Receptor kinase that regulates inflorescence architecture and organ shape as well as stomatal patterning, including density and clustering, together with ER and ERL2. Redundantly involved with ER in procambial development regulation. Forms a functional ligand-receptor pair with EPF1 (AC Q8S8I4) (PubMed:22241782). Forms a constitutive complex with TMM involved in the recognition of the stomatal regulatory peptides EPF1, EPF2 and EPFL9/STOMAGEN (PubMed:28536146). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Homodimer and heterodimer with ERECTA and TMM. Interacts with EPF1 and EPF2. Interacts with SERK1, SERK2, SERK3/BAK1 and SERK4 in a EPF1-induced manner (PubMed:26320950). A number of isoforms are produced. According to EST sequences. Mostly expressed in developing organs, including bud clusters, flowers, siliques and young rosettes. Also detected in mature aboveground organs, such as leaves, stems and pedicels, but barely in roots. At the vegetative stage, strongly expressed in the shoot meristem, leaf primordia and juvenile leaves. At the reproductive stage, localized in the young developing flowers. Expressed in inflorescence meristem and is up-regulated during flower initiation and formation of flower organs. Also found in cells that differentiate into pedicels. The kinase domain is not required for ligand binding. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family. Truncated N-terminus.