Plant Physiol, May 2002, Vol. 129, pp. 354-362

High-Level Production of -Linolenic Acid in Brassica juncea Using a 6 Desaturase from Pythium irregulare

Research and Development, Bioriginal Food and Science Corporation, 102 Melville Street, Saskatoon, Saskatchewan, Canada S7J 0R1 (H.H., N.D., X.Q.); and National Research Council of Canada, Plant Biotechnology Institute, 110 Gymnasium Place, Saskatoon, Saskatchewan, Canada S7N 0W9 (D.W.R., P.S.C., S.L.M.)

-Linolenic acid (GLA), a nutritionally important fatty acid in mammals, is synthesized by a 6 desaturase. Here, we report identification of PiD6, a new cDNA from the oleaginous fungus, Pythium irregulare, encoding a 459-amino acid protein that shares sequence similarity to carboxyl-directed desaturases from various species. Expression of PiD6 in yeast (Saccharomyces cerevisiae) revealed that it converts exogenously supplied linoleic acid into GLA, indicating that it encodes a 6 fatty acid desaturase. Expression of the desaturase in Brassica juncea under the control of the Brassica napus napin promoter resulted in production of three 6 unsaturated fatty acids (18:2-6, 9; 18:3-6, 9, 12; and 18:4-6, 9, 12, 15) in seeds. Among them, GLA (18:3-6, 9, 12) is the most abundant and accounts for up to 40% of the total seed fatty acids. Lipid class and positional analysis indicated that GLA is almost exclusively incorporated into triacylglycerol (98.5%) with only trace amounts found in the other lipids. Within triacylglycerols, GLA is more abundant at the sn-2 position.