Database Product Description
- Host Organism
- Zea mays (Maize)
- Trade Name
- Herculex® RW
Herbicide tolerant, glufosinate ammonium; Insect resistant, Coleoptera.
- Trait Introduction
- Agrobacterium tumefaciens-mediated plant transformation.
- Proposed Use
Production for human consumption and livestock feed.
- Product Developer
- DOW AgroSciences LLC and Pioneer Hi-Bred International 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, 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
This record was last modified on Thursday, May 21, 2015