Abstract
The Nudix (Nucleoside diphosphate linked to some other moiety X) hydrolases, NUDXs, are the protein family that hydrolyzes a wide variety of nucleoside diphosphate derivatives including canonical and oxidized nucleoside di- and triphosphates, nucleotide-sugars, and several coenzymes such as NAD(P) H, FAD, and CoA which are derived from niacin, Àavin, and pantothenic acid, respectively. Arabidopsis thaliana possesses 28 NUDX genes (AtNUDX1-27 and DCP2) divided into three types, i.e., cytosolic, chloroplastic, and mitochondrial types, based on their subcellular localization. There is increasing evidence that AtNUDXs play physiological roles in the regulation of the levels of various metabolic intermediates and stress responses. Recently, we have reported that the regulation of intracellular levels of GDP-D-mannose, a metabolic intermediate of ascorbate biosynthesis, by cytosolic AtNUDX9 is involved in the response of plants to NH4+ and that the modulation of the cellular levels and redox state of pyridine nucleotides including NADPH by chloroplastic AtNUDX19 participates in the responses of plants to photooxidative stress and hormones. Furthermore, we have demonstrated that the regulation of cellular NADH levels by both cytosolic AtNUDX6 and 7 contributes to the modulation of the poly(ADP-ribosyl)ation reaction which is associated with the post-translational modi¿cation of proteins in biotic/abiotic stress responses, although the existence of AtNUDX6 and 7 themselves or other interacting factors is important for the control of salicylic acid signaling pathway. These findings suggest that NUDXs play important roles in various cellular responses through degradation of vitamin-derived coenzymes and their intermediates.
