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Unintended Effects of Genetic Manipulation
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Bt maize has higher lignin content.

Manipulated Organism: Maize (Zea mays L.).

Inserted Transgenes: crylAb gene for producing insecticidal delta-endotoxin from Bacillus thuringiensis (Bt). The gene was fused to the cauliflower mosaic virus (CaMV-35S) promoter so that the gene would be expressed in all parts of the plant. The researchers tested different commercial varieties, including MON810 (trade name: YieldGard®), which is the main variety of Bt maize on the market.

Goal: Produce transgenic maize (called "Bt maize" or "Bt corn") that produces a toxin that can kill the larvae of the European corn borer and other insect pests. In these two studies, the researchers investigated whether the genetic manipulation may have affected other characteristics of the plant.

Intended Effect: Bt maize does produce the toxin and has been grown on millions of acres of farmland since 1996.

Unintended Effects: The stems of Bt maize plants have higher lignin content than normal (isogenic) controls: 18-25% higher according to Poerschmann et al. (2005); 33-97% higher according to Saxena and Stotzky (2001).

Additional Comments: The question arises whether the higher lignin content, which makes the stems woodier, may affect their digestibility in cattle or pigs, to which maize stems are fed. What other biochemical pathways may have been repressed or altered as a result of the increased production of lignin is unknown.

Source: Poerschmann, J., A. Gathmann, J. Augustin, U. Langer et al. (2005). "Molecular Composition of Leaves and Stems of Genetically Modified Bt and Near-Isogenic Non-Bt Maize - Characterization of Lignin Patterns," J. Environ. Quality vol. 34, pp. 1508-18.

Saxena, D. and G. Stotzky (2001). "Bt Corn has a Higher Lignin Content than Non-Bt Corn," American Journal of Botany vol. 88: pp. 1704-6.

Author Affiliations: Poerschmann et al.: UFZ-Center for Environmental Research, Leipzig-Halle, Germany; RWTH Aachen, Germany; Leibniz-Center for Agricultural Landscape and Land Use Research, Muncheberg, Germany; Department of Chemistry, University of Waterloo, Canada. Saxena and Stotzky: Laboratory of Microbial Ecology, New York University, USA.

Funding: Poerschmann et al.: German Research Council (DFG).
Saxena and Stotzky: U.S. Environmental Protection Agency (partial).

Product Status: Bt maize is on the market under a number of brand names (YieldGard® is the most widely used variety) and has been commercially grown since 1996.

Copyright 2008 The Nature Institute.

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