Extracellular pyridine nucleotides mediate systemic acquired resistance in Arabidopsis thaliana

Systemic acquired resistance (SAR) is a long-lasting broad-spectrum plant defense mechanism that is induced by mobile signals generated in the primarily infected leaves. Although multiple mobile SAR signals have been proposed, how these signals are perceived in the systemic leaves is unknown. Here, we show that extracellular nicotinamide adenine dinucleotide (phosphate) (eNAD(P)) accumulates in the systemic leaves and that both eNAD(P) and its receptor, the lectin receptor kinase (LecRK), LecRK-VI.2, are required in the systemic leaves for the establishment of SAR. Moreover, the mobile signal N-hydroxypipecolic acid (NHP) induces de novo NAD(P) leakage in the systemic leaves through the respiratory burst oxidase homolog RBOHF-produced reactive oxygen species (ROS). Importantly, NHP-induced systemic immunity depends on ROS, eNAD(P), and the eNAD(P) receptor complex LecRK-VI.2/ BAK1, indicating that NHP triggers SAR through the ROS-eNAD(P)-LecRK-VI.2/BAK1 signaling pathway. Our results uncovered a long-sought-after mechanism underlying the perception of mobile SAR signals in the systemic leaves To investigate how extracellular pyridine nucleotides mediate systemic acquired resistance in Arabidopsis thaliana by infiltrating the lower leaves with MgCL2 or Pseudomonas syrigae pv. Maculicola