A Tropaeolum majus FAD2 cDNA complements the fad2 mutation in transgenic Arabidopsis plants

Using a degenerate primers approach, a cDNA of a putative microsomal fatty acid desaturase showing high homology to other plant microsomal FAD2 (Δ12) desaturases was obtained from Tropaeolum majus. This cDNA contains an open reading frame of 1152 bp encoding a protein of 383 amino acids. Expression of the T. majus FAD2 oleate-Δ12 desaturase homolog in yeast cells resulted in accumulation of an appreciable amount of cis-9,12-hexadecadienoic (16:2Δ9,12) and linoleic acid (18:2Δ9,12), fatty acids not normally present in wild type yeast, indicating that the gene encodes a functional FAD2 enzyme. Genetic analyses showed that the T. majus FAD2 is represented by at least one constitutively expressed gene. Transformation of a low linoleic (18:2Δ9,12) Arabidopsis mutant line (AL63) with the T. majus FAD2 cDNA restored oleate-Δ12 desaturase activity and wild type proportions of linoleate in the seed oils of the transgenic plants.