Database Product Description
- Host Organism
- Zea mays (Maize)
- Resistance to corn root worm (Coleopteran, Diabrotica sp.)
- Trait Introduction
- Agrobacterium tumefaciens-mediated plant transformation.
- 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
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.
In the United States maize is typically used as animal feed, with roughly 70% of the crop fed to livestock, although an increasing share is now being used to produce ethanol for fuel. 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 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 MIR604 was genetically engineered to resist the western corn rootworm (D. virgifera virgifera), northern corn rootworm (D. barberi) and the Mexican corn rootworm (D. virgifera zeae) by producing an insecticidal protein. MIR604 contains two novel genes, a modified cry3A (mcry3A) gene encoding the mCry3A insecticidal protein and the pmi (manA) gene from Escherichia coli encoding the enzyme phosphomannose isomerase as a selectable marker.
The mcry3A gene encodes for a protein with a similar amino acid sequence to the Cry3Aa2 protein from Bacillus thuringiensis (Bt) subspecies tenebrionsis, with the inclusion of a protease cleavage site which results in a greater toxicity to certain species of corn rootworm. Cry proteins, of which mCry3A 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. mCry3A is lethal only when eaten by the larvae of coleopteran insects (i.e. , beetles) and exhibits no toxicity to other corn pests or non-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 phosphomannose isomerase protein (encoded by the pmi gene) was used as a selectable marker as plants expressing this gene can utilise mannose as a primary carbon source, whereas cells lacking this gene fail to proliferate on mannose-based medium.
The food and livestock feed safety of MIR604 maize grain and forage was established based on several standard criteria, including the potential toxicity and allergenicity of the two proteins, mCry3A and phosphomannose isomerase, which was determined to be negligible. As part of the safety assessment, the nutritional composition of MIR604 grain and forage was found to be equivalent to conventional maize as shown by the analyses of key nutrients including proximates, fatty acid profiles, minerals and vitamins, as well as anti-nutrient compounds.
Field trials with MIR604 were conducted during 2002 and 2003 with few significant differences between MIR604 and non-transgenic controls. None of these differences were outside the range of values expected for maize hybrids. Disease susceptibility was not different to existing maize hybrids, neither was there any difference in resistance to pests, except corn rootworms. It was thus determined that there would be little impact on potential weediness of MIR604 and commercial cultivation of MIR604 is unlikely to harm non-target organisms.
Links to Further Information Expand
This record was last modified on Monday, August 22, 2016