This proposal addresses "other topics that contribute to the development of the European Research Area in plant genomics" (Sub Call A). Plant performance including yield stability largely depends on the interaction with the biotic and abiotic environment as well as on cell-cell communication within the plant itself. Nutrient uptake and signaling are mediated by plasma membrane-localised proteins such as transporters and receptors whose activity is determined by interaction with downstream effectors as well as their availability through endosomal trafficking and sorting. Endosomal sorting results either in protein degradation via targeting to the vacuole or in protein recycling to the plasma membrane. To provide a necessary foundation for functional studies of plant performance as specified in other topics of Sub Call A, this project aims to analyse endosomal compartments of Arabidopsis by proteomics. Specifically, resident and cargo proteins of immuno-isolated, ultrastructurally defined endosomal compartments will be identified by MS and subsequently analysed for endosomal localisation in transgenic plants expressing Myc-tagged or GFP-fusion versions of newly-identified proteins. The anticipated results will establish the role of endosomal compartments in plasma-membrane protein trafficking and enable distinction of early/sorting from recycling endosomes.