Involved in the perception of symbiotic fungi and bacteria and required for the calcium spiking. Part of the perception/transduction system leading to nodulation or mycorrhizal infection. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] May be phosphorylated. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.