GM Crop Database

Database Product Description

AP602CL
Host Organism
Triticum aestivum (Wheat)
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 2003 2003 2003

Introduction Expand

Imidazolinone herbicides are active against the enzyme acetohydroxyacid synthase (AHAS), also known as acetolactate synthase (ALS) or acetolactate pyruvate- lyase.

This enzyme catalyzes the first step in the biosynthesis of the essential branched chain amino acids isoleucine, leucine and valine. Herbicide induced AHAS inhibition results in a lethal decrease in protein synthesis. Unmodified wheat is not tolerant to imidazolinones, while soybeans, peas, white beans and kidney beans are naturally tolerant to them.
Depending on the species, plants contain single or multiple copies of the AHAS genes. The genome of T. aestivum is believed to contain an AHAS multigene family.

Modifications of AHAS genes in various plant species can result in herbicide tolerant phenotypes and typically consist of one amino acid substitution, sufficient to alter the binding site for imidazolinones such that the herbicide no longer inhibits the AHAS enzyme. Several modified AHAS plants have been isolated.

AP602CL was selected from a population of T. aestivum derived by chemical-induced mutagenesis of seed of the wheat variety Gunner. One mutant, tolerant to imidazoline was selected and designated AP602CL. Tolerance to imadazoline was demonstrated by comparison of the activity of the AHAS enzyme extracted from AP602CL to that of wild type plants.

The novel tolerance to imadazoline is under control of the native AHAS promoter and is believed to be constitutively expressed. Sequence information for the modified AHAS gene in AP602CL was submitted.

The levels of valine, leucine and isoleucine produced in wheat are regulated by feedback inhibition of AHAS. Modified AHAS shows similar feedback inhibition to that of unmodified AHAS. AHAS is not known to be an allergen and modified AHAS also does not exhibit characteristics associated with allergens. The protein components of AHAS are not altered in comparison with unmodified Gunner wheat.

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

Seed of the wheat variety Gunner was subjected to chemical-induced mutagenesis with Ethyl methane sulfonate (EMS) and Diethyl sulphate (DES). Whole plant selection procedures for herbicide tolerance were used. One herbicide tolerant mutant was designated AP602CL.

Characteristics of the Modification Expand

The Introduced DNA

A single amino acid substitution is responsible for the imadazolinone tolerance mutation in the AHAS gene. The substitution is sufficient to alter the binding site for imadazolinones, resulting in a lack of inhibition of the AHAS enzyme.

Genetic Stability of the Introduced Trait

The segregation of herbicide tolerance in crosses with AP602CL is consistent with the inheritance of a single semi- or co-dominant allele. AP602CL segregated in a 3:1 ratio ( herbicide resistant: susceptibility to herbicide).

Expressed Material

The modified AHAS enzyme lacks a binding site for imadazolinone herbicides. This prevents the inhibition of the activity of this enzyme by the herbicide. AHAS is active in the production of valine, leucine and isoleucine and inhibition of this activity results in a decrease in protein production and eventual plant death. The modified AHAS has no significant difference in its activity in producing valine, leucine or isoleucine and the protein components of AP602CL are not substantially different from that of its parent line, Gunner.

Environmental Safety Considerations Expand

Outcrossing

Wheat line AP602CL is not intended for cultivation in Canada and there are no wild Triticum species in North America. There are no known naturally occurring hybrids between wheat and its only weedy relative occurring in Canada, Agropyron repens. Hybridization has been known to occur with Aegilops cylindrica which is present as a weed of winter wheat in the United States, but fertile offspring are not readily produced. Gene flow from AP602CL to wild or weedy species in Canada is very unlikely.

Weediness potential

Wheat plants can occur as volunteers in years following the cultivation of a wheat crop and are usually eliminated by the use of herbicides or mechanical means. The imadozolinone tolerance trait does not confer competitive advantage to AP602CL. Volunteers persisting after a crop can be controlled with the use of non-imadozolinone herbicides and/or mechanical means. Due to this and the stated intent not to cultivate AP602CL in Canada, there is no altered weed or invasiveness potential of this line compared to conventional varieties.

Secondary and Non-Target Effects

BASF submitted data indicating that the modified AHAS enzyme was substantially equivalent to its unmodified counterpart. The native AHAS enzyme does not confer resistance to agricultural pests and is found in many plants and micro-organisms. It is not a known toxin. The modified AHAS enzyme did not alter the biosynthesis of amino acids. As the line is not intended for cultivation in Canada, there were no expected impacts of AP602CL on non-target organisms due to the modified AHAS enzyme.

The use of a particular herbicide may provide selection pressure for the development of herbicide tolerant weeds. Agricultural extension officers should promote careful management practices for growers who use AP602CL to minimize the development of imidazolinone-tolerant weed populations.

Food and/or Feed Safety Considerations Expand

Dietary Exposure:

AP602CL Clearfield wheat is expected to be used in similar applications as other wheat varieties. There were no expected changes in gluten content in this variety, thus presenting no new or additional concern for individuals with celiac disease.

Nutritional Analysis:

Analysis for nutritional and anti-nutritional components of grain derived from AP602CL Clearfield wheat revealed no significant difference from grain derived from the parent line Gunner wheat. AP602CL had slightly lower fat content, lower oleic acid content and higher threonine content than Gunner, but these differences were determined to have no impact on livestock nutrition. There were no other substantial differences between AP602CL and Gunner in terms of nutritional composition.

Toxicity and Allergenicity:

The expression of the modified AHAS enzyme is not associated with any toxicity or allergenicity concerns. AHAS is expressed at very low amounts in the edible portion of wheat, its activity is heat-labile and degrades in the human gastrointestinal tract. The modified AHAS enzyme is not homologous to known allergens and is not different from the unmodified AHAS in its similarity to known allergens. AP602CL wheat does not express any other new proteins or altered amounts of other proteins, including known wheat allergens. It is also unlikely that AP602CL has unintended secondary mutagens that may cause effects on livestock or bystanders.

Abstract Collapse

AP602CL (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 is 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.

AP602CL (Clearfield™) spring wheat was developed to allow the use of imazamox, an imidazolinone herbicide, as a weed control option in spring wheat production. The mode of action of imazamox 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 cause the eventual death of the plant. While unmodified wheat is not tolerant to imazamox, the line AP602CL has been modified to survive an otherwise lethal application of this herbicide. AP602CL 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.

Depending on the species, plants contain single or multiple copies of the AHAS genes. The genome of T. aestivum is believed to contain an AHAS multigene family.

Modifications of AHAS genes in various plant species can result in herbicide tolerant phenotypes and typically consist of one amino acid substitution, sufficient to alter the binding site for imidazolinones such that the herbicide no longer inhibits the AHAS enzyme. Several modified AHAS plants have been isolated.

AP602CL was selected from a population of T. aestivum derived by chemical-induced mutagenesis of seed of the wheat variety Gunner. One mutant, tolerant to imidazoline was selected and designated AP602CL. Tolerance to imadazoline was demonstrated by comparison of the activity of the AHAS enzyme extracted from AP602CL to that of wild type plants.

The novel tolerance to imadazoline is under control of the native AHAS promoter and is believed to be constitutively expressed. Sequence information for the modified AHAS gene in AP602CL was submitted.

The levels of valine, leucine and isoleucine produced in wheat are regulated by feedback inhibition of AHAS. Modified AHAS shows similar feedback inhibition to that of unmodified AHAS. AHAS is not known to be an allergen and modified AHAS also does not exhibit characteristics associated with allergens. The protein components of AHAS are not altered in comparison with unmodified Gunner wheat.

Links to Further Information Expand

Canadian Food Inspection Agency, Plant Biosafety Office Office of Food Biotechnology, Health Canada

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