Characterisation of the Arabidopsis COG complex

The plant Golgi apparatus is not only a central hub for both protein and lipid trafficking/sorting, but is also a carbohydrate factory serving two major functions: it synthesises the complex polysaccharides of the cell wall matrix and processes the oligosaccharide side chains of glycoproteins. The conserved oligomeric Golgi (COG) complex is an evolutionary conserved peripheral membrane protein complex that is essential for establishing and/or maintaining the structural and functional organisation of the Golgi apparatus in animals and yeast. Therefore, it is part of the general machinery organising glycosylation enzymes within the Golgi stack by acting as a retrograde vesicle tethering factor in intra-Golgi trafficking. In animals and yeast, the COG complex exists as a bi-lobed structure consisting of eight subunits (Cog1 to Cog8). Loss of COG subunits causes perturbations in protein sorting, glycosylation and Golgi stack morphology. In contrast to these findings, virtually nothing is known about the existence of a COG complex as well as the function of single COG subunits in plants. 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.