Agricultural applications of genetic engineering
Agricultural applications of genetic engineering involve the modification of plants to enhance desirable traits, such as pest resistance, improved yield, and nutritional content. This process typically begins with the introduction of specific genes into a plant's genome using vectors, such as plasmids from the bacterium Agrobacterium tumefaciens. While this method is effective for dicotyledonous plants, alternative techniques like particle bombardment, microinjection, and electroporation are employed for monocotyledons.
Genetic engineering has led to the development of crops that can produce their own pesticides or are resistant to herbicides, significantly reducing reliance on chemical treatments. Techniques have also been used to create "golden rice," enriched with beta-carotene to combat vitamin A deficiency, and iron-rich varieties to help address global anemia. However, the rise of genetically modified (GM) foods has sparked debates concerning their safety, potential health risks, and environmental impact, including concerns about antibiotic resistance and gene flow to wild plants.
Acceptance of GM foods varies widely, with resistance prevalent in regions like Europe and parts of Asia, while countries like Brazil have embraced their cultivation. As agriculture continues to evolve with genetic engineering, the potential to address global hunger and improve food security remains significant, though careful consideration of safety and ethical implications is essential.
Agricultural applications of genetic engineering
Significance: Genetic engineering is the deliberate manipulation of an organism’s DNA by introducing beneficial or eliminating specific genes in the cell. For agricultural applications, the technology enables scientists to isolate, modify, and insert genes into the same or a different crop, clone an adult plant from a single cell of a parent plant, and create genetically modified (GM) foods.
Producing Transgenic Crop Plants
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 such as 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 are used to produce membrane holes through which some DNA can randomly enter.
Reducing Damage from Pests, Predators, and Disease
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 resistant to certain herbicides.
Improving Crop Yield and Food Quality
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. According to UNICEF, an estimated 250 million children globally are lacking in vitamin A, putting them at risk for permanent blindness and other serious diseases and increasing their risk of childhood mortality. Golden rice could help alleviate the problem of vitamin A deficiency. Iron deficiency is the world’s worst nutritional disorder, causing anemia in two billion people worldwide. The scientists have inserted genes into rice to make it iron-rich.
To improve fruit quality after harvest, genetic engineers insert genes to slow the rate of senescence (aging) and slow spoilage of harvested crops. Scientists at Calgene (Davis, California) inserted a gene into tomato plants that blocks the synthesis of the enzyme polygalacturonase, responsible for tomato softening, thereby delaying rotting. Other examples of genetically engineered foods include the graisin, or giant raisin, produced by National Institute of Genetics in Japan; grapples, a genetic cross between the grape and apple developed for UNICEF to combat world hunger, with the size of an apple and texture of a grape; pluots, a cross of plums and apricots; tangelos, a mix of tangerine and grapefruit; colorful carrots from Texas researchers that increase calcium absorption; diabetes-fighting lettuce, designed by a scientist at the University of Central Florida to include the insulin gene; and lematoes, an experiment by Israeli scientists to make a tomato produce a lemon scent.
Improved tolerance to environmental stress for agricultural plants is important to biotechnology, especially for drought, saline conditions, chilling temperatures, high light intensities, and extreme heat. Genetic engineers take genes from plants that adapt naturally to harsh environments and use them to produce similar effects in crop plants.
Biotechnology has produced a marked increase in crop productivity worldwide. In 1999, about 50 percent of the soybean, 33 percent of the corn, and 35 percent of the cotton crops in the United States and 62 percent of the canola crop in Canada were planted with genetically modified seed. In 1996, genetically engineered corn and soybeans were first grown commercially on 1.7 million hectares (4.2 million acres). The land planted in these crops had swelled to 39.9 million hectares (98.8 million acres) by 2003. By 2014, data from the US Department of Agriculture Economic Research Service showed the increased adoption of genetic modification in the United States, with 93 percent of all corn-planted acres; these data also reflected adoption in 96 percent of cotton and 94 percent of soybean-planted acres.
Impact and Implications
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 affects 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 the 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 treatment. With the current problem with antibiotic resistance, this may be a credible concern. Experiments with mice indicate that a healthy immune system can overcome any resulting damage. What impact this would have on those with compromised immune systems, however, is unknown.
Another issue is whether the nutrients in these GM foods would match that of natural foods. An additional problem is called crop-to-weed gene flow, whereby the weeds close by the engineered crops adopt undesirable characteristics such as herbicide resistance. As with humans, antibiotic resistance passed through transgenic farming can produce a secondary complication for the environment. These diverse concerns will remain points of continued study as scientists weigh the value of GM food products and society chooses to accept them.
Resistance to GM foods is widespread in Europe and parts of Asia, with a number of environmental groups strongly opposing all GM crops. Some call them “frankenfoods.” In 2001, Japan initiated testing of all GM foods. Although some Brazilian states had previously banned GM foods, by late 2013, Brazil had embraced GM production, with as much as 85 percent of its soybeans being GM and government researchers developing a GM strain of beans. Meanwhile, the Mexican government extended its 1998 ban on GM corn but has allowed GM soybean and cotton production. The United States has several departments that deal with the issue of GM foods: the Environmental Protection Agency (EPA) assesses for environmental safety, while the FDA evaluates whether the food is safe to eat. The US Department of Agriculture (USDA) investigates whether the GM plant is safe to grow in the United States.
Human and environmental safety will continue to be a concern in the successful development and distribution of GM foods. Some appear to be safe, holding great promise to address the world’s hunger and nutrition issues. They make it possible to breed varieties of desirable crop plants with a wider range of tolerance for different climatic and soil conditions, offering hope for the promotion of global agriculture to feed poorer nations. Genetic engineering can be an indispensable component of modern scientific advancement and social development for every nation, if handled wisely without exposing living organisms to harmful microorganisms and releasing toxic chemicals in the process.
Key terms
cloning : regeneration of a full-grown adult group of organisms from some form of asexual reproduction—for example, from protoplastsexogenous gene : a gene produced or originating from outside an organismgenome : the collection of all the DNA in an organismplasmid : a small, circular DNA molecule that occurs naturally in some bacteria and yeastsprotoplasts : plant cells whose cell walls have been removed by enzymatic digestionrecombinant DNA : a molecule of DNA formed by the joining of DNA segments from different sourcestransgenic crop plant : a crop plant that contains a gene or genes that have been artificially inserted into its genomevector : a carrier organism, or a DNA molecule used to transmit genes in a transformation procedure
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