NAD kinase (NADK) catalyzes the de novo synthesis of the diphosphopyridine nucleotide NADP from the substrates NAD and ATP, and plays an important role in the NADP(H)-based metabolism pathways.In plants, NADKs were involved in regulating the balance of redox, stress responses and various developmental processes, while NADK genes constitute a multigene family and functional divergence appears to have occurred repeatedly, based on the studies of this family in Arabidopsis.