Genetic Engineering of Crop Plants
Richard R. MacMahon, Ph.D.
Contents of Curriculum
; Biological Aspects
; The Process
For as long as man has been cultivating crops and raising animals, there have been modifications of the genomes of these plants and animals. Just think of the large number of breeds of horses and dogs, and the many varieties of corn and tomatoes. Now we have the ability to modify the genome very precisely, one gene at a time. This new technique is called genetic engineering (GE), and has become a rather common technique in those laboratories conducting such research. It has made possible precise changes in varieties of plants, changes that have enabled man to increase both yields and the quality of these crops (Abelson and Hines, 1999).
However, there has developed a rather large and vocal opposition to the use of genetically modified organisms (GMOs). This opposition has attempted to stop the use of GMOs entirely, claiming health concerns such as toxic and allergic reactions, despite the assurances of the United States government Department of Commerce (Palmer, 1999), the National Academy of Science (Yoon and Peterson, 2000) and the United States Food and Drug Administration that there is no danger (Maryanski, 1995; Sudduth, 2000).
There are also claims that Monsanto and other companies involved are trying to “lock up” control of seed production and thus dominate the world. (Lappe and Bailey, 1997; Cummins, 1999; Bereano, 1995). Thus the arguments involved in the issue of GMOs safety might be characterized as both political and biological (Verzola, 1999; Rifkin, 2000; Genetic ID, Inc, 1999a). Biological Aspects
There seem to be at least four major objectives being pursued at this time in crop plant genetic engineering research. These are:
1. To improve biological protection of crops against insects, weeds and fungi by inserting genes for the natural production of an insecticide (Feder, 1996) or for resistance to fungi or an herbicide
(Hinchee et al, 1988).
2. To elevate levels of important nutrients (e.g. methionine
levels in soybeans - Beardsley, 1996) so as to make crops more nutritious.
3. To obtain better control of ripening and post-harvest storage life to assure that produce are in peak condition when taken to market (Maryanski, 1995).
4. To specifically modify genomes to produce a specific product (e.g. a caffeine-less coffee bean, edible vaccines in potatoes - Pollack, 2000).
Genetic engineering is the insertion of a segment of DNA containing one or more genes from one organism into a chromosome of another organism. This process, when successful, allows the expression of the added gene in the host organism. The process involves using either a virus or bacterium nucleic acid as a vector of insertion, or else doing the job with a micropipette or by bio-ballistic DNA delivery with a “gene gun” (Nicholl, 1994; Ho, 1996). To be sure that the gene you are trying to insert is actually present, the added segment of DNA usually includes a “marker gene” which is most often a gene for antibiotic resistance. The organism is then grown in a culture containing the antibiotic. Only those individuals with the added segment of
DNA will survive, since they are the only organisms that are resistant to the antibiotic. At least this is how desired genes are usually identified, with a marker for antibiotic resistance. So far, there have been about 50 different food crop approvals for genetically engineered varieties (U.S.FDA, 2000).
Once the desired genes are inserted into the selected organism, the new genetically engineered organism is reproduced to obtain a generation of individuals that possess the desired trait. These individuals in turn are raised and utilized with the desired gene actively functioning. Some examples are the S-adenosylmethionine hydrolase gene from a bacterium which was added to cantaloupe to control ripening, the Phosphinothricin acetyltransferase gene from another bacterium which confers Glufosinate (Roundup?- an
herbicide) tolerance, and the potato that is insect resistant with the cryIIIA gene from Bacillus thuringiensis (Bt) sp. tenebrionis (another bacterium) (U.S.FDA, 2000).
There are many other GMOs that have been produced and are being used for crop production at this time. There are 50 examples of genetic engineering reported by the U.S.FDA (2000). These GMOs confer resistance to pesticides, more uniform ripening, resistance to insects and viruses and improved protein content
of several food crops. So why are there so many protests to genetic engineering?
In this case the new protein caused a “life-threatening allergic
reaction in people”(Beardsley, 1996). The company quickly stopped the project (Beardsley, 1996; Feder, 1996; Leary, 1996). Here again we see an unexpected result from an attempt at genetic engineering.
This “life-threatening allergic reaction” was a determination made in the laboratory using blood serum from nine patients who were allergic to Brazil nuts (Leahy, 1996). All nine reacted to extracts of the Brazil nut. Eight of nine reacted to the genetically engineered soybean extract, but none reacted to the extract from regular, plain soybeans. Skin prick tests on three volunteers showed the same results. This was part of the normal pre-release process that genetic engineering companies are required to perform on their own by the FDA (Sudduth, 2000). This example of a potentially serious result is often quoted by opponents to genetic engineering, even now, five years after the fact. And it is frequently implied that people were put at serious risk, even though all of the allergic reaction procedures were done in the laboratory on blood serum and no one became ill.
Insertion of a desired gene requires not only a vector for insertion, usually a viral gene, but also a marker gene for antibiotic resistance. One other problem is that each gene inserted into another organism needs an activator gene. The host organism is very unlikely to furnish this activator, so one is usually provided with the inserted gene. Virus activator genes have evolved to overcome host cell indifference to an added gene. These virus genes are very powerful activators, and are normally what is used to activate an inserted gene (Steinbrecher, 1999). There are also some bacterial activators used. We do not know the long-term effects of using these microbial genes in genetic engineering. If they are passed to other organisms there may be problems that we cannot imagine at the present time. Conclusions
Some of the opposition to GMOs seems almost irrational(Fong, 2000). Two Mothers for Natural Law web articles (1999 and 2000) assume that there is something to be avoided in genetically engineered foods. They furnish a list of food products to avoid, and a source for testing DNA of food products for genetic engineering. There is no discussion or justification for what they are saying. The assumption seems to be that if it is a GMO it is bad. There may
well be some problems with GMOs, such as allergic reactions, changed flavors and horizontal movement of genes, but these need to be investigated in a rational manner, not with blanket condemnations and ignorance.
It is probably a positive thing that protesters have called attention to the phenomenon of genetic engineering and have insisted that the government be more active in the testing and licensing of these products. At the same time, there seems to be much misinformation and some hysteria about the subject of genetic engineering. There have been all kinds of dire predictions about GMOs. But genetic engineering has been singularly free of tragic consequences to date. The one exception seems to be the production of tryptophan by a Japanese company. Eleven people died from consuming tryptophan that was improperly genetically engineered and purified. However, we may conclude that the general short-term effects of genetic engineering on humanity is positive.
However, there seems to be no research being done on the long-term effects of genetic engineering. There are several basic questions unanswered:
1. Will people over time develop allergic reactions to the transgenic proteins produced from genetic engineering?
2. Will the horizontal movement of genetic materials have a negative impact on ecosystems?
3. Will some virulent new pathogen develop from the transfer and transformation of microbial DNA made available by genetic engineering?
4. Will humans be able to make the correct ethical choices so that all of humanity may share in the potential benefits of genetic engineering?