Molecular biology of the cell, 24(4):510-20, 1, 2013. Paper Website abstract bibtex
The exocyst complex, an effector of Rho and Rab GTPases, is believed to function as an exocytotic vesicle tether at the plasma membrane before SNARE complex formation. Exocyst subunits localize to secretory active regions of the plasma membrane, exemplified by the outer domain of Arabidopsis root epidermal cells. Using VAEM microscopy we visualized the dynamics of exocyst subunits at this domain. The subunits colocalized in defined foci at the plasma membrane, distinct from endocytic sites. Exocyst foci were independent of cytoskeleton, although prolonged actin disruption led to changes in exocyst localization. Exocyst foci partially overlapped with vesicles visualized by VAMP721 v-SNARE, but the majority of the foci represent sites without vesicles, as was indicated by electron microscopy and drug treatments, supporting the concept of the exocyst functioning as a dynamic particle. We observed a decrease of SEC6-GFP foci in an exo70A1 exocyst mutant. Finally, we documented decreased VAMP721 trafficking to the plasma membrane in exo70A1 and exo84b mutants. Our data support the concept where the exocyst complex subunits dynamically dock and un-dock at the plasma membrane to create sites primed for vesicle tethering.