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Unintended Effects of Genetic Manipulation
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Wheat with transgene for low-molecular-weight glutenin showed anomalies in glutenin production and some plants had reduced levels of other storage proteins.

Manipulated Organism: Spring wheat (Triticum aestivum L.), cultivar Bobwhite.

Inserted Transgenes: Low-molecular-weight glutenin subunit gene for producing glutenin, derived from the wheat variety "Cheyenne," driven by its own promoter. A marker gene (UBI:BAR) conferring resistance to the herbicide BASTA (bialaphos) was part of the gene construct.

Goal: Increase the amount of glutenin stored in wheat kernels. Glutenin is a protein important for the elasticity of wheat dough used for baking. Researchers hope to improve the baking quality of wheat flour.

Intended Effect: In one (of eleven) transgenic line there was a 12- to 16-fold increase in the expression of transgenic glutenin above normal glutenin expression levels.

Unintended Effects:
  • Flour from the transgenic wheat kernels had, in contrast to the authors' expectations, poorer "visco-elastic properties" (p. 220).
  • Eleven lines were determined to be transgenic because of their ability to grow in a medium containing the herbicide bialaphos, but 10 of these lines showed no increase in the amount of the low-molecular-weight glutenin subunit.
  • The increased expression of the low-molecular-weight glutenin subunit was associated with a decrease in gliadin synthesis. Wheat gluten consists of both gliadin and glutenin.
  • In some transgenic plants in the fourth generation "a high level of transgene over-expression was associated with lower levels of other storage proteins, including high molecular weight glutenin subunits and gliadins. . . . This decrease may be the result of the diversion of the seed protein nitrogen reserves into making huge amounts of the transgenic [protein] at the expense of all the other seed proteins" (p. 219).
  • After the first generation, the number of plants expressing the transgene was lower than expected: only about one-third of the plants in each generation showed elevated expression, while the authors expected that three-fourths would have raised levels of the transgenic protein. "These observations could be indicative of transgene silencing or co-suppression in a subpopulation of the seeds, or of instability of the chromosome(s) carrying the transgenes" (p. 219).

Source: Masci, S., R. D'Ovidio, F. Scossa, C. Patacchini et al. (2003). "Production and Characterization of a Transgenic Bread Wheat Line Over-Expressing a Low-Molecular-Weight Glutenin Subunit Gene," Molecular Breeding vol. 12, pp. 209-22.

Author Affiliations: University of Tuscia, Italy, and U.S. Department of Agriculture, Agricultural Research Service.

Funding: Italian government.

Product Status: Not on the market as of 2008.

Copyright 2008 The Nature Institute.

This document: http://natureinstitute.org/nontarget/reports/wheat_002.php

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