Controls formative cell division in meristems, including root tips and lateral root initiation zones of the pericycle, in response to CLE40 signal. Acts with CLE40p peptide as a ligand-receptor pair in a signal transduction pathway, coordinating movement of the root tip and organization of cell divisions in the root meristem. Required during embryogenesis and development, probably for the differentiation of protoderm and epidermal cells. Involved in the regulation of cellular organization during the development of sepal margins and ovule integument outgrowth. Can phosphorylate ALE2. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Homodimer (Probable). Interacts with PP2A3 (PubMed:26792519). Also localized into protein export bodies. Internalization may be involved in degradation of ACR4 for its rapid turn-over. In the epidermis, mostly expressed in the lateral and basal planes of cells. Expressed in seedlings, floral buds, siliques, leaves, shoot apical meristems (SAM), and, to a lower extent, in roots. First observed in all young embryo cells. At the globular stage, restricted to apical region. Later confined to the protoderm area leading to cotyledon primordia and the root apex. In mature embryos, mostly localized in the L1 layer of the SAM, apical regions of cotyledons and the root apex, and, to a lower extent, in protoderm of other regions. In seedlings, expressed in developing tissues of the shoot, including the SAM and epidermis of organs primordia, especially in L1 layer cells. In roots, localized in quiescent center (QC) central cells, columella initials and cells below the QC, the lateral root cap (LRC) and the initial cells destined to give rise to the root epidermal cell file and the LRC. Expressed in epidermal emerged from under the LRC, with levels vanishing in elongation zone. Specifically detected in the small daughter cells after the first asymmetric pericycle cell division during lateral roots emergence. Subsequently, the expression expands to the adjacent small daughter cells from the second asymmetric cell division, resulting in a central core-specific expression pattern. By CLE40 in root quiescent center (QC). Autophosphorylated and phosphorylated by ALE2. Reduced fertility due to abnormal embryogenesis and integument formation. Abnormal seed coat and leaves epidermis, with transient fusion between adjacent developing leaves and reduced hydrophobicity of leaf surfaces. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.