Database Product Description
- Host Organism
- Zea mays (Maize)
- Trade Name
- NaturGard™ KnockOut™
- Resistance to European corn borer (Ostrinia nubilalis); phosphinothricin (PPT) herbicide tolerance, specifically glufosinate ammonium.
- Trait Introduction
- Microparticle bombardment of plant cells or tissue
- Proposed Use
Production for human consumption and livestock feed.
- Product Developer
- Syngenta Seeds, Inc.
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 amont 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 European corn borer (ECB), Ostrinia nubilalis, is the most damaging insect pest of maize in the United States and Canada; losses resulting from ECB damage and control costs exceed $1 billion each year. An average of one ECB cavity per maize stalk across an entire field can reduce yield by as much as 5% when caused by first generation larvae, and 2.5% when caused by second generation larvae, with annual yield losses estimated at 5 to 10 %.
Despite consistent losses to ECB, chemical insecticides are utilized on a relatively small acreage (less than 20%). Historically, this reluctance stems from the difficulties in identifying and managing ECB in maize crops: ECB larval damage is hidden, heavy infestations are unpredictable, insecticides are costly, timing of insecticide application is difficult and multiple applications may be required to guarantee ECB control.
The transgenic maize Event 176 was genetically engineered to resist ECB by producing its own insecticide. This line was developed by introducing the cry1Ab gene, isolated from the common soil bacterium Bacillus thuringiensis (Bt), into a maize line by particle acceleration (biolistic) transformation. The cry1Ab gene produces the insect control protein Cry1Ab, a delta-endotoxin. The Cry1Ab protein produced by the Bt maize is identical to that found in nature and in commercial Bt spray formulations. Cry proteins, of which Cry1Ab 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. Cry1Ab is lethal 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 the delta-endotoxins of B. thuringiensis on the surface of mammalian intestinal cells, therefore, livestock animals and humans are not susceptible to these proteins.
Maize Event 176 expressed the Cry1Ab protein at levels effective against first generation infestations of ECB. Protein expression declined as the growing season progressed, and was less effective against later generations of ECB. Event 176 was tested in field trials in the United States beginning in 1992. Data collected from these trials demonstrated that Event 176 was not different from conventional maize lines; agronomic characteristics, including seed germination rates, yield characteristics, and disease and pest susceptibilities, were within the normal range reported for conventional maize lines. It was demonstrated that the transformed maize line did not exhibit weedy characteristics, or negatively affect beneficial or non-target organisms. Event 176 maize was 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 characteristics such as pollen production, viability and dispersal were unchanged in Event 176. Gene exchange between maize Event 176 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.
Regulatory authorities in Canada and the United States have mandatory requirements for developers of Bt maize to implement specific Insect Resistant Management (IRM) Programs. The potential for ECB populations to develop tolerance or become resistant to the Bt toxin is expected to increase as more maize acreage is planted with Bt hybrids. These IRM programs are designed to reduce the potential development of Bt-resistant insect populations, as well as prolonging the effectiveness of plant-expressed Bt toxins, and the microbial Bt spray formulations of these same toxins.
The food and livestock feed safety of maize Event 176 was established based on several standard criteria. As part of the safety assessment, the nutritional composition of grain from Event 176 was analyzed in order to determine protein, fat, total ash, crude fibre, moisture, protein, starch, and carotenoid content. Amino acid composition was established and a fatty acid profile was completed. Maize Event 176 was found to be nutritionally equivalent to conventional maize and minor differences detected were all within the normal established ranges for maize.
The wholesomeness of maize Event 176, as compared to conventional maize, was confirmed in feeding studies in which mice and bobwhite quail were fed Cry1Ab protein prepared from maize leaves. These trials also demonstrated that there were no unintended effects experienced by these organisms when fed Event 176 grain.
The toxicity and allergenicity potential of the Cry1Ab protein in Event 176 maize was demonstrated by examining its physiochemical characteristics and amino acid sequence homology with known protein allergens. Digestibility studies and an acute oral toxicity study were also conducted. In the latter study, mice were fed high doses of native Cry1Ab protein with no negative consequences, demonstrating the protein’s lack of toxicity. The Cry1Ab protein has a history of safe use, demonstrated by its use in microbial Bt spray formulations in agriculture for more than 30 years with no evidence of adverse effects. This fact, combined with the lack of amino acid sequence homology between the Cry1Ab protein and known allergens and toxins, and the rapid degradation of the Cry1Ab protein in acidic gastric fluids, was sufficient to provide with reasonable certainty a lack of toxicity and allergenic potential.
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This record was last modified on Friday, August 4, 2017