Involved in resistance against the herbivorous insect brown planthopper (N.lugens, BPH). Member of the BPH3 (BPH resistance locus 3) cluster which contains LECRK1, LECRK2 and LECRK3. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.