Download Modification of plant fatty acid composition

Modification of plant fatty acid composition
Hangsik Moon
Department of Plant Cellular and Molecular Biology, The Ohio State University
Many properties of fats and oils are determined by their fatty acid composition.
Because of the commercial importance of seed oils for food and industrial use, considerable
attention has been given to the genetic/metabolic engineering of oil seed crops. Owing to
the fairly well-developed understanding of lipid biosynthesis in plants, it has been possible to
alter fatty acid composition in oil seeds by recombinant DNA technology.
One of the many objectives for genetically engineering plant oil composition is the
reduction of saturated fatty acid levels in edible oils. When introduced into tobacco under
control of CaMV 35S promoter, an animal stearoyl-CoA 9 desaturase reduced the levels of
saturated fatty acids. The decreased levels of saturated fatty acids were accompanied by
large increase in monounsaturated fatty acids including palmitoleic acid (16:19), which is
normally a very minor constituent in tobacco tissues. As in the case of the transgenic
tobacco, soybean somatic embryos expressing the animal desaturase under control of seedspecific phaseolin promoter contained significantly reduced levels of saturated palmitic (16:0)
and stearic (18:0) acids.
Hydroxy fatty acids are valuable industrial raw materials such as nylon, specialty
lubricants, paints and cosmetics. Castor bean is the only significant source of hydroxy fatty
acids but is less ideal as the seeds contain potent toxins and allergens. Lesquerella fendleri
seed oil contains up to 60% hydroxy fatty acids, nearly all of which is the 20-carbon hydroxy
fatty acid, lequerolic acid (20:111-OH14), which is formed by the elongation of the 18carbon hydroxy fatty, ricinoleic acid (18:19-OH12). By L. fendleri genomic DNA library
screening, two genomic clones encoding condensing enzymes were isolated: LfKCS3 and
LfKCS45. Heterologous expression of the clones demonstrated that LfKCS3 is a
condensing enzyme that specifically catalyzes the elongation of 18-carbon hydroxy fatty acid,
and LfKCS45 is involved in the synthesis of very-long-chain fatty acids.