NSF/αSNAP2-mediated cis-SNARE complex disassembly precedes vesicle fusion in Arabidopsis cytokinesis.

Eukaryotic membrane fusion requires trans-SNARE complexes bridging the gap between adjacent membranes. Fusion between a transport vesicle and its target membrane transforms the trans- into a cis-SNARE complex. The latter interacts with the hexameric AAA-ATPase N-ethylmaleimide-sensitive factor (NSF) and its co-factor alpha-soluble NSF attachment protein (αSNAP), forming a 20S complex. ATPase activity disassembles the SNAP receptor (SNARE) complex into Qa-SNARE, which folds back onto itself, and its partners. The fusion of identical membranes has a different sequence of events. The fusion partners each have cis-SNARE complexes to be broken up by NSF and αSNAP. The Qa-SNARE monomers are then stabilized by interaction with Sec1/Munc18-type regulators (SM proteins) to form trans-SNARE complexes, as shown for the yeast vacuole. Membrane fusion in Arabidopsis cytokinesis is formally akin to vacuolar fusion. Membrane vesicles fuse with one another to form the partitioning membrane known as the cell plate. Cis-SNARE complexes of cytokinesis-specific Qa-SNARE KNOLLE and its SNARE partners are assembled at the endoplasmic reticulum and delivered by traffic via the Golgi/trans-Golgi network to the cell division plane. The SM protein KEULE is required for the formation of trans-SNARE complexes between adjacent membrane vesicles. Here we identify NSF and its adaptor αSNAP2 as necessary for the disassembly of KNOLLE cis-SNARE complexes, which is a prerequisite for KNOLLE-KEULE interaction in cytokinesis. In addition, we show that NSF is required for other trafficking pathways and interacts with the respective Q-SNAREs. The SNARE complex disassembly machinery is conserved in plants and plays a unique essential role in cytokinesis.