Database Product Description
- Host Organism
- Zea mays (Maize)
- Trade Name
- Glufosinate ammonium herbicide tolerance and male sterility
- Trait Introduction
- Electroporation of immature embryos.
- Proposed Use
Production for human consumption and livestock feed.
- Product Developer
- Bayer CropScience (Aventis CropScience(AgrEvo))
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.), 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 roughly70% 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 maize line MS3 was genetically engineered to express male sterility and tolerance to glufosinate ammonium, the active ingredient in phosphinothricin herbicides (Basta®, Rely®, Finale®, and Liberty®). Glufosinate chemically resembles the amino acid glutamate and acts to inhibit an enzyme, called glutamine synthetase, which is involved in the synthesis of glutamine. Essentially, glufosinate acts enough like glutamate, the molecule used by glutamine synthetase to make glutamine, that it blocks the enzyme's usual activity. Glutamine synthetase is also involved in ammonia detoxification. The action of glufosinate results in reduced glutamine levels and a corresponding increase in concentrations of ammonia in plant tissues, leading to cell membrane disruption and cessation of photosynthesis resulting in plant withering and death.
Glufosinate tolerance in this maize line is the result of introducing a gene encoding the enzyme phosphinothricin-N-acetyltransferase (PAT) isolated from the common aerobic soil actinomycete, Streptomyces hygroscopicus. The PAT enzyme catalyzes the acetylation of phosphinothricin, detoxifying it into an inactive compound. The PAT enzyme is not known to have any toxic properties.
The male-sterile trait was introduced by inserting the barnase gene, isolated from Bacillus amyloliquefaciens, a common soil bacterium that is frequently used as a source for industrial enzymes. The barnase gene encodes for a ribonuclease enzyme (RNAse) that is expressed only in the tapetum cells of the pollen sac during anther development. The RNAse affects RNA production, disrupting normal cell functioning and arresting early anther development, thus leading to male sterility. The PAT enzyme was used as a selectable marker enabling identification of transformed plants during tissue culture regeneration, and as a field selection method to identify the male-sterile lines prior to flowering. Under field conditions, plants that were not male-sterile could be eliminated by application of the herbicide glufosinate ammonium. The novel hybrid system provided an efficient and effective way to identify male-sterile plants for use in hybrid seed production.
The male sterile maize line MS3 has been tested in the major maize growing regions of the United States since 1992 and has been extensively evaluated in laboratory, greenhouse, and field experiments. Agronomic characteristics such as seed germination, vegetative vigour, time to maturity, time to tassel emergence, time to and process of silk extrusion, male and female fertility, yield parameters, and disease and pest susceptibilities were compared to those of non-transgenic Zea mays counterparts and found to be within the normal range for commercial maize hybrids. Overall the field data reports and data on agronomic traits demonstrated that MS3 maize was as safe to grow as any other male sterile maize and had no potential to pose a plant pest risk. It was demonstrated that the transformed maize line did not exhibit weedy characteristics, or negatively affect beneficial or non-target organisms. Maize line MS3 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, multiple barriers, including sterility of the maize line MS3, ensured that gene flow from this transformed line into wild or cultivated sexually-compatible plants was extremely unlikely. Gene exchange between maize line MS3 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.
In an assessment of food and livestock feed safety the composition of grain from MS3-derived hybrid maize was compared to grain from non-transgenic maize. Parameters such as moisture, fibre, fat, protein, ash, starch, oil, and the fatty acid and amino acid composition were compared with no significant differences observed. It was therefore concluded that the use of grain from MS3-derived maize hybrids would have no significant impact on the nutritional quality of the food supply.
Potential toxicity and allergenicity of the PAT protein and the barnase RNase expressed in the transgenic maize line MS3 were investigated by searching for amino acid sequence homology with known toxins and allergens, and by examining their physiochemical properties. No significant homologies between the deduced amino acid sequence of the PAT protein or the barnase RNase and the sequences of known toxins or allergens were detected. Neither the PAT enzyme nor the RNase possess the proteolytic or heat stability characteristic of toxic compounds, and the PAT enzyme was readily digested under conditions simulating mammalian digestion. In summary, the barnase RNAse and PAT enzyme were not derived from allergenic sources, do not share amino acid sequence homology with known allergens, and do not possess the physiochemical properties (heat and proteolytic digestion stability) normally associated with allergens. Based on these properties, it was concluded that the RNase and the PAT protein, and thus MS3 maize, possessed little or no potential for allergenicity or toxicity.
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This record was last modified on Friday, March 26, 2010