Nicotinamidase participates in the salvage pathway of NAD biosynthesis in Arabidopsis

Abstract

SummaryNicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP), which is derived from NAD, have important roles as a redox carriers in metabolism. A combination of de novo and salvage pathways contribute to the biosynthesis of NAD in all organisms. The pathways and enzymes of the NAD salvage pathway in yeast and animals, which diverge at nicotinamide, have been extensively studied. Yeast cells convert nicotinamide to nicotinic acid, while mammals lack the enzyme nicotinamidase and instead convert nicotinamide to nicotinamide mononucleotide. Here we show that Arabidopsis thaliana gene At2g22570 encodes a nicotinamidase, which is expressed in all tissues, with the highest levels observed in roots and stems. The 244-residue protein, designated AtNIC1, converts nicotinamide to nicotinic acid and has a K m value of 118 AE 17 lM and a K cat value of 0.93 AE 0.13 sec )1 . Plants homozygous for a null AtNIC1 allele, nic1-1, have lower levels of NAD and NADP under normal growth conditions, indicating that AtNIC1 participates in a yeast-type NAD salvage pathway. Mutant plants also exhibit hypersensitivity to treatments of abscisic acid and NaCl, which is correlated with their inability to increase the cellular levels of NAD(H) under these growth conditions, as occurs in wild-type plants. We also show that the growth of the roots of wild-type but not nic1-1 mutant plants is inhibited and distorted by nicotinamide.

TheArabidopsis onset of leaf death5Mutation of Quinolinate Synthase Affects Nicotinamide Adenine Dinucleotide Biosynthesis and Causes Early Ageing

“…Measurement of pyridine nucleotide content revealed, indeed, that the mutant had significantly increased NAD, NADH, NADP, and NADPH levels after 27 d ( Figure 5A). The values we report for NAD, NADP, and NADPH in the wild type are similar to those of previous studies (Chai et al, 2005;Wang and Pichersky, 2007). Interestingly, the NAD/NADH and NADP/NADPH ratios in the mutant do not differ from the wild-type value, suggesting a similar redox balance for the pyridine nucleotides.…”

“…The maintenance of the NAD pool depends on the balance between de novo synthesis, active pyridine salvage, and degradation (Wang and Pichersky, 2007). The de novo synthesis and the pyridine salvage pathway result in the production of nicotinate mononucleotide, which by two enzymatic steps is converted to NAD ( Figure 5B).…”

Mutation of OsNaPRT1 in the NAD Salvage Pathway Leads to Withered Leaf Tips in Rice

“…Previous studies have investigated the biological significance of some genes associated with NAD(P)(H) biosynthesis in plants, including NMNAT, AtNIC1, NADK2, and so on (Hashida et al, 2007(Hashida et al, , 2009Wang and Pichersky, 2007). Here, we demonstrate that a mutation in OsNaPRT1, which encodes a NaPRTase capable of converting nicotinate to NaMN in the salvage pathway of NAD biosynthesis, accelerates the progress of leaf senescence in rice.…”

“…Like other organisms, Arabidopsis (Arabidopsis thaliana) contains two NAD(P)(H) biosynthetic pathways: the de novo and salvage pathways (Katoh et al, 2006;Wang and Pichersky, 2007). In the salvage pathway, nicotinate mononucleotide (NaMN; an intermediate in the de novo pathway) is formed from nicotinamide (a product of NAD degradation) through two enzymatic steps (Katoh et al, 2006;Wang and Pichersky, 2007).…”

“…In the salvage pathway, nicotinate mononucleotide (NaMN; an intermediate in the de novo pathway) is formed from nicotinamide (a product of NAD degradation) through two enzymatic steps (Katoh et al, 2006;Wang and Pichersky, 2007). Specifically, nicotinamide is hydrolyzed to nicotinate by nicotinamidase and is converted to NaMN by nicotinate phosphoribosyltransferase (NaPRTase; Wang and Pichersky, 2007;Hashida et al, 2009). NaPRTase is believed to be the rate-limiting enzyme in the NAD salvage pathway (Magni et al, 1999).…”