Abstract
The NACK-PQR pathway, which is composed by NACK1 kinesin-like protein, NPK1 MAPKKK, NQK1 MAPKK and NRK1/NTF6 MAPK in tobacco, is known as a key regulator for plant cytokinesis. This pathway is specifically activated during cytokinesis via the direct binding between NACK1 and NPK1, however, it remains to be determined how the interaction of these proteins is regulated. Here, we report that CDKs negatively regulate the NACK-PQR pathway before metaphase. Both NACK1 and NPK1 were highly phosphorylated during early M phase, and these phosphorylations were dependent on the activity of CDKs. Phosphorylations of NACK1 and NPK1 by CDKs inhibited the interaction between NACK1 and NPK1. In Arabidopsis plants, HINKEL (homologue of NACK1 in Arabidopsis) gene in which have phospho-mimic mutations at CDK-phopshorylation conserved motifs was not able to complement the phenotype of hik mutants that exhibit severe dwarfism, seedling lethality and cytokinetic defects. These results suggest that CDKs suppress the activation of NACK-PQR pathway until the onset of cytokinesis.
