PARENT SESSION
Posters P6D Crop photosynthesis, agricultural biotechnology. Abstracts (742-753)

Glycolate oxidation inside the chloroplast: A novel method for the suppression of photorespiration. Krishnaveni Thiruveedhi^*,1, Rashad Kebeish¹, Rafijul Bari¹, Ruben Rosenkranz¹, Fritz Kreuzaler¹, Christoph Peterhänsel¹, ¹ Aachen University,Institute for Biology I, Aachen, NRW, Germany

ABSTRACT- Photosynthetic carbon metabolism is initiated by the bifunctional enzyme ribulosebisphosphate carboxylase/oxygenase (Rubisco), which uses both CO₂ and O₂ as substrates. Carboxylation accounts for net CO₂ fixation whereas oxygenation leads to the loss of CO₂ in the photorespiratory pathway. Moreover, NH₃ is lost in this cycle that has to be refixed. Our project aims to introduce a novel method for the partial suppression of photorespiration in C₃ plants. For this, a biochemical pathway from E. coli converting glycolate to glycerate will be installed inside plant chloroplasts. In a first step, glycolate has to be oxidised to glyoxylate by a glycolate dehydrogenase (GDH) dependent on organic co-factors. To this end, a cDNA from A. thaliana encoding a GDH was cloned and characterised. It was shown to resemble the GDH enzymes present in many green algae but is distinct in its biochemical characteristics and its subcellular localisation from the so far known plant glycolate oxidases. The enzyme is naturally present in mitochondria but was re-targeted to the chloroplast as a starting point for the establishment of the novel pathway. In the second step, two molecules of glyoxylate will be condensed to form one molecule of tartronic semialdehyde (TS) under release of CO₂ that is immediately available for refixation by the carboxylase activity of RUBISCO. TS will be reduced to glycerate, a component that can be re-integrated into the plant basal metabolism. We constructed transgenic tobacco and Arabidopsis lines containing all necessary enzymatic activities in order to proof the function of this approach.

KEY WORDS: Photorespiration, Photosynthesis, Glycolate