Genetically modified (GM) or transgenic crops (sometimes also called genetically engineered—or GE—crops) contain one or more genes that have been artificially inserted instead of received through pollination (fertilization by the transfer of pollen from an anther to a stigma of a plant). The inserted gene sequence, termed the transgene, may be introduced to produce very different results—either to overexpress or silence (direct a gene not to synthesize a specific protein) an existing plant gene, and it may come from another unrelated plant or from a completely different species. Transgenics is the science of inserting a foreign gene into an organism's genome. The ultimate product of this technology is a "transgenic organism." Figure 9.1 shows a worker at a Monsanto lab collecting pollen samples from genetically modified corn.
For example, the transgenic corn that produces its own insecticide contains a gene from a bacterium, and Macintosh apples with a gene from a moth that encodes an antimicrobial protein are resistant to fire blight, a bacterial infection. (Figure 9.2 shows genetically modified corn, which is visibly indistinguishable from non-GM corn.) Although all crops have been genetically modified from their original wild state by domestication, selection, and controlled breeding over long periods of time, the terms "transgenic crops" and "GM crops" usually refer to plants with transgenes (inserted gene sequences).
Introducing genes into a crop plant aims to make it as useful and productive as possible by acting to protect the crop, improve the harvest, or enable the plant to perform a new function or acquire a new trait. Specific objectives of genetically modifying a plant include increasing its yield, improving its quality, or enhancing its resistance to pests or disease, as well as its tolerance for heat, cold, or drought. Some of the GM traits that have been introduced into food crops are enhanced flavor, slowed ripening, reduced reliance on fertilizer, self-generating insecticide, and added nutrients. Examples of transgenic food crops include frost-resistant strawberries and tomatoes; slow-ripening bananas, melons, and pineapples; and insect-resistant corn. Figure 9.3 compares spoilage of a conventionally bred cantaloupe after five days and a transgenic melon after
A worker at a Monsanto lab collects pollen samples from genetically modified corn.© Jim Richardson/Corbis.
fifteen days that was still usable because it had been modified to remain edible for a longer period.
Transgenic technology enables plant breeders to bring together in one plant useful genes from a wide range of living sources, not just from within the crop species or from closely related plants. It provides reliable means for identifying and isolating genes that control specific characteristics in one kind of organism and enables researchers to move copies of these genes into another organism that will then develop the chosen characteristics. This technology gives plant breeders the ability to generate more useful and productive crop varieties containing new combinations of genes and it significantly expands the range of trait manipulation and enhancements well beyond the limitations of traditional cross-pollination and selection techniques.
Although genetic modification of plants generates the same types of changes produced by conventional agricultural techniques, because it precisely alters a single gene, the results are often more rapid and more complete. Traditional breeding techniques may require an entire generation or more to introduce or remove a single gene, and using conventional methods for breeding a polygenic trait into crops with multiyear generations could take several decades.
Creating Transgenic Crops
The first step in creating a transgenic plant is locating genes with the traits that growers, marketers, and consumers consider important. These are usually genes that increase productivity and yield, and improve resistance to environmental stresses such as frost, heat, salt, and insects. Identifying the gene associated with a specific trait is necessary but not sufficient; researchers must determine how the gene is regulated, its other influences on the plant, and its interactions with other genes to express or silence various traits. Researchers must then isolate and clone the gene in order to have sufficient quantities to modify. Establishing the genomic sequence, termed "plant genomics," and the functions of genes of the most important crops is a priority of public- and private-sector plant genomic research projects.
Currently, most genes introduced into plants come from bacteria; however, increasing understanding of plant genomics is anticipated to permit greater use of
Genetically modified corn
SOURCE: "Corn," in "Global GM Standards," Environmental Health Perspectives, vol. 111, no. 14, U.S. Public Health Service, U.S. Department of Health and Human Services, National Institutes of Health, National Institute of Environmental Health Sciences (NIEHS) November 2003, http://ehp.niehs.nih.gov/%20docs/2003/111-14/forum.html (accessed March 8, 2005)
plant-derived genes to genetically engineer crops. In 2000 the first entire plant genome Arabadopsis thaliana was sequenced, which provided researchers with new insight into the genes that control specific traits in many other agricultural plants. There are several approaches to introducing genes into plant cells: vector- or carrier-mediated transformation, particle-mediated transformation, and direct deoxyribonucleic acid (DNA) absorption.
Vector-mediated transformation involves infecting plant cells with a virus or bacterium that during the process of infection inserts foreign DNA into the plant cell. The most convenient is through the soil bacterium Agrobacterium tumefaciens, which infects tomatoes, potatoes, cotton, and soybeans. This bacterium attacks cells by inserting its own DNA. When genes are added to the bacterium, they are transferred to the plant cell along with the other DNA.
Particle-mediated transformation involves gene transfer using a special particle tool known as a gene gun, which shoots tiny metal particles that contain DNA into the cell.
To perform direct DNA insertion or "electroporation," cells are immersed in the DNA and electrically shocked to stimulate DNA uptake. Figure 9.4 shows an electroporation machine that administers the electric shocks to cells to open their walls. The cell wall then opens for less than a second, allowing DNA to seep into the cell. (See Figure 9.5.) Following gene insertion, the cell incorporates the foreign DNA into its own chromosomes and undergoes normal cell division. The new cells ultimately form the organs and tissues of the "regenerated" plant. To ensure the systematic sequence of these steps, other genes may be added along with the gene associated with the desired trait. These helper genes are called "promoters." They encourage growth of cells that have integrated the inserted DNA, provide resistance to stresses (such as toxins present in the medium used to grow the cells), and may help regulate the functions of the gene linked to the desired trait.
To be certain that the new genes are in the organism, marker genes are sometimes inserted along with the gene for the desired trait. One common marker gene confers resistance to the antibiotic kanamycin. When this gene is used as a marker, investigators are able to confirm that the transfer was successful when the organism resists the antibiotic. The ultimate success of gene insertion is measured by whether the inserted gene functions properly by expressing, amplifying, or silencing the desired trait.
Are GM Crops Helpful or Harmful?
According to the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), an international nonprofit, nonpartisan organization for science-based agricultural development, genetic modification of crops has proven to be the most rapidly adopted technology in the world. ICRISAT estimates that as of 2000 about 70% of crops in the United States and 10% of Canadian crops were transgenic.
ICRISAT contends that transgenic crops benefit developing countries by enabling greater use of crop area, increasing the variety of crops that may be grown, affording better protection of crops from disease and pests, and improving harvest yields to deliver more food and nutrition to people in need. ICRISAT also cites environmental benefits of transgenic organisms. These include a 30% to 40% reduction in the use of herbicides and as much as an 80% reduction in the use of insecticides, as well as a reduction in environmental pollution and harmful emissions resulting from production of chemical pesticides.
ICRISAT also commends the use of transgenic organisms, specifically transgenic microbes (microorganisms) for purposes of bioremediation (environmental cleanup). Researchers have harnessed genes that code for proteins that naturally degrade toxic wastes such as chlorinated pesticides, naphthalene, toluene, and some hydrocarbons. Efforts are underway to combine genes from several microbes to create a single, multipurpose
A normal melon and a transgenic melon after 15 days. Phototake. Reproduced by permission.
supermicrobe that is capable of effectively combating several contaminants.
Opposition to GM crops takes several forms. Bioethicists who contend that freedom of choice is a central tenet of ethical science oppose what they deem to be interference with other forms of life. Environmentalists argue that transgenic technology poses the risk of altering delicately balanced ecosystems—biological communities and their environments—and causing unintended harm to other organisms. They are concerned that transgenic crops will replace traditional crop varieties, especially in developing countries, causing loss of biological diversity.
One controversial example is the relatively recent use of genetically engineered forest trees to change the trees' reproductive cycles, growth rates, and chemical composition so they can resist disease and absorb toxins such as mercury from soil and convert it into a less toxic form that is safe for release into the air. The aptly named "toxic avenger trees" remove heavy metals from contaminated soils in places where other approaches to environmental cleanup are costly and labor intensive. Environmentalists are concerned, however, about the use of GM trees because they are not convinced that relocating heavy metals from the soil to the air is worth the risk of the altered genes migrating via the tree pollen to natural populations, potentially damaging existing ecosystems (Hillary Resner, "Turning Genetically Engineered Trees into Toxic Avengers," New York Times, August 3, 2004).
Pests may develop resistance to transgenics in much the same way certain bacteria have become resistant to the antibiotics that once effectively eradicated them. Critics also decry the infiltration of transgenic crops beyond their intended areas and fear inadvertent gene transfer to species not targeted for transgenics. In 2001 transgenic corn was found in a remote mountain region of Mexico and transgenic cotton was discovered in India (Rex Dalton, "Transgenic Corn Found Growing in Mexico," Nature, vol. 413, no. 6,854, September 27, 2001; K. S. Jayaraman, "Illicit GM Cotton Sparks Corporate Fury," Nature, vol. 413, no. 6,856, October 11, 2001). One way unintended gene exchange between plants may occur is through pollen. Recommendations for
SOURCE: "Electroporation Machine," in "Step 3: Transformation," How Sequencing is Done, U.S. Department of Energy, Joint Genome Institute, Office of Science, September 2004, http://www.jgi.doe.gov/education/how/how_3.html (accessed March 23, 2005)
Cell incorporating DNA in a process known as transformation
SOURCE: "Transformation," in "Step 3: Transformation," in How Sequencing is Done, U.S. Department of Energy, Joint Genome Institute, Office of Science, September 2004, http://www.jgi.doe.gov/education/how/how_3.html (accessed March 23, 2005)
preventing unintended gene exchange include creation of transgenic plants that do not produce pollen or of pollen that does not contain introduced genes and establishment of buffer zones around fields of transgenic crops.
Transgenic crops are big business, and their value increased twenty-fold during the late 1990s. ICRISAT estimates that the commercial value of GM crops will be $8 billion in 2005 and $25 billion by 2010. Opponents fear consequences such as economic concentration—the potential for companies that grow transgenic crops to drive out smaller farmers and create monopolies. In 2003 the techniques to genetically modify seeds, as well as the seeds themselves, were held by a few multinational corporations. Related issues are patent infringement and intellectual property rights for transgenic crops and absence of regulatory oversight. Patents may increase the price of seeds and effectively exclude small farmers from growing their crops.
Health risks also concern those who object to widespread acceptance of transgenic crops. They call for the labeling of GM food to alert consumers that they are purchasing foods that contain GM organisms. As of 2005 more than half of all processed foods sold in the United States contained GM organisms, and there was no requirement that these foods be identified as transgenic or GM. Opponents cite safety issues such as possible allergies to transgenic foods and products because some transgenes may pose health risks when consumed. For example, a plan to insert a Brazil nut protein gene into soybeans was halted when early tests indicated that people allergic to nuts suffered reactions when they consumed the modified soy products. Critics also fear that there will be unforeseen and potentially harmful long-term adverse health consequences resulting from consumption of foods containing foreign genes.
ICRISAT expresses its vision as "science with a human face" and aims to use science and technology to combat hunger and poverty by engaging in participatory research combining indigenous knowledge, conventional research methods, and cutting-edge technology. The organization's current focus is on three cereals—sorghum; pearl millet, the staple food in the driest parts of the semiarid tropics; and finger millet, a cereal consumed in Africa and the Himalayan region—as well as three legumes—chickpeas, a traditional protein source for people in Asia and northern Africa; pigeonpeas; and peanuts, also known as groundnuts.
One of the most controversial developments in agricultural bioengineering is called "terminator technology," which is designed to genetically switch off a plant's ability to germinate a second time. Traditionally, farmers save seeds for the next harvest; however, the use of terminator technology effectively prevents this practice, forcing them to purchase a fresh supply of seeds each year.
The advocates of terminator technology are generally corporations and the organizations that represent them.
They contend that the practice protects corporations from corrupt farmers. Controlling seed germination helps prevent growers from pirating the corporations' licensed or patented technology. If crops remained fertile, there is a chance that farmers could use any saved transgenic seed from a previous season. This would result in reduced profits for the companies that own the patents.
Opponents of the terminator technology believe it threatens the livelihood of farmers in developing countries such as India where many poorer farmers have been unable to compete, and some have been forced out of business. Opponents considered it a victory when Monsanto, a major investor in this technology, decided not to market terminator technology. In addition to Monsanto, terminator patents are held by Delta & Pine Land, the U.S. Department of Agriculture, Syngenta, DuPont, and BASF, as well as the universities Purdue, Iowa State, and Cornell. Syngenta owns more terminator patents than any other company—eight patents and one patent application, but the company has stated publicly that it will not commercialize the trait.
Still, even without terminator technology, under patent laws in Canada, the United States, and many other industrialized nations, it is illegal for farmers to reuse patented seed, or to grow Monsanto's GM seed without signing a licensing agreement. This has the same effect on poor farmers as terminator technology; it renders them unable to compete. In a widely publicized case, a Canadian farmer was found guilty of growing patented seeds, even though he did it inadvertently. Pollen from the patented canola seeds at a nearby farm had pollinated his plants, and he was ordered to pay Monsanto for licensing and profit from the seeds.
A January 2005 investigative report released by the Center for Food Safety (CFS), a nonprofit public interest and environmental advocacy organization, reviewed Monsanto's legal actions against American farmers. The report found that Monsanto engaged in investigations of farmers, out-of-court settlements, and litigation against farmers allegedly in breach of contract or engaged in patent infringement. The report documented ninety Monsanto lawsuits in twenty-five states that involve 147 farmers and thirty-nine small businesses or farm companies. Monsanto has allocated an annual budget of $10 million and seventy-five employees exclusively devoted to investigating and taking action against farmers.
By 2005 the largest judgment in favor of Monsanto as a result of these lawsuits was more than $3 million, and the total recorded judgments granted to Monsanto was more than $15 million. Farmers have paid a mean of $412,259.54 for cases with recorded judgments. Some farmers are even forced to pay Monsanto's costs while they are under investigation.
In a January 13, 2005, press release, Andrew Kimbrell, executive director of CFS, asserted that "these lawsuits and settlements are nothing less than corporate extortion of American farmers. Monsanto is polluting American farms with its genetically engineered crops, not properly informing farmers about these altered seeds, and then profiting from its own irresponsibility and negligence by suing innocent farmers. We are committed to stopping this corporate persecution of our farmers in its tracks" ("Monsanto Assault on U.S. Farmers Detailed in New Report," http://www.centerforfoodsafety.org:80/press_release1.13.05.cfm).
In 2004 the biotechnology industry introduced what it terms "exorcist technology" to some genetically engineered (GE) crops. This new technology introduces chemical "inducers" that shed their foreign DNA before they are harvested. The industry sees this technology as an effective way to counter anti-GE critics since the harvested crops will not contain foreign DNA. But detractors assert that the intent of exorcist technology is to shift the responsibility from the biotechnology industry to farmers and society. If gene flow poses a problem, farmers will have to use chemical inducers to remove the offensive transgenes.