Receptor kinase that, together with ERL1 and ERL2, regulates aerial architecture, including inflorescence (e.g. shoot apical meristem-originating organ shape, elongation of the internode and pedicels, and adaxial-abaxial polarity), and stomatal patterning (e.g. density and clustering), probably by tuning cell division and expansion. Redundantly involved with ERL1 in procambial development regulation. Forms a functional ligand-receptor pair with EPF2 (AC Q8LC53) (PubMed:22241782). Modulates plant transpiration efficiency by controlling stomatal density, leaf photosynthetic capacity, epidermal cell expansion, mesophyll cell proliferation and cell-cell contact. A phloem-specific expression of ER is sufficient for proper inflorescence architecture (PubMed:22474391). Probable major trait regulating canalization (maintenance of phenotype despite varying environment) in many aspect of the plant physiology (e.g. plant morphology, light-dependent leaves number, branch number, flowering time, phytate and mineral concentrations) by transducing microenvironmental variation into phenotypic differentiation (ecological amplifier). May maintain development integrity in heat stress conditions. Regulates cell wall composition and structure. Confers resistance to the pathogenic bacteria Ralstonia solanacearum and to the necrotrophic fungi Plectosphaerella cucumerina and Pythium irregulare, and required for callose deposition upon infection. Resistance to P.cucumerina seems cell wall-mediated. 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 ERL1 and TMM. Interacts with EPF1, EPF2, EPFL4, EPFL5 and EPFL6. Interacts with SERK1, SERK2, SERK3/BAK1 and SERK4 in a EPF2-induced manner (PubMed:26320950). Interacts with EPFL9/STOMAGEN (PubMed:26083750). Mostly expressed in shoot apical meristems (SAM), organ primordia, flowers, siliques and young rosette leaves, and, to a lower extent, in stems and cauline leaves. Expressed in growing inflorescence stems and pedicels. Detected in epidermis, phloem and xylem. Strongly expressed in organ primordia and immature organs but weakly in mature organs. Observed in SAM at low levels during the vegetative growth with an increase at the transition to the reproductive growth phase. 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. The cultivar Landsberg erecta (cv. Ler) derives from cv. Landsberg (cv. La-0) in which ERECTA is mutated at Ile-750 (variant er). In er-104 and er-105, small curly leaves and compact inflorescence with short thick siliques, increased canalization of rosette leaf number during long days. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family. A complicated affair - Issue 116 of April 2010