NAD Acts as an Integral Regulator of Multiple Defense Layers

Abstract

(J.T.).Pyridine nucleotides, such as NAD, are crucial redox carriers and have emerged as important signaling molecules in stress responses. Previously, we have demonstrated in Arabidopsis (Arabidopsis thaliana) that the inducible NAD-overproducing nadC lines are more resistant to an avirulent strain of Pseudomonas syringae pv tomato (Pst-AvrRpm1), which was associated with salicylic acid-dependent defense. Here, we have further characterized the NAD-dependent immune response in Arabidopsis. Quinolinate-induced stimulation of intracellular NAD in transgenic nadC plants enhanced resistance against a diverse range of (a)virulent pathogens, including Pst-AvrRpt2, Dickeya dadantii, and Botrytis cinerea. Characterization of the redox status demonstrated that elevated NAD levels induce reactive oxygen species (ROS) production and the expression of redox marker genes of the cytosol and mitochondrion. Using pharmacological and reverse genetics approaches, we show that NAD-induced ROS production functions independently of NADPH oxidase activity and light metabolism but depends on mitochondrial respiration, which was increased at higher NAD. We further demonstrate that NAD primes pathogen-induced callose deposition and cell death. Mass spectrometry analysis reveals that NAD simultaneously induces different defense hormones and that the NAD-induced metabolic profiles are similar to those of defense-expressing plants after treatment with pathogen-associated molecular patterns. We thus conclude that NAD triggers metabolic profiles rather similar to that of pathogen-associated molecular patterns and discuss how signaling cross talk between defense hormones, ROS, and NAD explains the observed resistance to pathogens.

Pyridine nucleotides induce changes in cytosolic pools of calcium in Arabidopsis

“…This is accompanied by the accumulation of SA, JA and ABA as has been shown in NAD C -infiltrated leaves. 5 [Ca 2C ] cyt response was dose-dependent, could be mimicked by the positive controls ADPr/H 2 O 2 and was particularly intense upon NADP C application, thus suggesting its effect was explained by the donation of its ADPr moiety to form cyclic ADPr and NAADP so as to release Ca 2C from intracellular compartments. [1][2][3] In conclusion, our study revealed that pyridine nucleotides modulated Ca 2C fluxes in Arabidopsis.…”

“…4 Recently, we have detailed the NAD-inducible defense responses that are effective against biotrophic and necrotrophic pathogens. 5 Our study reveals that NAD C acts as an elicitor by stimulating basal defenses (i.e. ROS production, callose deposition, cell death) and influencing hormonal balance.…”

“…ROS production, callose deposition, cell death) and influencing hormonal balance. 5 Metabolomics further demonstrated similarities between plants treated with NAD C and the fungal elicitor chitin.…”

“…6,9 After infection with Pst-AvrRpm1 and upon NAD build-up, we detected enhanced cell death and ROS levels. 5 Furthermore, [Ca 2C ] cyt levels regulate SA-, JA-, and ABA-mediated stress responses in plants. 6 In fact, cycam mutants affected in [Ca 2C ] cyt showed increased levels of SA, ABA and bioactive JA (JAisoleucine) with or without infection with the necrotrophic fungus Alternaria brassicae.…”

Photoperiod Affects the Phenotype of Mitochondrial Complex I Mutants

“…sugars, and other metabolites involved in central metabolism (Supplemental Methods S1; Paglia et al, 2012;Pétriacq et al, 2016). Accurately detected mass-to-charge features (error = 0.4 ppm) in negative (ESI 2 ; 17,326 ions) and positive (ESI + ; 18,341 ions) ionization modes were integrated using XCMS (Smith et al, 2006).…”