerevisiae identified fatty acid Δ6‐desaturases with a strong specificity for the n‐3 substrate α‐linolenic acid (18:3Δ9,12,15). These results indicate that the accumulation of octadecatetraenoic acid (18:4Δ6,9,12,15) in planta is due to the activity of a novel n‐3‐specific fatty acid Δ6‐desaturase.