Database Product Description
- Host Organism
- Brassica napus (Argentine Canola)
- Trade Name
- Roundup Ready®
- Glyphosate herbicide tolerance.
- Trait Introduction
- Agrobacterium tumefaciens-mediated plant transformation.
- Proposed Use
This experimental line will not be commercialized.
- Product Developer
- Monsanto Company
Summary of Regulatory Approvals
Summary of Introduced Genetic Elements Expand
Characteristics of Brassica napus (Argentine Canola) Expand
Donor Organism Characteristics Expand
Modification Method Expand
Characteristics of the Modification Expand
Environmental Safety Considerations Expand
Food and/or Feed Safety Considerations Expand
Argentine or oilseed rape (Brassica napus) was grown as a commercial crop in over 50 countries, with a combined harvest of 48.9 million metric tonnes in 2006. The major producers of rapeseed are China, Canada, India, Germany, France, the United Kingdom and Australia. Canola is a genetic variation of B. napus that was developed through conventional breeding to contain low levels of the natural rapeseed toxins, glucosinolate and erucic acid. Canola is grown for its seed, which represents a major source of edible vegetable oil and is also used in livestock feeds.
The only food use of canola is as a refined oil. Typically, canola oil is used by itself as a salad oil or cooking oil, or blended with other vegetable oils in the manufacture of margarine, shortenings, cooking and salad oils. Canola meal, a byproduct of the oil production process, is added to livestock feed rations. An increasing amount of oil is being used for biodiesel production, especially in Europe.
The removal of weeds early in the growing season is extremely important in canola production. Young canola seedlings are not very competitive and early weed pressure has detrimental effects on final yield. Precautions such as pre-plant tillage or herbicide application are common approaches for reducing weed competition. Once established, canola forms a dense canopy and is very competitive, making weed control less of a concern.
At present, it is expensive, but possible, to control annual grassy weeds (wild oats, volunteer cereals), perennial weeds (Canada thistle, perennial sow thistle, quackgrass), and certain annual broadleaf weeds in canola. The broadleaves are the most difficult to control because there are few herbicide options available. Many producers will use as many as four herbicides per year in an effort to control weeds.
Traditionally, it has been difficult to manage weeds in canola rotations because of the need to use Group 1 herbicides (Assure®, Fusion®, Poast®, Select®, Venture DG®) that are also commonly used to control weeds in flax, wheat and other cereals. Growers favour these herbicides because they are easy to work with, are extremely effective, and may be applied over a period of time. However, the constant use of Group 1 herbicides has placed large acreages of cultivated land at high risk of developing Group 1 weed resistance. The establishment of several herbicide-tolerant weed populations demonstrates this problem.
The herbicide-tolerant canola line GT200 was developed to allow for the use of glyphosate, the active ingredient in the herbicide Roundup®, as a weed control option. In order to obtain field tolerance to glyphosate herbicide, two novel genes, CP4 EPSPS and goxv247, were introduced into B. napus cv. Westar by Agrobacterium-mediated transformation.
The CP4 EPSPS gene codes for the enzyme 5-enolpyruvylshikimate-3-phosphate synthase that is present in all plants, bacteria and fungi. The EPSPS gene put into GT200 was isolated from strain CP4 of the common soil bacterium Agrobacterium tumefaciens and is a glyphosate tolerant form of EPSPS. The EPSPS enzyme is part of an important biochemical pathway in plants called the shikimate pathway that is involved in the production of aromatic amino acids and other aromatic compounds. When conventional canola plants are treated with glyphosate, the plants cannot produce the aromatic amino acids needed to grow and survive. EPSPS is not present in mammals, birds or aquatic life forms, which do not synthesize their own aromatic amino acids. For this reason, glyphosate has little toxicity to these organisms. The EPSPS enzyme is naturally present in foods derived from plant and microbial sources.
The canola line GT200 contains a second gene that codes for a modified version of glyphosate oxidase (GOX) enzyme that is ubiquitous in nature. The goxv247 gene inserted into GT200 was isolated from strain LBAA of the bacterium Ochrobactrum anthropi. Glyphosate oxidase (GOX) enzyme accelerates the normal breakdown of the herbicide glyphosate into two non-toxic compounds, aminomethylphosphonic acid (AMPA) and glyoxylate. AMPA is the principal breakdown product of glyphosate and is degraded by several microorganisms, while glyoxylate is commonly found in plant cells and is broken down by the glyoxylic pathway for lipid metabolism.
The canola line GT200 was field tested in Canada from 1992 to 1994. Agronomic characteristics such as vegetative vigor, overwintering capacity, time to maturity, seed production and yield of the transformed line GT200 were compared to unmodified canola counterparts and determined to be within the normal range of expression found in commercial canola cultivars. The only significant difference between GT200 canola and the parental non-transformed variety was tolerance to glyphosate. It was demonstrated that the transformed canola line did not exhibit weedy characteristics, or negatively affect beneficial or non-target organisms. Canola line GT200 was not expected to impact on threatened or endangered species.
Brassica napus may outcross (up to 30% of the time) with plants of the same species, and potentially with plants of related species B. rapa, B. juncea, B. carinata, B. nigra, Diplotaxis muralis, Raphanus raphanistrum, and Erucastrum gallicum. Previous studies have demonstrated that cross hybridization is most likely to occur with B. rapa. Because of the ability of canola to outcross with related plants, the formation of glyphosate tolerant hybrids is possible. However, the glyphosate-tolerance trait is not expected to provide a competitive advantage to hybrid plants unless grown in managed environments routinely subjected to glyphosate applications. In the event that a glyphosate tolerant hybrid survived, the herbicide-tolerant individual could be easily controlled using mechanical and/or other available chemical means.
The human consumption of canola products is limited to the purified oil. Refined edible canola oil consists of purified triglycerides (96-97%) and does not contain any detectable protein, hence no amounts of CP4 EPSPS or GOX proteins were detected in the refined oil of GT200 canola. As the introduced gene products are not detectable in the refined oil produced from transgenic canola, there will be no human exposure to these proteins and the consumption of refined oil from GT200 was judged to have no significant impact on the nutritional quality of the food supply.
The livestock feed safety of GT200 canola was established based on several standard criteria. The analysis of nutrients from transgenic GT200 canola and non-transgenic canola did not reveal any significant differences in the levels of crude protein, crude fat, crude fibre, ash and gross energy in either the whole seed or processed meal. Raw seeds of GT200 were shown to have the same levels of glucosinolates and erucic acid as commercial canola varieties. Seed protein profiles, amino acid and fatty acid compositions were all within the range of the unmodified counterparts.
Several animal feeding studies were conducted to demonstrate the wholesomeness of glyphosate-tolerant canola meal. Canola meal is used only for animal feed and is not considered a human food fraction. These studies included a four-week rat study on processed and unprocessed meal, a five-day quail (Northern Bobwhite) study on unprocessed meal, and a ten-week trout study on processed meal. The studies all supported the safety of the inclusion of GT200 canola in animal feed.
It was determined that there were no toxicity and allergenicity concerns with GT200. There is no dietary exposure to CP4 EPSPS and GOX since these proteins are not present in the refined canola oil consumed by humans. Furthermore, the structure and function of CP4 EPSPS protein was determined to be similar to the same enzyme naturally present in foods. Neither CP4 EPSPS nor GOX were found to have any amino acid sequence similarities with known toxins or allergens, and there are no known reports of toxicity or allergenicity of EPSPS or GOX proteins derived from plants, bacteria and fungi. Direct laboratory studies of the CP4 EPSPS and GOX proteins revealed the ready digestibility of both proteins under conditions simulating mammalian digestion, providing further evidence supporting the lack of toxicity or allergenicity concerns with GT200.
Links to Further Information Expand
This record was last modified on Friday, March 26, 2010