GM Crop Database

Database Product Description

CL121, CL141, CFX51
Host Organism
Oryza sativa (Rice)
Trade Name
CLEARFIELD™
Trait
Imidazolinone herbicide tolerance.
Trait Introduction
Chemically induced seed mutagenesis
Proposed Use

Production for human food, livestock feed and industrial uses.

Product Developer
BASF Inc.

Summary of Regulatory Approvals

Country Food Feed Environment Notes
Canada 2002 2002

Introduction Expand

Rice lines CL121, CL141, and CFX51, were developed through a combination of chemically-induced accelerated mutagenesis and traditional cross-breeding to exhibit tolerance to imidazolinone containing herbicides, such as imazethapyr. Imidazolinone herbicides are active against the acetolactate synthase (ALS) enzyme in plants, which catalyzes the first reaction in the biosynthesis of branched-chain amino acids. Imidazolinone inhibits the production of these essential amino acids (valine, leucine and isoleucine), resulting in a decrease in protein synthesis and 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 Whole plant selection of imidazolinone tolerant mutants, followed by introgression of HT trait into commercial varieties through cross-breeding.

Characteristics of Oryza sativa (Rice) Expand

Center of Origin Reproduction Toxins Allergenicity
Northern India and Southeast Asia, and southern China are believed to be the centre of origin of Asian rice (O. sativa). Wild progenitors of African cultivated rice (O. glaberrima) are grasses endemic to West Africa. Basically an autogamous plant propagating through seeds produced by self-pollination. Cross pollination between wild species and O. sativa cultivars has been reported to occur in natural habitats. Antinutrients including phytic acid, trypsin inhibitor, hemagglutinins (lectins) are present in the bran fraction. Allergenic proteins, 14-15 kDa range, present in the albumin plus globulin protein fraction from rice endosperm. Major 16 kDa allergenic protein is a member of the alpha-amylase/trypsin inhibitor family of proteins.

Modification Method Expand

The original herbicide-tolerant rice mutant, 93AS3510, was selected following chemically-induced accelerated mutagenesis of AS3510 seeds treated with ethyl methanesulfonate (EMS). This mutant line was then crossed with the commercial rice varieties Cocodrie, Maybelle, and Cypress to create the imazethapyr tolerant lines CL121, CL141, and CFX51, respectively.

Characteristics of the Modification Expand

The Introduced DNA

As these were products of accelerated mutagenesis and conventional cross-breeding, there was no introduction or incorporation of heterologous DNA into the rice genome. The tolerance to imidazolinone-containing herbicides is due to a single point mutation within the ALS encoding gene such that the amino acid sequence of the mutated enzyme differs by one amino acid from that of the wild-type enzyme.

Genetic Stability of the Introduced Trait

The segregation of herbicide tolerance in crosses with 93AS3510 was consistent with the inheritance of a single semi- or co-dominant allele.

Expressed Material

There were no new novel proteins expressed. The level of expression of ALS within plant tissue is generally low (~0.001% of total protein in rice seed), and this level of expression was not altered because of the genetic modification. Sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis (PAGE) and high pressure liquid chromotagraphy (HPLC) of protein extracts from unmodified and modified rice varieties did not indicate the expression of new proteins, or altered expression of existing proteins, as a result of the mutagenic event.

Environmental Safety Considerations Expand

Outcrossing

There are no sexually compatible species for rice in Canada. The wild “rice” which does occur in Canada (Zizania aquatica) is not sexually compatible with domesticated rice, Oryza sativa. In addition, these herbicide-tolerant lines will not be cultivated in Canada and if released, would not persist in the environment.

Weediness Potential

Rice is not adapted to the environmental conditions encountered in Canada. The vegetative vigour, time to maturity, and seed production, for these herbicide-tolerant lines were within the normal range of these parameters as measured for other commercial rice varieties. In unmanaged ecosystems, the herbicide-tolerant trait will not confer a competitive advantage and will not, in itself, render rice more weedy or invasive of natural habitats.

Secondary and Non-Target Adverse Effects

There are no anticipated changes in ecological toxicity that would adversely impact on other organisms within managed or unmanaged ecosystems.

Impact on Biodiversity

As these lines did not display altered weediness or plant pest potential, or potential to adversely impact non-target organisms, and will not be cultivated in Canada, there was no anticipated impact on biodiversity in Canada.

Food and/or Feed Safety Considerations Expand

Nutritional Data (Livestock Feed Purposes)

Data on fatty acid profiles, protein content, amino acid composition, crude fibre, ash, phytate, and moisture content were provided for grain samples from lines CL121, CL141, and CFX51, and five commercial varieties grown in three locations in the United States. Comparisons of these parameters between the herbicide-tolerant lines and conventional commercial varieties did not reveal any biologically significant differences.

Toxicity and Allergenicity

The single amino acid change within the native ALS enzyme was not anticipated to have any effect on the potential toxicity or allergenicity of this protein. The unmodified form of this enzyme does not display amino acid sequence homology with known protein toxins or allergens. Studies on the modified ALS protein isolated from the original mutant line, 93AS3510, demonstrated that it was rapidly inactivated by heat (1 minute at 100°C) and was completely degraded within 5 minutes of treatment with trypsin. Susceptibility to heat inactivation and sensitivity to proteolytic degradation are not characteristics of known protein toxins or allergens.

Measurements of the concentrations of normally occurring rice antinutritional factors (e.g., phytic acid, trypsin inhibitor, and lectin) did not reveal any differences between these herbicide-tolerant lines and five conventional commercial rice varieties. For all of these varieties, the concentrations of trypsin inhibitor and hemagglutinins (i.e. lectins) were below the threshold of detection.

Abstract Collapse

This product 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, but not for environmental release as these lines were not intended for cultivation in Canada.

Harvested rice, or rough rice, is encased by an inedible hull or husk, which is removed before milling. The hulls are utilized as fuels, mulch, abrasives and animal feed products. Brown rice is what remains after the hulls are removed. The light brown colour of brown rice is due to the presence of bran layers and the rice germ surrounding the rice kernel. Brown rice can be milled into regular white or ‘polished rice’, where white rice is distinguished by the fact that the hulls, bran layers and rice germ are removed. The bran and rice germs are high in protein and nutrients and are used in specialty foods such as rice bran oil and also in livestock feed. Both brown and white rice kernels can be parboiled and/or milled into rice flour for use in breakfast cereals, baby foods and desserts and numerous other food products. Rice kernels are also used to produce beer and rice wine.

Weeds are a significant production problem in rice cultivation. Weeds of rice producing areas, such as the United States, include red rice (Oryza spp.), barnyard grass, sprangletop, fall panicum, large crabgrass, rice flatsedge, yellow nutsedge, and smartweed. These are typically managed using a combination of cultural practices (e.g., dry vs wet tillage, using clean seed, crop rotations) and chemical controls (herbicides such as molinate and propanil).

Rice lines CL121, CL141, and CFX51, were developed through a combination of accelerated mutagenesis and traditional cross-breeding to exhibit tolerance to imidazolinone containing herbicides, such as imazethapyr. Imidazolinone herbicides are active against the acetolactate synthase (ALS) enzyme in plants, which catalyzes the first reaction in the biosynthesis of branched-chain amino acids. Imidazolinone inhibits the production of these essential amino acids (valine, leucine and isoleucine), resulting in a decrease in protein synthesis and the eventual death of the plant. ALS is also active in the glycolytic pathway of plant metabolism, by which sugars are broken down to produce acids and release energy.

The original mutant line, 93AS3510, was used as a parental line in a breeding program with Cocodrie, Maybelle, and Cypress rice varieties to create lines CL121, CL141, and CFX51, respectively.

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