Determination of environmental safety of Monsanto Canada Inc.'s Roundup herbicide-tolerant brassica napus canola line GT73.

  • Agriculture and Agri-Food Canada
Date:
1995
Catalogue details

Licence: In copyright

Credit: Determination of environmental safety of Monsanto Canada Inc.'s Roundup herbicide-tolerant brassica napus canola line GT73. Source: Wellcome Collection.

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    the shikimate biochemical pathway for the production of the aromatic amino acids phenylalanine, tyrosine and tryptophan. The plant version of this enzyme, ubiquitous in nature, is sensitive to glyphosate - the herbicide disrupts this essential pathway, leading to growth suppression or death of the plant. However, the bacterial derived version of this enzyme is highly insensitive to glyphosate and fulfils the aromatic amino acid needs of the plant. ¢ The second gene, also bacterial derived from a strain of a species ubiquitous in nature, expresses an enzyme that degrades glyphosate, thereby deactivating the herbicidal effect. The coding sequence of this gene has been altered to enhance the efficiency of glyphosate degradation, compared to the original bacterial version. e A plant-derived coding sequence expressing a chloroplast transit peptide was co- introduced with each of the Roundup-Ready™ genes. This peptide facilitates the import of the newly translated Roundup-Ready™ enzymes into the chloroplasts, the site of both the shikimate pathway and glyphosate mode-of-action. ¢ Both genes associated with their transit peptide coding sequence, are linked to the same constitutive promoter. Roundup-Ready™ protein expression was monitored in leaf and seed tissue of plants in two years of confined field trials. ¢ The Roundup-Ready™ proteins showed no significant homology with any known toxins or allergens. The novel enzyme associated with the shikimate pathway, is a version of an enzyme that is ubiquitous in nature, and therefore would not be expected to be toxic or allergenic to non-target organisms. For the second novel enzyme, which degrades glyphosate, Monsanto describes experiments with a variety of substrates that show that it has a narrow substrate specificity, and appears not to affect any plant specific pathways. Both proteins were inactivated during processing of canola seed into feed ingredients. 2. Development Method Brassica napus variety “Westar” was transformed using a disarmed non-pathogenic Agrobacterium tumefaciens vector, i.e., the T-DNA region of an A. tumefaciens plasmid from which virulence and disease causing genes were removed, and replaced with the Roundup-Ready™ genes. The T-DNA portion of A. tumefaciens plasmids are generally known to insert randomly into the plant’s genome and the insertion is usually stable, as was shown to be the case in GT73. 3. Stable Integration into the Plant’s Genome Monsanto has provided information on segregation and Southern blot analysis that demonstrates that GT73 has a single genetic insert, consisting of single copies of the Roundup-Ready™ genes.
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