The plant secretory pathway consists of several membrane-bound organelles including the endoplasmic reticulum (ER), Golgi apparatus, trans-Golgi network (TGN), prevacuolar compartment (PVC) and vacuole, whereas the endocytic pathway contains various endosomal compartments.Each of these compartments fulfills a specific set of tasks in cargo sorting, distribution, and catabolism.These complicated processes mainly rely on the cascades of Rab GTPases, a large family of small GTPases.Rab GTPases function as molecular switches that alternate between two conformational states: the GTP-bound form and the GDP-bound form.Rab GTPases are reversibly associated with membranes by hydrophobic geranylgeranyl groups that are attached to one or two carboxy-terminal Cys residues, and this is intrinsic to their role in regulating membrane traffic.We are interested in the molecular mechanisms of organelle formation in plant cells, in particular, the endosome or prevacuolar compartment and the vacuole.