Database Product Description
- Host Organism
- Zea mays (Maize)
- Trade Name
- Phosphinothricin (PPT) herbicide tolerance, specifically glufosinate ammonium.
- Trait Introduction
- Chemically mediated introduction into protoplasts and regeneration.
- Proposed Use
Production for livestock feed.
- Product Developer
- Bayer CropScience (Aventis CropScience(AgrEvo))
Summary of Regulatory Approvals
Summary of Introduced Genetic Elements Expand
Characteristics of Zea mays (Maize) Expand
Donor Organism Characteristics Expand
Modification Method Expand
Characteristics of the Modification Expand
Environmental Safety Considerations Expand
Food and/or Feed Safety Considerations Expand
Maize (Zea mays L.), or corn, is grown primarily for its kernel, which is largely refined into products used in a wide range of food, medical, and industrial goods.
Only a small amount of whole maize kernel is consumed by humans. Maize oil is extracted from the germ of the maize kernel and maize is also a raw material in the manufacture of starch. A complex refining process converts the majority of this starch into sweeteners, syrups and fermentation products, including ethanol. Refined maize products, sweeteners, starch, and oil are abundant in processed foods such as breakfast cereals, dairy goods, and chewing gum.
In the United States and Canada maize is typically used as animal feed, with roughly 70% of the crop fed to livestock, although an increasing amount is being used for the production of ethanol. The entire maize plant, the kernels, and several refined products such as glutens and steep liquor, are used in animal feeds. Silage made from the whole maize plant makes up 10-12% of the annual corn acreage, and is a major ruminant feedstuff. Livestock that feed on maize include cattle, pigs, poultry, sheep, goats, fish and companion animals.
Industrial uses for maize products include recycled paper, paints, cosmetics, pharmaceuticals and car parts.
The maize line T14 was genetically engineered to express tolerance to glufosinate ammonium, the active ingredient in phosphinothricin herbicides (Basta®, Rely®, Finale®, and Liberty®). Glufosinate chemically resembles the amino acid glutamate and acts to inhibit an enzyme, called glutamine synthetase, which is involved in the synthesis of glutamine. Essentially, glufosinate acts enough like glutamate, the molecule used by glutamine synthetase to make glutamine, that it blocks the enzyme's usual activity. Glutamine synthetase is also involved in ammonia detoxification. The action of glufosinate results in reduced glutamine levels and a corresponding increase in concentrations of ammonia in plant tissues, leading to cell membrane disruption and cessation of photosynthesis resulting in plant withering and death.
Glufosinate tolerance in T14 maize is the result of introducing a gene encoding the enzyme phosphinothricin-N-acetyltransferase (PAT) isolated from the common aerobic soil actinomycete, Streptomyces viridochromogenes, the same organism from which glufosinate was originally isolated. The PAT enzyme catalyzes the acetylation of phosphinothricin, detoxifying it into an inactive compound. The PAT enzyme is not known to have any toxic properties.
Cultured protoplasts obtained from a yellow dent corn line were transformed using a chemically mediated direct DNA introduction method. Transformed cell colonies were selected for the presence of the pat gene by regeneration on medium containing glufosinate ammonium. The primary transformants, T14 and T25, were then backcrossed with parental lines of the yellow dent corn type. The resulting lines displayed field tolerance to phosphinothricin-containing herbicides, thereby permitting farmers to use this herbicide for weed control in maize cultivation.
The maize event T14 has been field tested in the major maize growing regions of the United States since 1992 and in Canada since 1993. Field reports on T14 were compared to those of their non-transgenic counterparts, and it was determined that agronomic characteristics such as yield, plant height, over-wintering capacity, flowering period, and disease susceptibility were within the normal range of expression currently displayed by commercial maize hybrids. Overall the field data reports indicated that the transformed maize lines did not exhibit weedy characteristics, or negatively affect beneficial or non-target organisms, and were not expected to impact on threatened or endangered species.
Maize does not have any closely related species growing in the wild in the continental United States and Canada. Cultivated maize can naturally cross with annual teosinte (Zea mays ssp. mexicana) when grown in close proximity, however, these wild maize relatives are native to Central America and are not naturalized in North America. Additionally, reproductive and growth characteristics were unchanged in T14. Gene exchange between the modified lines and maize relatives was determined to be negligible in managed ecosystems, with no potential for transfer to wild species in Canada and the United States.
Compositional analyses of T14 maize grain and of current commercial maize varieties were compared for a number of parameters, including moisture, crude fat, crude protein, crude fibre, ash, carbohydrates, mineral content (calcium and phosphorous), amino acid profile, phytates and oil composition. Overall protein content in the grain and whole plant was significantly higher in the transgenic lines than in the unmodified controls. It was determined that this variation arose from genetic differences unrelated to the transformation event. In all cases protein content and nutrient values were within the normal published range for maize. The use of grain from T14-derived maize lines was determined not to have a significant impact on the nutritional quality of the North American food supply.
Potential toxicity and allergenicity of the PAT protein expressed in the transgenic maize lines T14 was investigated by searching for amino acid sequence homologies with known toxins and allergens, by examining its physiochemical properties, and by acute oral toxicity testing in mice. No homologies between the deduced amino acid sequence of the PAT protein and the sequences of known toxins or allergens were detected. The PAT enzyme does not possess the stability to digestive enzymes or heat stability characteristic of toxic compounds, and was readily degraded under conditions simulating mammalian digestion. In the acute mouse toxicity study mice were fed high doses of the PAT protein, with no observable adverse effects. Based on these properties, it was concluded that the PAT protein, and thus T14 maize, possessed little or no potential for allergenicity or toxicity.
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This record was last modified on Wednesday, January 13, 2016