Receptor with a dual specificity kinase activity acting on both serine/threonine- and tyrosine-containing substrates that controls floral organ abscission. May interact with the 'INFLORESCENCE DEFICIENT IN ABSCISSION' (IDA) ligands family. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] ATP + L-tyrosyl-[protein] = ADP + H(+) + O-phospho-L-tyrosyl-[protein] Have significantly greater activity in the presence of Mn(2+) than Mg(2+). Interacts with CST (PubMed:21628627). Binds to IDA (PubMed:27058169). Expressed in roots and rosettes. Expressed at the base of petioles and pedicels, and in the abscission zones of the floral organs. Autophosphorylated on Ser, Thr and Tyr residues. No visible phenotype; due to the redundancy with HSL2. Hae and hsl2 double mutants have a strong abscission defect. The name HAESA derives from a Latin word meaning 'to adhere to'. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.