Abstract
Nucleotide-binding domain leucine-rich repeat (NLR) protein complexes sense infections and trigger robust immune responses in plants and humans. Activation of plant NLR resistance (R) proteins by pathogen effectors launches convergent immune responses, including programmed cell death (PCD), reactive oxygen species (ROS) production and transcriptional reprogramming with elusive mechanisms. Functional genomic and biochemical genetic screens identified six closely related Arabidopsis Ca2+-dependent protein kinases (CPKs) in mediating bifurcate immune responses activated by NLR proteins, RPS2 and RPM1. The dynamics of differential CPK1/2 activation by pathogen effectors controls the onset of cell death. Sustained CPK4/5/6/11 activation directly phosphorylates a specific subgroup of WRKY transcription factors, WRKY8/28/48, to synergistically regulate transcriptional reprogramming crucial for NLR-dependent restriction of pathogen growth, whereas CPK1/2/4/11 phosphorylate plasma membrane-resident NADPH oxidases for ROS production. Our studies delineate bifurcation of complex signaling mechanisms downstream of NLR immune sensors mediated by the myriad action of CPKs with distinct substrate specificity and subcellular dynamics.
Highlights
The first line of nonself recognition and immune responses in multicellular organisms is triggered by conserved pathogen- or microbe-associated molecular patterns (PAMPs/MAMPs) through pattern recognition receptors (PRRs)
Using the ArabidopsisPseudomonas interaction as a model system, we discovered the molecular link between Nucleotide-binding domain leucine-rich repeat (NLR) immune sensors and the convergent immune responses triggered by distinct pathogen effectors
Integrated functional genomic and biochemical genetic screens identified six closely related Ca2+-dependent protein kinases (CPKs) that orchestrate bifurcate NLR immune signaling via distinct substrate specificity and subcellular dynamics
Summary
The first line of nonself recognition and immune responses in multicellular organisms is triggered by conserved pathogen- or microbe-associated molecular patterns (PAMPs/MAMPs) through pattern recognition receptors (PRRs). MAMPs, such as bacterial flagellin and peptidoglycan (PGN) or fungal chitin, are perceived by cell-surface receptors to mount PAMP/MAMP-triggered immunity (PTI) for broad-spectrum microbial resistance in plants [1,2]. The most common R proteins are intracellular immune sensors with the nucleotide-binding domain (NB) and leucine-rich repeat (LRR), a structural feature shared by mammalian NOD-like receptors that perceive intracellular MAMPs and danger signals to initiate inflammation and immunity [6,8,9,10,11,12]. Whether and how distinct intracellular and cell-surface immune sensors trigger overlapping or/and differential primary immune signaling responses are still largely open questions
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