Database Product Description
- Host Organism
- Zea mays (Maize)
- Trade Name
- Resistance to European corn borer (Ostrinia nubilalis); glyphosate herbicide tolerance.
- Trait Introduction
- Microparticle bombardment of plant cells or tissue
- Proposed Use
Production for human consumption and livestock feed.
- Product Developer
- Monsanto Company
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 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 line MON802 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 the maize line by particle acceleration (biolistic) transformation. MON802 was further engineered to express resistance to glyphosate, the active ingredient in the herbicide Roundup®, allowing for its use as a weed control option. In order to obtain field tolerance to glyphosate herbicide, two novel genes, CP4 EPSPS and goxv247, were introduced maize 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.
In plants, the enzyme 5-enolpyruvylshikimate-3-phosphate synthase (abbreviated EPSPS) plays a key role in the biochemical pathway that results in the synthesis of the aromatic amino acids phenylalanine, tyrosine, and tryptophan. This enzyme is only present in plants and microorganisms, such as bacteria and fungi, and is not present in animals and humans. In the early 1970s, it was discovered that the simple amino acid analogue, glyphosate, could selectively inhibit the activity of the EPSPS enzyme, thus shutting off aromatic amino acid synthesis. Because these amino acids are needed for protein synthesis, which is required for plant growth and maintenance, the application of glyphosate quickly results in plant death. EPSPS is not present in mammals, birds or aquatic life forms, which do not synthesize their own aromatic amino acids. For this reason, glyphosate has little toxicity to these organisms.
A gene encoding a glyphosate-tolerant form of the EPSPS enzyme was isolated from the CP4 strain of Agrobacterium tumefaciens, a common soil bacterium, and introduced into the maize genome using micro-particle bombardment. MON802 contains a third gene that codes for a modified version of the enzyme glyphosate oxidase (GOX), which accelerates the normal breakdown of glyphosate into two non-toxic products, aminomethylphosphonic acid (AMPA) and glyoxylate. AMPA is the principal breakdown product of glyphosate and is degraded by several microorganisms, while glyoxylate is commonly found in plant cells and is broken down by the glyoxylic pathway for lipid metabolism. The GOX encoding gene (goxv247 was isolated from the bacterium Ochrobactrum anthropi strain LBAA.
MON802 expressed the Cry1Ab protein at an effective dosage over the growing season, as indicated by its efficacy in controlling both first and second-generation infestations of ECB. Protein expression was found to decrease over the growing season, as evidenced by declining Cry1Ab protein concentrations in assayed leaves. MON802 maize has been field tested since 1993 in the major maize growing regions of the United States and Puerto Rico, as well as in Canada (1995, 1996), Chile, Argentina, France, Italy, South Africa, and Costa Rica. The studies demonstrated that MON802 maize retained the agronomic characteristics of the parental line. The transgenic line provided significant protection from feeding damage from ECB throughout the season, while some protection was noted from Southwestern corn borer (Diatraea grandiosella) and corn earworm (Heliothis zea). No significant differences were observed in resistance to a number of other significant insect pests or diseases compared to non-transgenic controls. It was demonstrated that the transformed maize line did not exhibit weedy characteristics, or negatively affect beneficial or nontarget organisms. MON802 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 and growth characteristics were unchanged in MON802. Gene exchange between MON802 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 MON802 maize was established based on several standard criteria. Analyses determined that MON802 grain was nutritionally equivalent to non-transgenic grain, posing no health risks to either humans or livestock. Proximate analysis (ash, crude fat, crude protein, and moisture content), and fatty acid and amino acid composition of MON802 grain revealed only minor differences from the levels reported for non-transgenic maize. These differences were within the normal range of variation for maize and were not linked to the presence of the introduced genes.
The toxicity and allergenicity potential of the Cry1Ab, CP4 EPSPS and GOX proteins expressed in MON802 was assessed by examining their physiochemical characteristics, degree of amino acid sequence homology to known protein allergens, and digestibility. An acute oral gavage feeding study was conducted in which mice were fed high doses of each of the three novel proteins, and did not exhibit any toxic effects. The Cry1Ab protein has a history of safe use, demonstrated by its use in microbial Bt spray formulations in agriculture for more than 40 years with no evidence of adverse effects. No significant amino acid sequence homologies were observed between the Cry1Ab, CP4 EPSPS or GOX proteins and known allergens and toxins. Neither Cry1Ab, CP4 EPSPS, nor GOX possess the characteristics of stability to digestion, heat stability, and glycosylation commonly associated with allergenic proteins.
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This record was last modified on Monday, March 28, 2016