Nicotinamide mononucleotide and related metabolites induce disease resistance against fungal phytopathogens in Arabidopsis and barley

Abstract

Nicotinamide mononucleotide (NMN), a precursor of nicotinamide adenine dinucleotide (NAD), is known to act as a functional molecule in animals, whereas its function in plants is largely unknown. In this study, we found that NMN accumulated in barley cultivars resistant to phytopathogenic fungal Fusarium species. Although NMN does not possess antifungal activity, pretreatment with NMN and related metabolites enhanced disease resistance to Fusarium graminearum in Arabidopsis leaves and flowers and in barley spikes. The NMN-induced Fusarium resistance was accompanied by activation of the salicylic acid-mediated signalling pathway and repression of the jasmonic acid/ethylene-dependent signalling pathways in Arabidopsis. Since NMN-induced disease resistance was also observed in the SA-deficient sid2 mutant, an SA-independent signalling pathway also regulated the enhanced resistance induced by NMN. Compared with NMN, NAD and NADP, nicotinamide pretreatment had minor effects on resistance to F. graminearum. Constitutive expression of the NMNAT gene, which encodes a rate-limiting enzyme for NAD biosynthesis, resulted in enhanced disease resistance in Arabidopsis. Thus, modifying the content of NAD-related metabolites can be used to optimize the defence signalling pathways activated in response to F. graminearum and facilitates the control of disease injury and mycotoxin accumulation in plants.

The possible roles of <i>AtERF71</i> in the defense response against the <i>Fusarium graminearum</i>

“…The disease severity of inoculated leaves were classified into four categories (Miwa et al 2017). A total of 32-40 inoculated leaves per genotype were used for this disease scoring.…”

“…The F. graminearum conidia were prepared as described previously (Miwa et al 2017). The conidia were collected by centrifugation and washed with a phosphate-buffered saline solution at least three times.…”

“…RT-PCR was carried out with Quick Taq HS DyeMix (TOYOBO Co., Ltd., Osaka, Japan), and the RT-qPCR analysis was performed as described by Miwa et al (2017) with the following pairs of primers for AtERF71: AtERF71_Fw (5′-GTC TGG CTT GGC ACA TTC AAA AC-3′) and AtERF71_Re (5′-CCA TCA GGT CCT CCG ATA AGC TC-3′); other primer sets as described previously.…”

“…The amounts of fungal gDNA in inoculated leaves were quantified by qPCR, as described previously (Miwa et al 2017). The primer sets for the Arabidopsis Act2/8 and Fusarium EF-1α genes were used to quantify the plant gDNA and fungal gDNA, respectively (Miwa et al 2017).…”

“…In a prior study, we reported that a nicotine amide mononucleotide (NMN) pretreatment suppressed the ET signaling pathway and enhanced disease resistance against F. graminearum (Miwa et al 2017). Microarray analysis findings showed that expression of seven AtERF genes was down-regulated by NMN-pretreatment of leaves inoculated with F. graminearum.…”