GM Crop Database

Database Product Description

MON809
Host Organism
Zea mays L. (Maize)
Trait
Resistance to European corn borer (Ostrinia nubilalis); glyphosate herbicide tolerance.
Trait Introduction
Microparticle bombardment of plant cells or tissue
Proposed Use

Production of Z. mays for human consumption (wet mill or dry mill or seed oil), and meal and silage for livestock feed. These materials will not be grown outside the normal production area for corn.

Product Developer
Pioneer Hi-Bred International Inc.

Summary of Regulatory Approvals

Country Food Feed Environment Notes
Canada 1996 1996 1996
Japan 1998 1997
United States 1996 1996 1996

Introduction Expand

Maize line MON809 was developed through a specific genetic modification to be resistant to attack by European corn borer (ECB; Ostrinia nubilalis), a major insect pest of maize in agriculture. The novel variety produced the insecticidal protein, Cry1Ab, derived from Bacillus thuringiensis subsp. kurstaki (B.t.k.) HD-1 strain. Delta-endotoxins, such as the Cry1Ab protein expressed in MON809, act by selectively binding to specific sites localized on the brush border midgut epithelium of susceptible insect species. Following binding, cation-specific pores are formed that disrupt midgut ion flow and thereby cause paralysis and death. Cry1Ab is insecticidal only to lepidopteran insects, 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.

Summary of Introduced Genetic Elements Expand

Code Name Type Promoter, other Terminator Copies Form
cry1Ab Cry1Ab delta-endotoxin (Btk HD-1) IR enhanced CaMV 35S A. tumefaciens nopaline synthase (nos) 3'-untranslated region 1 Truncated, modified; second partial copy present
CP4 epsps 5-enolpyruvyl shikimate-3-phosphate synthase SM enhanced CaMV 35S chloroplast transit peptide from A. thaliana EPSPS gene (CTP2) 2
goxv247 glyphosate oxidoreductase HT chloroplast transit peptide from A. thaliana SSU1A gene (CTP1) partial copy, no expression detected

Characteristics of Zea mays L. (Maize) Expand

Center of Origin Reproduction Toxins Allergenicity

Mesoamerican region, now Mexico and Central America

Cross-pollination via wind-borne pollen is limited, pollen viability is about 30 minutes. Hybridization reported with teosinte species and rarely with members of the genus Tripsacum.

No endogenous toxins or significant levels of antinutritional factors.

Although some reported cases of maize allergy, protein(s) responsible have not been identified.

Donor Organism Characteristics Expand

Latin Name Gene Pathogenicity
Bacillus thuringiensis subsp. kurstaki cry1Ab-Ac

While target insects are susceptible to oral doses of Bt proteins, no evidence of toxic effects in laboratory mammals or birds given up to 10 µg protein/g body weight.

Agrobacterium tumefaciens strain CP4 CP4 epsps

A. tumefaciens is a common soil bacterium that is responsible for causing crown gall disease in susceptible plants. There have been no reports of adverse affects on humans or animals.

Modification Method Expand

Maize line MON809 was produced by biolistic transformation of embryogenic maize cells with a mixture of DNA from two plasmids, PV-ZMBK07 and PV-ZMGT10. Plasmid PV-ZMBK07 contained the synthetic cr1Ab gene regulated by the enhanced duplicated cauliflower mosaic virus 35S promoter (CaMV E35S) and the maize hsp70 heat shock protein intron. The polyadenylation signal was from the Agrobacterium tumefaciens nopaline synthase (nos) gene. Plasmid PV-ZMBK07 also contained sequences from lacZ operon (a partial E. coli lacI coding sequence, the promoter plac and a partial coding sequence for beta-galactosidase from pUC119), ori-pUC (replication origin for pUC plasmids), and the neo gene, which encodes neomycin phosphotransferase II (NPT II) that imparts resistance to the antibiotic kanamycin. The second plasmid, PV-AMGT10, contained genes encoding the CP4 EPSPS enzyme from the common soil bacterium, A. tumefaciens sp. CP4, and glyphosate oxidoreductase (goxv247) from Ochrobactrum anthropi. The expression of these genes was used as a selectable marker to identify transformed plants on medium containing glyphosate but was not sufficient to provide field level tolerance to glyphosate containing herbicides. Constitutive expression of these genes in plant cells was under the control of the CaMV E35S promoter, the hsp70 intron, and nos 3' terminator. Post-translational targeting of the CP4 EPSPS and glyphosate oxidoreductase enzymes to the chloroplast was accomplished by fusion of the 5'-terminal coding sequences with the chloroplast transit peptide DNA sequences from the Arabidopsis thaliana EPSPS gene (CTP2) and from A. thaliana SSU1A gene (CTP1), respectively. Plasmid PV-ZMGT10 also contained sequences from the lacZ operon, ori-pUC and the neo gene. The neo gene on both plasmids was included as a selectable marker to identify bacteria transformed with recombinant plasmid DNAs. Expression of the neo gene was regulated by a bacterial promoter and therefore is not functional in plants.

Characteristics of the Modification Expand

The Introduced DNA

Southern blot analysis of MON809 genomic DNA indicated one integrated DNA segment, of approximately 23Kb DNA, which included a complete and a partial copy of the cry1Ab gene, two complete copies of the CP4 EPSPS encoding gene, a partial gox gene and the NPT II encoding antibiotic resistance marker gene. Additional Southern blot analyses were performed to demonstrate that additional plasmid backbone DNA sequences from PV-ZMBK07 were not integrated into the host genome.

Genetic Stability of the Introduced Trait

Segregation analysis over five generations of crossing indicated that the cry1Ab gene was stably integrated and segregated according to Mendelian rules of inheritance.

Expressed Material

Western blot analysis of protein extracts from MON809 demonstrated the presence of an immunoreactive protein of the predicted size. Lower molecular weight species corresponding to the predicted size of the truncated cry1Ab gene were not detected, indicating that this partial gene sequence is not expressed. The expression of Cry1Ab protein was evaluated using enzyme linked immunosorbent assay (ELISA) of tissue samples obtained from plants grown at 6 locations. The average levels of expressed Cry1Ab protein were: 1.63 ± 0.75 µg/g fresh weight (fwt) in leaves, 0.55 ± 0.23 µg/g fwt in grain and 1.23 ± 0.5 µg/g fwt in the whole plant. Cry1Ab protein was not detected in pollen and the levels expressed in leaves declined over the growing season. Similarly, CP4 EPSPS gene activity, used as a selectable marker conferring tolerance to glyphosate, was quantified by testing for EPSPS protein levels and averaged results were as follows: 21.68 µg/g fwt in leaves, 9.41 µg/g fwt in grain and 1.6 µg/g fwt in the whole plant. Data were provided showing that the level of expression of CP4 EPSPS was too low to confer significant glyphosate resistance in the field. Expression of the second gyphosate tolerance gene, gox, which encodes the enzyme glyphosate oxidase, could not be detected by Western blot analysis. The Cry1Ab protein was shown to degrade readily in the environment. The plant expressed protein had DT50 and DT90 values (time to degrade to 50% and 90 % of the original bioactivity) of 2 and 15 days respectively.

Environmental Safety Considerations Expand

Field Testing

MON809 maize was field tested under confined conditions in Canada from 1994-1996. Field reports on MON809 and corn hybrids derived from MON809 determined that early stand establishment, vegetative vigour, time to maturity and seed production were within the normal range of expression of these traits in commercial corn hybrids. Hybrids derived from MON809 produced similar yields in the absence of ECB, but under heavy infestations of ECB, MON809 hybrids out-yielded their non-transgenic counterparts by 10-15%. Hybrids derived from MON809 were not tolerant to the concentrations of glyphosate herbicide that are typically used for weed control. No significant differences were observed in resistance to a number of other significant insect pests or diseases compared to non-transgenic controls. Overall the field data reports and data on agronomic traits showed that MON809 lines have no potential to pose a plant pest risk.

Outcrossing

Since pollen production and viability were unchanged by the genetic modification resulting in maize line MON809, pollen dispersal by wind and outcrossing frequency should be no different than for other maize varieties. Gene exchange between MON809 and other cultivated maize varieties will be similar to that which occurs naturally between cultivated maize varieties at the present time. In Canada and the United States, where there are few plant species closely-related to maize in the wild, the risk of gene flow to other species is remote. Cultivated maize, Zea mays L. subsp. mays, is sexually compatible with other members of the genus Zea, and to a much lesser degree with members of the genus Tripsacum.

Weediness Potential

No competitive advantage was conferred to MON809, other than that conferred by resistance to ECB, which will not, in itself, render maize weedy or invasive of natural habitats since none of the reproductive or growth characteristics were modified. Cultivated maize is unlikely to establish in non-cropped habitats and there have been no reports of maize surviving as a weed. In agriculture, maize volunteers are not uncommon but are easily controlled by mechanical means or by using herbicides. Zea mays is not invasive and is a weak competitor with very limited seed dispersal.

Secondary and Non-Target Adverse Effects

MON809 maize and the Cry1Ab protein, in particular, should not have a significant potential to harm organisms beneficial to agricultural ecosystems. The history of use and literature suggest that the bacterial Bt protein is not toxic to humans, other vertebrates, and beneficial insects. Most insecticidal protein toxins from B. thuringiensis subspecies kurstaki, including Cry1Ab, have been shown to be specifically toxic to Lepidopteran larvae on ingestion and appear non-toxic to other species of insects, either directly or through secondary ingestion (predation). Laboratory studies of honeybee larvae and adults, predaceous insects (green lacewing larvae, ladybird beetles), and parasitic hymenoptera exposed to the Cry1Ab protein recorded no discernible effects at approximately 10 times the usual LC50 dose for a target insect. Field examination of beneficial arthropods (the Anthocorid Orius insidiosus and spiders) in genetically modified MON809 maize, concluded that any potential impact on non-target arthropods would be less than that from the use of conventional insecticides. Results from feeding studies of young quail fed with modified maize meal in their diet showed no adverse effects. Studies were conducted to evaluate the impact of residual MON809 maize on soil organisms and soil function. It was shown that the Bt endotoxin may become adsorbed to some soil fractions and that degradation was by microbial action. However, since very little of the crop material remains after harvest for incorporation it was concluded based on evidence available that the risks to organisms and soil function were very low. In summary, it was determined that genetically modified maize MON809 did not present an increased risk to, or impact on interacting organisms, including humans, with the exception of specific lepidopteran insect species. Furthermore, MON809 will not impact on threatened or endangered lepidopteran species, as none are listed which feed on maize plants in Canada or the United States. In addition, these organisms are not expected to be affected by the expressed CP4 EPSPS.

Impact on Biodiversity

MON809 has no novel phenotypic characteristics that would extend its use beyond the current geographic range of maize production. Since the risk of outcrossing with wild relatives in Canada and the United States is remote, it was determined that the risk of transferring genetic traits from MON809 maize to species in unmanaged environments was insignificant.

Other Considerations

In order to prolong the effectiveness of plant-expressed Bt toxins, and the microbial spray formulations of these same toxins, regulatory authorities in Canada and U.S. have required developers to implement specific Insect Resistant Management (IRM) Programs. These programs are mandatory for all transgenic Bt-expressing plants, including MON809 maize, and require that growers plant a certain percentage of their acreage to non-transgenic varieties in order to reduce the potential for selecting Bt-resistant insect populations. Details on the specific design and requirements of individual IRM programs are published by the relevant regulatory authority. MON809 maize plants are not likely to eliminate the use of chemical insecticides, which are traditionally applied to about 25 to 35% of the total planted maize acreage. MON809 maize may positively impact current agricultural practices used for insect control by 1) offering an alternative method for control of European corn borer (and potentially other Cry1Ab-susceptible pests of maize); 2) reducing the use of insecticides to control European corn borer and the resulting potential adverse effects of such insecticides on beneficial insects, farm worker safety, and ground water contamination; and 3) offering a new tool for managing insects that have become resistant to other insecticides currently used or expressed in maize, including other Bt-based insecticides.

Food and/or Feed Safety Considerations Expand

Dietary Exposure

MON809 maize was intended mainly for use in animal feed. The major human food uses for maize are extensively processed starch and oil fractions prepared by wet or dry milling procedures and products include corn syrup and corn oil, neither containing protein. The potential human exposure to the modified protein from whole grain corn in the diet was considered to be very low due both to its low abundance in the protein fraction of the grain and to the proportionately low percentage of protein in the kernel, compared with the major starch component. Overall, the dietary exposure of consumers in the United States and Canada to insect resistant hybrids of MON809 maize was anticipated to be the same as for other lines of commercially available field maize.

Nutritional Data

The nutritional quality of grain from MON809 maize was similar to that of grain from an equivalent non-transgenic line and to grain currently available in commerce. Grain was subjected to proximate analysis (e.g., ash, moisture content, crude protein, crude fat), amino acid and fatty acid composition. Some minor differences were observed between MON809 and an equivalent non-transgenic line, but the levels were within the range of variation normally observed in the commercial grain supply and were attributed to variations in the plant genotypes rather than to the presence of the introduced genes.

Toxicity

Data were submitted that demonstrated that the active Cry1Ab protein product of the inserted cry1Ab gene was equivalent to the protein contained in microbial Bt spray formulations that have been safely used in agriculture for more than 40 years. Studies on the Cry1Ab protein expressed in plants and the resulting proteolytic fragments were compared to the bacterial proteins and shown to be of similar molecular weight, amino acid sequence, immunological reactivity and trypsin resistance. The protein was not glycosylated and showed similar bioactivity and host range specificity to the native protein. The Cry1Ab and CP4 EPSPS proteins should pose no risks for consumption of products produced from insect resistant maize. The introduced proteins were compared to databases of known protein toxins and neither showed any significant amino acid sequence similarity to known protein toxins. Neither protein was toxic when fed to mice.

Allergenicity

The Cry1Ab and CP4 EPSPS proteins are extremely unlikely to be allergens. The deduced amino acid sequences of the introduced proteins were compared to sequences of known allergens contained in the public domain databases GenBank, EMBL, Pir and SwissProt. No significant sequence homologies were detected. Neither the Cry1Ab and CP4 EPSPS protein originated from an allergenic source, or were structurally similar to known allergens. EPSPS is ubiquitous in bacteria, plants and animals and no toxic or allergenic effects have ever been reported. In addition, the potential for allergenicity was assessed based upon the characteristics of known food allergens (stability to digestion, stability to processing, abundance in foods). Protein allergens are normally resistant to digestion unlike the Cry1Ab protein that was shown to degrade readily in simulated gastric fluid. Similarly, data were presented showing that the CP4 EPSPS enzyme was rapidly inactivated by heat and by digestion in simulated mammalian gastric fluid.

Maize products are an important alternative to wheat flour for individuals afflicted with coeliac disease, an immune mediated food intolerance for which wheat gliadins have been implicated as the causal agent. In light of the importance of corn products to these individuals, a sequence similarity search was conducted and no amino acid sequence homologies between the Cry1Ab protein and gliadins were detected.

Abstract Collapse

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 ethanol production. 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 MON809 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. 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. MON809 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. MON809 was tested in field trials in Canada from 1994 to 1996. Data collected from these trials demonstrated that MON809 was not different from conventional maize lines; agronomic characteristics, including vegetative vigour, time to maturity, seed production, 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 nontarget organisms. MON809 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 MON809. Gene exchange between MON809 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 MON809 maize was established based on several standard criteria. Analyses determined that MON809 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 MON809 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 attributed to normal genotypic variation rather than to the presence of the introduced genes. The toxicity and allergenicity potential of the Cry1Ab protein in MON809 was assessed by examining its physiochemical characteristics, degree of amino acid sequence homology to known protein allergens, and digestibility. 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. 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.

Links to Further Information Expand


This record was last modified on Friday, May 10, 2013