The Role of Photorespiration and Glycine-Decarboxylase-Complex in Cyanobacteria

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The process of photorespiration leads to a loss of about 30% of newly fixed organic carbon in C3 plants, but its role is poorly understood. The main function of the photorespiratory cycle seems to be the conversion of 2-phophoglycolate to 3-phosphoglycerate and was found to be essential for plants at ambient CO2 concentration. The ubiquitous glycine-decarboxylase-complex (GDC) and serine-hydroxymethyl transferase are part of this cycle. In the genomes of cyanobacteria, which are believed to represent the ancestors for plant chloroplasts and photosynthesis, genes were assigned, which code for proteins of high similarities to photorespiratory enzymes including GDC from plants. These proteins and generally the role of photorespiration in cyanobacteria are only scarcely investigated. During this proposal we want to investigate the physiological role of these proteins in the cyanobacterial model strain Synechocystis by generating and functional analyzing corresponding mutants. The possible interaction of GDC subunits from cyanobacteria and plants will be analyzed in vivo (complementation of cyanobacterial mutants by plant cDNAs) or in vitro (reconstitution of heterologous complexes). Additionally cyanobacterial genes may be expressed in Arabidopsis to assess possible different performance in photorespiration and/or oxidative stress resistance.