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Unintended Effects of Genetic Manipulation
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Transgenic expression of a disease-resistance gene activated the oxidative-stress response in rice.

Manipulated Organism: Rice (Oryza sativa).

Inserted Transgenes: An optimized version of the gene for cecropin A, an antimicrobial peptide originally from the moth Hyalophora cecropia. The maize ubiquitin promoter was used to express this gene in all parts of the plant.

Goal of This Study: To create rice plants resistant to the rice blast fungus Magnaporthe grisea and to characterize the effects of transgene expression on the rest of the genome.

Intended Effect: Rice plants expressing cecropin A showed various degrees of resistance to rice blast fungus in the greenhouse.

Unintended Effects:
  • Most of the transgenic plants engineered to secrete cecropin A into the intercellular fluid (apoplast) were infertile.

  • Plants in which cecropin A was allowed to accumulate inside the cell appeared to have normal fertility and morphology, but unintended effects on gene expression were discovered. A fourfold increase in expression was detected for 58 genes covering a wide range of functions.

  • In particular, three different peroxidase genes were strongly activated in the transgenic rice plants. Peroxidase enzymes detoxify oxygen free radicals, which are normal by-products of photosynthesis but can also be elevated by certain stresses. When hydrogen peroxide was applied externally to transgenic and parent rice plants, the transgenic plants showed less signs of injury, thereby confirming high levels of peroxidase activity.

  • Expression also increased for several genes related to protein synthesis, folding, and secretion, most likely in response to the high expression levels of cecropin A.

Sources: Coca, M., G. Penas, J. Gomez, S. Campo et al. (2006). "Enhanced Resistance to the Rice Blast Fungus Magnaporthe grisea Conferred by Expression of a cecropin A Gene in Transgenic Rice," Planta vol. 223, pp. 392-406.

Campo, S., S. Manrique, J. Garcia-Martinez, and B. San Segundo (2008). "Production of Cecropin A in Transgenic Rice Plants Has an Impact on Host Gene Expression," Plant Biotechnology Journal vol. 6, pp. 585-608.

Author Affiliations: CSIC and IRTA, Spain.

Funding: European Commission; Ministerio de Ciencia y Tecnologia; MEC; Generalitat de Catalunya.

Product Status: Not on the market as of 2009.

Copyright 2009 The Nature Institute.

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