Potatoes with altered sugar metabolism had changed levels of many
metabolites, some not thought to be associated with sugar
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.
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).
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,
Max-Planck-Institut für Molekulare Pflanzenphysiologie, Golm, Germany;
Institut für Informatik, University of Potsdam, Germany.
Brandenburg Ministry of Science, Research and Culture, Germany.
Not on the market as of 2008.
Copyright 2008 The Nature