Threonine-protein kinase that phosphorylates histone H3 in vitro at 'Thr-3' (H3T3ph) and 'Thr-11' (H3T11ph), but not at 'Ser-10' (H3S10ph) or 'Ser-28' (H3S28ph). Plays a role in mitotic cell division during plant growth (PubMed:21527018). Threonine-protein kinase that phosphorylates histone H3 in vitro at 'Thr-3' (H3T3ph), but not at 'Thr-11' (H3T11ph), 'Ser-10' (H3S10ph) or 'Ser-28' (H3S28ph). Involved in histone H3 phosphorylation in mitotic cells. Contributes to organ and plant development, as well as embryonic patterning (PubMed:21749502). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] During interphase, localized in the cytoplasm and at the nuclear periphery. During prometaphase and metaphase, localized on chromosomes, and around the cell plate during cytokinesis. Expressed in meristems and primordia of root tips, lateral roots, shoot apex, leaves and flowers. During embryogenesis, expressed in embryos and suspensors from the one-cell stage to the four-cell stage. Expressed in the embryo until the torpedo stage. Expression peaks at mitosis. Embryonic lethality when homozygous. Over-expression of an inactive kinase mutant decreases the size of the root meristem and delays root growth. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family. Haspin subfamily.