Transport of photorespiratory intermediates between cellular compartments

光呼吸代谢是一个高度区隔化的途径，包括叶绿体、过氧化物酶体、线粒体和细胞质。至少14个不同的运输步骤是必要的，以允许光呼吸中间体在不同的车厢之间有效穿梭。与表征良好的光呼吸酶相比，代谢物转运体的情况相当差。这个项目的目的是识别这些转运体，从而缩小光呼吸知识的主要差距。我们可以确定代谢转运体BOU1和MEP1在光呼吸中的关键功能。相应的拟南芥突变体表现出典型的光呼吸表型。我们认为，线粒体载体蛋白BOU1运输对甘氨酸脱羧酶复合物活性至关重要的底物。mep1基因编码一种叶绿体代谢物转运蛋白，这种转运蛋白是在质体包膜中运输乙醇酸和甘油所必需的。由于转运蛋白的活性不能通过体外试验证明，我们将在下一个资助期采用体内方法。此外，我们最近可以证明拟南芥二羧酸转运体DiT1是光呼吸所必需的。为了进一步鉴定新的光呼吸转运体，我们正在继续筛选基于转录共表达分析选择的拟南芥突变体。At1g78620和ucp1-3可以检测到4个新的候选基因。目前正在研究这些基因的突变体。PROMICS加入“中心实验”的目的是揭示光呼吸代谢、相关途径和C/N信号传导的新见解。我们可以建立成功的样品制备和转录组学分析的工作流程。在下一轮中，我们将扩展样本输入并专注于完整数据集的评估。我们相信，我们可以利用整合的转录组学和代谢数据来运行一个旨在提高光合途径效率的计算模型。

Photorespiratory metabolism is a highly compartmentalized pathway, comprising chloroplasts, peroxisomes, mitochondria and cytosol. At least 14 different transport steps are necessary to allow for effective shuttling of photorespiratory intermediates in between the different compartments. In contrast to the well-characterized photorespiratory enzymes the situation for the metabolite transporters is rather poor. The aim of this project was and is to identify those transporters and thus close a major gap in knowledge about photorespiration. We could establish a crucial function of the metabolite transporters BOU1 and MEP1 in photorespiration. Corresponding Arabidopsis mutants showed a typical photorespiratory phenotype. We suggest that the mitochondrial carrier protein BOU1 transports a substrate that is essential for glycine decarboxylase complex activity. The gene mep1 encodes for a chloroplast metabolite transporter required for the transport of glycolate and glycerate across the plastid envelope membrane. Since transporter activities could not be demonstrated by in vitro assays, we will follow an in vivo approach in the next funding period. Additionally, we could recently show that the Arabidopsis dicarboxylate transporter DiT1 is required for photorespiration. To identify further novel photorespiratory transporters we are continuing with screening Arabidopsis mutants selected on the basis of transcript co-expression analyses. With At1g78620 and ucp1-3 four new candidate genes could be detected. Mutants in these genes are currently under investigation. The aim of the PROMICS joined “Central experiment” is to unravel new insights into photorespiratory metabolism, associated pathways and C/N signalling. We could establish the workflow for successful sample preparation and transcriptomic analysis. In the next round we will expand the sample input and concentrate on the evaluation of the full dataset. We believe that we can use the integrated transriptomic and metabolic data to run a computational model aimed at improving the efficiency of the photosynthetic pathway.