The NAD kinase OsNADK1 affects the redox and enhances the tolerance to drought in rice

NAD(H) and NADP(H) are crucial coenzymes and play important and distinguishable roles in all living organisms. NAD(H) is primarily involved in catabolic reactions, whereas NADP(H) participates in anabolic reactions, such as NADP(H)-dependent reductive anabolic pathways, signal transduction, and defense against oxidative stress. Hence, regulation of the intracellular balance of NAD(H) and NADP(H) is critical. NAD(H) kinase (NADK) is the key enzyme in the de novo biosynthesis of NADP(H), catalyzing the transfer of a phosphoryl group from ATP to NAD(H), and thus plays an important role in the regulation of intracellular NAD(H)/NADP(H) balance for NADP(H)-based metabolic pathways. We used microarrays to detail the global programme of gene expression between WT and osnadk1 and identified distinct classes of up-regulated and down-regulated genes during this process. The youngest fully expanded leaves from 2.5-month-old WT and osnadk1 plants (three replicates each), grown under normal growth (soil moisture, 47.3%) and drought conditions (soil moisture, 8.5%), were used for RNA extraction and hybridization on Affymetrix microarrays. Control: normal growth condition; Drought: drought stress condition.