Cytokinesis in eukaryotes involves specific arrays of microtubules (MTs), which are known as the central spindle in animals, the anaphase spindle in yeasts, and the phragmoplast in plants. In plants, a mitogen-activated protein kinase (MAPK) cascade stimulates the turnover of phragmoplast MTs, which allows the expansion of the phragmoplast that is essential for cytokinesis including the formation of cell plates. A prerequisite for activation of this cascade is the interaction between mitotic kinesin NACK1 in tobacco (HINKEL in Arabidopsis) and MAPK kinase kinase NPK1 (ANP1, 2, 3 in Arabidopsis). Other members of this cascade are NQK1 MAPK kinase and NRK1/NTF6 MAPK in tobacco and the respective orthologs in Arabidopsis. All the components in the pathway (designated the NACK-PQR pathway) concentrate at the midzone of the phragmoplast in plant cells during cytokinesis. Downstream MAPKs in both plant species phosphorylate microtubule-associated protein 65 (MAP65). Interestingly, activities of components in the NACK-PQR pathway are downregulated by depolymerization of MTs. In the present review, we summarize current views on the mechanisms involved in activating the kinase cascade, a role of MAP65 phosphorylation by MAPK during cytokinesis, and the feedback mechanism for regulating inactivation of the kinase cascade.
Copyright © 2012 Wiley Periodicals, Inc.