The Arabidopsis KNOLLE and KEULE genes interact to promote vesicle fusion during cytokinesis

Partitioning of the cytoplasm during cytokinesis or cellularisation require s syntaxin-mediated membrane fusion [1-3], Whereas in animals, membrane fus ion promotes ingression of a cleavage furrow from the plasma membrane [4,5] , somatic cells of higher plants form de novo a transient membrane compartm ent, the cell plate, which is initiated in the centre of the division plane and matures into a new cell wall and its flanking plasma membranes [6,7]. Cell plate formation results from the fusion of Golgi-derived vesicles deli vered by a dynamic cytoskeletal array, the phragmoplast. Mutations in two A rabidopsis genes, KNOLLE (KN) and KEULE (KEU), cause abnormal seedlings wit h multinucleate cells and incomplete cell walls [1,8], The KN gene encodes a cytokinesis-specific syntaxin which localises to the cell plate [9], Here , we show that KN protein localisation is unaffected in keu mutant cells, w hich, like kn, display phragmoplast microtubules and accumulate ADL1 protei n in the plane of cell division but vesicles fail to fuse with one another, Genetic interactions between KN and KEU were analysed in double mutant emb ryos. Whereas the haploid gametophytes gave rise to functional gametes, the embryos behaved like single cells displaying multiple, synchronously cycli ng nuclei, cell cycle-dependent microtubule arrays and ADL1 accumulation be tween pairs of daughter nuclei. This complete inhibition of cytokinesis fro m fertilisation indicates that KN and KEU, have partially redundant functio ns and interact specifically in vesicle fusion during cytokinesis of somati c cells.