GM Crop Database

Database Product Description

DAS-59122-7 (DAS-59122-7)
Host Organism
Zea mays L. (Maize) Herculex® RW
Trait
Phosphinothricin (PPT) herbicide tolerance, specifically glufosinate ammonium, and resistance to corn root worm (Coleoptera, Diabrotica spp.
Trait Introduction
Agrobacterium tumefaciens-mediated plant transformation.
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
DOW AgroSciences LLC and Pioneer Hi-Bred International Inc.

Summary of Regulatory Approvals

Country Food Feed Environment Notes
Australia 2005
Canada 2005 2005 2005 View
China 2006 2006
Colombia 2011
European Union 2007 2007
Japan 2006 2006 2006
Korea 2005 2005
Mexico 2004 2004
Philippines 2006 2006
Taiwan 2005
United States 2004 2004 2005

Introduction Expand

Maize line DAS-59122-7 was genetically modified to contain three novel genes, cry34Ab1 and cry35Ab1 for insect resistance, and pat, for herbicide tolerance used as a selectable marker. All three genes were introduced into the parental maize hybrid line Hi-II by Agrobacterium-mediated plant transformation.

The cry34Ab1 and cry35Ab1 genes, isolated from the common soil bacterium Bacillus thuringiensis (Bt) strain PS149B1, produce the insect control proteins (delta-endotoxins) Cry34Ab1 and Cry35Ab1. Cry proteins, of which Cry34Ab1 and Cry35Ab1 are only two among many, 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. Cry34Ab1 and Cry35Ab1 are both lethal only when eaten by the larvae of coleopteran insects (i.e., beetles), 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.
The pat gene introduced into DAS-59122-7 maize allows the use of the herbicide glufosinate ammonium as a breeding tool for selecting plants containing the cry34Ab1 and cry35Ab1 genes. The herbicidal mode of action of glufosinate ammonium is related to the activity of glutamine synthetase (GS), the enzyme required for the synthesis of the amino acid glutamine. L-phosphinothricin, the active ingredient of glufosinate ammonium, is a structural analog of glutamate, and acts as a competitive inhibitor. After application of the herbicide, L-phosphinothricin competes with glutamine for its active sites on GS. The results of the inhibition of GS are an accumulation of ammonia in the plant, a reduction in the synthesis of glutamine, and an inhibition of photosynthesis. This causes the death of plant cells, and eventually, the entire plant. The pat gene codes for the production of the enzyme phosphinothricin acetyl-transferase (PAT). This enzyme acetylates L-phosphinothricin rendering it inactive in the plant. The PAT enzyme is not known to have any toxic properties. The pat gene was isolated from the soil bacterium Streptomyces viridochromogenes, the same organism from which L-phosphinothricin was originally isolated.

Summary of Introduced Genetic Elements Expand

Code Name Type Promoter, other Terminator Copies Form
cry34Ab1 Cry34Ab1 delta-endotoxin IR Zea mays ubiquitin gene promoter, intron and 5' UTR Solanum tuberosum proteinase inhibitor II (PINII) 1 functional Altered coding sequence for optimal expression in maize
cry35Ab1 Cry35Ab1 delta-endotoxin IR Triticum aestivum peroxidase gene root-preferred promoter Solanum tuberosum proteinase inhibitor II (PINII) 1 functional Altered coding sequence for optimal expression in maize
pat phosphinothricin N-acetyltransferase SM Cauliflower Mosaic Virus (CaMV) 35S Cauliflower Mosaic Virus (CaMV) 35S 1 functional

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 strain PS149B1 cry34Ab1 While target insects are susceptible to oral doses of Bt proteins, there is no evidence of toxic effects in laboratory mammals, in birds or in non-target arthropods.
Bacillus thuringiensis strain PS149B1 cry34Ab1 While target insects are susceptible to oral doses of Bt proteins, there is no evidence of toxic effects in laboratory mammals, in birds or in non-target arthropods.
Streptomyces viridochromogenes pat S. viridochromogenes is ubiquitous in the soil. The spore chains are Spirales and the spore surface is spiny. The spore mass is blue, the reverse is green and its pigments are pH sensistive. It exhibits very slight antimicrobial activity, is inhibited by streptomycin, and there have been no reports of adverse affects on humans, animals, or plants.

Modification Method Expand

DAS-59122-7 maize was produced by Agrobacterium-mediated transformation of the hybrid maize line Hi-II. The T-DNA segment of the vector plasmid PHP17662 contained sequences corresponding to synthetic forms of the cry34Ab1 and cry35Ab1 genes from Bacillus thuringiensis strain PS149B1, and the phosphinothricin N-acetyltransferase (PAT) encoding pat gene from Streptomyces viridochromogenes. The cry34Ab1 and cry35Ab1 gene sequences were modified to contain codons to optimize their expression in maize. Transcription of the cry34Ab1 gene was directed by the promoter, intron and 5' untranslated region (UTR) sequences from the maize ubiquitin gene. Terminator sequences were derived from Solanum tuberosum proteinase inhibitor II (PINII). The expression of the cry35Ab1 gene was regulated by the root-preferred promoter from the Triticum aestivum peroxidase gene. Terminator sequences for the cry35Ab1 gene were identical to those for cry34Ab1. The expression of the pat gene was regulated by the 35S promoter from the Cauliflower Mosaic Virus (CaMV). Terminator sequences were derived from the CaMV 35S terminator.

Characteristics of the Modification Expand

The Introduced DNA

Southern blot analysis of the genomic DNA of DAS-59122-7 demonstrated the integration of a single intact copy of the T-DNA of the vector plasmid PHP17662. All three novel genes, cry34Ab1, cry35Ab1, and pat, along with their respective promoter, enhancer and terminator sequences, were completely integrated. None of the vector backbone sequences, including the spectinomycin resistance and tetracycline resistance genes, were integrated into the genome of DAS-59122-7.

Genetic Stability of the Trait

Southern blot analysis demonstrated that the integration of the T-DNA insert was stable within and across generations. Segregation analysis also demonstrated a stable insertion consistent with a Mendelian inheritance pattern for a dominant trait.

Environmental Safety Considerations Expand

Field Testing

Maize event DAS-59122-7 was field tested in the United States in 2001, 2002 and at 18 separate sites in 2003. Agronomic characteristics of hybrids derived from DAS-59122-7 such as seed dormancy, vegetative vigour, early stand establishment, time to maturity, flowering period, susceptibilities to various pests and pathogens, and seed production were compared to those of unmodified counterparts. Nutritional components of DAS-59122-7, such as proximates, amino acids and fatty acids were compared with those of unmodified counterparts.

Outcrossing

Pollen production and viability were unchanged by the genetic modification resulting in DAS-59122-7, therefore pollen dispersal by wind and outcrossing frequency should be no different than for other maize varieties. Gene exchange between DAS-59122-7 and other cultivated maize varieties will be similar to that which occurs naturally between cultivated maize varieties at the present time. In the United States and Canada, where there are no plant species closely-related to maize in the wild, the risk of gene flow to other species appears remote. Feral species in the United States related to corn cannot be pollinated due to differences in chromosome number, phenology (periodicity or timing of events within an organism’s life cycle as related to climate, e.g., flowering time) and habitat.

Maize (Zea mays ssp. mays) freely hybridizes with annual teosinte (Zea mays ssp. mexicana) when in close proximity. These wild maize relatives are native to Central America and are not present in the United States, except for special plantings. Tripsacum, another genus related to Zea, contains sixteen species, of which twelve are native to Mexico and Guatemala. Three species of Tripsacum have been reported in the continental United States: T. dactyloides, T. floridanum and T. lanceolatum. Of these, T. dactyloides, Eastern Gama Grass, is the only species of widespread occurrence and of any agricultural importance. It is commonly grown as a forage grass and has been the subject of some agronomic improvement (i.e., selection and classical breeding). T. floridanum is known from southern Florida and T. lanceolatum is present in the Mule Mountains of Arizona and possibly southern New Mexico. Even though some Tripsacum species occur in areas where maize is cultivated, gene introgression from maize under natural conditions is highly unlikely, if not impossible. Hybrids of Tripsacum species with Zea mays are difficult to obtain outside of the controlled conditions of laboratory and greenhouse. Seed obtained from such crosses are often sterile or progeny have greatly reduced fertility.

Weediness Potential

The history and biology of maize indicates that non-transgenic plants of this species are not invasive in unmanaged habitats. Maize does not possess the potential to become weedy due to traits such as lack of seed dormancy, the non-shattering nature of corn cobs, and the poor competitive ability of seedlings. The data generated from field trials shows that DAS-59122-7 and derived hybrids are similar to their counterparts in this respect. Data submitted by the developer on the reproductive and survival biology of hybrids derived from DAS-59122-7 determined that early stand establishment, flowering period, vegetative vigor, time to maturity and seed production were within the normal range of expression of these traits currently displayed by commercial hybrids. No competitive advantage was conferred to DAS-59122-7, other than that conferred by resistance to rootworm and tolerance to glufosinate herbicide. These traits were demonstrated not to render maize weedy or invasive of natural habitats since none of the reproductive or growth characteristics were modified. The above considerations lead to the conclusion that DAS-59122-7 has no altered weed or invasive potential compared to currently commercialized corn.

Secondary and Non-Target Adverse Effects

The agronomic characteristics of DAS-59122-7 hybrids were shown to be within the range of values displayed by currently commercialized maize hybrids, and indicate that the growing habit of maize will not be inadvertently altered by cultivation of DAS-59122-7. Field observations did not indicate modifications of disease and pest susceptibilities, other than to rootworm, which is not known to be a principal factor restricting the establishment or distribution of maize.

Some of the genetic elements introduced into DAS-59122-7 were derived from known plant pathogens, but in all cases the genes responsible for the pathogenic qualities of the pathogen were not introduced. Therefore, the introduction of genetic material for Diabotica spp. resistance and glufosinate tolerance would not be expected to result in DAS-59122-7 expressing novel pathogenic characteristics.

The history of use and literature suggest that the bacterial Cry34Ab1 and Cry35Ab1 toxins are not toxic to humans, other vertebrates, and non-coleopteran invertebrates. This protein is active only against specific coleopteran insects and, as the specificity of the Cry34Ab1 and Cry35Ab1 protein insecticidal activity is dependent upon their binding to specific receptors present in the insect mid-gut, these insecticidal proteins are not expected to adversely affect other invertebrates or vertebrate organisms, including non-target birds, mammals and humans. Laboratory and field studies on representative species supported these expectations.

A series of diet bioassays was conducted with microbially-expressed Cry34Ab1 and Cry35Ab1 proteins to characterize the insecticidal specificity. Test species were: northern corn rootworm (Diabrotica barberi), western corn rootworm (Diabrotica virgifera virgifera), southern corn rootworm (Diabrotica undecimpunctata howardi), European corn borer (Ostrinia nubilalis), corn earworm (Helicoverpa zea), black cutworm (Agrotis ipsilon) and corn leaf aphid (Rhopalosiphum maidis). Only corn rootworm (Diabrotica spp.) experience high mortality when exposed to microbially-expressed Cry34 and Cry35 proteins.

Acute dietary toxicity studies were conducted in laboratory tests on the effect of the Cry34 and Cry35Ab1 proteins on non-target invertebrates, including honeybee larvae, green lacewing larvae, ladybird beetles (Hippodamia convergens and Coleomegilla maculate), parasitic wasp, ground beetle, daphnia, collembola, and earthworm. Data were also submitted on non-target vertebrates including mice and the rainbow trout. Cry34 and Cry35Ab1 proteins were demonstrated to be safe to these indicator species when ingested alone or in combination, at doses exceeding the levels of direct or indirect exposure to Cry34 and Cry35Ab1 proteins from corn 59122 tissues. Although growth inhibition was reported when Coleomegilla maculate larvae were fed Cry34Ab1 protein at about 10 times the field pollen value, no delay in development or weigh reduction were observed when larvae were fed a diet composed of 50% corn line 59122 pollen, which represents a conservative estimate of the potential exposure in the field. Therefore, no sub-lethal effects on C. maculate ladybird beetle are expected from exposure to event DAS-59122-7.

Field based observational studies were also performed on the stability and abundance of non-target arthropods communities and individual species where Cry34 and Cry35Ab1 expressing corn is grown. The species studied were representatives of various functional groups (predators, parasitoids, herbivores and detritivores) and were sampled using visual observations of corn plants, sticky traps, pitfall traps or litterbag traps. The studies did not reveal any negative impact on the abundance of these non-target organisms relative to the non-transgenic control hybrid. The Cry34 and Cry35Ab1 protein was shown to degrade readily in soil, indicating that it is unlikely to accumulate and persist in soil.

The herbicide tolerance trait of event DAS-59122-7 is conferred by expression of the phosphinothricin N-acetyltransferase (PAT) gene. The PAT protein has been studied extensively and has been found to be safe for non-target organisms, including human beings. This gene has been used in a number of other approved transgenic maize events, such as T25, BT11, DLL25 and DAS-06275-8.

Maize is not known for the production of significant levels of endogenous toxins and the transformation event that produced event DAS-59122-7 would not be expected to induce their synthesis. Maize is however, known to produce low levels of trypsin inhibitor and phytic acid and the levels of these compounds in DAS-59122-7 were found to be within the range of conventional corn lines. The genetic modification, therefore did not alter the expression of endogenous anti-nutrients.

Impact on Biodiversity

DAS-59122-7 has no novel phenotypic characteristics which would extend its use beyond the current geographic range of maize production. Since maize does not out-cross to wild relatives in the united States or Canada, there will be no transfer of novel traits to unmanaged environments. In addition the novel traits were determined to pose minimal risks to non-target organisms.

DAS-59122-7 provides an alternative method to existing methods of control of rootworms, an important agricultural pest of maize. The control of agricultural pest species is a common practice that is not restricted to the environmental release of transgenic plants. Therefore, the reduction in local pest species as a result of the cultivation of DAS-59122-7 does not present a significant change from existing agricultural practices. At present, the use of chemical insecticides to control rootworm is permitted, although crop rotation represents a major method of rootworm control in some countries.

DAS-59122-7 also provides an alternative method of weed control in maize production. The use of broad spectrum herbicides has the intended effect of reducing local weed populations within agricultural fields and this may reduce local weed species biodiversity, and possibly other trophic levels which utilize these weed species. It must be noted, however, that reduction in weed biodiversity in agricultural fields is not unique to the use of transgenic plants, and is a common practice in virtually all modern agricultural systems. It was therefore concluded that DAS-59122-7 does not present a significantly altered impact on biodiversity in comparison to maize varieties currently being grown.

Food and/or Feed Safety Considerations Expand

Dietary Exposure

Humans consume relatively little whole kernel or processed maize, compared to maize-based food ingredients. Maize is a raw material for the manufacture of starch, the majority of which is converted to a variety of sweetener and fermentation products, including high fructose syrup and ethanol. Maize oil is commercially processed from the germ. These materials are components of many foods including bakery and dairy goods, and the human food uses of grain from DAS-59122-7 are not expected to be different from the uses of non-transgenic field maize varieties. As such, the dietary exposure to humans of grain from insect resistant hybrids will not be different from that for other commercially available field maize varieties.

The highest levels of expression of Cry34Ab1 and Cry35Ab1 in the grain of DAS-59122-7 were measured to be 117 mg/kg and 1.83 mg/kg, respectively. The actual exposure in the diet is expected to be lower than this due to a number of factors including protein degredation during transport, storage and processing of the grain. The level of PAT expressed in the grain was below the limit of quantitation for this protein (0.06 mg/kg).

Toxicity and Allergenicity

The acute oral toxicity of the two Cry proteins was studied, both individually and combined, using single dose studies in mice. The mice received either a single dose of 2700 mg/kg bw Cry34Ab1, 1850 mg/kg bw Cry35Ab1 or 482 mg/kg bw Cry34Ab1 and 1520 mg/kg bw Cry35Ab1 together, and observed for two weeks. Apart from some fluctuations in body weights common in large dose oral gavage studies, there were no clinical signs noted during the study. All mice survived the observation period and there were no gross pathological changes noted upon post mortem examination of the mice.

Extensive animal testing has shown that the PAT protein is non-toxic to humans and animals and this gene has been expressed in other transgenic crops approved in a number of countries. An acute oral toxicity study with 5000 mg/kg bw of the PAT protein showed no effects in mice.

The protein concentrations tested were orders of magnitude greater than the dose range for this endpoint typically associated with protein toxins. Additionally the PAT protein present in this corn has been extensively studied and has been found safe for consumption in food or feed according to a consensus document concerning the genes and associated enzymes that confer tolerance to phosphinothricin herbicide (OECD, 1999).

Based on the expression levels of these proteins in grain and dietary intake data, exposure to these proteins would be extremely low. The novel proteins were not homologous to known food allergens, as established by amino acid sequence comparisons with allergenic proteins from extensive computerized databases. In digestibility studies using simulated mammalian gastric fluid, the novel proteins were more rapidly digested than non-allergen protein controls. The Cry34Ab1 and Cry35Ab1 proteins are completely inactivated by exposure for 30 min to 90ºC and 60ºC respectively, indicating that both proteins are heat labile. Based on the preceding evidence, the novel proteins expressed in this corn line do not share characteristics of known food allergens.

Nutritional and Compositional Data

Forage and grain from DAS-59122-7 maize, grown at three locations, were analyzed for nutritional composition and compared to a non-transgenic maize control which was derived from the parental line Hi-II, and to published literature values. Samples for analysis were collected from field trials grown at six different locations.

Forage was harvested at the dough stage (R4) and was analyzed for proximates (crude protein, crude fat, moisture, ash, carbohydrate, acid detergent fibre (ADF), neutral detergent fibre (NDF)), and minerals (calcium and phosphorus). No significant differences in the levels crude protein, crude fat, crude fibre, ADF and NDF were observed between DAS-59122-7 and the non-transgenic control. While significant differences were observed in the levels of ash, carbohydrates, calcium and phosphorus, these values were within the ranges reported in the literature for conventional maize hybrids.

Grain samples were obtained from mature (growth stage R6) plants and analyzed for the several components, including proximates (crude protein, crude fat, moisture, ash, carbohydrate, acid detergent fibre and neutral detergent fibre); minerals (calcium, phosphorus, magnesium, copper, iron, manganese, potassium, sodium, and zinc); amino acids; fatty acids; vitamins (A, B1, B2, folic acid, E ); anti-nutrients (phytic acid, trypsin inhibitor, raffinose); and secondary metabolites (ferulic acid, p-coumaric acid, furfural).

Statistical analysis of the mean levels of proximates across all locations revealed no significant differences between DAS-59122-7 and the non-transgenic control, with the exception of crude protein, ash, and carbohydrates. The levels of crude protein and ash were higher, and carbohydrate levels were lower in DAS-59122-7 compared to the control line. Statistically significant differences were reported in the mean levels of most of the fatty acids measured. The levels of linoleic and linolenic acid were higher, while palmitic and stearic acid levels were lower in DAS-59122-7 compared to the control. No significant differences were observed in the levels of oleic acid. The levels of nine of the amino acids measure, i.e., tryptophan, isoleucine, histidine, valine, leucine, arginine, phenylalanine, proline and tyrosine, were higher in DAS-59122-7 compared to the control. No significant differences were observed in the levels of minerals, except for calcium, which was higher in the transgenic line. Statistically significant differences were observed in the levels folic acid and vitamin E. Despite all of the observed statistically significant differences between DAS-59122-7 and the non-transgenic control, all of the nutritional component values were within the ranges reported in the literature for conventional maize hybrids.

The levels of the antinutritional compounds phytic acid, trypsin inhibitor and raffinose, as well as the secondary metabolites ferulic acid, p-coumaric acid, and furfural were determined in the grain. Phytic acid occurs naturally in maize and other cereals. It is indigestible by humans and non-ruminant livestock, and inhibits the absorption of iron and other minerals. Trypsin inhibitor interferes with enzymes involved in protein digestion. Raffinose is an oligosaccharide found in cereals and legumes which is indigestible in humans and monogastric livestock, thereby limiting the amount of metabolizable engery in foods and feeds. Ferulic acid and p-coumaric acid are compounds which become covalently linked to hemicelluloses during cell wall development. In ruminants, these compounds inhibit cell wall degradation by rumen microorganisms. Furfural is an aromatic aldehyde which can result from the dehydration of pentose sugars in cereals. No significant differences were observed in the levels of these antinutrients, and the secondary metabolites ferulic acid and p-coumaric acid, between DAS-59122-7 and the non-transgenic control maize line. Furfural was not detected in any of the samples analyzed.

The results of these compositional analyses led to the conclusion that DAS-59122-7 forage and grain is not different in nutritional and antinutritional composition compared to maize hybrids currently marketed, grown and consumed.
No introduced health concerns would be expected to be associated with the consumption of corn event DAS-59122-7 compared with its non-transgenic parent. DAS-59122-7 corn is deemed to be similar to the non-transgenic parental strain of corn in terms of being an acceptable food source.

Abstract Collapse

Maize, or corn (Zea mays L.) is grown commercially in over 100 countries with a combined harvest of nearly 700 million metric tonnes in 2006. The top five producers of maize in 2005 were the United States, China, Brazil, Argentina, and Mexico, accounting for 70% of world production. Maize is grown primarily for its kernel (grain), the majority of which is used for animal feed, but with significant amounts refined into products used in a wide range of food, medical, and industrial goods.

Maize is a raw material for the manufacture of starch, the majority of which is converted by a complex refining process into sweeteners, syrups, and fermentation products, including ethanol. Maize oil is extracted from the germ of the maize kernel. Only a small proportion of the whole kernel is consumed by humans (e.g., corn meal, grits, oil), while refined maize products such as sweeteners, starch, and oil are abundant in processed foods (e.g., breakfast cereals, dairy goods, chewing gum). Maize is also processed into masa, which is used for tortillas, tacos and corn chips.

In the United States maize is typically used as animal feed, with roughly 70% of the crop fed to livestock, however a growing amount is now 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, car parts. Refined maize products are also used in bioproducts such as antibiotics.

Corn rootworm (Diabrotica spp.) is considered one of the most damaging insects pests of maize. The species of corn rootworm most prevalent in the United States are the northern corn rootworm (Diabrotica barberi) and the western corn rootworm (D. virgifera). The larvae of these beetles (coleopterans) feed on the corn roots. Feeding damage to the roots impedes the absorption of water and nutrients. Corn rootworms also feed on the brace roots and cause plant lodging. Adults feed on the silks thus interfering with pollination and seed set. Crop rotation is a recommended practice to reduce the population of these insects; thus, corn should not follow corn in a rotation. The protection offered by insecticides is limited: these will protect the crop from rootworm damage, but will only reduce a small percentage of the beetles from emerging.

The transgenic maize line DAS-59122-7 was genetically engineered to resist the Coleopteran insects western corn rootworm (Diabrotica virgifera), northern corn rootworm (D. barberi), and Mexican corn rootworm (D. virgifera zeae) by producing insecticidal proteins (delta-endotoxins). Three novel genes, cry34Ab1, cry35Ab1, and pat were introduced into the maize hybrid line Hi-II using Agrobacterium-mediated transformation.

The cry34Ab1 and cry35Ab1 genes, isolated from the common soil bacterium Bacillus thuringiensis (Bt) strain PS149B1, produce the insect control proteins (delta-endotoxins) Cry34Ab1 and Cry35Ab1. Cry proteins, of which Cry34Ab1 and Cry35Ab1 are only two among many, 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. Cry34Ab1 and Cry35Ab1 are both lethal only when eaten by the larvae of coleopteran insects (i.e., beetles), 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.
The pat gene introduced into DAS-59122-7 maize allows the use of glufosinate ammonium as a breeding tool for selecting plants containing the cry34Ab1 and cry35Ab1 genes. The herbicidal mode of action of glufosinate ammonium is related to the activity of glutamine synthetase (GS), the enzyme required for the synthesis of the amino acid glutamine. L-phosphinothricin, the active ingredient of glufosinate ammonium, is a structural analog of glutamate, and acts as a competitive inhibitor. After application of the herbicide, L-phosphinothricin competes with glutamine for its active sites on GS. The results of the inhibition of GS are an accumulation of ammonia in the plant, a reduction in the synthesis of glutamine, and an inhibition of photosynthesis. This causes the death of plant cells, and eventually, the entire plant. The pat gene codes for the production of the enzyme phosphinothricin acetyl-transferase (PAT). This enzyme acetylates L-phosphinothricin rendering it inactive in the plant. The PAT enzyme is not known to have any toxic properties. The pat gene was isolated from the soil bacterium Streptomyces viridochromogenes, the same organism from which L-phosphinothricin was originally isolated.

The food and livestock feed safety of DAS-59122-7 maize was established based on several standard criteria. As part of the safety assessment, the nutritional composition of DAS-59122-7 grain was found to be equivalent to conventional maize as shown by the analyses of key nutrients including proximates (e.g., moisture, protein, fat, fibre, ash, carbohydrate, acid detergent fibre, and neutral detergent fibre), amino acid composition, fatty acid profiles, minerals, and vitamins (e.g., vitamin A, E, folic acid) as well as antinutrients compounds and secondary metabolites. Similar compositional analyses were conducted on DAS-59122-7 forage.

Links to Further Information Expand

Canadian Food Inspection Agency, Plant Biosafety Office European Commission: Community Register of GM Food and Feed European Food Safety Authority Food Standards Australia New Zealand Health Canada Novel Foods Japanese Biosafety Clearing House, Ministry of Environment Philippines Department of Agriculture, Bureau of Plant Industry U.S. Environmental Protection Agency U.S. Food and Drug Administration U.S.Department of Agriculture, Animal and Plant Health Inspection Service

This record was last modified on Friday, March 26, 2010