GM Crop Database

Database Product Description

Teal 11A
Host Organism
Triticum aestivum (Wheat)
Trait
Imidazolinone herbicide tolerance, specifically imazethapyr.
Trait Introduction
Chemically induced seed mutagenesis
Proposed Use

Production for human consumption and livestock feed.

Product Developer
BASF Inc.

Summary of Regulatory Approvals

Country Food Feed Environment Notes
Canada 2004 2004 2004

Introduction Expand

Teal 11A (Clearfield™) spring wheat was developed to allow the use of imazamox and imazethapyr, both imidazolinone herbicides, as weed control options in spring wheat production. This trait was developed using chemically induced seed mutagenesis and whole plant selection procedures. This wheat line expresses a mutated form of the acetohydroxyacid synthase (AHAS) enzyme, which renders the plant tolerant to levels of imazamox and imazethapyr used in weed control.

AHAS catalyses the first step in the biosynthesis of the branched-chain amino acids isoleucine, leucine, and valine, and is active in the glycolytic pathway of plant metabolism. When conventional plants are treated with either imazamox or imazethapyr, the herbicide binds to a specific site on the enzyme, thereby inhibiting its activity. The result of this enzyme inhibition is a decrease in the synthesis of these amino acids, and an accumulation of toxic levels of alpha-ketoglutarate, all of which results in the eventual death of the plant.

Summary of Introduced Genetic Elements Expand

Code Name Type Promoter, other Terminator Copies Form
als acetolactate synthase MUT Native AHAS Selected following chemical mutagenesis

Characteristics of Triticum aestivum (Wheat) Expand

Center of Origin Reproduction Toxins Allergenicity
Asia Minor, Tigris-Euphrates drainage basin of the Middle East, as well as the regions of southern Caucasus and Crimea. Primarily self-pollinated (autogamous). Some outcrossing by wind-pollination of less than 10%. Seed does not display dormancy. Phytic acid, trypsin inhibitor, lectins. Gliadins responsible for celiac enteropathy. Glutenins and gliadins (e.g., the IgE-inducing alpha-gliadin).

Modification Method Expand

The wheat line Teal 11A was isolated from a population derived from seed of the variety ‘CDC Teal’ which had been treated with ethyl methanesulfonate (EMS), a substance known to induce point mutations within the genome of organisms. The selection of herbicide tolerant plants was made from whole plants treated with imazamox and imazethapyr. The designation Teal 11A was given to the mutant that had exhibited tolerance to both herbicides. Seed from this line was obtained from self-fertilization.

Characteristics of the Modification Expand

The Introduced DNA

Since Teal 11A is a product of mutagenesis and conventional seed increase techniques there was no introduction or incorporation of heterologous DNA into the plant genome. The tolerance to imazamox and imazethapyr is due to a single point mutation of a single nucleotide in one (als2) of the three AHAS genes. The amino acid sequence of the mutated enzyme differs by one amino acid from that of the unmodified enzyme. This single change in the amino acid sequence alters the binding site on AHAS to imazamox and imazethapyr, such that neither herbicide can inhibit the enzyme’s activity. The mutation of the AHAS gene was identified from information on the gene sequence.

Genetic Stability of the Introduced Trait

Segregation analysis of crosses with Teal 11A demonstrated the inheritance of a single semi-dominant or co-dominant gene.

Expressed material

The modified AHAS gene, conferring tolerance to imazamox and imazethapyr, is under control of the native AHAS promoter and is believed to be constitutively expressed. Whole plant tolerance to these herbicides was expressed in Teal 11A.

In the unmodified plant, the levels of valine, leucine and isoleucine are regulated by feedback inhibition of AHAS. A mutation in the AHAS enzyme could affect the regulation of the biosynthesis of these amino acids. Data were submitted to show that the modified AHAS was feedback inhibited by valine and leucine, similar to the unmodified enzyme. Levels of valine, leucine and isoleucine in Teal 11A were comparable to those in the unmodified plant.

Environmental Safety Considerations Expand

Outcrossing

Wheat (Triticum aestivum) is primarily a self-pollinating plant. Gene transfer can occur by wind-mediated pollination to other T. aestivum plants; however, outcrossing rates are usually low (The potential for introgression of the novel trait into weedy relatives of wheat in Canada and the United States is also very low. Two species closely related to wheat are Aegilops cylindria Host (jointed goat grass) and Agropyron repens (L.) Beauv. (quackgrass). Both of these are introduced species, native to Eurasia, and are considered weedy and invasive in Canada and the United States. Jointed goatgrass is an annual, found in most of the United States, but not in Canada. It is considered a noxious weed in British Columbia due to the proximity of populations in Washington, Idaho and Montana, but is also found in other states contiguous to Canada, i.e., North Dakota, Michigan, Ohio and New York. It would not be expected to become established in Canada except in southwestern British Columbia and southwestern Ontario (Darbyshire, 2003). Hybridization of jointed goatgrass with wheat can occur under field conditions and has been reported in wheat fields in Oregon. The hybridization was successful to the first backgross generation with jointed goat grass as the female plant. This has raised concerns of possible introgression of wheat into jointed goatgrass populations (Morrison et al., 2002). Quackgrass is a perennial species found extensively in Canada and the United States. Reports of hybridization between wheat and quackgrass have been reported; however, these have not been successfully reproduced by manual pollination (CFIA, 1999). Due to the doubtful nature of any hybridization between wheat and quackgrass, gene introgression into quackgrass populations is not expected to occur.

Weediness potential

Cultivated wheat is not considered a weed of agriculture. Wheat plants can volunteer in fields following a wheat crop but these can be controlled by cultivation or herbicides. No competitive advantage was conferred to Teal 11A, other than resistance to two imidazolinone herbicides. Results from agronomic performance field trials and compositional data show that the physiology of Teal 11A was not affected by the mutation of the AHAS gene. Teal 11A is not expected to become weedy or invasive of natural habitats since neither vegetative growth or reproductive characteristics were altered. Wheat volunteers expressing the modified AHAS gene are therefore not expected to become weedier than conventional wheat volunteers. These volunteers could be managed with conventional weed control practices, including herbicides other than imidazolinones.

Secondary and Non-Target Effects

The characterization of the modified AHAS gene containing a single base pair change, and the resulting modified enzyme led to the conclusion that the expression of the modified does not result in altered toxic or allergenic properties. The modified AHAS enzyme was found to be substantially equivalent to AHAS in nonmodified plants. The AHAS enzyme is not a known toxin, does not confer resistance to agricultural pests, and is naturally present in plans and micro-organisms. It is similar to conventional wheat in terms of vegetative growth and seed production. Based on this information, Teal 11A would not result in altered impacts on non-target organisms, compared to conventional wheat varieties.

Impact on Biodiversity

Teal 11A does not possess novel phenotypic characteristics that would extend its cultivation beyond the current geographic range of spring wheat. Neither does it possess characteristics that would allow it to grow and compete under soil and climatic conditions for which it is not adapted. The herbicide-tolerant trait, in itself, will not confer to any potential hybrids any competitive advantage other than tolerance to imidazolinone herbicides. Teal 11A has also been found safe to non-target organisms and does not display altered plant pest potential since agronomic and biological characteristics were within the range of conventional wheat varieties.

Food and/or Feed Safety Considerations Expand

Dietary exposure

The modification to the AHAS enzyme in Teal 11A will not result in any change in the consumption or use pattern of wheat and wheat-based products. The availability of many wheat cultivars for cultivation, the diversity of wheat in phenotypic traits, and the normal variation in wheat composition due to differences in growing conditions all result in a wide variation in the composition of conventional wheat grain. Since the modification to the AHAS enzyme would not be expected to change the gluten content in Teal 11A, the cultivation and use of this wheat would not result in any new or additional concern for individuals with celiac disease. The cultivation of Teal 11A would not be expected to change the dietary exposure in Canada and the United States, any more than commercially available wheat cultivars.

Nutritional Data

Nutritional components of Teal 11A wheat were measured analytically and compared to those of the parental line CDC Teal. These components included: moisture, crude protein, crude fat, crude fibre, the amino acids valine, isoleucine, leucine, threonine, cystine, lysine and methionine. Also measured were fatty acids, B vitamins (thiamine HCL, niacin, pantothenic acid, pyridoxine), and minerals (phosphorus, zinc, magnesium and iron). Other than small but significant differences in crude fibre and oleic acid, which were lower in Teal 11A, there were no differences between Teal 11A and CDC Teal in the levels of all other nutritional components. The nutritional composition of Teal 11A wheat was found to be similar to its nonmodified parent, and within the range of commercial wheat varieties.

The anti-nutrients phytic acid and trypsin inhibitor were measured in Teal 11A and CDC Teal. Phytic acid occurs naturally in wheat 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 protein digestion. Phytic acid levels in Teal 11A were equivalent to those in CDC Teal. Trypsin inhibitor levels in both Teal 11A and CDC Teal were below the limit of detection.

Toxicity and Allergenicity

The potential for toxicity and allergenicity of Teal 11A wheat was determined by examining the characteristics of the modified AHAS protein and the amino acid sequence homology between the modified protein and known toxins and allergens. The unmodified form of AHAS is heat sensitive and susceptible to trypsin degradation. Data from studies on the heat sensitivity and trypsin degradability of the modified AHAS in Teal 11A showed similar sensitivity to heat and trypsin degradability compared to unmodified AHAS. The unmodified form of AHAS shows no amino acid similarity to known toxins and allergens. The modified AHAS is substantially equivalent to the unmodified enzyme in that it differs by only one amino acid. Evidence was also provided to show that the protein components of Teal 11A were not altered compared to those of unmodified control. Results from HPLC on protein extracts demonstrated that no new major proteins or increased protein expression occurred as a result of the mutation to the AHAS enzyme. From these results it was concluded that Teal 11A wheat did not demonstrate any potential for toxicity and allergenicity compared to conventional unmodified wheat.

Abstract Collapse

Teal 11A (Clearfield™) spring wheat was not subject to regulation in any jurisdiction except Canada since the development of this herbicide-tolerant line did not employ recombinant DNA technologies. In Canada, regulatory approval was required for use in human food and livestock feed, and for environmental release.

Commercial wheat is comprised mainly of two species: common, or bread wheat (T. aestivum L.) and durum wheat (T. durum Desf.). Bread wheat is classified into several types, based on vernalisation requirement (winter and spring types) and kernel hardness. The hard types of bread wheat are high in protein, especially gliadins and glutenins. The high levels of these protein fractions in the flour impart elasticity to bread dough and allow it to expand during leavening and baking. Soft wheats are low in protein, and have low levels of gliadin and glutenin; these qualities are desirable in products such as cakes and pastries, and in unleavened breads. Durum wheat produces very hard, almost vitreous kernels due to its high protein content. This wheat is milled into semolina for the production of pasta and couscous.

Harvested wheat consists of a naked kernel, unlike other cereals such as rice, barley or oats that retain their hull (i.e., the palea and lemma). The wheat kernel is loosely enclosed within the palea and lemma of each spikelet; these are eliminated as chaff during threshing. The wheat kernel is milled into white flour by removing the bran, aleurone layers and the germ prior to grinding; whole-wheat flour retains these fractions. By-products of wheat milling include: bran, germ, shorts and middlings. Some of these by-products are used as human food (i.e., bran, germ), and others, as livestock feed. Grain that does not meet the grade for food use can be used as animal feed, mainly for poultry and swine, but also for cattle. Wheat can also be fed as forage, either as pasture prior to stem elongation, or as ensilage. Wheat is also used in the brewing and distilling industries.

Weeds are a major production problem in wheat cultivation. Weeds compete for light, water and nutrients, and can also cause lodging and problems with harvesting. The seeds of several weed species are almost impossible to clean out of harvested wheat (e.g., Avena fatua L. wild oats), causing loss of quality and downgrading of the crop. Weeds can be managed using a combination of cultural practices (e.g., seed bed preparation, use of clean [certified] seed, narrow row spacing, fertilizer banding), integrated weed management (e.g., weed scouting, economic thresholds) and the use of herbicides. Depending on the weed species present, herbicides can be applied before the crop emerges (e.g., amitrole, glyphosate, trifluralin), or after (e.g., 2-4D, bromoxynil, dicamba, fenoxaprop-p-ethyl, MCPA, metsulfuron methyl). The build-up of weed populations can be stemmed by applying herbicides on summer-fallowed fields, and by practicing crop rotation, which allows the use of different herbicides. Rotating among herbicide groups also prevents the development of herbicide-resistant biotypes.

Teal 11A (Clearfield™) spring wheat was developed to allow the use of imazamox and imazethapyr, both imidazolinone herbicides, as weed control options in spring wheat production. The mode of action of imazamox and imazethapyr consists of inhibiting the activity of acetohydroxyacid synthase (AHAS), an enzyme in plants active in glycolysis and in the biosynthesis of the branched-chain amino acids isoleucine, leucine and valine. The result of the inhibition of AHAS activity is a decrease in protein synthesis, and in an accumulation of toxic levels of alpha-ketoglutarate, all of which causes the eventual death of the plant. While unmodified wheat is not tolerant to either imazamox or imazethapyr, the line Teal 11A has been modified to survive an otherwise lethal application of these herbicides. Teal 11A was developed using chemically induced seed mutagenesis and whole plant selection procedures. The herbicide tolerance is due to a mutation in the AHAS gene, which codes for an alteration in the binding site for imazamox in the AHAS enzyme.

Teal 11A spring wheat has been field tested in Canada in Saskatchewan and the United States, in Minnesota and North Dakota, from 1999 to 2001. Data collected from replicated field trials demonstrated that Teal 11A did not differ significantly from the parental line in terms of vegetative growth, time to maturity, seed production (yield), disease resistance, and tendency to weediness.

The potential for transfer of the herbicide tolerant trait from Teal 11A wheat to other nonmodified wheat plants, or to wild relatives of wheat, has been investigated. Common wheat (T. aestivum) is primarily self-pollinating. While outcrossing can occur by wind-pollination, the rates are usually low (Wild species closely related to T. aestivum in the continental United States and Canada are Aegilops cylindria Host (jointed goatgrass) and Agropyron repens (L.) Beauv. (quackgrass). Both of these are introduced species, native to Eurasia, and are considered weedy and invasive in Canada and the United States. Jointed goatgrass is an annual, found in most of the United States, but not in Canada. It is considered a noxious weed in British Columbia due to the proximity of populations in Washington, Idaho and Montana, but is also found in other states contiguous to Canada, i.e., North Dakota, Michigan, Ohio and New York. It would not be expected to become established in Canada except in southwestern British Columbia and southwestern Ontario (Darbyshire, 2003). Hybridization of jointed goatgrass with wheat can occur under field conditions and has been reported in wheat fields in Oregon. The hybridization was successful to the first backgross generation with jointed goat grass as the female plant. This has raised concerns of possible introgression of wheat into jointed goatgrass populations (Morrison et al., 2002). Quackgrass is a perennial species found extensively in Canada and the United States. Reports of hybridization between wheat and quackgrass have been reported; however, these have not been successfully reproduced by manual pollination (CFIA, 1999). Due to the doubtful nature of any hybridization between wheat and quackgrass, gene introgression into quackgrass populations is not expected to occur.

The food and livestock safety of Teal 11A wheat was based on an evaluation of the similarity of AHAS, in structure and function, to the enzyme naturally present in food and livestock feeds, and the lack of toxicity or allergenicity of the modified AHAS. The nutritional equivalence and wholesomeness of Teal 11A wheat compared to conventional wheat was demonstrated by the analysis of key nutrients in the grain including proximates (e.g., crude protein, crude fat, crude fibre, ash, moisture), amino acids, fatty acids, B vitamins (thiamine, niacin, panthothenic acid, and pyridoxine), and minerals (phosphorus, magnesium, zinc and iron), as well the composition in the anti-nutrients phytic acid and trypsin inhibitor.

Links to Further Information Expand

Canadian Food Inspection Agency, Plant Biosafety Office Health Canada, Novel Foods

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