Driving Plant Cytokinesis

Plant cytokinesis involves formation of a cell plate that is generated from the phragmoplast, a membranous structure located between two daughter nuclei that contains a network of microtubules and proteins related to vesicle trafficking. Nucleus- and phragmoplast-localized protein kinase 1 (NPK1) is a mitogen-activated protein kinase kinase kinase (MAPKKK) that accumulates in the phragmoplast and is required for normal cytokinesis. Nishihama et al. have identified a kinesin-like motor protein called NACK1 that activates NPK1 in tobacco cells. NPK1 interacts directly with the noncatalytic region of NPK1in vitro and in vivo and phosphorylates NACK1 and itself. NACK1 also colocalized with NPK1 the equatorial zone of the phramoplast. Disruption of the interaction or expression of a truncated NACK1 lacking the motor domain caused mislocalization of NPK1 and defective cytokinesis. The authors propose that NPK1 is transported to the phragmoplast equator by NACK1, although the role of NPK1 signaling in cell-plate formation remains unclear. R. Nishihama, T. Soyano, M. Ishikawa, S. Araki, H. Tanaka, T. Asada, K. Irie, M. Ito, M. Terada, H. Banno, Y. Yamazaki, Y. Machida, Expansion of the cell plate in plant cytokinesis requires a kinesin-like protein/MAPKKK complex, Cell 109 , 87-99 (2002). [Online Journal]