Arabidopsis thaliana MAP65-1 and MAP65-2 function redundantly with MAP65-3/PLEIADE in cytokinesis downstream of MPK4.

Plant cytokinesis occurs by the growth of cell plates from the interior to the periphery of the cell. These dynamic events in cytokinesis are mediated by a plant-specific microtubule (MT) array called the phragmoplast, which consists of bundled antiparallel MTs between the two daughter nuclei. The NACK-PQR pathway, a NACK1 kinesin-like protein and mitogen activated protein kinase (MAPK) cascade, is a key regulator of plant cytokinesis through the regulation of phragmoplast MTs. The MT-associated protein MAP65 has been identified as one of the structural components of MT assays involved in cell division, and we recently showed that Arabidopsis AtMAP65-3/PLEIADE (PLE) is a substrate of MPK4 that is a component of the NACK-PQR pathway in Arabidopsis. Here we show that AtMAP65-1 and AtMAP65-2 are also phosphorylated by MPK4. AtMAP65-1 and AtMAP65-2 that localize to the phragmoplast were phosphorylated by MPK4 in vitro. Although mutants of the Arabidopsis AtMAP65-1 and AtMAP65-2 genes exhibited a wild-type phenotype, double mutations of AtMAP65-3 and AtMAP65-1 or AtMAP65-2 caused more severe growth and cytokinetic defects than the single atmap65-3/ple mutation. These results suggest that AtMAP65-1 and AtMAP65-2 also function in cytokinesis downstream of MPK4.