Carolina Digital Repository (University of North Carolina at Chapel Hill), 2017
Plants evolved intracellular immune receptors that belong to the NOD-like receptor (NLR) family t... more Plants evolved intracellular immune receptors that belong to the NOD-like receptor (NLR) family to recognize the presence of pathogenderived effector proteins. NLRs possess an N-terminal Toll-like/IL-1 receptor (TIR) or a non-TIR domain [some of which contain coiled coils (CCs)], a central nucleotide-binding (NB-ARC) domain, and a C-terminal leucine-rich repeat (LRR). Activation of NLR proteins results in a rapid and high-amplitude immune response, eventually leading to host cell death at the infection site, the so-called hypersensitive response. Despite their important contribution to immunity, the exact mechanisms of NLR activation and signaling remain unknown and are likely heterogenous. We undertook a detailed structure-function analysis of the plasma membrane (PM)-localized CC NLR Resistance to Pseudomonas syringae pv. maculicola 1 (RPM1) using both stable transgenic Arabidopsis and transient expression in Nicotiana benthamiana. We report that immune signaling is induced only by activated full-length PM-localized RPM1. Our interaction analyses demonstrate the importance of a functional P-loop for in planta interaction of RPM1 with the small host protein RPM1-interacting protein 4 (RIN4), for constitutive preactivation and postactivation self-association of RPM1 and for proper PM localization. Our results reveal an additive effect of hydrophobic conserved residues in the CC domain for RPM1 function and RPM1 self-association and their necessity for RPM1-RIN4 interaction. Thus, our findings considerably extend our understanding of the mechanisms regulating NLR activation at, and signaling from, the PM. plant immunity | effector-triggered immunity | NLR receptor | oligomerization | Arabidopsis thaliana
Plants evolved a sophisticated, receptor-based, innate immune system. Cell surface localized patt... more Plants evolved a sophisticated, receptor-based, innate immune system. Cell surface localized pattern recognition (PRR) and intracellular nucleotide-binding leucine-rich repeat (NLR) receptors detect pathogen-associated molecular patterns or pathogen-derived effector molecules, respectively, and induce a range of common immune responses. These include Ca 2+ fluxes, reactive oxygen species production, and mitogen-activated protein kinase activation [1]. Recent studies have demonstrated an interdependency and mutual potentiation of the 2 receptor systems [2,3]. Based on their N-terminal domains and their phylogeny, NLRs are classified in coiled-coil (CC) domain, Toll-like/interleukin-1 receptor resistance (TIR) domain, and RESISTANCE TO POWDERY MILDEW 8-like CC (CC R) domain containing NLRs, referred to as CNLs, TNLs, and RNLs, respectively [4]. In Arabidopsis thaliana (hereafter Arabidopsis), multiple PRRs and effector sensing NLRs (some CNLs and all tested TNLs) require the presence of RNLs, also termed helper NLRs, to activate full immunity [5,6]. RNLs form a small and evolutionary conserved clade comprised of 2 subfamilies, the ACTIVATED DISEASE RESISTANCE 1 (ADR1) and N REQUIREMENT GENE 1 (NRG1) families that have separated before the divergence of angiosperms [4]. The Arabidopsis genome bares 3 ADR1 and 2 NRG1 full-length genes required for full immunity [7-9]. Although RNLs represent only a relatively small part of the NLR gene repertoire in most angiosperms [4,10], they are of outmost importance for plants to fight off invading pathogens. Here, we highlight recent findings of how RNLs function during immunity and discuss mechanisms of RNL activation.
Intracellular plant immune receptors, termed NLRs, respond to pathogen effectors delivered into p... more Intracellular plant immune receptors, termed NLRs, respond to pathogen effectors delivered into plant cells. Activation of NLRs typically confers strong immunity. Sensor NLRs, involved in effector recognition, are either TIR-NLRs (TNLs) or CC-NLRs (CNLs). Helper NLRs, required for sensor NLR signaling, include CCR-NLRs (RNLs) and a special class of CNLs known as NRCs. Activated TNLs produce small molecules that induce an association between the EDS1/SAG101 heterodimer and the NRG1s helper RNLs. Auto active NRG1s oligomerize and form calcium signaling channels largely localized at the plasma membrane (PM). The molecular mechanisms of helper NLR PM association and effector induced NRG1 oligomerization remain uncharacterized. We find that both RNLs and NRCs require positively charged residues in the second and fourth helices of their CCRor CC domain for phospholipid binding and PM association before and after activation, despite conformational changes that accompany activation. We demo...
Intracellular plant immune receptors, termed NLRs, respond to pathogen effectors delivered into p... more Intracellular plant immune receptors, termed NLRs, respond to pathogen effectors delivered into plant cells. Activation of NLRs typically confers strong immunity. Sensor NLRs, involved in effector recognition, are either TIR-NLRs (TNLs) or CC-NLRs (CNLs). Helper NLRs, required for sensor NLR signaling, include CCR-NLRs (RNLs) and a special class of CNLs known as NRCs. Activated TNLs produce small molecules that induce an association between the EDS1/SAG101 heterodimer and the NRG1s helper RNLs. Auto active NRG1s oligomerize and form calcium signaling channels largely localized at the plasma membrane (PM). The molecular mechanisms of helper NLR PM association and effector induced NRG1 oligomerization remain uncharacterized. We find that both RNLs and NRCs require positively charged residues in the second and fourth helices of their CCRor CC domain for phospholipid binding and PM association before and after activation, despite conformational changes that accompany activation. We demo...
TIR domains are NAD-degrading enzymes that function during immune signaling in prokaryotes, plant... more TIR domains are NAD-degrading enzymes that function during immune signaling in prokaryotes, plants, and animals. In plants, most TIR domains are incorporated into intracellular immune receptors. In Arabidopsis, TIR-derived small molecules bind and activate EDS1 heterodimers, which in turn activate RNLs, a class of cation channel-forming immune receptors. RNL activation drives cytoplasmic Ca2+influx, transcriptional reprogramming, pathogen resistance and host cell death. We screened for mutants that suppress an RNL activation mimic allele and identified a TIR-containing immune receptor, SADR1. Despite functioning downstream of an auto-activated RNL, SADR1 is not required for defense signaling triggered by other tested TIR-containing immune receptors. SADR1 is required for defense signaling initiated by some trans-membrane pattern recognition receptors and contributes to the unbridled spread of cell death inlesion simulating disease 1. Together with RNLs, SADR1 regulates defense gene ...
Membrane vesicles delivered to the cell-division plane fuse with one another to form the partitio... more Membrane vesicles delivered to the cell-division plane fuse with one another to form the partitioning membrane during plant cytokinesis, starting in the cell center. In Arabidopsis, this requires SNARE complexes involving the cytokinesis-specific Qa-SNARE KNOLLE. However, cytokinesis still occurs in knolle mutant embryos, suggesting contributions from KNOLLE-independent SNARE complexes. Here we show that Qa-SNARE SYP132, having counterparts in lower plants, functionally overlaps with the flowering plant-specific KNOLLE. SYP132 mutation causes cytokinesis defects, knolle syp132 double mutants consist of only one or a few multi-nucleate cells, and SYP132 has the same SNARE partners as KNOLLE. SYP132 and KNOLLE also have non-overlapping functions in secretion and in cellularization of the embryo-nourishing endosperm resulting from double fertilization unique to flowering plants. Evolutionarily ancient non-specialized SNARE complexes originating in algae were thus amended by the appeara...
Plant nucleotide-binding leucine-rich repeat receptors (NLRs) regulate immunity and cell death. R... more Plant nucleotide-binding leucine-rich repeat receptors (NLRs) regulate immunity and cell death. RPW8 domain-containing “helper” NLRs (RNLs) are required by many “sensor” NLRs. Our crystal structure of the RNL N REQUIREMENT GENE 1.1 (NRG1.1) N-terminal signaling domain resembled that of the resting state plant resistosome-forming HOPZ-ACTIVATED RESISTANCE 1 (ZAR1) and the animal MIXED-LINEAGE KINASE-LIKE (MLKL) cation channel. Active NRG1.1 oligomerized, was enriched in plasma membrane puncta and conferred cytoplasmic Ca2+ influx in plant and human HeLa cells. NRG1.1-dependent Ca2+ influx and cell death were sensitive to Ca2+ channel blockers. Ca2+ influx and cell death mediated by NRG1.1 and ACTIVATED DISEASE RESISTANCE 1 (ADR1), another RNL, required conserved negatively charged N-terminal residues. Thus, RNLs apparently form influx channels to directly regulate cytoplasmic [Ca2+] and consequent cell death.One Sentence SummaryA specific class of plant immune receptors function as c...
Uploads
Papers by Farid El Kasmi