A lectin receptor kinase as a potential sensor for extracellular nicotinamide adenine dinucleotide in Arabidopsis thaliana

Abstract

Nicotinamide adenine dinucleotide (NAD+) participates in intracellular and extracellular signaling events unrelated to metabolism. In animals, purinergic receptors are required for extracellular NAD+ (eNAD+) to evoke biological responses, indicating that eNAD+ may be sensed by cell-surface receptors. However, the identity of eNAD+-binding receptors still remains elusive. Here, we identify a lectin receptor kinase (LecRK), LecRK-I.8, as a potential eNAD+ receptor in Arabidopsis. The extracellular lectin domain of LecRK-I.8 binds NAD+ with a dissociation constant of 436.5 ± 104.8 nM, although much higher concentrations are needed to trigger in vivo responses. Mutations in LecRK-I.8 inhibit NAD+-induced immune responses, whereas overexpression of LecRK-I.8 enhances the Arabidopsis response to NAD+. Furthermore, LecRK-I.8 is required for basal resistance against bacterial pathogens, substantiating a role for eNAD+ in plant immunity. Our results demonstrate that lectin receptors can potentially function as eNAD+-binding receptors and provide direct evidence for eNAD+ being an endogenous signaling molecule in plants.DOI: http://dx.doi.org/10.7554/eLife.25474.001

Chemical genetic identification of a lectin receptor kinase that transduces immune responses and interferes with abscisic acid signaling

“…Lectin receptor kinases are composed of an extracellular lectin domain known to bind carbohydrates and an intracellular protein kinase domain, separated by a single hydrophobic transmembrane domain (Figure a; Bellande et al ., ). In A. thaliana and other plant species, LecRKs play a role in pathogen‐associated molecular pattern (PAMP)‐triggered immune signaling (PTI) by perceiving PAMPs or molecules released to the apoplast during pathogen infection (Chrispeels and Raikhel, ; Chen et al ., , ; Singh and Zimmerli, ; Vaid et al ., ; Lannoo and Van Damme, ; Ranf et al ., ; Bellande et al ., ; Wang et al ., ).…”

“…G‐type LecRK LIPOOLIGOSACCHARIDE‐SPECIFIC REDUCED ELICITATION (LORE) was shown to sense lipopolysaccharides (Ranf et al ., ). Recent studies have also shown that LecRKs can recognize extracellular ATP and nicotinamide adenine dinucleotide (NAD + ) that could be a sign of pathogen infection (Choi et al ., ; Wang et al ., ). This binding activity of LecRKs to non‐carbohydrate ligands has been suggested as a result of neofunctionalization of duplicated LecRK genes (Van Holle and Van Damme, ).…”

“…Our experiments to examine the subcellular localization of the RDA2‐GFP fusion protein were not successful due to possible mis‐localization at endosomal organelles, because of high expression of the ectopically expressed proteins. A study with a lectin receptor kinase LecRK‐I.8 failed to observe LecRK‐I.8 fused with GFP in stably transformed plant lines, suggesting tight regulation of LecRK protein expression (Wang et al ., ).…”

Roles of Nicotinamide Adenine Dinucleotide (NAD+) in Biological Systems

“…Extracellular NAD + is sensed in the apoplast as a DAMP, and is recognized by a NAD + specific lectin-type receptor, LecRK-I.8, localized at the plasma membrane, possessing an active cytoplasmic kinase domain sensing NAD + as extracellular ligand. The saturation curve for NAD + binding showed a dissociation constant (Kd) of 436.5 ± 104.8 nM, which falls well below the extracellular NAD(H) concentration (~0.4 mM) in pathogen-infected leaf tissues, and thus indicates a relatively high affinity [78]. Binding assays with 32 P-labeled NAD + detected NAD + binding activity for the immunoprecipitated eLecRK-I.8-GFP protein, showing NAD + binding activity specific to eLecRK-I.…”

Pattern Recognition Receptors—Versatile Genetic Tools for Engineering Broad-Spectrum Disease Resistance in Crops

“…Typical examples of DAMPs are fragments of cell wall components generated during attack by microbial cell wall-degrading enzymes, e.g., oligogalacturonides (OGs, derived from pectin) [20] or cutin monomers [21], and intracellular plant components released into the extracellular space upon cell lysis, such as extracellular ATP (eATP) [22], extracellular NAD (eNAD) [23], or intracellular proteins (e.g., Arabidopsis HMGB3) [24]. Like MAMPs, DAMPs are sensed by cell surface-resident PRRs and activate typical PTI signaling and defense responses [4].…”