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Unintended Effects of Genetic Manipulation
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Unintended changes in gene expression were observed in Arabidopsis plants engineered for resistance to the herbicide glufosinate.

Manipulated Organism: Arabidopsis thaliana (thale cress; mustard family).

Inserted Transgenes: bar gene from Streptomyces hygroscopicus, which produces the enzyme PAT. The PAT enzyme inactivates the herbicide glufosinate, which is sold under the tradenames Liberty and Basta.

Background: The bar gene, or a closely related gene called pat, has been inserted into many crops for two reasons. One is for use in cropping systems where the herbicide glufosinate is sprayed to control weeds. The second is for use as a selectable marker during tissue culture to confirm integration of the transgene.

Goal of This Study: Investigate the effects of bar gene insertion and treatment with glufosinate on gene expression levels in Arabidopsis.

Results of This Study:
  • Three different transgenic lines were created, none of which showed differences in germination, leaf number, root length, or fresh weight compared with the parent when grown in the laboratory.

  • Despite the lack of recognizable morphological differences, the gene expression patterns of the transgenic plants were different than the control. In particular, "four genes were found to be significantly repressed only in the three transgenic lines" (p. 267).

  • Plants were then grown in media containing the herbicide glufosinate at a concentration sufficient to kill non-transgenic plants but not the transgenic ones. Compared with plants grown in herbicide-free media, changes in gene expression were observed for 80 genes in the transgenic plants. Of these, 51 also changed in non-transgenic plants exposed to glufosinate, while 29 were unique to the transgenic plants. The functions of these genes included such diverse roles as detoxification, embryogenesis, lipid transfer, and cytokinin biosynthesis, and a number had no known function.

Additional Comments: "Although the wild-type plants undergo extensive transcriptional reprofiling [that is, changes] in response to herbicide-induced stress and, finally, plant death, the transgenic plants appear to activate other detoxification processes to offset the toxic effects of the residual herbicide or its derivatives" (p. 266).

Source: Abdeen, A., and B. Miki (2009). "The Pleiotropic Effects of the bar Gene and Glufosinate on the Arabidposis Transcriptome," Plant Biotechnology Journal, vol. 7, pp. 266-82.

Author Affiliations: Agriculture and Agri-Food Canada.

Funding: Canadian Food Inspection Agency.

Product Status: The bar or pat gene is present in many GM crops on the market.

Copyright 2009 The Nature Institute.

This document: http://natureinstitute.org/nontarget/reports/arabidopsis_005.php

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