Analysis of ER-Export of vacuolar transporter using the example of the V-ATPase in Arabidopsis thaliana

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The sorting and targeting of many transporters remains elusive in the plant cell. Even the transport routes between ER and vacuole are more complex and less understood in plants than e.g. in yeast. Plant cells further sort different isoforms of several primary active transporters into different subcellular compartments. This sorting is of central interest since the isoforms then take on different responsibilities in the cell. Therefore, the project deals with the ER-export of a primary active transporter, the vacuolar proton translocating ATPase (V-ATPase). This enzyme offers the advantage of at least three isoenzymes that differ in their subcellular localization, so that an ER-resident isoenzyme can be compared with an endosomal and a vacuolar isoenzyme. Furthermore, individual subunits of the V-ATPase seem to be capable to take an alternative route from the ER to the vacuole bypassing the Golgi and endosomal compartments. In yeast, the ER-export involves ER exit sites (ERES), the cargo receptor Erv14p for membrane integral proteins, and the COPII-coat for completing sorting and vesicle formation. These components are available in the plant cell, but their relevance for ER-export is still unclear. In the present project, the ERES-dependency of V-ATPase’s ER-export will be analyzed in the plant cell with respect to the individual isoenzymes and transport routes. The next key-questions that will be addressed are the function of the COP II-coat in sorting the V-ATPase and the role of an Erv14p ortholog in mediating between coat and cargo proteins in Arabidopsis thaliana. The project aims at elucidating the mechanism of ER-export of transport proteins in A. thaliana.