Genetic dissection of cytokinesis.

Higher plants have evolved specific mechanisms for partitioning the cytoplasm of dividing cells. In the predominant mode of phragmoplast-assisted cytokinesis, a cell wall and flanking plasma membranes are made de novo from a transient membrane compartment, the cell plate. which in turn forms by vesicle fusion from the centre to the periphery of the dividing cell. Other modes of cytokinesis appear to occur in meiotic cells and developing gametophytes. Here we review recent progress in the analysis of plant cytokinesis, focusing on genetic studies in Arabidopsis which are beginning to identify structural and regulatory components of phragmoplast-assisted cytokinesis. Two classes of mutations have been described. In one class, the defects appear to be confined to cell plate formation, suggesting that the execution of cytokinesis is specifically affected. Mutations in the other class display more general defects in cell division. We also discuss possible roles of proteins that have been localised in cytokinetic cells but not characterised genetically. Finally, mutations affecting meiotic or gametophytic cell divisions suggest that mechanistically different modes of cytokinesis occur in higher plants.