|Pepperman Jr, Armand|
Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/25/2002
Publication Date: 12/1/2002
Citation: Dyer, J.M., Chapital, D.C., Kuan, J.W., Mullen, R.T., Pepperman Jr, A.B. 2002. MOLECULAR ANALYSIS OF A BIFUNCTIONAL FATTY ACID CONJUGASE/DESATURASE FROM TUNG: IMPLICATIONS FOR THE EVOLUTION OF PLANT FATTY ACID DIVERSITY. Plant Physiology. (130):2027-2038. Interpretive Summary: Many plants accumulate unusual fatty acids in their seeds that have potential uses in pharmaceutical and industrial applications. For example, the oil obtained from tung seeds is enriched in an unusual fatty acid that imparts important drying qualities, making tung oil a useful component in formulations of inks, dyes, coatings, and resins. Identification of the enzymes in tung seeds that are responsible for making this special fatty acid might allow one to use the tung enzymes to convert common vegetable oils into value-added industrial drying oils. We have identified and characterized the enzymes from tung seeds that make the essential fatty acid in tung oil. We transferred the enzymes to common baker's yeast and demonstrated the conversion of common fatty acids into the valuable fatty acid present in tung oil. Identification of the tung enzymes will allow us to explore the potential of converting common vegetable oils into value added industrial oils. Common vegetable oils such as soybean cost roughly $0.10 to $0.15 per pound, whereas tung oil may cost over $1.00 per pound. The characterization of the tung enzymes also provides significant information to scientists who study the production of unusual fatty acids in the seeds of plants.
Technical Abstract: The seed oil derived from the tung tree (Aleurites fordii Hemsl.) contains approximately 80% eleostearic acid (18:3-9cis,11trans,13trans), an unusual conjugated fatty acid that imparts industrially-important drying qualities to tung oil. Here we describe the cloning and functional analysis of two closely related delta-12 oleate desaturase-like enzymes that constitute consecutive steps in the biosynthetic pathway of eleostearic acid. Expression of the cDNAs encoding these enzymes in the yeast Saccharomyces cerevisiae revealed that one enzyme, termed FAD2, converted oleic acid (18:1-9cis) into linoleic acid (18:2-9cis,12cis), while the other, termed FADX, converted linoleic acid into eleostearic acid. The FADX enzyme exhibited remarkable enzymatic plasticity, capable of generating a variety of alternative conjugated and desaturated fatty acid products in yeast cells cultured in the presence of exogenously-supplied fatty acid substrates. Several of these alternative fatty acids were also detected in developing tung seeds, and their abundance correlated with the relative amounts of their respective fatty acid substrates. These results suggest that a single divergent enzyme can produce several different types of unusual fatty acids depending upon the metabolic context in which it operates. Tissue- and organelle-specific properties of tung FAD2 and FADX are described, and evolutionary relationships and conserved amino acid features of lipid-modifying enzymes (desaturase, hydroxylase, epoxygenase, acetylenase, and conjugase) are discussed.