Involved in defense response to geminivirus and begomovirus infection via regulation of the nuclear trafficking of RPL10A. Phosphorylates RPL10A in vitro (PubMed:15489295, PubMed:18789471, PubMed:19112492, PubMed:19492062, PubMed:25707794). Activation of NIK1 down-regulates cytosolic translation (PubMed:25707794). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Inhibited by the viral nuclear shuttle protein (NSP) that binds to the region required for oligomerization. Oligomer. Interacts with geminivirus nuclear shuttle protein (NSP) (PubMed:15489295). Interacts with RPL10A and RPL18B (PubMed:18789471, PubMed:19112492). Expressed in seedlings, leaves, roots, stems and flowers. Autophosphorylated. Enhanced susceptibility to geminivirus infection. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family. Truncated N-terminus.