Identification of an animal omega-3 fatty acid desaturase by heterologous expression in Arabidopsis

In animals, fatty acid desaturases catalyze key reactions in the synthesis of arachidonic acid and other polyunsaturated fatty acids, A search of the Caenorhabditis elegans DNA databases, using the sequences of Arabidopsis genes, identified several putative desaturases. Here we describe the characterization of the first of these genes,fat-1. The predicted protein encoded by a fat-1 cDNA showed 32-35% identity with both FAD2 and FAD3 of Arabidopsis. When expressed in transgenic plants,fat-1 resulted in a 90% increase in the proportion of alpha-linolenic acid in root lipids, Wild-type Arabidopsis incorporated omega-6 fatty acids (Delta 8,11,14-20:3 and Delta 5,8,11,14-20:4) into membrane lipids but did not desaturate them, By contrast, fat-1 transgenic plants efficiently desaturated both of these fatty acids to the corresponding omega-3 products, These findings indicate that the C. elegans fat-1 gene encodes the first animal representative of a class of glycero-lipid desaturases that have previously been characterized in plants and cyanobacteria. The FAT-1 protein is an omega-3 fatty acyl desaturase that recognizes a range of 18- and 20-carbon omega-6 substrates.