Identification and Characterization of NADH Kinase-3 from a Stress-Tolerant Wild Mung Bean Species (Vigna luteola (Jacq.) Benth.) with a Possible Role in Waterlogging Tolerance.

In plants, reactive oxygen species accumulate to a toxic level under various abiotic stresses. Many antioxidant defense systems require NADPH as a principal reducing energy equivalent. However, the source of NADPH and the molecular mechanisms associated with the maintenance of cytoplasmic redox balance are still unknown. The present study describes Vigna NADH kinase (VlNADHK), an enzyme involved in NADPH synthesis and prefers NADH as a diphospho-nicotinamide nucleotide donor. We analyzed the enzymatic activity of a putative cytoplasmic NADH kinase during waterlogging in contrasting mung bean genotypes Vigna luteola (tolerant) and Vigna radiata cv. T44 (susceptible) under pot-culture condition. The tolerant cultivar showed higher enzymatic activity under waterlogging as well as after recovery. Similarly, the transcript level of waterlogging-induced NADHK expression was also studied and found to be upregulated in response to waterlogging in the roots of V. luteola and T44. PCR amplicons of partial and full-length sequences were cloned and sequenced from V. luteola. To the best of our knowledge, this is the first time an ATP-dependent NADH kinase gene has been recognized as a component of waterlogging stress tolerance in legumes. Our study indicated that this cytoplasmic NADH kinase is a primary source of the cytosolic NADPH and might have a role in waterlogging tolerance in legumes. [ABSTRACT FROM AUTHOR]