Regulation of membrane fusion during cytokinesis - specificity and redundancy of SNARE complexes and regulatory SM proteins

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Plant cytokinesis is mechanistically different from cytokinesis in non-plant eukaryotes, with Golgi/TGN-derived membrane vesicles undergoing homotypic fusion to form the partitioning membrane between the two daughter nuclei. Although a plant-specific and cytokinesis-specific syntaxin named KNOLLE in Arabidopsis has been identified as a major regulator of membrane fusion in cytokinesis, its knockout still allows for the completion of embryogenesis. In contrast, a double mutant lacking both KNOLLE and its regulatory SM protein KEULE fails to undergo cytokinesis already at the zygote stage, suggesting functional redundancy of both syntaxins and SM proteins in cytokinesis. This proposal aims to identify the "back-up" system. Likely candidates are the SYP1 syntaxin SYP132 and the close paralogues of KEULE, SEC1A and SEC1B. We will perform experiments to test this idea, using a combination of genetic analysis, co-immunoprecipitation, subcellular localisation and yeast two-hybrid interaction assays. These experiments are to reveal SNARE complexes and their requirements in cytokinesis as well as their regulation by SM proteins in Arabidopsis. We will also perform functional studies in the moss Physcomitrella to explore the evolutionary origin of the cytokinesis machinery that operates in flowering plants.