The cloning and characterization of hypersensitive to salt stress mutant, affected in quinolinate synthase, highlights the involvement of NAD in stress‐induced accumulation of ABA and proline

Abstract

Nicotinamide adenine dinucleotide (NAD), a ubiquitous coenzyme, is required for many physiological reactions and processes. However, it remains largely unknown how NAD affects plant response to salt stress. We isolated a salt-sensitive mutant named hypersensitive to salt stress (hss) from an ethyl methanesulfonate-induced mutation population. A point mutation was identified by MutMap in the encoding region of Quinolinate Synthase (QS) gene required for the de novo synthesis of NAD. This point mutation caused a substitution of amino acid in the highly-conserved NadA domain of QS, resulting in an impairment of NAD biosynthesis in the mutant. Molecular and chemical complementation have restored the response of the hss mutant to salt stress, indicating that the decreased NAD contents in the mutant were responsible for its hypersensitivity to salt stress. Furthermore, the endogenous levels of abscisic acid (ABA) and proline were also reduced in stress-treated hss mutant. The application of ABA or proline could alleviate stress-induced oxidative damage of the mutant and partially rescue its hypersensitivity to salt stress, but not affect NAD concentration. Taken together, our results demonstrated that the NadA domain of QS is important for NAD biosynthesis, and NAD participates in plant response to salt stress by affecting stress-induced accumulation of ABA and proline.

Changes in intracellular NAD status affect stomatal development in an abscisic acid‐dependent manner

“…Furthermore, unbalanced NAD + levels have been previously linked to increased ROS production rates and oxidative stress (Chai et al ., 2006; Katoh et al ., 2006; Schippers et al ., 2008; Luo et al ., 2019). Given the upregulation of the ROS marker transcript At ZAT12 (Xu et al ., 2017) in the mutant lines (Figure S3), and the role of NAD + homeostasis in plant abiotic stress tolerance (Hong et al ., 2020; Wei et al ., 2020), we suggest that NAD + transporter mutants may be suffering from increased oxidative stress and/or deregulated RBOH‐mediated signaling.…”

“…A recent functional characterization of NDT1 and NDT2 mutants had shown reduced seed germination, a phenotype previously explained by possible enhanced ABA levels and/or signaling (de Souza Chaves et al ., 2019; Feitosa‐Araujo et al ., 2020). Furthermore, NAD(P)(H) homeostasis has previously been associated with ABA biosynthesis and signaling (Hunt and Gray, 2009a; Arias et al ., 2018; Wei et al ., 2020; Hong et al ., 2020). Taken together, these observations raised the hypothesis that altered subcellular NAD + compartmentation may trigger changes in ABA metabolism, which in turn represses entry into the stomatal lineage.…”

“…Different studies have supported the relation of NAD + and ABA metabolism (Vanderauwera et al ., 2007; Hunt and Gray, 2009a; Zeng et al ., 2014; Hong et al ., 2020; Wei et al ., 2020). NAD + is required as NADH for zeaxanthin epoxidase (ABA1) and as NADPH for xanthoxin dehydrogenase (ABA2) activities, both belonging to the pathway of ABA biosynthesis (González‐Guzmán et al ., 2002; Barrero et al ., 2005).…”

Reciprocal regulation between nicotinamide adenine dinucleotide metabolism and abscisic acid and stress response pathways in Arabidopsis

“…These results strongly support that the deficiency of NAD is responsible for the ABA-hypersensitivity of qs-2. It was recently reported that NAD is involved in plant response to salt stress by increasing stress-induced ABA accumulation [42]. We determined the ABA contents in the wild-type and qs-2 mutant under normal growth conditions.…”

“…The old5 mutation in QS enzyme in the de novo NAD biosynthesis pathway decreases the Cys desulfurase activity of the QS enzyme and increases the steady state levels of NAD, which coincides with increased expression of oxidative stress marker genes and an early onset of senescence [41]. A recent report suggested that NAD is required for the biosynthesis of ABA and proline and plant response to salt stress [42]. However, the role of NAD synthesis in plant response to ABA has remained largely unknown.…”