Pathogen recognition by nucleotide-binding (NB), leucine-rich repeat (LRR) receptors (NLRs) plays roles in plant immunity. The
pv.
effector AvrAC uridylylates the
PBL2 kinase, and the latter (PBL2
) ...acts as a ligand to activate the NLR ZAR1 precomplexed with the RKS1 pseudokinase. Here we report the cryo-electron microscopy structures of ZAR1-RKS1 and ZAR1-RKS1-PBL2
in an inactive and intermediate state, respectively. The ZAR1
domain, compared with animal NLR
domains, is differently positioned to sequester ZAR1 in an inactive state. Recognition of PBL2
is exclusively through RKS1, which interacts with ZAR1
PBL2
binding stabilizes the RKS1 activation segment, which sterically blocks ZAR1 adenosine diphosphate (ADP) binding. This engenders a more flexible NB domain without conformational changes in the other ZAR1 domains. Our study provides a structural template for understanding plant NLRs.
NLRs constitute intracellular immune receptors in both plants and animals. Direct or indirect ligand recognition results in formation of oligomeric NLR complexes to mediate immune signaling. Over the ...past 20 years, rapid progress has been made in our understanding of NLR signaling. Structural and biochemical studies provide insight into molecular basis of autoinhibition, ligand recognition, and resistosome/inflammasome formation of several NLRs. In this review, we summarize these studies focusing on the structural aspect of NLRs. We also discuss the analogies and differences between plant and animal NLRs in their mechanisms of action and how the available knowledge may shed light on the signaling mechanisms of other NLRs.
Direct or indirect recognition of pathogen-derived effectors by plant nucleotide-binding leucine-rich repeat (LRR) receptors (NLRs) initiates innate immune responses. The
effector ATR1 activates the ...N-terminal Toll-interleukin-1 receptor (TIR) domain of
NLR RPP1. We report a cryo-electron microscopy structure of RPP1 bound by ATR1. The structure reveals a C-terminal jelly roll/Ig-like domain (C-JID) for specific ATR1 recognition. Biochemical and functional analyses show that ATR1 binds to the C-JID and the LRRs to induce an RPP1 tetrameric assembly required for nicotinamide adenine dinucleotide hydrolase (NADase) activity. RPP1 tetramerization creates two potential active sites, each formed by an asymmetric TIR homodimer. Our data define the mechanism of direct effector recognition by a plant NLR leading to formation of a signaling-active holoenzyme.
Nucleotide-binding, leucine-rich repeat receptors (NLRs) are major immune receptors in plants and animals. Upon activation, the Arabidopsis NLR protein ZAR1 forms a pentameric resistosome in vitro ...and triggers immune responses and cell death in plants. In this study, we employed single-molecule imaging to show that the activated ZAR1 protein can form pentameric complexes in the plasma membrane. The ZAR1 resistosome displayed ion channel activity in Xenopus oocytes in a manner dependent on a conserved acidic residue Glu11 situated in the channel pore. Pre-assembled ZAR1 resistosome was readily incorporated into planar lipid-bilayers and displayed calcium-permeable cation-selective channel activity. Furthermore, we show that activation of ZAR1 in the plant cell led to Glu11-dependent Ca2+ influx, perturbation of subcellular structures, production of reactive oxygen species, and cell death. The results thus support that the ZAR1 resistosome acts as a calcium-permeable cation channel to trigger immunity and cell death.
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•Resistosome formed by the immune receptor ZAR1 is a cation-selective channel•The ZAR1 channel is permeable to calcium•The activated ZAR1 forms a pentamer in the plasma membrane•The channel activity triggers immune signaling and cell death in plants
ZAR1 resistosome is a calcium-permeable channel that triggers immune signaling and cell death in plants.
Nucleotide-binding domain, leucine-rich repeat receptors (NLRs) mediate innate immunity by forming inflammasomes. Activation of the NLR protein NLRP1 requires autocleavage within its function-to-find ...domain (FIIND)
. In resting cells, the dipeptidyl peptidases DPP8 and DPP9 interact with the FIIND of NLRP1 and suppress spontaneous NLRP1 activation
; however, the mechanisms through which this occurs remain unknown. Here we present structural and biochemical evidence that full-length rat NLRP1 (rNLRP1) and rat DPP9 (rDPP9) form a 2:1 complex that contains an autoinhibited rNLRP1 molecule and an active UPA-CARD fragment of rNLRP1. The ZU5 domain is required not only for autoinhibition of rNLRP1 but also for assembly of the 2:1 complex. Formation of the complex prevents UPA-mediated higher-order oligomerization of UPA-CARD fragments and strengthens ZU5-mediated NLRP1 autoinhibition. Structure-guided biochemical and functional assays show that both NLRP1 binding and enzymatic activity are required for DPP9 to suppress NLRP1 in human cells. Together, our data reveal the mechanism of DPP9-mediated inhibition of NLRP1 and shed light on the activation of the NLRP1 inflammasome.
Plants can achieve amazing lifespans because of their continuous and repetitive formation of new organs by stem cells present within meristems. The balance between proliferation and differentiation ...of meristem cells is large- ly regulated by the CLAVATA3/ENDOSPERM SURROUNDING REGION （CLE） peptide hormones. One of the well-characterized CLE peptides, CLE41/TDIF （tracheary elements differentiation inhibitory factor）, functions to suppress tracheary element differentiation and promote procambial cell proliferation, playing important roles in vascular development and wood formation. The recognition mechanisms of TDIF or other CLE peptides by their respective receptors, however, remain largely elusive. Here we report the crystal structure of TDIF in complex with its receptor PXY, a leucine-rich repeat receptor kinase （LRR-RK）. Our structure reveals that TDIF mainly adopts an ＂t＇l＂-like conformation binding to the inner surface of the LRR domain of PXY. Interaction between TDIF and PXY is predominately mediated by the relatively conserved amino acids of TDIF. Structure-based sequence alignment showed that the TDIF-interacting motifs are also conserved among other known CLE receptors. Our data provide a structural template for understanding the recognition mechanism of CLE peptides by their receptors, offering an op- portunity for the identification of receptors of other uncharacterized CLE peptides.
The endogenous peptides AtPepl-8 in Arabidopsis mature from the conserved C-terminal portions of their precursor proteins PROPEP1-8, respectively. The two homologous leucine-rich repeat-receptor ...kinases （LRR-RKs） PEPR1 and PEPR2 act as receptors of AtPeps. AtPep binding leads to stable association of PEPR1,2 with the shared receptor LRR-RK BAK1, eliciting immune responses similar to those induced by pathogens. Here we report a crystal structure of the extraceUular LRR domain of PEPRI （PEPR1LRR） in complex with AtPepl. The structure reveals that AtPepl adopts a fully extended conformation and binds to the inner surface of the superhelical PEPRILRR. Biochemical assays showed that AtPepl is capable of inducing PEPR1LRR-BAK1LRR heterodimerization. The conserved C-terminal portion of AtPepl dominates AtPepl binding to PEPRILRR, with the last amino acid of AtPepl Asn23 forming extensive interactions with PEPR1LRR. Deletion of the last residue of AtPepl significantly compromised AtPep1 interaction with PEPRILRR. Together, our data reveal a conserved structural mechanism of AtPep1 recognition by PEPR1, providing significant insight into prediction of recognition of other peptides by their cognate LRR-RKs.
Abstract
Sessile plants encode a large number of small peptides and cell surface-resident receptor kinases, most of which have unknown functions. Here, we report that the
Arabidopsis
receptor kinase ...MALE DISCOVERER 1-INTERACTING RECEPTOR-LIKE KINASE 2 (MIK2) recognizes the conserved signature motif of SERINE-RICH ENDOGENOUS PEPTIDEs (SCOOPs) from
Brassicaceae
plants as well as proteins present in fungal
Fusarium
spp. and bacterial
Comamonadaceae
, and elicits various immune responses. SCOOP signature peptides trigger immune responses and altered root development in a MIK2-dependent manner with a sub-nanomolar sensitivity. SCOOP12 directly binds to the extracellular leucine-rich repeat domain of MIK2 in vivo and in vitro, indicating that MIK2 is the receptor of SCOOP peptides. Perception of SCOOP peptides induces the association of MIK2 and the coreceptors SOMATIC EMBRYOGENESIS RECEPTOR KINASE 3 (SERK3) and SERK4 and relays the signaling through the cytosolic receptor-like kinases
BOTRYTIS
-INDUCED KINASE 1 (BIK1) and AVRPPHB SUSCEPTIBLE1 (PBS1)-LIKE 1 (PBL1). Our study identifies a plant receptor that bears a dual role in sensing the conserved peptide motif from phytocytokines and microbial proteins via a convergent signaling relay to ensure a robust immune response.
Peptide-mediated cell-to-cell signaling has crucial roles in coordination and definition of cellular functions in plants. Peptide-receptor matching is important for understanding the mechanisms ...underlying peptide-mediated sig- naling. Here we report the structure-guided identification of root meristem growth factor （RGF） receptors important for plant development. An assay based on a signature ligand recognition motif （Arg-x-Arg） conserved in a subfamily of leucine-rich repeat receptor kinases CLRR-RKs） identified the functionally uncharacterized LRR-RK At4926540 as a receptor of RGF1 （RGFR1）. We further solved the crystal structure of RGF1 in complex with the LRR domain of RGFR1 at a resolution of 2.6 A, which reveals that the Arg-x-Gly-Gly （RxGG） motif is responsible for specific rec- ognition of the sulfate group of RGF1 by RGFR1. Based on the RxGG motif, we identified additional four RGFRs. Participation of the five RGFRs in RGF-induced signaling is supported by biochemical and genetic data. We also of- fer evidence showing that SERKs function as co-receptors for RGFs. Taken together, our study identifies RGF receptors and co-receptors that can link RGF signals with their downstream components and provides a proof of principle for structure-based matching of LRR-RKs with their peptide ligands.
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