Lectin-domain containing receptor kinase involved in salt stress response (PubMed:24907341). Acts as negative regulator of salt tolerance (PubMed:24907341). Mediates salt sensitivity by phosphorylating and activating MPK3 and MPK6 (PubMed:24907341). Promotes ethylene production and mediates salt-induced ethylene signaling (PubMed:24907341). Promotes the accumulation of reactive oxygen species (ROS) under salt stress conditions (PubMed:24907341). Its kinase activity is triggered by salt stress and is required for its function in salt stress response (PubMed:24907341). Phosphorylates B'KAPPA, a B regulatory subunit of phosphatase 2A (PP2A) (PubMed:31221736). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Activated by autophosphorylation in response to salt stress. Interacts with B'KAPPA. Expressed in root epidermal cells. Induced by salt stress. Autophosphorylated at THR-511, THR-515 or THR-516, and THR-521 in response to salt stress (PubMed:31221736). Dephosphorylated by phosphatase 2A in response to salt stress (PubMed:31221736). Plants silencing SIT1 exhibit increased tolerance to salt stress. In the C-terminal section; belongs to the protein kinase superfamily. Ser/Thr protein kinase family. In the N-terminal section; belongs to the leguminous lectin family.