The impact of short-cutting photorespiration on carbon and nitrogen metabolism

最近，我们培育出了拟南芥植物，这些植物被改造成氧化质体内的乙醇酸。这些植物表现出良好的生长效应，单位面积的CO2同化率和叶绿素含量都较高。为了实现这一点，在质体中引入过氧化氢酶以消除乙醇酸氧化酶产生的过氧化氢是至关重要的。在这里，我们建议进一步使用乙醇酸脱氢酶(GlcDH)来优化这一原始途径，而不产生过氧化氢。为此，我们将遵循两个策略，(I)使用微单胞菌GlcDh和(Ii)联合使用聚球藻Glcd1和GlcD2。将选择带有新途径的转基因株系，并将在不同水平上分析对植物表现的影响。此外，还将深入研究这些活性酶的动力学性质。另一方面，光呼吸已被清楚地证明与其他细胞过程相互作用。在这方面，我们以前的工作表明，在shm1-1突变体中2-羟基戊二酸(2HG)的积累是光依赖的，这与高水平的甘氨酸、2-酮戊二酸和许多氨基酸有关。此外，我们首次发现在正常条件下生长的植物的野生型叶提取物中同时存在2HG，D-和L-2HG的对映体，尽管含量极低。因此，我们的小组将专门关注光呼吸与2HG过程(如衰老、新陈代谢修复)之间的相互作用。为此目的，基因组、生化、代谢和通量分析方法的组合将被应用于一组光呼吸突变体，它们积累不同水平的甘氨酸。

We recently produced Arabidopsis plants engineered to oxidise glycolate inside the plastids. These plants showed beneficial effects on growth and had higher CO2 assimilation rates per unit area and chlorophyll. To achieve this, it was of radical importance to introduce catalase in the plastids to eliminate H2O2 produced by glycolate oxidase. Here, we propose to work further in the optimization of this original pathway using a glycolate dehydrogenase (GlcDH), without production of H2O2. To this end, we will follow two strategies, (i) the use of Micromonas GlcDH and (ii) the combined use of Synechocystis GlcD1 and GlcD2. Transgenic lines bearing the new pathways will be selected and the impact on plant performance will be analysed at different levels. Moreover, the kinetic properties of these activities enzymes will be thoroughly investigated. On the other hand, photorespiration has been clearly demonstrated to interact with other cellular processes. In this regard, our previous work indicated a light-dependent accumulation of 2-hydroxyglutarate (2HG) in the shm1-1 mutant, which was correlated with high levels of glycine, 2-ketoglutarate and many amino acids. Moreover, we showed for the first time that both enantiomeric forms of 2HG, D-and L-2HG can be found, although at extremely low levels, in wild-type leaf extracts of plants growing in normal conditions. Our group will thus specifically focus on the cross-talk of photorespiration with processes involving 2HG (e.g. senescence, metabolic repair). For this purpose a combination of genomic, biochemical, metabolomic and flux profiling approaches will be applied to a set of photorespiratory mutants, which accumulate glycine to different levels.