Database Product Description
- Host Organism
- Gossypium hirsutum (Cotton)
- Resistance to lepidopteran insects; oxynil herbicide tolerance, including bromoxynil.
- Trait Introduction
- Agrobacterium tumefaciens-mediated plant transformation.
- Proposed Use
Production for fibre, livestock feed, and human consumption.
- Product Developer
- Calgene Inc.
Summary of Regulatory Approvals
Summary of Introduced Genetic Elements Expand
Characteristics of Gossypium hirsutum (Cotton) Expand
Donor Organism Characteristics Expand
Modification Method Expand
Characteristics of the Modification Expand
Environmental Safety Considerations Expand
Food and/or Feed Safety Considerations Expand
Cotton (Gossypium hirsutum L.) is primarily grown for its seed bolls that produce fibres used in numerous textile products. The major producers of cotton seed and lint are China, the United States, India, Pakistan, Brazil, Uzbekistan and Turkey.
About two thirds of the harvested cotton crop is seed, which is separated from the lint during ginning. The cotton seed is crushed to produce cottonseed oil, cottonseed cake (meal) and hulls. Cottonseed oil is used primarily as cooking oil, in shortening and salad dressing, and is used extensively in the preparation of snack foods such as crackers, cookies and chips. The meal and hulls are an important protein concentrate for livestock, and may also serve as bedding and fuel. Linters, or fuzz, which are not removed in ginning, are used in felts, upholstery, mattresses, twine, wicks, carpets, surgical cottons, and in industrial products such as rayon, film, shatterproof glass, plastics, sausage skins, lacquers, and cellulose explosives.
Effective weed management is critical to cotton production. The removal of weeds early in the growing season extremely important in cotton production. Young cotton seedlings grow slowly early in the season and are not very competitive. Early weed pressure has detrimental effects on final yield. Weeds can also be detrimental later in the growing season; weeds can interfere with harvesting, and can result in a reduction in lint quality due to trash or staining. Precautions such as pre-plant tillage or herbicide application are common approaches for reducing weed competition, as are multiple herbicide treatments. The broadleaf weeds are the most difficult to control because there are few herbicide options available. Many producers will use as many as four herbicides per year in an effort to control weeds.
Tobacco budworm (Heliothis virescens), pink bollworm (Pectinophora gossypiella), and cotton bollworm (Helicoverpa zea) are three of the most destructive pests in cotton. In the United States alone the combined costs of control and yield loss attributed to these pests is up to $476 million per year. In Egypt, China and Brazil, pink bollworm commonly causes cotton losses of up to 20 percent.
More insecticides are applied to conventionally grown cotton than to any other single crop. Each year cotton producers around the world use nearly $2.6 billion worth of pesticides, which include pesticides such as aldicarb, phorate, methamidophos and endosulfan. Cotton pests, such as the tobacco budworm, have developed some resistance to many of the insecticides used to control them. In regions where insecticide-resistant populations have developed budworm damage can reduce yields by 29%, despite an average of six insecticide applications each growing season.
The cotton lines 31807 and 31808 were genetically engineered to resist attack from the major lepidopteran pests of cotton and to tolerate herbicides in the oxynil family, including bromoxynil and ioxynil. Oxynil herbicides act by blocking electron flow during the light reaction of photosynthesis, inhibiting cellular respiration in dicotyledonous plants. Oxynil herbicides applied at rates recommended for effective weed control are toxic to conventional cotton varieties. These transgenic cotton lines contain the bxn gene for oxynil tolerance, and the cry1Ac gene from Bacillus thuringiensis, which codes for the insect control protein Cry1Ac, a delta-endotoxin. These genes were introduced into the cotton genome by Agrobacterium-mediated transformation.
The Cry1Ac protein produced by the transgenic cotton is almost identical to that found in nature and in commercial Bt spray formulations. Cry proteins, of which Cry1Ac is only one, act by selectively binding to specific sites localized on the lining of the midgut of susceptible insect species. Following binding, pores are formed that disrupt midgut ion flow, causing gut paralysis and eventual death due to bacterial sepsis. Cry1Ac is insecticidal only when eaten by the larvae of lepidopteran insects (moths and butterflies), and its specificity of action is directly attributable to the presence of specific binding sites in the target insects. There are no binding sites for delta-endotoxins of B. thuringiensis on the surface of mammalian intestinal cells, therefore, livestock animals and humans are not susceptible to these proteins.
The bxn gene, conferring tolerance to oxynil compounds, was isolated from the bacterium Klebsiella pneumoniae subspecies ozaenae and codes for the enzyme nitrilase, which hydrolyses ioxynil and bromoxynil into non-toxic compounds. The nitrilase enzyme in cotton lines 31807 and 31808 is a bacterial version of an enzyme that is widespread in nature, found in monocot plants such as corn, wheat and barley.
The transgenic cotton lines 31807 and 31808 were field tested in the United States. Based on data from these trials it was concluded that the transformed cotton lines 31807 and 31808 did not exhibit weedy characteristics and had no effect on non-target organisms or the general environment. The transformed lines were not expected to impact on threatened or endangered species.
Cotton plants are primarily self-pollinating, but insects, especially bumblebees and honeybees, also distribute cotton pollen. Cotton can cross-pollinate with compatible species including G. hirsutum (wild or under cultivation), G. barbadense (cultivated Pima cotton), and G. tomentosum. Overall, the probability of gene transfer to wild species in unmanaged ecosystems is low due to the relatively isolated distribution of Gossypium species, different breeding systems, and genome incompatibility. Assuming proximity, synchronicity of flowering and availability of insects, transgenic cotton lines 31087 and 31808 may freely hybridize with other G. hirsutum varieties.
Regulatory authorities in the United States have mandatory requirements for developers of Bt cotton to implement specific Insect Resistant Management (IRM) Programs. The potential for Bt-resistant insect populations to develop increases as acreages planted with transgenic Bt cotton hybrids expand. Hence, these IRM programs are designed to reduce this potential and prolong the effectiveness of plant-expressed Bt toxins, and the microbial Bt spray formulations that contain these same toxins.
Human consumption of cotton products is limited to refined cottonseed oil and cellulose from processed linters of cottonseed. Processed linters are essentially pure cellulose, and are subjected to heat and solvent treatment that would be expected to remove and destroy DNA. It is generally accepted that the refined oil does not contain protein as the refining process includes heat, solvent and alkali treatments that would remove and destroy any DNA and protein present. The refined cottonseed oil from the transgenic lines was tested for the presence of the nitrilase and Cry1Ac proteins, which were undetectable. It was concluded that there was little potential for human dietary exposure to the novel proteins expressed in these transgenic cotton lines.
Compositional comparison of cottonseed oil, cottonseed and meal from lines 31807 and 31808 was made to the same materials from commercial non-transgenic cotton. Parameters measured included proximate analysis (moisture, crude fat/oil, protein, and ash) of cottonseed meal; fibre analysis (crude fibre, acid detergent, and neutral detergent fibres) of cottonseed; fatty acid composition of refined cottonseed oil; and amino acid profiles of cottonseed meal. No significant differences between the transgenic lines and the traditionally bred lines were observed for any of these parameters. It was also determined that the transgenic cotton contained levels of gossypol and cyclopropenoid fatty acids, toxic substances naturally found in cotton, within the normal range of variation reported for conventional cotton cultivars.
Refined cottonseed oil and cellulose from linters are devoid of protein and, given that most allergens are proteins, their consumption is unlikely to result in an allergic reaction. The potential for cottonseed oil or linters from 31807 or 31808 cotton to constitute a source of allergens is therefore extremely low. The presence of the nitrilase protein in monocot food sources such as corn and barley further supported the conclusion that the nitrilase enzyme posed little risk of toxicity. It was concluded that the nitrilase and Cry1Ac proteins, and thus 31807 and 31808 cotton, possessed little or no potential for allergenicity or toxicity.
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This record was last modified on Tuesday, February 24, 2015