Genetically Modified Products

Recombinant DNA procedures like those described here now have a number of practical applications. One of the most promising is the development of genetically modified (GM) foods and agricultural products, substances whose genetic composition has been altered by rDNA or some similar process. Some examples of genetically modified products are corn plants that have been altered to emit a poison when attacked by pests; tomato plants that spoil at a significantly slower rate than natural plants; rape plants that have been engineered to be resistant to pesticides; and rice that has been enriched with a gene that codes for the production of vitamin A.

One of the first GM agricultural products to be developed was a biological control agent named Frostban. The principle behind

Recombinant DNA procedures are commonly used to introduce pesticide resistance into a crop. (Maximilian Stock Ltd./Photo Researchers, Inc.)

the development of Frostban is that frost does not begin to form on plants in nature, even if the temperature is low enough, in the absence of certain frost-promoting bacteria. Frostban was a spray that contained other types of bacteria that had been genetically modified to destroy the frost-promoting bacteria. When Frostban was sprayed on a crop, these genetically modified bacteria attacked and destroyed frost-promoting bacteria, preventing plants from freezing even when the temperature was low enough for that process to occur normally.

The first field-testing of Frostban in 1986 was met by strong reaction from activists who were concerned about the unknown effects the new product might have on the surrounding environment. On the night before the test spray was to occur, these activists crawled through the field where Frostban was to be tested and pulled up all the strawberry plants on which the test was to occur. In spite of this effort, the spray was eventually tested and found to be effective. It was never produced on a large scale for commercial use, however.

The first GM product to reach the marketplace was a tomato produced by Calgene, Inc., that was given the name of Flavr Savr. The tomato was approved for use by the FDA on May 18, 1994. It was developed to provide consumers with fresher-tasting tomatoes during the winter months, when fresh tomatoes are generally not available. At the time, the only way for people in cold climates to get fresh tomatoes during the winter months was for those tomatoes to be picked while they were still green, allowing them to reach the marketplace before they began to rot.

To solve this problem Calgene scientists synthesized a copy of the gene in tomatoes that causes them to soften over time. That gene normally promotes the production of an enzyme, polygalac-turonase, that breaks down cell walls. The scientists then inserted the gene into tomato plants in reverse sequence (a process known as antisense insertion) so that it would produce an effect opposite that which it normally causes; that is, it inhibited the production of polygalacturonase, causing the tomatoes to soften more slowly than would normally be the case in nature. The advantage of the Flavr Savr tomato was that it could be left on the vine longer, until it had actually ripened, before being picked.

In 1991 Calgene asked the U.S. Food and Drug Administration (FDA) to review the company's research on the Flavr Savr and determine whether it was safe for consumer sales. In May 1994, the FDA agreed that it was. It reported that Flavr Savr was "as safe as tomatoes bred by conventional means" and authorized Calgene to market its new product to the general public.

In spite of FDA's approval, Flavr Savr tomatoes were never a commercial success. Some observers have blamed the product's failure on consumer resistance (because the altered tomatoes cost too much or did not taste good enough). Others claimed that the company did not market the new product correctly or aggressively enough, and still others suggested that complaints about the use of GM products led to the product's downfall. In any case, Calgene was bought out by the chemical giant Monsanto in 1995 and shortly thereafter the parent company ceased research on and production of the Flavr Savr tomato.

A number of other GM foods have, however, met with greater commercial success than either Frostban or Flavr Savr. Some examples are golden rice and various Bt foods.

Golden rice is the name given to a genetically modified food that supporters hope will solve vitamin A deficiency (VAD), a widespread health problem in many developing nations. The most serious consequences of VAD are blindness and, in some cases, death. By some estimates, as many as 125 million children worldwide may suffer from VAD.

In the 1990s, the Swiss botanist Ingo Potrykus (1933 - ) developed a possible solution to the problem of VAD. Potrykus and his colleagues at the Institute of Plant Sciences at ETH Zurich (Eidgenossische Technische Hochschule Zurich) developed a modified form of common rice seed that includes three additional genes: psy (phytocene synthase), lcy (lycopene cyclase), and crt1 (phytoene desaturase). These genes have critical roles in the synthesis of beta-carotene, a precursor of vitamin A. Golden rice is so named because GM rice containing these three genes has a yellowish color because the lcy gene is obtained from the daffodil.

Like other GM food products, golden rice has its share of critics. Some authorities suggest that children for whom golden rice is intended may not be able to digest, absorb, and convert the beta-carotene produced in the product. These children require an adequate, more complete diet that includes sufficient levels of protein and fat if they are to benefit from the engineered product. Some observers suggest that much simpler solutions, such as providing a few teaspoons of red palm oil, readily available in many areas, would provide as much benefit as that provided by golden rice. Proponents argue that no single food product can be expected to meet all the needs of hungry people in developing nations, but that golden rice has many attractive features that can help with at least one major health problem, VAD. (For an extended discussion of the pros and cons of golden rice, see "Golden Rice" at biotech-info. net/golden.html.)

Bt corn is a genetically modified food named for the organism from which the transmitted gene is taken, the common soil bacterium Bacillus thuringiensis. These bacteria produce proteins known as delta endotoxins (or insecticidal crystal proteins [ICP]) that are toxic to a wide variety of insects. More than 150 insects belonging to the orders Lepidoptera (such as butterflies and moths), Diptera (flies), and Coleoptera (beetles) are known to be susceptible to the action of Bt delta endotoxins.

The mechanism of this action is now well understood. While intact, the proteins are nontoxic to the insect. When an insect ingests one of these proteins, however, it dissolves in the animal's intestinal fluid. Once the protein has dissolved, enzymes in the insect's guts known as proteases attack it. These proteases break the protein of Plant Physiology at the University of Hohenheim in Stuttgart. "Even at the peak

down into smaller units, some of which are toxic to the animal. The smaller units formed by the degradation of delta endotoxins bind to the insect's stomach wall and begin to destroy epithelial cells, thus paralyzing its digestive system. The insect stops feeding and may begin to vomit and have diarrhea. After a few hours or a few days of reduced activity and generalized paralysis, the insect dies.

A number of variants of the Bt delta endotoxin are known in nature, each toxic to specific types of insects in the orders Lepidoptera, Diptera, and Coleoptera. Insects against which these endotoxins are effective include alfalfa caterpillar, alfalfa looper, cabbage

A culture of Bacillus thuringiensis culture bacteria. (SciMAT/Photo Researchers, Inc.)

looper, cabbage worm, Colorado potato beetle, diamondback moth, European corn borer, fall webworm, green worm, gypsy moth, hemlock looper, leafrollers, pine budworm, pine butterfly, red-humped caterpillar, spiny elm caterpillar, spruce budworm, tent caterpillars, tomato fruit worm, tobacco hornworm, and tussock moth.

The Bacillus thuringiensis bacterium was discovered in 1901 by a Japanese bacteriologist by the name of Shigetane Ishiwatari. Its insecticidal effects were not noted until a decade later, when the German bacteriologist Ernst Berliner observed them. Bt-based insecticides that could be sprayed on plants were first introduced in the 1920s and were first licensed in the United States in 1961. With the growth of recombinant DNA technology in the 1990s, scientists found methods to incorporate B. thuringiensis genes directly into plants rather than having the insecticide sprayed on them. Today, several genetically engineered crops containing Bt genes are commercially available for agriculture use, including Bt corn, Bt tomatoes, Bt cotton, and a Bt potato:

> Bt corn is sold under the names Maximizer and YieldGard by Novartis and Monsanto, respectively. The product provides resistance to the European corn borer. A third Bt corn, StarLink, produced by Aventis, was withdrawn from the market when some consumers claimed severe allergic reactions to the product and questioned its safety.

> Bt tomatoes developed by Monsanto have been approved for human consumption by regulatory agencies in the United States, Canada, and other nations, although they have not yet been made commercially available.

> Bt cotton is another genetically modified food produced by Monsanto, resistant to attack by a variety of pests, including the cotton bollworm, tobacco budworm, and the pink bollworm.

> Bt potato is produced by Monsanto and marketed under its NewLeaf brand name. In this potato, Bt genes are incorporated that provide resistance to the Colorado potato beetle, a pest that can destroy as much as 85 percent of the potato crop in some areas. The U.S. Environmental Protection Agency (EPA) gave approval for the product in 1995, but it never received a very large share of the market (usually less than 5 percent), and it was withdrawn from use in 2001.

Recombinant DNA techniques have also been used to provide herbicide resistance to a variety of agricultural crops. A leader in this field has again been the Monsanto corporation, which markets the very successful and highly profitable herbicide Roundup. The problem with using Roundup, as with other herbicides, is that the product is as likely to kill a cash crop (such as corn or soybeans) as it is to kill the weeds for which it is intended. Monsanto's solution to this problem was to insert a gene into the cash crops that provides resistance to the herbicide. A crop thus modified can be sprayed with Roundup without fear that the herbicide will kill the desired crop as well as weeds.

The active ingredient in Roundup is a compound known as glyphosphate (N-(phosphonomethyl)glycine). Glyphosphate attacks a plant by binding to the active site in an enzyme known as enol-pyruvalshikimate phosphate (ESP) synthase. EPSP synthase has an essential role in the synthesis of certain aromatic amino acids (tyrosine, phenylalanine, and tryptophan). When its EPSP synthase enzyme is inactivated, a plant cannot make essential amino acids or synthesize proteins. It stops growing and eventually dies.

The problem is that glyphosphate acts in essentially the same way on all kinds of plants, both weeds and crops. Someone using the herbicide has to be very careful, then, to make sure that the product is sprayed only on weeds and not on crops themselves. (Note that Roundup has no effect on animals since they do not produce tyrosine, phenylalanine, and tryptophan by the mechanism used by plants.)

Monsanto's method of providing herbicide resistance to crop plants has been to introduce a gene that codes for the production of a compound similar to EPSP synthase but sufficiently different in molecular structure that glycophosphate will not block it. With this gene, the crop plant can continue to make tyrosine, phenylalanine, and tryptophan and the proteins on which they are based; that is, it can continue to grow and develop normally at the same time that weeds in its vicinity are being killed off by Roundup. Crops that contain the gene for the modified EPSP synthase are marketed by Monsanto under the Roundup Ready label.

The vast majority of GM foods developed so far have been designed to improve agricultural techniques, to provide plants with greater pest and pesticide resistance. However, researchers see a much broader range of applications for recombinant DNA techniques. Some of the most important of these applications are in the field of improving human health. The development of golden rice, described above, is one such development. Another example of the use of genetic engineering to improve the nutritional value of food is the invention in the 1990s of a modified form of canola, a form of rapeseed. Canola and rapeseed are members of the mustard family.

People have grown rapeseed for thousands of years for use as a food and a source of oils for household and industrial purposes. Over a long period of time, a program of selective plant breeding led to the development of a modified form of rapeseed that came to be known as canola. In 1985, the FDA announced that rapeseed and canola were different enough from each other to qualify as separate plant forms. Since that time, researchers have used recombinant DNA procedures to develop a broad range of canola varieties with nutritional properties superior to those of earlier varieties.

For example, in the early 1990s the Calgene company began testing a form of genetically engineered canola high in lauric acid. The high-laurate canola was given the trade name of Laurical. Laurical has most of the desirable nutritional properties of tropical oils, such as coconut and palm oil, with better shelf life and a silky texture that makes it highly desirable for use in confectionery products. In other words, the engineered oil was, overall, healthier and commercially more attractive than any existing natural product.

Another way that GM foods may improve human health is through the development of edible vaccines. An edible vaccine is a vaccine produced when one or more genes for an antigen are added to some natural food, such as potatoes or bananas. When a person eats that food, he or she ingests the antigen, which may provide immunity to a given disease.

Transgenic plants are also being considered for a number of industrial applications. For example, researchers are attempting to design and breed genetically modified plants to produce biofuels that are less harmful to the environment than traditional fossil fuels. Engineered plants may be developed that yield biolubricants to replace traditional hydraulic fluids or that produce biodegradable plastics with specially designed physical and chemical properties.

Since the first appearance of commercial GM crops in the 1990s, their popularity among farmers in the United States has exploded. Between 1996 and 2002, the amount of farmland devoted to the growth of GM crops has increased by 3,000 percent in the United States. The new agricultural technology has been far less successful in other parts of the world, however. As of 2004, six countries accounted for 99 percent of all the GM crops grown in the world. The United States led the way with 63 percent of all GM cropland, followed by Argentina (20 percent), Canada (6 percent), Brazil (5 percent), China (4 percent), and South Africa (1 percent). According to some estimates, about 70 percent of all the food products currently available to American consumers contain one or more GM products.

The most widely grown engineered food is GM soybeans, which account for 63 percent of all the cropland devoted to engineered crops in the United States, followed by GM corn (19 percent), GM cotton (13 percent), and GM canola (5 percent). The table below shows the percentage of three crops grown in the United States in 2002-2003 that consisted of modified plants. The major characteristics for which modified plants in the United States have been developed are herbicide tolerance and insect resistance. The circle graph accompanying the following table shows the plant characteristics for which GM foods in the United States have been tested as of 2003.

The year 2006 marked the end of the first decade during which genetically modified crops were available in the United States. Studies of agricultural changes during that decade produced mixed findings. On the one hand, many farmers had enthusiastically adopted GM crops, corn, soybeans, and cotton in particular. The main reasons

< PERCENT OF ALL FARMLAND DEVOTED TO GM CROPS IN THE UNITED STATES (2003) V
CROP	INSECT-RESISTANT VARIETIES (BT)	HERBICIDE- RESISTANT VARIETIES
2002	2003	2002	2003
corn	22	26	9	9
cotton	13	16	36	30
soybeans	75	80	75	80
Source: National Agricultural Statistics Service.

Insect resistant 34%

Herbicide Other

tolerant 16%

Pathogen resistant 15%

Product quality 14%

Agronomic properties 6%

15%

Percentage of characteristics in engineered foods in the United States in 2002-03

for their decisions were expectations of higher yields, savings in management time, and lower pesticide costs. As a result, nearly 100 percent of the soybeans planted in the United States in 2006 came from GM seeds and about half of all the cotton planted had also been genetically engineered. Still, GM crops caused concern among the general public, with a number of groups calling for a halt to further planting of GM seeds. These demands were especially pronounced in the European Union, where a number of nations had by 2006 passed legislation to prohibit the planting, sale, or transport of modified foods.