Plant Biotechnology PDF

# Plant Biotechnology After completing this chapter, you should be able to: - Describe the impact of biotechnology on the agricultural industry. - Discuss the limitations of conventional crossbreeding techniques as a means of developing new plant products. - Explain why plants are suitable for gene...

# Plant Biotechnology After completing this chapter, you should be able to: - Describe the impact of biotechnology on the agricultural industry. - Discuss the limitations of conventional crossbreeding techniques as a means of developing new plant products. - Explain why plants are suitable for genetic engineering. - List and describe several methods used in plant transgenesis, including protoplast fusion, the leaf fragment technique, and gene guns. - Describe the use of *Agrobacterium* and the Ti plasmid as a gene vector. - Define antisense technology and give an example of its use in plant biotechnology. - List some genetically engineered crops. - Outline the environmental impacts, both pro and con, of biotechnologically enhanced crops. - Describe the phytochemical opportunities in plant biotechnology. - Outline several ways in which biotechnology has the potential to reduce hunger and malnutrition around the world. ## The Future of Agriculture: Plant Transgenics The red juicy tomatoes on sale at the grocery store are a true feat of engineering. Countless generations of selective breeding have transformed a puny acidic berry into the delicious fruit we know today. In the last few decades, conventional hybridization (by cross-pollination) has produced tomatoes that are easy to grow, quick to ripen, and resistant to disease. Pioneering efforts in biotechnological research have created tomatoes that can stay on store shelves longer without losing flavor. The future holds the possibility of an even more amazing transformation for the tomato: it, and other foods, could someday supplement or possibly replace inoculation as a means of vaccination against human disease. For example, researchers have successfully vaccinated volunteer patients against Norwalk virus in clinical trials by having them eat transgenic potatoes that express the vaccine. ### Forecasting the Future The transfer of genes to plants has been firmly established as a reliable method to meet the need of future generations for food and energy. Fourteen million farmers in 25 countries currently benefit from genetically engineered (GE) crops, according to the International Service for the Acquisition of Agri-biotech Applications (ISAAA). There are limitations, however, to the entry of new plants to the market, and only a small number of crops have done so. These limitations are due in part to the fact that most of the thousands of existing patents for transgenic plants are held by only three companies: Syngenta, Monsanto, and DuPont. The high royalty fees and restrictions these companies have in place make the costs of developing crops based on these patents prohibitive for most farmers and researchers. This has led several biotech companies to develop their own novel gene transfer methods, and now nonprofit research groups such as the Public Sector Intellectual Property Research for Agriculture (PIPRA) are involved. The Animal and Plant Health Inspection Service (APHIS) of the U.S. Department of Agriculture (USDA) is also assisting. They have launched a pilot program to improve compliance with APHIS field trials and restricted the movement of regulated organisms by certifying companies through the new Biotechnology Quality Management Service (BQMS). A company that qualifies for BQMS certification can overcome many of the expensive barriers to marketing GE crops by testing the effectiveness of transgenic plants in the field and focusing on products that are safe, affordable, and driven by public need. The future of plant biotechnology is brighter with changes that make producing genetically engineered crops less expensive and improve consumer perceptions of new crops. ### The Future of Agriculture: Plant Transgenics Over the past 40 years, the world population has nearly doubled while the amount of land available for agriculture has increased by a scant 10%. Yet we still live in a world of comparative abundance. In fact, world food production per person has increased 25% over the past 40 years. How has it been possible to feed so many people with only a marginal increase in available land? Most of that improved productivity has depended on crossbreeding methods developed hundreds of years ago to provide animals and plants with specific traits. Recently, however, the development of new, more productive crops has been accelerated by the direct transfer of genes, as shown in Figure 6.1. ## Methods Used in Plant Transgenesis Genetic manipulation of plants is not new. Ever since the birth of agriculture, farmers have selected for plants with desired traits. Since then, technologies have been ever evolving to meet the world's increasing world for agricultural products. ### Conventional Selective Breeding and Hybridization Even though careful crossbreeding has continued to improve plants through the millennia-giving us larger corn cobs, juicier apples, and a host of other modernized crops the methods of classic plant breeding are slow and uncertain. Creating a plant with desired characteristics requires facilitating a sexual cross between two different plant lines and repeated backcrossing between the hybrid plant's offspring and one of the original parent plants. Isolating a desired trait in this fashion can take years. For instance, Luther Burbank's development of the white blackberry involved 65,000 unsuccessful crosses. In fact, plants from different species generally do not hybridize, so a genetic trait cannot be isolated and refined unless it already exists in a plant strain. ### Cloning: Growing Plants from Single Cells Plant cells are different from animal cells in many ways, but one characteristic of plant cells is especially important to biotechnology: many types of plants can regenerate from a single cell. The resulting plant is a genetic replica-or clone of the parent cell. Animals can be cloned too, of course, but the process is more complicated. (Chapter 7 discusses animal cloning in detail.) This natural ability of plant cells has made them ideal for genetic research. After new genetic material is introduced into a plant cell, the cell rapidly produces a mature plant, and the researcher can see the results of the genetic modification in a relatively short time. Next we consider some of the methods used to insert genetic information into plant cells. ### Protoplast Fusion When a plant is injured, a mass of cells called a callus may grow over the site of the wound. Callus cells have the capability to redifferentiate into shoots and roots, and a whole flowering plant can be produced at the site of the injury. You may have taken advantage of this capability if you have ever "cloned" a favorite house plant by rooting a cutting. The natural potential of these cells to be reprogrammed makes them ideal candidates for genetic manipulation. Like any plant cells, however, callus cells are surrounded by a thick wall of cellulose, a barrier that hampers any uptake of new DNA. Fortunately the cell wall can be dissolved with the enzyme cellulase, leaving a denuded cell called a protoplast. The protoplast can be fused with another protoplast from a different species, creating a cell that can grow into a hybrid plant. This method, called protoplast fusion, as shown in Figure 6.2, has been used to create broccoflower, a fusion of broccoli and cauliflower, as well as other novel plants. ### Leaf Fragment Technique Genetic transfer occurs naturally in plants in response to some pathogenic organisms. For instance, a wound can be infected by a soil bacterium called *Agrobacterium tumefaciens* (recently reclassified as *Rhizobium radiobacter* by genome analysis, but the name *Agrobactor* is still in common usage; we use it throughout our discussion). This bacterium contains a large circular double-stranded DNA molecule called a plasmid, which triggers an uncontrolled growth of cells (tumor) in the plant. For this reason, it is known as a tumor-inducing (TI) plasmid. The resulting tumor is known as crown gall. If you have ever seen a swelling on a tree or rose bush, you may have seen *Agrobacter*'s effects (see Figure 6.3). The bacterial plasmid gives biotechnologists an ideal vehicle for transferring DNA. To put that vehicle to use, researchers often employ the leaf fragment technique. In this method, small discs are cut from a leaf. When the fragments begin to regenerate, they are cultured briefly in a medium containing genetically modified *Agrobacter*, as shown in Figure 6.4. During this exposure, the DNA from the TI plasmid integrates with the DNA of the host cell, and the genetic payload is delivered. The leaf discs are then treated with plant hormones to stimulate shoot and root development before the new plants are planted in soil. The major limitation to this process is that *Agrobacter* cannot infect monocotyledonous plants (plants that grow from a single seed embryo) such as corn and wheat. Dicotyledonous plants (plants that grow from two seed halves) like tomatoes, potatoes, apples, and soybeans are all good candidates for the process, however. ### Gene Guns Instead of relying on a microbial vehicle, researchers can use a gene gun to literally blast tiny metal beads coated with DNA into an embryonic plant cell, as shown in Figure 6.5. The process is rather hit or miss and more than a little messy-but some of the plant cells will adopt the new DNA. Gene guns are typically used to shoot DNA into the nucleus of a plant cell, but they can also be aimed at the chloroplast, the part of the cell that contains chlorophyll. Plants have between 10 and 100 chloroplasts per cell, and each chloroplast contains its own bundle of DNA. Whether they target the nucleus or the chloroplast, researchers must be able to identify the cells that have incorporated the new DNA. In one common approach, they combine the gene of interest with a gene that makes the cell resistant to certain antibiotics. This gene is called a marker gene or reporter gene. After firing the gene gun, the researchers collect the cells and try to grow them in a medium that contains a specific antibiotic. Only the genetically transformed cells will survive. The antibiotic-resistant gene can then be removed before the cells grow into mature plants, if the researcher so desires (for a more detailed explanation of gene markers, see Chapter 5). ### Chloroplast Engineering The chloroplast can be an inviting target for bioengineers. Unlike the DNA in a cell's nucleus, the DNA in a chloroplast can accept several new genes at once. Also, a high percentage of genes inserted into the chloroplast will remain active when the plant matures. Another advantage is that the DNA in the chloroplast is completely separate from the DNA released in a plant's pollen. When chloroplasts are genetically modified, there is no chance that transformed genes will be carried on the wind to distant crops. This process is shown in Figure 6.6, on page 164. ### Antisense Technology Recall the tomato. It is red, juicy, and tasty-and extremely perishable. When picked ripe, most tomatoes will turn to mush within days. But the *Flavr Savr* tomato, introduced in 1994 after years of experimentation, stayed ripe and fresh for weeks. The *Flavr Savr* tomato was the first genetically modified food approved by the U.S. Food and Drug Administration and, although it was not an economic success and is no longer available, it is common to find other varieties of genetically modified food, including tomatoes, on the market today. These foods were developed using antisense technology, in which a gene that encodes for a specific trait is removed from plant cells, used to produce a complementary copy of itself, and transferred back to the original cells using *Agrobacter* as a vector organism. Ripe tomatoes normally produce the enzyme polygalacturonase (or PG), a chemical substance that digests pectin in the wall of the plant. This digestion induces the normal decay that is part of the natural plant cycle. The gene that encodes PG was identified, removed from plant cells, and used to produce a complementary copy of itself. Using *Agrobacter* as a vector, the gene was then transferred into tomato cells. Once in the cell, the gene encoded an mRNA molecule (antisense molecule) that united antisense RNA with and inactivated (complementary sequence) the normal mRNA molecule (the sense molecule) for PG production. With the normal mRNA inactivated, no PG is produced, no pectin is digested, and natural "rotting" is slowed. This process is shown in Figure 6.7. ## Practical Applications Protecting plants from viruses, insects, and weeds while improving their nutrition and properties is the goal of commercial growers, and biotechnology has produced some interesting examples. ### Vaccines for Plants Crops are vulnerable to a wide range of plant viruses. Infections can lead to reduced growth rates, poor crop yields, and low crop quality. Fortunately farmers can protect their crops by stimulating a plant's natural defenses against disease with vaccines. Just like a human vaccine for polio, plant vaccines contain dead or weakened strains of the plant virus that turn on the plant's version of an immune system, making it resistant to the real virus. Vaccinating an entire field is not easy, but it is no longer necessary. Instead of injecting the vaccine, the vaccine can be encoded in a plant's DNA. For example, researchers have recently inserted a gene from the tobacco mosaic virus (TMV) into tobacco plants. The gene produces a protein found on the surface of the virus and, like a vaccine, turns on the plant's immune system. Tobacco plants with this gene are immune to TMV. The tomato mosaic virus is similar enough to be stopped by this technique. Figure 6.8 shows this process. ### Genetic Pesticides For the last 50 years, many farmers have relied on a natural bacterial pesticide to prevent insect damage to crops. *Bacillus thuringiensis* (Bt) produces a crystallized protein that kills harmful insects and their larvae. The crystalline protein (from the *Cry* gene) breaks down the cementing substance that fuses the lining cells of the digestive tract in certain insects. Insects subjected to this protein die in a short time from "autodigestion." The *Cry* gene causing this event is the subject of an expanding market of "insect-resistant" genetically engineered plants. By spreading spores of the bacterium across their fields, farmers can protect their crops without using harmful chemicals. Now, instead of spreading the bacterium directly across their fields, farmers can grow plants containing Bt genes. Plants that contain the gene for the Bt toxin have a built-in defense. This biotechnologically enhanced pesticide has been successfully introduced into a wide range of plants, including tobacco, tomatoes, corn, and cotton. In fact, most soybean seeds planted today contain the gene for Bt toxin, which effectively kills cotton-infesting insects. Bt with its insecticidal protein is shown in Figure 6.9a. The widespread use of the Bt gene is one of the most remarkable success stories in biotechnology. It is also one of the biggest sources of controversy. Cornell researchers conducted a laboratory experiment in 1999 suggesting that the pollen produced by bioengineered corn could be deadly to monarch butterflies. The results were expected. Researchers had known for years that, in large doses, the toxin naturally produced by *B. thuringiensis* could be harmful to butterflies. Still, the report set off a firestorm of controversy. It was the first tangible evidence that genetically altered food could harm the environment, and the monarch butterfly quickly became the unofficial mascot of opponents of genetic engineering. When researchers took their experiments out of the laboratory and into the field, many of their concerns quickly faded. Several studies found that few butterflies in the real world would be exposed to enough pollen to cause any harm. In fact, butterflies are unlikely to ingest toxic amounts of pollen even if they feed on milkweed plants less than 1 meter from the typical field of genetically modified corn. Still, scientists speculate that a small percentage of butterflies will inevitably get dusted with a lethal amount of pollen. Some of the monarchs that survive the exposure may then be unfit for their long migrations. On the whole, however, concerns that genetically altered corn could devastate monarchs seem to have been disproven: after 2 years of study, the Agricultural Research Service (a division of the USDA) announced in 2002 that Bt toxin posed little risk to monarch butterflies in real-world situations. ### Herbicide Resistance Traditional weed killers have a fundamental flaw: they often kill desirable plants along with weeds. Today, biotechnology allows farmers to use herbicides without threatening their livelihood. Crops can be genetically engineered to be resistant to common herbicides such as glyphosphate. This herbicide works by blocking the enzyme EPSPS, which functions in a biochemical pathway responsible for the synthesis of aromatic amino acids and other compounds vital to plant growth and survival. Through bioengineering, scientists have created transgenic crops that produce an alternative enzyme that is not affected by glyphos-phate, meaning that weeds are susceptible while desirable plants are not. This approach has been especially successful in soybeans. Most soybeans grown today contain herbicide-resistant genes. The process is shown in Figure 6.10. Glyphosphate is currently the world's most widely used herbicide, effectively controlling of a wide group of unwanted plant species. Since 1996, the high usage of transgenic glyphosphate-resistant crops in the Americas has led to exclusive use of glyphosphate for weed control over very large areas. Unfortunately, in regions where transgenic glyphosphate-resistant crops dominate, glyphosphate-resistant populations of damaging weed species have now evolved. A single-site mutation of a proline amino acid at position 101 in EPSPS has been implicated in these glyphosate-resistant weeds, which have been found in the United States, Argentina, and Brazil. As more transgenic glyphosphate-resistant crops are planted over the next few years, it is anticipated that other glyphosphate-resistant weed species will evolve. In response to this development, Monsanto has added a broad-spectrum weed killer to reduce the development of resistant weeds. Future use of glyphosphate-resistant plants will require engineering to combat this event. Other companies are at work on similar products to combat glyphosphate-resistant weeds. Glyphosphate is considered essential for present and future world food production, and any action to secure its sustainability has become a global imperative. Farmers who plant herbicide-resistant crops are generally able to control weeds with chemicals that are milder and more environmentally friendly than typical herbicides. This development is significant because, before the advent of resistant crops, U.S. cotton farmers spent $300 million per year on harsh chemicals to spray on their fields, exclusive of the large cost in human manual labor necessary to keep cotton plants weed-free, which is no longer necessary. ### Enhanced Nutrition Of all the potential benefits of biotechnology, nothing is more important than the opportunity to save millions of people from the crippling effects of malnutrition. One potential weapon against malnutrition is Golden Rice-rice that has been genetically modified to produce large amounts of beta carotene, a provitamin that the body converts to vitamin A. According to recent estimates, 500,000 children in many parts of the world will eventually become blind because of vitamin A deficiency. Currently health workers carry doses of vitamin A from village to village in an effort to prevent blindness. Simply adding this nutrient to the food supply would be much more efficient and, in theory, much more effective. Biotechnology may not, however, be the magic bullet that ends malnutrition. Although promising, genetically modified foods have their limitations. For instance, the provitamin in Golden Rice must dissolve in fat before it can be used by the body. Children who do not get enough fat in their diets may not be able to reap the full benefits of the enriched rice. Some groups would like to see more conventional breeding techniques used to combat world hunger. For example, although Golden Rice was ready to appear within 2 years of its development, no farmers have, as of 2011, yet planted the rice, largely because of concerns voiced by environmental organizations. These groups endorse programs such as Harvest Plus in place of the introduction of transgenic crops in developing countries. Harvest Plus is a collection of 12 crops that aim to boost levels of vitamin A, iron, and zinc, and it relies on conventional breeding. However, other groups support transgenic crops in these same locations: the Bill and Melinda Gates Foundation, for example, is spending $36 million to support Golden Rice, GM cassava, sorghum, and bananas. ### The Future of Plant Biotechnology in Pharmacology Recall that plants can be ideal protein factories (Chapter 4). A single field of a transgenic crop can produce a large amount of commercially valuable protein. At this time, transgenic corn has the highest protein yield per invested dollar of any bioreactor organism. The possibilities are practically endless. In the not-so-distant future, farmers will grow human medicine along with their crops. It is already possible to harvest human growth hormone from transgenic tobacco plants. Plants can also manufacture vaccines for humans, as we've seen. Edible vaccines can be produced by introducing a gene for a subunit of the virus or bacterium. The plant expresses this protein subunit, and it is eaten with the plant. When the subunit antigen enters the bloodstream, the immune system produces antibodies against it, providing immunity. The need for inexpensive vaccines that do not require refrigeration was first voiced by the World Health Organization in the early 1990s and has resulted in studies of vaccines in bananas, potatoes, tomatoes, lettuce, rice, wheat, soybeans, and corn. Researchers at Cornell University have recently created tomatoes and bananas that produce a human vaccine against the viral infection hepatitis B. Researchers are actively studying the tomato as another source of pharmaceuticals. Through engineering of the chloroplast (abundant in green tomatoes), scientists hope to create an edible source of vaccines and antibodies, as shown in Table 6.1. Plants express a wide range of chemical compounds called phytochemicals, and biotechnologists are converting plants into small-scale factories to produce chemicals useful to human health. Biotechnology can alter the production of complex technical therapeutic proteins via plant pathways, with examples including antibodies, blood products, cytokines, growth factors, hormones, and recombinant enzymes. This "molecular farming" will likely bring several products to market in the near future with applications to the treatment of diseases and conditions such as cystic fibrosis, non-Hodgkin's lymphoma, hepatitis, Norwalk virus, rabies, and a range of gastrointestinal illnesses. Rather than growing human or animal cells on expensive nutrient-rich media, biopharmers insert genes into the cell of plants and the plants do the work of transcribing and folding the protein. Since plants can be grown in larger quantities than cell cultures, they can offer a much greater volume of product than a manufacturing plant would. However, since the first human-like enzyme was first produced in transgenic tobacco plants in 1992 at Virginia Polytechnic Institute, the biopharma industry has had a wave of trials with no approvals. Nevertheless, the first plant-based pharmaceutical products may be on the market before long. Protalix, a biotech company in Israel, has FDA approval for a drug to treat Gaucher's disease. The disease has no cure, but the product in development breaks down the accumulating fatty substances, and patients would have to take this drug throughout their lives. Since there is no other ready supply, the drug received fast-track approval (see Chapter 12 for a full description of approvals for "orphan" drugs). The drug is manufactured by producing proteins from carrot cell cultures in disposable plastic bioreactors. Another company, Medicago, a U.S. company, is developing flu vaccines in tobacco plants (see Figure 6.11 on page 170) grown in greenhouses. After the plants are transformed by *Agrobacter*, they produce the necessary protein shell, which is then harvested and made into a vaccine. ### The Future of Plant Biotechnology: Fuels Biofuels (fuels produced from biological products, such as plants) can be produced almost anywhere in the world from homegrown raw materials and may be an important use of plant biotechnology in the future. As the need for alternatives to fossil fuels increases, the U.S. government is looking toward biotechnology to offer solutions. The 2007 Biofuels Initiative increased federal funding 60% over the 2006 budget with the stated intention of replacing 30% of U.S. current fuel with bioethanol by 2030 (see Figure 6.12). Bioethanol refineries have sprung up all over the Midwest (resulting largely from subsidies and incentives) and can be used to convert sugars from any cellulosic source. However it takes 7 gallons of gasoline to produce 10 gallons of kernel corn ethanol, which represents a relatively modest net gain. For this reason biotechnology is needed to convert the readily available cellulosic sources into biofuels-perhaps by developing biofuel-producing organisms-and thus making this procedure more economically viable. ### Biofuels from Plant Waste In the future, there may be other opportunities for plants to provide fuels. Specifically, scientists are developing methods to capture energy trapped in plant wastes. The solar energy captured through photosynthesis enables the storage of energy in plant cell wall polymers (cellulose, lignin, and hemicelluloses in straw, husks, hulls, and trees). This energy remains trapped unless plants are burned. Despite the increasing use of starch-based ethanol and biodiesel, fuel produced from plant by-products has been unavailable up to now. If that energy could be released, grasses, wood, and crop residues would offer the possibility of a renewable, geographically distributed source of sugars for conversion to fuel. This process would include collection, destruction of the cell walls (pretreatment), and conversion of the sugars to biofuels. One such sugar is hemicellulose-a family of polysaccharides composed of five- and six-carbon sugars fibrils. Lignin is the glue that crosslinks these fibrils to provide strength. One challenge in the development of plant wastes as fuel has been finding enzymes that can function in the high acid conditions needed for the pretreatment of hemicellulose in order to break down lignin. Research continues; the refineries developed in this research might also be useful for manufacturing biofuels from plant wastes. ## Health and Environmental Concerns Ever since the inception of transgenic plants, people have worried about potentially harmful effects to humans and the environment. In an age when "natural" is often equated with "safe," these decidedly unnatural plants carry an air of danger. Activists have staged protests against companies producing genetically modified plants (GMOs, or genetically modified organisms) (see Figure 6.13). Such fears have the power to shake up an industry. In 2000, potato-processing plants in the Northwest stopped buying genetically modified potatoes. There was never any sign that these potatoes-engineered to be pest-resistant—were inferior or dangerous. They looked and tasted just like non-genetically modified potatoes, and farmers did not need to use gallons of chemicals to get them to grow. They were able to survive aphids and potato bugs but not the tide of public opinion (see Figure 6.14). What are some opponents of plant biotechnology saying, and what are some of the other points of view? What are the pros and cons of GMO crop production? ## Tools of the Trade ### Excision of Reporter Genes Researchers know that a gene has been transferred to a plant cell because antibiotic-resistant genes (for example, kanamycin antibiotic resistance) are usually used as "reporters" for commercial plant engineering. They allow only those transformed plant cells that can live on the antibiotic medium to be selected. The presence of antibiotic genes (and small amounts of antibiotics) in plants has caused some public concern. However, we know that it is possible to remove specific genes after transformation and selection because four scientists at Rockefeller University have developed the process. It involves the use of a promoter that can be activated to stimulate excision through naturally existing mechanisms in the plant embryo or plant organ tissue after the antibiotic selection for the transformed cells has occurred (see Chapter 3 to learn more about the specific scientific tools used in the process described above). ### Concerns about Human Health Every plant contains DNA. Whenever you munch a carrot or a bite into a slice of bread, you're eating more than a few genes. Opponents of genetic engineering have nothing against genes per se. Instead, they fear the effects of foreign genes, bits of DNA that would not naturally be found in the plant. A 1996 report in the *New England Journal of Medicine* seemed to confirm at least some of those fears. The study found that soybeans containing a gene from the Brazil nut could trigger an allergic reaction in people who were sensitive to Brazil nuts. Because of this discovery, this type of transgenic soybean never made it to market. We can look at this incident in two different ways. Opponents say that this case of the soybean clearly demonstrates the pitfalls of biotechnology. They envision many scenarios where novel proteins trigger dangerous reactions in unsuspecting customers. Supporters see it as a success story: the system detected the unusual threat before it ever reached the public. At this time, most experts agree that genetically modified foods are unlikely to cause widespread allergic reactions. According to a recent report from the American Medical Association, very few proteins have the potential to trigger allergic reactions, and most of them are already well known to scientists. The odds of an unknown allergen "sneaking" into a genetically modified food on the grocery shelf are very small. In fact, biotechnology may someday help prevent allergy-related deaths. Researchers are now working to produce peanuts that lack the proteins that can trigger violent allergic reactions. Allergies are not the only concern. Some scientists have speculated that the antibiotic-resistant genes used as markers in some transgenic plants could spread to disease-causing bacteria in humans. In theory, these bacteria would then become harder to treat. Fortunately bacteria do not regularly scavenge genes from our food. According to a recent report in the journal *Science*, there is only a "minuscule" chance that an antibiotic-resistant gene could ever pass from a plant to bacterium. Furthermore, many bacteria have already evolved antibiotic-resistant genes. If you scan the antibiotechnology literature, you'll see many more accusations. Headlines such as "Frankenfoods may cause cancer" are common. To this date, however, science has not supported any of these concerns. The National Academy of Sciences recently reported that the transgenic food crops on the market today are perfectly safe for human consumption. ### Concerns about the Environment Recall from the section on genetic pesticides that recent studies have put to rest fears that bioengineered corn could kill large numbers of monarch butterflies. However, worries about the environment have not disappeared. For one thing, genetic enhancement of crops could lead to new breeds of so-called superweeds. Just as genes for antibiotic resistance could theoretically spread from plants to bacteria, genes for pest or herbicide resistance could potentially spread to weeds. Because many crops including squash, canola, and sunflowers are close relatives to weeds, crossbreeding occasionally occurs, allowing the genes from one plant to mix with the genes of another. At this time, however, few experts predict any sort of explosion of genetically enhanced weeds. Further studies are needed to gauge the full extent of this threat and develop ways to minimize the risk. The potential ecological hazards of biotechnologically enhanced crops must be weighed against the clearly established benefits. First and foremost, biotechnology can dramatically reduce the use of chemical pesticides, as seen in Figure 6.14. One of the key environmental benefits of biotech crops is the reduction in insecticide and herbicide applications to crops. In countries where biotech crops have been planted, pesticide use on four biotech crops-soybeans, corn, cotton, and canola-has fallen by 791 million pounds per year. (8.8%). This has resulted in a 17.2% reduction in the associated environmental impact. ## You Decide: The StarLink Episode In 2000, traces of genetically modified StarLink corn turned up in taco shells sold in grocery stores. Intended for animal consumption, the corn contained the gene for herbicide resistance, which breaks down in the soil or the stomach of cattle. On the surface, this news was not shocking. Many processed foods on market shelves contain genetically altered corn or soybean products. This particular type of corn, however, had never been approved for human consumption because of lingering concerns over potential allergic reactions. The Environmental Protection Agency (EPA)-the agency that regulates the use of all pesticides-had approved StarLink only for animal feed and industrial use. The discovery of StarLink corn in the food supply triggered a massive recall of potentially "tainted" products. Soon after the recall, Aventis, the company that produced StarLink, struck a deal with the EPA and agreed to stop planting the corn. Had this "unapproved pesticide" really done any harm? The Centers for Disease Control and Prevention (CDC) took immediate steps to find out. A handful of people had complained of allergic-type reactions after eating the genetically altered corn, and the CDC investigated each case closely. A total of 28 people were found to have had symptoms consistent with an allergic reaction. However, blood tests showed that none of these people were sensitive to the Bt protein. How should this episode have been handled? Was the public adequately protected from harm? Did the government overreact? What is the best balance between regulations and commercial interests? You decide. ## Regulations Biotechnology is not a lawless frontier. As we have already seen, several different agencies regulate the production and marketing of genetically modified foods. The FDA regulates foods on the market, the USDA oversees growing practices, and the EPA controls the use of Bt proteins and other so-called pesticides. The approach of these agencies has changed over the years, especially in the case of the FDA, but they are actively involved in approving plant crops. (Chapter 12 discusses the regulation of plant biotechnology in much greater detail.) As early as 1992, at the beginning of the biotechnology revolution-the FDA announced that genetically altered food products would be regulated by the same tough standards applied to regular foods-nothing more, nothing less. Even though they were not bound by law, food companies voluntarily consulted with the FDA before marketing any product. In 2001, the agency adopted a stricter, more formal approach. Under these rules, companies must notify the FDA at least 120 days before a genetically altered food reaches the market. The manufacturer must also provide evidence that the new product is no more dangerous than the food it replaces. The determining factor for plant-based foods or products will be the attitude of consumers. The Center for Food Safety and the Grocery Manufacturers Association and Food Products Association have informed the USDA of their "strong opposition to the use of food crops to produce plant manufactured pharmaceuticals in the absence of controls and procedures that assure essentially 100% of the food supply." There are many nonfood plants and contained-growth plant systems that will satisfy this concern, and no manufacturer has violated these rules to date. Forests of genetically altered trees could pull billions of tons of carbon from the atmosphere each year and reduce global warming, according to researchers at Lawrence Berkeley National Laboratory and Oak Ridge National Laboratory. They claim that it might be possible to alter trees genetically so that they would send more carbon into their roots, keeping it out of circulation for centuries. These innovations could substantially boost the amount of carbon that vegetation naturally extracts from air. This change would require a modification of the current regulatory climate for producing genetically engineered trees in the United States and require a change in societal perceptions of the issues surrounding the use of genetically altered organisms. The potential exists, but the implementation depends on greater acceptance of genetically modified organisms in our environment. On the whole, biotechnology does not seem to be taking us to the brink of ecological disaster and may actually offer some solutions to environmental problems. Indeed, the National Academy of Sciences recently reported that biotechnologically enhanced crops pose no greater environmental threat than traditional crops.