The ANPs-MKK6-MPK4 module is involved in the regulation of plant cytokinesis during meiosis and mitosis. MKK6-MPK13 module positively regulates lateral root formation. Phosphorylates and activates MPK4. Activates MPK5 and MPK13 in vitro. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] ATP + L-tyrosyl-[protein] = ADP + H(+) + O-phospho-L-tyrosyl-[protein] Activated through serine and threonine phosphorylation. Interacts with P.syringae type III effector HopF2. Interacts with MPK4, MPK6, MPK11 and MPK13. Interacts with ANP3. Localized at the equatorial plane of the phragmoplast. Expressed in roots, stems and flower buds. Higher levels in shoot apices and flowers. Phosphorylation at Ser-221 and Thr-227 by MAP kinase kinase kinases positively regulates kinase activity. Plants exhibit a dwarf phenotype with fewer flowers, large cells with multiple nuclei in various organs and large malformed pollen grains. Defects in the formation of the cell plate. RNAi MKK6 displays fewer lateral roots. Belongs to the protein kinase superfamily. STE Ser/Thr protein kinase family. MAP kinase kinase subfamily.