Abstract
The tobacco protein kinase NPK1 is a MAPKKK that regulates formation of the cell plate during cytokinesis. In this study, we have identified tobacco NQK1 as a MAPKK and NRK1 as a MAPK that act downstream of NPK1. NQK1, NRK1, and NPK1 are activated at the late M phase of the cell cycle in tobacco cells. In addition, they are rapidly inactivated by depolymerization of phragmoplast microtubules. Overexpression of kinase-negative NQK1 in tobacco cells generates multinucleate cells with incomplete cross-walls. Arabidopsis plants with a mutation in the ANQ1 gene, an ortholog of NQK1, display a dwarf phenotype, with unusually large cells that contain multiple nuclei and cell-wall stubs in various organs. Thus, NQK1 MAPKK appears to be a positive regulator of cytokinesis and responsible for the growth and development of plants. Our results also suggest that activities of these kinases are related to the architecture of phragmoplast microtubules.
