Plant cell division: building walls in the right places

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Abstract
ONLINE SUMMARY In plant cells, the division plane is predicted before mitosis by the location of a preprophase (PPB) band of microtubules and actin filaments in the cell cortex. The phragmoplast, a cytoskeletal structure that guides the formation of the new cell wall after mitosis, interacts with the cortical site formerly occupied by the preprophase band to position the new wall at that site. This interaction requires actin, and recent evidence indicates a possible role for myosins as well The plane of division for many plant cells can be predicted by their shapes. Cytoskeletal filaments radiating from the nucleus to the cortex may 'read' cell shape to determine the plane of division. In asymmetrically dividing cells, the plane of division is coordinated with cell polarity, which has been shown to depend on actin, the cell wall and secretion. In asymmetrically dividing cells of the maize leaf epidermis, Brick1 and Pangloss 1 are required for polarization of the mother cell and two Discordia genes are required for guidance of phragmoplasts to the former PPB site. The Tangled1 gene of maize is required for phragmoplast guidance in most or all leaf cells. Molecular analysis of the Tangled1 gene and protein indicates that TAN1 protein might participate in the orientation of cytoskeletal structures in dividing cells through an association with microtubules.