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Unintended Effects of Genetic Manipulation
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Potatoes with altered sugar metabolism had changed levels of many metabolites, some not thought to be associated with sugar metabolism.

Manipulated Organism: Potato (Solanum tuberosum), cultivar Desiree.

Inserted Transgenes and Intended Effect: Three types of transgenic potatoes were compared that had been genetically altered to break down sucrose in their tubers in different ways. In each type a gene for a different enzyme related to sucrose catabolism had been added: genes for bacterial sucrose phosphorlase; a yeast invertase; or bacterial glucokinase in combination with the yeast invertase. The palatin B33 promoter was used to target gene expression specifically in the potato tubers. The overall context of this research is the effort by scientists to find ways to enhance the ability of potatoes to store starch. This entails modifying the sugar metabolism, since sugars are converted into starch.

Goal of This Study: The researchers wanted to carry out a metabolic profile of transgenic potato lines, each with a differently altered sugar metabolism, to see what other effects on substance formation the genetic alteration might have. They investigated a total of 88 substances.

Results of This Study: To their surprise, the researchers found that there were changes in the amounts of most of the 88 metabolites they investigated, and that many changes seemed unrelated to the sucrose breakdown pathway. The transgenic lines differed both from each other and from the non-manipulated potatoes in the production of different metabolites. For example, the transgenic potatoes often produced more amino acids than the non-manipulated potatoes, and nine substances were found in the transgenic potatoes that could not be detected in the non-manipulated potatoes.

Additional Comments: A review article remarks that the above study "revealed a massive elevation in the content of each individual amino acid. This was particularly surprising since it had previously been thought that the majority of the tuber's need for amino acids was met by supply from the leaves, and that the tuber did not possess the necessary machinery for de novo synthesis of amino acids. It, furthermore, demonstrates the need for considering the effect of genetic manipulation on pathways other than those targeted" (Carrari, F., E. Urbanczyk-Wochniak, L. Willmitzer, and A. Fernie (2003). "Engineering Central Metabolism in Crop Species: Learning the System," Metabolic Engineering vol. 5, pp. 191-200).

Source: Roessner, U., A. Luedemann, D. Brust, O. Fiehn et al. (2001). "Metabolic Profiling Allows Comprehensive Phenotyping of Genetically or Environmentally Modified Plant Systems," The Plant Cell vol. 13, pp. 11-29.

Author Affiliations: Max-Planck-Institut für Molekulare Pflanzenphysiologie, Golm, Germany; Institut für Informatik, University of Potsdam, Germany.

Funding: Brandenburg Ministry of Science, Research and Culture, Germany.

Product Status: Not on the market as of 2008.

Copyright 2008 The Nature Institute.

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