Serine/threonine-protein kinase involved in the spatial and temporal control system organizing cortical activities in mitotic and postmitotic cells (PubMed:15292395). Required for the normal functioning of the plasma membrane in developing pollen (PubMed:16965555). Involved in the regulation of cell expansion and embryo development (PubMed:23087695). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Accumulates in the nucleolus during interphase (PubMed:15292395). Localized to the plasma membrane in developing pollen grains (By similarity). Expressed in both the sporophytic and the gametophytic tissues, especially in dividing cells. Mostly present in flower buds and mature flowers. Accumulates also in embryos and in roots. Expressed during embryo development. Expression is cell cycle-regulated, with higher expression in G2-M phases. Autophosphorylated. Pollen lethality in plants lacking both MAP3KE1 and MAP3KE2, associated with plasma membrane irregularities following pollen mitosis I (PubMed:16965555). Smaller plants with shorter roots due to reduced cell elongation in roots and reduced cell expansion in rosette leaves, as well as embryos arrest in the early stages of development (PubMed:23087695). Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.