Comparison of nicotinamide adenine dinucleotide phosphate-induced immune responses against biotrophic and necrotrophic pathogens in Arabidopsis thaliana.

The pyridine nucleotide nicotinamide adenine dinucleotide phosphate (NADP) is a universal coenzyme in anabolic reactions and also functions in intracellular signaling by serving as a substrate for production of the Ca(2+)-mobilizing agent nicotinic acid adenine dinucleotide phosphate (NAADP). It has recently been shown that, in mammalian cells, cellular NADP can be released into the extracellular compartment (ECC) upon environmental stresses by active exocytosis or diffusion through transmembrane transporters in living cells or passive leakage across the membrane in dying cells. In the ECC, NADP can either serve as a substrate for production of NAADP or act directly on purinoceptors to activate transmembrane signaling. In the last several years, extracellular NADP has also been suggested to function in plant immune responses. Here, we compared exogenous NADP-induced immune responses against biotrophic and necrotrophic pathogens in the Arabidopsis thaliana ecotype Columbia and found that NADP addition induces salicylic acid-mediated defense signaling but not jasmonic acid/ethylene-mediated defense responses. These results suggest the specificity of exogenous NADP-activated signaling in plants.