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Unintended Effects of Genetic Manipulation
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The transgenic sequences of some Bt maize plants have changed since they were approved.

Manipulated Organism: Maize (Zea mays).

Inserted Transgenes: The MON810 transgene includes the Cry1Ab gene from Bacillus thuringiensis (Bt), which produces a protein toxic to the larvae of the European corn borer and other moth (Lepidoptera) species. The Cry1Ab gene is controlled by the Cauliflower Mosaic Virus (CaMV) 35S promoter to ensure high levels of expression throughout the plant.

Goal of This Study: The importation and cultivation of genetically engineered food and feed is regulated by law in most countries, including the U.S. In many cases, tolerance levels have been set for how much unapproved GM material is allowed in shipments of grain. To enforce these tolerance levels, tests have been developed to detect transgenic sequences, but such efforts are undermined if the sequences change over time. The goal of the study by Aguilera et al. (2008) was to determine whether the MON810 transgene was intact for various Bt corn varieties grown in Europe.

Results of This Study:
  • Twenty-six different MON810 varieties, all but one of which were approved for cultivation in Europe, were analyzed with three tests:

    1. The first test was for a 123-base-pair DNA sequence from the CaMV-35S promoter, which is not found naturally in maize. One variety from Spain, called ARISTIS BT, did not test positive.

    2. The second test was for a 4028-base-pair sequence of DNA that included the entire MON810 transgene and flanking sequences from the maize genome. This sequence was detected in all but two varieties: ARISTIS BT and CGS4540, the latter being the one variety in the study without regulatory approval (it was withdrawn from consideration by the crop developer).

    3. The third test was for the Bt protein Cry1Ab itself, which was detected in all varieties except ARISTIS BT.

  • From this study the researchers concluded that the MON810 transgene had remained intact in 24 of the 26 varieties tested. The ARISTIS BT specimen did not contain the transgene but presumably did at one time or farmers would have noticed European corn borer damage. (The possibility of a seed mix-up was not addressed by the authors.) The CGS4540 specimen appeared to have the transgene but not in the proper location for MON810. Either CGS4540 was mistakenly submitted as a MON810 variety by the crop developer or its transgene had moved to a different location in the genome.

Additional Comments: In a related study, Morisset et al. (2009) discovered while testing transgene detection methods that the sequence of the CaMV-35S promoter in a different type of Bt maize called TC1507 was not what it was supposed to be. There was a single base pair change compared with the sequence submitted by the crop developer to regulatory authorities.

Source: Aguilera, M., M. Querci, B. Balla, A. Prospero et al. (2008). "A Qualitative Approach for the Assessment of the Genetic Stability of the MON810 Trait in Commercial Seed Maize Varieties," Food Analytical Methods vol. 1, pp. 252-8.

Morisset, D., T. Demsar, K. Gruden, J. Vojvoda et al. (2009). "Detection of Genetically Modified Organisms--Closing the Gaps," Nature Biotechnology vol. 27, pp. 700-1.

Author Affiliations: European Commission Joint Research Center (Italy); National Institute of Biology (Slovenia).

Funding: Slovenian Research Agency.

Product Status: Corn with the MON810 transgene, marketed as YieldGard, was one of the first GM crops to be grown commercially. It is also the only GM crop grown on any significant acreage in Europe. Corn with the TC1507 transgene, marketed as Herculex, has been approved for commercial production in the U.S. since 2001.

Copyright 2009 The Nature Institute.

This document: http://natureinstitute.org/nontarget/reports/maize_008.php

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