Submitted to: Phytochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2006
Publication Date: 6/9/2006
Citation: Cahoon, E.B., Dietrich, C.R., Meyer, K., Damude, H.G., Dyer, J.M., Kinney, A.J. 2006. Conjugated fatty acids accumulate to high levels in phospholipids of metabolically engineered soybean and Arabidopsis seeds. Phytochemistry. 67:1166-1176.
Interpretive Summary: Vegetable oils obtained from oilseed crops such as soybean hold considerable promise as renewable feedstocks for industry. The value of these oils for industrial applications, however, could be enhanced by the biotechnological introduction of novel fatty acid structures with greater chemical functionality. This research was conducted to identify metabolic factors that limit the ability of engineered seeds to accumulate high levels of conjugated fatty acids, which are highly desired as drying agents in inks and paints. These studies demonstrated that engineered seeds can produce conjugated fatty acids, but they do not properly sequester these fatty acids into triacylglycerols, the primary component of vegetable oils. These fatty acids instead accumulate to abnormally high levels in membrane lipids of the seeds. This research provides useful information for plant biochemists and molecular biologists who are attempting to develop vegetable oils with enhanced industrial value. It is anticipated that this research will result in oilseed crops that are of greater value for US farmers and vegetable oil processors and will give the consumer a renewable alternative to petroleum-derived materials.
Technical Abstract: Expression of FAD2-related fatty acid conjugases from Calendula officinalis, Momordica charantia, and Vernicia fordii in seeds of soybean (Glycine max) or an Arabidopsis thaliana FAD3/FAE1 mutant was accompanied by the accumulation of the unusual conjugated fatty acids calendic acid or alpha-eleostearic acid to amounts as high as 20% of the total fatty acids. Conjugated fatty acids, which are synthesized from phosphatidylcholine (PC)-linked substrates, accumulated in PC and phosphatidylethanolamine, and relative amounts of these fatty acids were higher in PC than in triacylglycerol (TAG) in the transgenic seeds. The highest amounts of conjugated fatty acids were detected in PC from seeds of soybean and A. thaliana that express the C. officinalis and M. charantia conjugases, where they accounted for nearly 25% of the fatty acids of this lipid. In these seeds, >85% of the conjugated fatty acids in PC were detected in the sn-2 position, and these fatty acids were also enriched in the sn-2 position of TAG. In marked contrast to the transgenic seeds, conjugated fatty acids comprised <1.5% of the fatty acids in PC from seeds of five unrelated species that naturally synthesize a variety of conjugated fatty acid isomers, including seeds that accumulate conjugated fatty acids to >80% of the total fatty acids. These results indicate that soybean and A. thaliana seeds are deficient in their metabolic capacity to efficiently and selectively catalyze the flux of conjugated fatty acids from their site of synthesis on PC to storage in TAG.