Update on Vesicle Trafficking during Somatic Cytokinesis Vesicle Trafficking during Somatic Cytokinesis

Plant cytokinesis, the final event of cell division, generates two daughter cells by partitioning the cytoplasm of a mother cell. This depends on targeted secretion to generate a new plasma membrane (PM; Whaley and Mollenhauer, 1963; Samuels et al., 1995; Jurgens, 2005a, 2005b). Plant cells control cytokinesis by constructing a plant-specific cytoskeletal configuration, the phragmoplast (Zhang et al., 1993; Granger and Cyr, 2000; Assaad, 2001). The phragmoplast consists of a double array of parallel-oriented microtubules, actin filaments, associated molecules, and a cell plate assembly matrix acting as a framework to transport cell plate-building vesicles to the cell equator (Lambert, 1993; Staehelin and Hepler, 1996; Otegui et al., 2001; Wasteneys, 2002; SeguiSimarro et al., 2004). Homotypic fusion of these vesicles, constricted by dynamins, gives rise to dumbbell-shaped tubular structures and the formation of a transient membrane compartment, the cell plate. The tubulovesicular network created by end-to-end fusion of vesicles evolves into a fenestrated sheet (Samuels et al., 1995; Otegui et al., 2001; Segui-Simarro et al., 2004). The cell plate grows outward to the cortex of the cell by peripheral vesicle fusion directed by the depolymerization of the central microtubules and polymerization of microtubules at the periphery (Strompen et al., 2002; Sasabe and Machida, 2006; Sasabe et al., 2006). When the cell plate reaches the cortex, it fuses with the parental PM, a process requiring heterotypic vesicle fusion. Fusion activates the maturation of the plate to a rigid cell wall, a process that includes closure of the plate fenestrae, removal of excess membrane, and replacement of callose by cellulose (Samuels et al., 1995; Segui-Simarro et al., 2004). This review provides an update on the membrane-trafficking events during plant somatic cytokinesis involved in initial plate formation, fusion of the cell plate with the parental PM, and trafficking events associated with cell plate maturation (Fig. 1).