Dephosphorylates the Ser/Thr receptor-like kinase RLK5. May function as a signaling component in a pathway involving RLK5 (PubMed:15592873). Binds and dephosphorylates CLAVATA1 (CLV1). Functions as a negative regulator of the CLV1 signaling in plant development (PubMed:9294234, PubMed:9701578). Dephosphorylates SERK1 receptor kinase on threonine residues in the A-loop. Dephosphorylation of SERK1 controls SERK1 internalization (PubMed:12101128). Component of a signaling pathway which mediates adaptation to NaCl stress. Is not a component of the SALT OVERLY SENSITIVE (SOS) pathway (PubMed:18162596). H2O + O-phospho-L-seryl-[protein] = L-seryl-[protein] + phosphate H2O + O-phospho-L-threonyl-[protein] = L-threonyl-[protein] + phosphate Binds 2 magnesium or manganese ions per subunit. Association of RLK5 with kapp domain is dependent on phosphorylation of RLK5 and can be abolished by dephosphorylation. Interacts with SERK1 and CDC48A. Component of the SERK1 signaling complex, composed of KAPP, CDC48A, GRF6 or GRF7, SERK1, SERK2, SERK3/BAK1 and BRI1 (PubMed:15592873). Interacts with CLV1 (PubMed:9294234, PubMed:9701578). A number of isoforms are produced. According to EST sequences. Expressed in all tissues examined. No visible phenotype under normal growth conditions, but mutant seedlings show increased sensitivity of roots to salt stress.