Genetic engineering: Agricultural applications
Producing Transgenic Crop Plants (Genetics & Inherited Conditions)
To produce a transgenic crop, a desirable gene from another organism, of the same or a different species, must first be spliced into a vector such as a virus or a plasmid. In some cases additional modification of the gene may be attempted in the laboratory. A common vector used for producing transgenic plants is the “Ti” plasmid, or tumor-inducing plasmid, found in the cells of the bacterium called Agrobacterium tumefaciens. A. tumefaciens infection causes galls or tumorlike growths to develop on the tips of the plants. Botanists use the infection process to introduce exogenous genes of interest into host plant cells to generate entire crop plants that express the novel gene.
Unfortunately, A. tumefaciens can infect only dicotyledons such as potatoes, apples, pears, roses, tobacco, and soybeans. Monocotyledons like rice, wheat, corn, barley, and oats cannot be infected with the bacterium. Three primary methods are used to overcome this problem: particle bombardment, microinjection, and electroporation. Particle bombardment is a process in which microscopic DNA-coated pellets are shot through the cell wall using a gene gun. Microinjection involves the direct injection of DNA material into a host cell using a finely drawn micropipette needle. In electroporation, the recipient plant cell walls are removed with hydrolyzing enzymes to make protoplasts, and a few pulses of electricity...
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Reducing Damage from Pests, Predators, and Disease (Genetics & Inherited Conditions)
Geneticists have identified many genes for resistance to insect predation and damage caused by viral, bacterial, and fungal diseases in agricultural plants. For instance, seeds of common beans produce a protein that blocks the digestion of starch by two insect pests, cowpea weevil and Azuki bean weevil. The gene for this protein has now been transferred to the garden pea to protect stored pea seeds from pest infestation.
Bacillus thuringiensis (Bt), a common soil bacterium, produces an endotoxin called the Bt toxin. The Bt toxin, considered an environmentally safe insecticide, is toxic to certain caterpillars, including the tobacco hornworm and gypsy moth. An indirect approach to pest management bypasses the problem of plant transformation. This method inserts the Bt gene into the genome of a bacterium that colonizes the leaf, synthesizes, and secretes the pesticide on the leaf surface. Transgenic corn and cotton are modified with the Bt gene, enabling the plants to manufacture their own pesticide, which is nontoxic to humans.
Glyphosate, the most widely used nonselective herbicide, and other broad-spectrum herbicides are toxic to crop plants, as well as the weeds they are intended to kill. A major thrust is to identify and transfer herbicide resistance genes into crop plants. Cotton plants have been genetically engineered to be...
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Improving Crop Yield and Food Quality (Genetics & Inherited Conditions)
Genetic engineering is used to modify crops, to improve the quality of food taste, fatty acid profile, protein content, sugar composition, and resistance to spoilage. New, useful, or attractive horticultural varieties are also produced, by transforming plants with new or altered genes. For example, plants have been engineered that have additional genes for enzymes that produce anthocyanins, which has resulted in flowers with unusual colors and patterns.
Cereals, the staple food and major source of protein for the earth’s population, contain 10 percent protein in the dry weight. Grains lack one or more essential amino acids, producing incomplete nutrition. Efforts to engineer missing amino acids into cereal protein and to insert genes for higher yields may be an answer. The development of a high-yielding dwarf rice plant dramatically helped the nutritional status of millions of people in Southeast Asia, so much so that it has been called the “miracle rice.”
Researchers based at Zurich’s Swiss Federal Institute of Technology genetically engineered a more nutritious type of rice by inserting three genes into rice to make the plant produce beta-carotene, provitamin A. The color of the rice from the vitamin gives it the name “golden rice.” Mammals, including humans, use beta-carotene from their food to produce vitamin A, necessary for good eyesight. In 2003 some 124 million children...
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Impact and Implications (Genetics & Inherited Conditions)
The various applications of genetic engineering to agriculture make it possible to alter genes and modify crops for the benefit of humankind, in addition to industrial and medical applications. This impacts every aspect of daily living and calls for ideas to be tapped from all sectors of our communities. This modern innovative trend has become a major thrust in agriculture by production of genetically modified (GM) foods that are sometimes more nutritious and better preserved but raises concerns because of potential dangers of microbial infections and chemical hazards.
Many nonscientists and some scientists are leery of GM foods, thinking that too little is understood about the environmental effects of growing GM plants and the potential health dangers of eating GM foods. An article in Lancet details one study of genetically engineered potatoes and the differences in the intestines of the rats in the treatment population from those in the control group, demonstrating the unknown impact of these GM foods. Other concerns include threats to human health such as increased incidence of food allergies to GM food, although there is currently no clear evidence to support this. Another concern is the transfer of antibiotic resistance; when a human eats transgenic food, pathogenic bacteria within the human may come in contact with the antibiotic and through horizontal transfer of DNA develop resistance to antibiotic...
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Further Reading (Genetics & Inherited Conditions)
Borlaug, Norman E. “Ending World Hunger: The Promise of Biotechnology and the Threat of Antiscience Zealotry.” Plant Physiology 124 (2000): 487-490. The father of the Green Revolution and a Nobel Peace Prize winner expresses support for GMOs.
Gressel, Jonathan. Genetic Glass Ceilings: Transgenics for Crop Biodiversity. Baltimore: Johns Hopkins University Press, 2008. Author discusses agrobiodiversity and challenges the idea that the four main crops grown throughout the world (wheat, maize, soybean, and rice) limit population growth options.
Potrykus, Ingo. “Golden Rice and Beyond.” Plant Physiology 125 (2001): 1157-1161. The originator of the wonder rice presents scientific, ethical, intellectual, and social challenges of developing and using the GMOs.
Pua, E. C., and M. R. Davey, eds. Transgenic Crops IV. Vol. 4 in Biotechnology in Agriculture and Forestry. New York: Springer, 2007. Extensive resource on topics such as crops and genomics, boosting shelf life, and plant nutrition. Other sections include information on cereals, vegetables, root crops, and spices.
Rost, Thomas L., et al. Plant Biology. New York: Wadsworth, 1998. Vital botanical information on all aspects of plant biology plus genetics. Excellent photographs and illustrations, summaries, questions, further readings, glossary, and index.
Simpson, Beryl Brintnall, and Molly...
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Web Sites of Interest (Genetics & Inherited Conditions)
Agricultural Biotechnology, Pew Charitable Trusts. http://www.pewtrusts.org/our_work_detail.aspx?id=442. Describes the Pew Initiative on Food and Biotechnology, an honest, credible project ended in 2007. Provides resources and links to persons with differing views.
Seedquest News Section: USDA/ERS Report: Adoption of Genetically Engineered Crops in the U.S.. http://www.seedquest.com/News/releases/2009/july/26734.htm. Graphically details and updates the increased rates of adoption of genetically engineered Ht corn, Ht cotton, and Ht soybeans as well as Bt cotton and Bt corn.
Transgenic Crops: An Introduction and Resource Guide. http://cls.casa.colostate.edu/TransgenicCrops/index.html. Developed at the Colorado State University with a three-year grant, this online resource offered resources for students, teachers, nutritionists, journalists, and agents at agricultural extension centers through December, 2004. The basic information is still educational today.
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