Adaptor proteins in protein trafficking between endomembrane compartments in plants

Clathrin is a highly conserved coat protein that plays a critical role in lipid vesicle-mediated trafficking at multiple routes in various post-Golgi compartments. It consists of large and small subunits, and exists in the cytosol as triskelions composed of three pairs of small and large subunits. For vesicle formation, the triskelions are recruited to the membrane of specific compartments where they undergo self-polymerization to produce coats for lipid vesicles. However, clathrin has no ability to bind directly to lipid membranes. Therefore, accessory proteins are necessary for its recruitment to the donor compartment where vesicles are formed. A large number of accessory proteins, called adaptor proteins, have been identified and characterized extensively at the molecular and cellular levels in animal cells and yeast. Recently, the roles of many adaptor proteins have been elucidated in plant cells. As expected from the conserved nature of lipidmediated trafficking in eukaryotic cells, these plant adaptor proteins for clathrin show a high degree of functional conservation with those found in animal cells and yeast. At the same time, they are also involved in plant-specific processes such as the transition from the PSV to the lytic vacuole and cell-plate formation. Here, we summarize recent advances in the physiological roles of adaptor proteins in plant cells.