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BIOCHEMICAL PROCESSES AND MACROMOLECULAR STRUCTURES

Seed-Specific Heterologous Expression of a Nasturtium FAE Gene in Arabidopsis Results in a Dramatic Increase in the Proportion of Erucic Acid¹

National Research Council of Canada, Plant Biotechnology Institute, Saskatoon, Saskatchewan, Canada S7N 0W9 (E.M., E.M.G., S.W., J.D., J.M.B., D.C.T.); CanAmera Foods, Osler, Saskatchewan, Canada S0K 3A0 (D.L.B., V.K.); and Plant Breeding and Acclimatization Institute, Mlochow Research Center, Mlochow 05–831, Poland (E.M.)

The fatty acid elongase [often designated FAE or -(or 3-) ketoacyl-CoA synthase] is a condensing enzyme and is the first component of the elongation complex involved in synthesis of erucic acid (22:1) in seeds of garden nasturtium (Tropaeolum majus). Using a degenerate primers approach, a cDNA of a putative embryo FAE was obtained showing high homology to known plant elongases. This cDNA contains a 1,512-bp open reading frame that encodes a protein of 504 amino acids. A genomic clone of the nasturtium FAE was isolated and sequence analyses indicated the absence of introns. Northern hybridization showed the expression of this nasturtium FAE gene to be restricted to the embryo. Southern hybridization revealed the nasturtium -ketoacyl-CoA synthase to be encoded by a small multigene family. To establish the function of the elongase homolog, the cDNA was introduced into two different heterologous chromosomal backgrounds (Arabidopsis and tobacco [Nicotiana tabacum]) under the control of a seed-specific (napin) promoter and the tandem 35S promoter, respectively. Seed-specific expression resulted in up to an 8-fold increase in erucic acid proportions in Arabidopsis seed oil, while constitutive expression in transgenic tobacco tissue resulted in increased proportions of very long chain saturated fatty acids. These results indicate that the nasturtium FAE gene encodes a condensing enzyme involved in the biosynthesis of very long chain fatty acids, utilizing monounsaturated and saturated acyl substrates. Given its strong and unique preference for elongating 20:1-CoA, the utility of the FAE gene product for directing or engineering increased synthesis of erucic acid is discussed.

Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.104.046839.

^* Corresponding author; e-mail david.taylor{at}nrc-cnrc.gc.ca; fax 306–975–4839.

Received May 27, 2004; returned for revision June 16, 2004; accepted June 16, 2004.

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