During nodulation, plays a central role in bacterial infection and contributes to nodule organogenesis (PubMed:22874912). Protein kinase that recognizes the calcium spiking induced by Nod factors and translates this signal to components controlling nodulation and mycorrhizal infection responses. May phosphorylate the NSP1 protein (PubMed:14963335, PubMed:15070781). Required in epidermal and cortical cells to promote infection thread (IT) formation in root hairs (PubMed:22874912). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Activated by calcium. Autophosphorylation may play an important role in the regulation of the kinase activity (By similarity). Interacts with IPD3. Highly expressed in roots (PubMed:17722695, PubMed:22874912). Expressed in root hairs and nodules (PubMed:17722695, PubMed:22874912). Expressed at low levels in flowers. Not detected in leaves or stems (PubMed:22874912). In non inoculated roots, present at low levels in both epidermis and cortex. Levels increase two days after inoculation with Sinorhizobium meliloti, especially in root hair cells. During infection, mostly expressed in cortical cells where infection thread (IT) progresses and in underlying layers. Detected in the whole cortex of young nodules. In mature nodules, localized in the infection zone. Small up-regulation in nodules. Autophosphorylation. Belongs to the protein kinase superfamily. CAMK Ser/Thr protein kinase family. CaMK subfamily.