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

ABSTRACT: Reactive oxygen species (ROS) production is a conserved immune response, primarily mediated in Arabidopsis by the 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 hence maintain ROS production. However, the molecular mechanism underlying the NADPH generation for fueling RBOHD remains unclear. In this study, we isolated a new mutant allele of flagellin-insensitive 4 (FIN4), encoding the first enzyme in de novo NAD biosynthesis. fin4 mutants show reduced NADPH levels and impaired ROS production. However, FIN4 and other genes involved in the NAD- and NADPH-generating pathways are not highly upregulated upon elicitor treatment. Therefore, we hypothesized that a cytosolic NADP-linked dehydrogenase might be post-transcriptionally activated to keep the NADPH supply close to RBOHD. RPM1-INDUCED PROTEIN KINASE (RIPK), a receptor-like cytoplasmic kinase, regulates broad-spectrum ROS signaling in plant immunity. We then isolated the proteins associated with RIPK 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, as well as 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 NADP-ME2 S371 residue contributes to ROS production upon immune elicitor treatment and the susceptibility to the necrotrophic bacterium, Pectobacterium carotovorum. Overall, our study suggests that RIPK activates NADP-ME2 to rapidly increase cytosolic NADPH, hence fueling RBOHD to sustain ROS production in plant immunity.

ORGANISM(S): Arabidopsis thaliana

PROVIDER: GSE198017 | GEO | 2022/03/10

REPOSITORIES: GEO