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Published on October 1, 2008; 10.1104/pp.108.126516

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Received July 16, 2008
Accepted September 24, 2008

Decreased expression of cytosolic pyruvate kinase in potato tubers leads to a decline in pyruvate resulting in an in vivo repression of the alternative oxidase

Sandra N. Oliver , John E. Lunn , Ewa Urbanczyk-Wochniak , Anna Lytovchenko , Joost T. van Dongen , Benjamin Faix , Elmar Schmalzlin , Alisdair R. Fernie , and Peter Geigenberger *

Max-Planck Institute of Molecular Plant Physiology, Am Muehlenberg 1, 14476 Potsdam-Golm, Germany; Leibniz-Institute of Vegetable and Ornamental Crops, Theodor-Echtermeyer-Weg 1, 14979 Grossbeeren, Germany; University of Potsdam, Institute of Chemistry and Interdisciplinary Center for Photonics, Karl-Liebknecht-Strasse 24-25, 14476 Potsdam-Golm, Germany

* Corresponding author; email: geigenberger{at}igzev.de.

The aim of this work was to investigate the effect of decreased cytosolic pyruvate kinase on Solanum tuberosum (potato) tuber metabolism. Transgenic potato plants with strongly reduced levels of cytosolic pyruvate kinase were generated by RNAi gene silencing under the control of a tuber-specific promoter. Metabolite profiling showed that decreased cytosolic pyruvate kinase activity led to a decrease in the levels of pyruvate and some other organic acids involved in the tricarboxylic acid cycle. Flux analysis showed that this was accompanied by changes in carbon partitioning, with carbon flux being diverted from glycolysis towards starch synthesis. However, this metabolic shift was relatively small and hence did not result in enhanced starch levels in the tubers. Although total respiration rates and the ATP/ADP ratio were largely unchanged, transgenic tubers showed a strong decrease in the levels of alternative oxidase protein and a corresponding decrease in the capacity of the alternative pathway of respiration. External feeding of pyruvate to tuber tissue or isolated mitochondria resulted in activation of the alternative oxidase pathway, both in the wild type and the PKc transgenic lines, providing direct evidence for the regulation of alternative oxidase by changes in pyruvate levels. Overall, these results provide evidence for a crucial role of cytosolic pyruvate kinase in the regulation of pyruvate levels as well as the level of the alternative oxidase in heterotrophic plant tissue, and furthermore reveal that these parameters are interlinked in vivo.




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