Food Lipids: Chemistry, Nutrition, and Biotechnology

characteristic of various vegetable oils—which define the uses of specific vegetable
oils in the food industry—are determined by the genes of each plant variety. The
advent of genetic engineering technology in agriculture has enabled the directed
modification of the gene set that determines oil composition in a given oilseed crop.
There is a long and fruitful history of plant breeders who have deliberately
selected for lines in which the seed oil is different in chemical composition. Examples
include high-oleic sunflower, low-linolenic flax, and low-erucic rapeseed. These successes
appear to be cases in which a specific gene or genes become nonfunctional.
Although genetic engineering techniques in yeasts and bacteria allow the specific
targeting of genes to be ‘‘knocked out,’’ this is not yet the case with plants. However,
it is possible now to add genes to a plant, and some of these approaches can indeed
be used to decrease the functional expression of genes resident in the host crop plant
genome.
There is an ever increasing knowledge base to explain the genetic bases that
determine the chemical composition of seed oils. In summary (2), a number of lipidsrelated
genes have been individually cloned in the laboratory, and most of these
genes turn out to encode specific enzymes used by the plant to synthesize the triacylglycerols
that make up vegetable oils. For example, cloning a gene from Cuphea
lanceolata that encodes a specific enzyme in the seed with a unique activity on a
capric acid precursor may help to explain why high levels of capric acid are found
in C. lanceolata seed oil. Moreover, failure to find that enzyme in canola seed may
at least partly explain why capric acid is not naturally found in canola oil. And in
its simplest manifestation, a genetic engineering approach would suggest taking the
cloned C. lanceolata gene, transferring it into the chromosomes of a canola plant,
and seeing whether the oil from the seeds of the resulting transgenic canola plant
contains capric acid.
Currently, then, genetic engineering of plants allows the addition of genes.
These genes are incorporated directly into plant chromosomes and basically behave
in subsequent generations of progeny plant like other genes. That is, they are inherited
in a Mendelian manner and are subject to the same modifications to which the
genes preexisting in the plant genome are subject. The gene’s specific ‘‘behavior,’’
however, may be something entirely novel to the host plant. For example, it may
encode for an enzyme that has never been found in that plant species. The ability to
introduce such modifications is what genetic engineering adds to the plant breeder’s
tool kit. A breeder, of course, could not cross a coconut tree with a canola plant to
get a canola plant with certain coconut tree properties. But a discrete number of
coconut genes can be transferred into a canola plant to make some facet of a canola
plant’s metabolism more closely resemble that of a coconut tree.
As in the example of Cuphea lanceolata and canola above, one can add a novel
gene from a wide range of sources, including not only any plant but also animals,
bacteria, and even genes encoding enzymes that were ‘‘designed’’ on a computer and
synthesized in the laboratory. It is possible to clone gene from a specific plant species,
engineer the gene so that it expresses the same enzyme at an unusually high
level at the targeted stage of seed development, and add it back to the same plant
species. By having more of an enzyme controlling a rate-limiting step in oil biosynthesis,
one might achieve more oil and/or an oil with a different fatty acid composition.
And finally, it is possible to add genes that interfere with the function of
Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.