Photorespiration, also called C2 photosynthesis or “breathing in the light”, is essential process in photosynthetic organisms. The unspecificity of the CO2-fixing enzyme Rubisco, to also accept oxygen as substrate results in the production of 2-phosphoglycolate. Accumulating 2-phosphoglycolate inhibits several enzymes of the Calvin-Benson-Bassham cycle and needs to be detoxified. Although the core enzymes of the photorespiratory cycle are known,  A) several required transport proteins are unknown and B) the metabolic interaction of photorespiration with accessory metabolic pathways is less well understood. Within these projects we aim at A) characterizing novel photorespiratory transport protein and B) understand the integration of photorespiration in the cellular metabolic network.

Researchers: Nicole Linka, Marion Eisenhut, Franziska Kuhnert, Marc-Sven Röll, Anastasjia Plett

Subcellular compartmentalization enabled pro- and eukaryotic organisms to target metabolic reaction into distinct organelles. To ensure metabolite flow within the metabolic network of the cell, organellar membranes contain pores, channels and transporters. This project aims to understand the roles of transport proteins in cellular metabolism by (A) biochemical characterization of recombinant proteins in vitro using liposome systems, (B) physiological characterization of loss-of-function mutants, and (C) in vivo analyses with isolated intact organelles.

Researcher: Franziska Kuhnert

The peroxisomal hub - Connecting metabolic pathways in plants

Peroxisomes are essential hubs for plant metabolism. They are involved in numerous metabolic processes, including photorespiration, fatty acid degradation, synthesis of signalling molecules and secondary products. These pathways require an interplay with other compartments, such as plastids and mitochondria. Consequently, a high number of substrates, intermediates and cofactors needs to be transported across the   peroxisomal   membrane.   However,   very   little   is   known   regarding   peroxisomal transport proteins, mediating the exchange of these structural divers molecules and ions.

In   the   last   decade,   considerable   progress   has   been   made   in   peroxisome   biology through genomics, transcriptomics and proteomics. Using these data our group has discovered   the   first   carrier   proteins   for   plant   peroxisomes   mediating   the   import   of ATP, NAD and CoA which are required for a wide range of metabolic reactions inside peroxisomes. We study the exchange of metabolites by combining molecular biology, genetics   and   biochemistry. Our   goal   is   to   describe   and   fully   understand how peroxisomes are connected to the cellular metabolism of plant cell.

Researchers: Anastasija Plett, Jeannine Schlebusch and Nicole Linka

Plastids in plants and other plastid-harboring eukaryotes fulfil a broad range of metabolic functions, ranging from photosynthesis to fatty acid and amino acid biosynthetic pathways. It is still unknown how amino acids, which are mostly biosynthesized in the plastid stroma, are exported to the cytoplasm and how plastids during the early stages of plastid development are supplied with amino acids from, e.g., seed storage proteins. In yeast and animal cells, mitochondria are tethered to the endoplasmic reticulum by specific proteins. It is unknown how plastids (and mitochondria) in plant cells interact with the endoplasmic reticulum and which proteins mediate the interactions between these organelles and other cellular membrane systems. In the proposed work, we will test the hypothesis that plastidial membrane proteins containing a domain of unknown function (DUF3411) represent a novel class of amino acid transporters in plant cells. Further, we will develop novel methodology to identify proteins that mediate the interactions between plastids and mitochondria in plant cells with the endoplasmic reticulum. In this SFB-funded project we collaborate with the proteomics facility at the BMFZ at the HHU.

Researcher: Franziska Kuhnert