Identification of a novel downstream factor of MAP kinase cascade involved in plant cytokinesis: biochemical analysis of Atkinesin13B in Arabidopsis thaliana

Abstract

The NACK-PQR pathway is MAPK cascade that consists of NPK1 MAPKKK, NQK1 MAPKK, NRK1 MAPK and NACK1 kinesin like protein in tobacco and is activated during late M phase. During cytokinesis, these factors are found at the phragmoplast equator. These results have proposed that this cascade is involved in cytokinesis. Homologs of these factors are identified in Arabidopsis thaliana. Here we searched target proteins of AtMPK4 that is a homolog of NRK1 to identify downstream factors of this cascade. We found proteins phosphorylated by NRK1 in microtubule-associated proteins fraction purified from tobacco BY-2 cells. Atkinesin13B was identified from these proteins by in silico assays with database of Arabidopsis thaliana. When we performed kinase assays using Atkinesin13B, Atkinesin13B was phosphorylated by AtMPK4. Furthermore Atkinesin13B localized at the phragmoplast equator during cytokinesis. These results suggested the possibility that Atkinesin13B is a downstream factor of AtMPK4.