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Current projects
Organisation and dynamics of the ER
Anne Osterrieder: Matrix proteins and Golgi biogeneis
Plant Golgi stacks need to maintain their structural integrity while moving through the cell. A Golgi matrix formed by structural proteins and tethering factors could hold the stacks together and might also be required during Golgi biogenesis. In animals the golgins, a protein family with long coiled-coil domains, play a role in the formation and structural maintenance of the Golgi apparatus.
Several plant golgins have been identified in our group by database mining and their location within the Golgi stack has been determined. AtCASP, p115 and two isoforms of golgin-84 are found at the cis-Golgi face, whereas TMF and AtGRIP locate to the trans-face of the Golgi stack. Their function is as yet unknown.
Does a Golgi matrix exist in plants and if yes, is it a stable or dynamic structure? What role do golgins play in Golgi biogenesis and stack maintenance? Do they function as tethering factors between Golgi stacks and the ER surface? We address those questions using microscopic methods such as confocal/electron microscopy and fluorescent lifetime imaging as well as molecular biology and biochemistry.
Pengwei Wang: Function of VAP proteins in the ER
The structure and dynamic property of the plant cortical endoplasmic reticulum (ER) network is regulated by the actin cytoskeleton. However, there must be a mechanism that holds the ER in position while remodelling. Two recent studies on ER persistency mapping and optical laser trapping have revealed the existence of the anchoring points of the ER to the plasma membrane (PM). Proteins involved in forming these ER/PM anchor points are largely unknown. Recently, we have focused on a family of proteins called VAPs (vesicles-associated membrane protein-associated protein). Proteins in this family play a role in binding lipid-binding proteins and in intracellular trafficking in mammalian systems. We are investigating whether proteins in this family may also be involved in the ER/PM anchoring process. They are localised to the ER and label immobile punctate structure when over-expressed in tobacco leaves (image shows VAP36-YFP co-expressed with a calnexin transmembrane domain fused to YFP and expressed in tobacco leaf epidermal cells). Their functions are currently being studied as part of our overall research programme on the organisation of the cortical endoplasmic reticulum.
Jennifer Schoberer: Organisation and function of the plant COG complex
The Golgi-mediated processing of N-linked oligosaccharide side-chains on glycoproteins is catalysed by a series of glycosidases and glycosyltransferases that are non-uniformly distributed within successive cisternae of the plant Golgi stack [2,3]. The mechanisms responsible for the non-uniform distribution of Golgi-resident enzymes and proteins are poorly understood. The conserved oligomeric Golgi (COG) complex is an evolutionary conserved peripheral membrane protein complex consisting of eight subunits, which is essential for establishing and/or maintaining the structural and functional organisation of the Golgi apparatus in animals and yeast. This project will look at the location and function of plant COG homologues and putative interacting proteins in Arabidopsis and tobacco using live-cell imaging and mass spectrometry. Besides investigating the subcellular location of COG homologues in plants, the project will aim to determine a COG subunit interaction map as well as to describe potential interactions between COG subunits and structural, regulatory and processing proteins and enzymes that we know to be located in or associated with the membrane of the cisternal Golgi stack. The analysis of COG mutants will shed light on the putative function of the COG complex in plant cells.
