Abstract
We have identified a tobacco MAPK cascade which consists of NPK1 MAPKKK, NQK1 MAPKK, and NRK1 MAPK. The cascade is activated at late M phase of cell cycle by binding of NPK1 to NACK1 kinesin-like protein. We named this pathway NACK-PQR. NACK1, NPK1, and NQK1 associate with the phragmoplast in tobacco BY-2 cells. Dominant-negative proteins of NACK1, NPK1, and NQK1 inhibits cell plate formation to generate multinucleate cells with incomplete cross walls. These findings have suggested that NACK-PQR positively regulates cell plate formation. However, biological function of NRK1 has been not clear. In the present study, we identified Arabidopsis MAPK that was specifically phosphorylated by ANQ1 (Arabidopsis NQK1) and named it ANR1. anr1 mutant plants exhibited dwarfism. Large cells with multiple nuclei and aberrant cross walls were observed in the mutant. These results indicated that ANR1 controls plant cytokines downstream of ANQ1. It is consistent with the idea of NACK-PQR.
