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

光呼吸过程导致C3植物中约30%的新固定有机碳的损失，但其作用知之甚少。光呼吸循环的主要功能似乎是将2-磷酸乙醇酸转化为3-磷酸甘油酸，并被发现在环境CO2浓度下对植物至关重要。普遍存在的甘氨酸脱羧酶复合物（GDC）和丝氨酸羟甲基转移酶是这个循环的一部分。在被认为代表植物叶绿体和光合作用祖先的蓝藻的基因组中，分配了编码与植物的光呼吸酶（包括GDC）高度相似的蛋白质的基因。这些蛋白质和一般的作用，光呼吸蓝藻只是很少调查。在本研究中，我们希望通过产生相应的突变体并进行功能分析，来研究这些蛋白在蓝藻模式菌株集胞藻中的生理作用。GDC亚基从蓝藻和植物的可能的相互作用将在体内（蓝藻突变体的植物cDNA互补）或在体外（异源复合物的重建）进行分析。此外，蓝藻基因可以在拟南芥中表达，以评估光呼吸和/或氧化胁迫抗性中可能的不同表现。

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.