Regulates negatively the abscisic acid (ABA) signaling pathway (PubMed:25274985). Required for full susceptibility to filamentous (hemi)biotrophic oomycetes (e.g. H.arabidopsidis and P.parasitica) and fungal (e.g. E.cruciferarum) pathogens, probably by triggering the repression of ABA-sensitive COLD REGULATED and RESISTANCE TO DESICCATION genes during infection, but independently of immune responses (PubMed:21711359, PubMed:25274985). Involved in BAK1-dependent and BAK1-independent microbe-associated molecular patterns (MAMPs)-triggered immunity (PTI) leading to defense responses, including callose deposition and MAPK cascade activation, toward pathogenic bacteria (e.g. P.syringae). Required for chitin-mediated PTI (PubMed:27317676). Homodimerization. Interacts with BAK1 and FLS2; triggers FLS2-BAK1 complex formation upon microbe-associated molecular patterns (MAMPs) treatment. Binds also to CERK1 and EFR. Expressed in roots, cotyledons, leaves, flowers and siliques. Predominantly expressed in tissue with fates controlled by the phytohormone abscisic acid (ABA). In roots, expressed in the radicle emerging from the testa, in the elongation zones of roots, and in root cap border cells undergoing detachment. In hypocotyls, detected only during etiolation in the dark. In cotyledons and leaves, restricted to cells surrounding stomata. In reproductive organs, observed in the style after pollination, in the abscission zones of sepals and petals, in the transmitting tract of developing fruits, and in the abscission zones of mature siliques. Also present in pollen tubes. Accumulates during infection by filamentous (hemi)biotrophic oomycetes (e.g. H.arabidopsidis and P.parasitica) and fungal (e.g. E.cruciferarum) pathogens, being locally expressed in cells surrounding the pathogens both at early and late stages of infection (PubMed:21711359, PubMed:25274985). Induced by microbe-associated molecular patterns (MAMPs) flg22 or elf18 (PubMed:27317676). Reduced infection by filamentous (hemi)biotrophic oomycetes (e.g. H.arabidopsidis and P.parasitica) and fungal (e.g. E.cruciferarum) pathogens, independently of plant defense mechanism (PubMed:21711359, PubMed:25274985). Hypersensitivity to abscisic acid (ABA), displaying enhanced ABA-mediated inhibition of seed germination, root elongation, and stomatal opening. Impaired repression of ABA-sensitive COLD REGULATED and RESISTANCE TO DESICCATION genes upon oomycete infection. No obvious modification of defense-related gene induction during pathogen attack (PubMed:25274985). Hypersusceptibility to the necrotrophic bacteria P.syringae. Defective pattern-triggered immunity (PTI) responses, delayed up-regulation of PTI marker genes, reduced callose deposition, and mitogen-activated protein kinase activation upon microbe-associated molecular patterns (MAMPs) treatment. Impaired beta-aminobutyric acid (BABA)-induced resistance and priming (PubMed:27317676). Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.