Abstract
Nicotinamide adenine dinucleotide (NAD) is a pivotal coenzyme that has emerged as a central hub linking redox equilibrium and signal transduction in living cells. The homeostasis of NAD is required for plant growth, development, and adaption to environmental stresses. Quinolinate phosphoribosyltransferase (QPRT) is a key enzyme in NAD de novo synthesis pathway. T-DNA-based disruption of QPRT gene is embryo lethal in Arabidopsis thaliana. Therefore, to investigate the function of QPRT in Arabidopsis, we generated transgenic plants with decreased QPRT using the RNA interference approach. While interference of QPRT gene led to an impairment of NAD biosynthesis, the QPRT RNAi plants did not display distinguishable phenotypes under the optimal condition in comparison with wild-type plants. Intriguingly, they exhibited enhanced sensitivity to an avirulent strain of Pseudomonas syringae pv. tomato (Pst-avrRpt2), which was accompanied by a reduction in salicylic acid (SA) accumulation and down-regulation of pathogenesis-related genes expression as compared with the wild type. Moreover, oxidative stress marker genes including GSTU24, OXI1, AOX1 and FER1 were markedly repressed in the QPRT RNAi plants. Taken together, these data emphasized the importance of QPRT in NAD biosynthesis and immunity defense, suggesting that decreased antibacterial immunity through the alteration of NAD status could be attributed to SA- and reactive oxygen species-dependent pathways.
Highlights
Pyridine nucleotide co-enzymes are ubiquitous in living organisms [1]
Overexpression of Arabidopsis Nudix hydrolase gene, hydrolase homolog 6 (AtNUDT6), encoding an ADP-ribose/NADH pyrophosphohydrolase, and disruption of AtNUDT6 [12], AtNUDT7 [13,14], or AtNUDT8 [15] all lead to changes in intracellular NADH levels and salicylic acid (SA)-mediated immune signaling
Reduced quinolinate phosphoribosyltransferase (QPRT) expression did not cause aberrant phenotypes when plants were grown under the conditions of these experiments (Figure S2)
Summary
Nicotinamide adenine dinucleotide (NAD) and its phosphate derivative NADP, exist in oxidized forms (NAD+ or NADP+ , respectively) or reduced forms (NADH or NADPH, respectively). They mediate a wide range of redox reactions, and impact virtually all metabolic reactions in the cell [2]. Quinolinate-induced stimulation of intracellular NAD in Arabidopsis expressing nadC gene from Escherichia coli, which encodes quinolinate phosphoribosyltransferase (QPRT), enhances defense gene expression and resistance to diverse bacterial and fungal pathogens [10,11]. Overexpression of Arabidopsis Nudix (nucleoside diphosphates linked to some moiety X) hydrolase gene, hydrolase homolog 6 (AtNUDT6), encoding an ADP-ribose/NADH pyrophosphohydrolase, and disruption of AtNUDT6 [12], AtNUDT7 [13,14], or AtNUDT8 [15] all lead to changes in intracellular NADH levels and salicylic acid (SA)-mediated immune signaling
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