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

光呼吸过程导致C3植物中新固定有机碳损失约30%，但其作用尚不清楚。光呼吸循环的主要功能似乎是将2-磷酸甘油酸转化为3-磷酸甘油酸，并被发现对环境CO2浓度下的植物至关重要。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。蓝藻被认为是植物叶绿体和光合作用的祖先，在蓝藻的基因组中，基因被分配，编码与植物光呼吸酶（包括GDC）高度相似的蛋白质。这些蛋白质和一般作用的光呼吸在蓝藻只有很少的调查。在本提案中，我们希望通过生成和功能分析相应的突变体来研究这些蛋白质在蓝藻模型菌株联胞菌中的生理作用。来自蓝藻和植物的GDC亚基可能的相互作用将在体内（通过植物cdna进行蓝藻突变体的互补）或体外（异源复合物的重组）进行分析。此外，蓝藻基因可能在拟南芥中表达，以评估可能在光呼吸和/或氧化应激抗性方面的不同表现。

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.