Extracellular pyridine nucleotides trigger plant systemic immunity through a lectin receptor kinase/BAK1 complex

Area of Science:

• Plant pathology
• Molecular plant-microbe interactions
• Plant signaling

Background:

• Systemic acquired resistance (SAR) is a crucial plant defense mechanism against pathogens.
• The mobile signals and perception mechanisms underlying SAR remain largely unknown.
• Extracellular signaling molecules are increasingly recognized in plant immunity.

Purpose of the Study:

• To identify novel mobile signals involved in SAR.
• To elucidate the molecular mechanisms of SAR signal perception in systemic tissues.
• To investigate the role of nicotinamide adenine dinucleotide (NAD+) in plant immunity.

Main Methods:

• Exogenous application of nicotinamide adenine dinucleotide (NAD+) to Arabidopsis thaliana.
• Genetic analysis using mutants deficient in LecRK-VI.2 and BAK1 homologs.
• Biochemical assays to determine protein-protein interactions and kinase activity.
• Confocal microscopy to track signal movement.

Main Results:

• Exogenously applied NAD+ moves systemically and confers broad-spectrum immunity.
• Lectin receptor kinase VI.2 (LecRK-VI.2) functions as a receptor for extracellular NAD+ (eNAD+) and NAD+ phosphate (eNADP+).
• The receptor complex LecRK-VI.2/BRASSINOSTEROID INSENSITIVE1-ASSOCIATED KINASE1 (BAK1) is essential for eNAD(P)+ signaling and SAR induction.

Conclusions:

• Extracellular NAD+ is a putative mobile signal that triggers SAR in plants.
• The LecRK-VI.2/BAK1 receptor complex plays a central role in perceiving eNAD+ signals.
• Kinase activities of LecRK-VI.2 and BAK1 are indispensable for SAR.