The receptor-like cytosolic kinase RIPK activates NADP-malic enzyme 2 to generate NADPH for fueling ROS production

Reactive oxygen species(ROS)production is a conserved immune response in Arabidopsis primarily medi-ated by respiratory burst oxidase homolog D(RBOHD),a nicotinamide adenine dinucleotide phosphate(NADPH)oxidase associated with the plasma membrane.A rapid increase in NADPH is necessary to fuel RBOHD proteins and thus maintain ROS production.However,the molecular mechanism by which NADPH is generated to fuel RBOHD remains unclear.In this study,we isolated a new mutant allele of FLAGELLIN-INSENSITIVE 4(FIN4),which encodes the first enzyme in de novo NAD biosynthesis.fin4 mu-tants show reduced NADPH levels and impaired ROS production.However,FIN4 and other genes involved in NAD-and NADPH-generating pathways are not highly upregulated upon elicitor treatment,raising a pos-sibility that a cytosolic NADP-linked dehydrogenase might be post-transcriptionally activated to maintain the NADPH supply close to RBOHD.To verify this possibility,we isolated the proteins associated with RPM1-INDUCED PROTEIN KINASE(RIPK),a receptor-like cytoplasmic kinase that regulates broad-spectrum ROS signaling in plant immunity,and identified NADP-malic enzyme 2(NADP-ME2),an NADPH-generating enzyme.Compared with wild-type plants,nadp-me2 mutants display decreased NADP-ME activity,lower NADPH levels,and reduced ROS production in response to immune elicitors.Furthermore,we found that RIPK can directly phosphorylate NADP-ME2 and enhance its activity in vitro.The phosphorylation of the NADP-ME2 S371 residue contributes to ROS production upon immune elicitor treatment and susceptibility to the necrotrophic bacterium Pectobacterium carotovorum.Collectively,our study suggests that RIPK phosphorylates and activates NADP-ME2 to rapidly increase cytosolic NADPH,thus fueling RBOHD to sustain ROS production in plant immunity.

Existence of a Heterogeneous Pathway in Palladium-Catalyzed Carbon–Carbon Coupling Reaction:Evidence from Ag@Pd_(3)Cu Intermetallic Nanoplates

Palladium(Pd)-catalyzed cross-coupling reaction is a widely studied process with significant economic interest and represents one of the most successful nanocatalytic examples.Owing to the observed leaching of Pd ions from both monometallic and short-range-ordered Pd bimetallic nanocatalysts,there is ambiguity regarding whether the coupling reaction has a heterogeneous component.Herein,facilitated by theoretical calculations,we discovered that the Pd ion leaching-free Pd_(3)Cu intermetallic compound was able to catalyze the cross-coupling reaction heterogeneously with activity comparable with that of Pd ions leached from monometallic Pd.The observation that Pd_(3)Cu acted as a heterogeneous catalyst was further confirmed by the reaction-promoting effect of hot electrons generated by the Ag core in Ag@Pd_(3)Cu nanoplates upon photon adsorption and could only participate in the reaction on the surface of the nanocatalyst.Additionally,it demonstrated experimentally the effectiveness of the heterogeneous route in the coupling reaction.This study shows that the combination of plasmonic catalysis and intermetallic compounds is a promising strategy for designing robust nanocatalysts to synthesize value-added chemicals.