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 membranes¹. 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^2,3. ATPase activity disassembles the SNAP receptor (SNARE) complex into Qa-SNARE, which folds back onto itself, and its partners^4,5. The fusion of identical membranes has a different sequence of events⁶. 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 vacuole⁷. Membrane fusion in Arabidopsis cytokinesis is formally akin to vacuolar fusion⁸. 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 plane⁹. The SM protein KEULE is required for the formation of trans-SNARE complexes between adjacent membrane vesicles¹⁰. 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.