Sorting of seed storage proteins in developing seeds: Formation of transport vesicles and interdependence of different sorting pathways

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Plant seed storage proteins are essential for human nutrition, either directly or indirectly as staple food. Storage proteins can make up to more than 30% of the dry weight of the seed. During maturation of dicotyledonous plants, like legumes and rape, seed storage proteins are deposited in specialized vacuoles, the protein storage vacuoles PSV), in the developing embryo. Proteins reach these vacuoles via different vesicular transport routes, the Clathrin Coated Vesicle (CCV), and the, hitherto unique, Dense Vesicle (DV) mediated pathways. These pathways appear to be interdependent. This proposal aims at investigating the interdependence of these two pathways into the PSV of Arabidopsis embryos on a molecular and ultrastructural level, employing immuno electron-microscopy. We will compare the sorting of molecular transport markers with defined vacuolar sorting determinants in seeds of transgenic Arabidopsis wild type plants and deletion mutants devoid of receptors and cytosolic proteins important for these two transport routes. We will investigate the formation of the DV at the cis-Golgi apparatus on a molecular level. We will employ biochemical, proteomic, and reverse genetic approaches to identify and characterize proteins which are involved in the aggregation of cargo proteins.