The cytokinesis gene KEULE encodes a Sec1 protein that binds the syntaxin KNOLLE

KEULE is required for cytokinesis in Arabidopsis thaliana. We have position ally cloned the KEULE gene and shown that it encodes a Sec1 protein. KEULE is expressed throughout the plant, yet appears enriched in dividing tissues . Cytokinesis-defective mutant sectors were observed in all somatic tissues upon transformation of wild-type plants with a KEULE-green fluorescent pro tein gene fusion, suggesting that KEULE is required not only during embryog enesis, but at all stages of the plant's life cycle. KEULE is characteristi c of a Sec1 protein in that it appears to exist in two forms: soluble or pe ripherally associated with membranes. More importantly, KEULE binds the cyt okinesis-specific syntaxin KNOLLE. Secl proteins are key regulators of vesi cle trafficking, capable of integrating a large number of intra- and/or int ercellular signals. As a cytokinesis-related Sec1 protein, KEULE appears to represent a novel link between cell cycle progression and the membrane fus ion apparatus.