Molecular insights into the biochemical functions and signalling mechanisms of plant NLRs

Activation and Autoinhibition Mechanisms of NLR Immune Receptor Pi36 in Rice

Nucleotide-binding and leucine-rich repeat receptors (NLRs) are the most important and largest class of immune receptors in plants. The Pi36 gene encodes a canonical CC-NBS-LRR protein that confers resistance to rice blast fungal infections. Here, we show that the CC domain of Pi36 plays a role in cell death induction. Furthermore, self-association is required for the CC domain-mediated cell death, and the self-association ability is correlated with the cell death level. In addition, the NB-ARC domain may suppress the activity of the CC domain through intramolecular interaction. The mutations D440G next to the RNBS-D motif and D503V in the MHD motif autoactivated Pi36, but the mutation K212 in the P-loop motif inhibited this autoactivation, indicating that nucleotide binding of the NB-ARC domain is essential for Pi36 activation. We also found that the LRR domain is required for D503V- and D440G-mediated Pi36 autoactivation. Interestingly, several mutations in the CC domain compromised the CC domain-mediated cell death without affecting the D440G- or D503V-mediated Pi36 autoactivation. The autoactivate Pi36 variants exhibited stronger self-associations than the inactive variants. Taken together, we speculated that the CC domain of Pi36 executes cell death activities, whereas the NB-ARC domain suppressed CC-mediated cell death via intermolecular interaction. The NB-ARC domain releases its suppression of the CC domain and strengthens the self-association of Pi36 to support the CC domain, possibly through nucleotide exchange.

Sequential Evaluation of Hematology Markers as a Prognostic Factor in Glioblastoma Patients

In our study, we investigated the prognostic significance of hematological markers-NLR (Neutrophil-to-Lymphocyte Ratio), PLR (Platelet-to-Lymphocyte Ratio), and RDW-CV (Red Blood Cell Distribution Width-Coefficient of Variation)-in 117 glioblastoma patients. The data collected from January 2016 to December 2018 included demographics, clinical scores, and treatment regimens. Unlike previous research, which often examined these markers solely before surgery, our unique approach analyzed them at multiple stages: preoperative, postoperative, and before adjuvant therapies. We correlated these markers with the overall survival (OS) and progression-free survival (PFS) using statistical tools, including ANOVA, Cox regression, and Kaplan-Meier survival analyses, employing SPSS version 29.0. Our findings revealed notable variations in the NLR, PLR, and RDW-CV across different treatment stages. The NLR and PLR decreased after surgery, with some stabilization post-STUPP phase (NLR: p = 0.007, η2p = 0.06; PLR: p = 0.001, η2p = 0.23), while the RDW-CV increased post-surgery and during subsequent treatments (RDW-CV: p < 0.001, η2p = 0.67). Importantly, we observed significant differences between the preoperative phase and other treatment phases. Additionally, a higher NLR and RDW-CV at the second-line treatment and disease progression were associated with an increased risk of death (NLR at 2nd line: HR = 1.03, p = 0.029; RDW-CV at progression: HR = 1.14, p = 0.004). We proposed specific marker cut-offs that demonstrated significant associations with survival outcomes when applied to Kaplan-Meier survival curves (NLR at 2nd line < 5: p < 0.017; RDW-CV at progression < 15: p = 0.007). An elevated NLR and RDW-CV at later treatment stages correlated with poorer OS and PFS. No significant preoperative differences were detected. These biomarkers may serve as non-invasive tools for glioblastoma management.

Defense signaling pathways in resistance to plant viruses: Crosstalk and finger pointing

Resistance to infection by plant viruses involves proteins encoded by plant resistance (R) genes, viz., nucleotide-binding leucine-rich repeats (NLRs), immune receptors. These sensor NLRs are activated either directly or indirectly by viral protein effectors, in effector-triggered immunity, leading to induction of defense signaling pathways, resulting in the synthesis of numerous downstream plant effector molecules that inhibit different stages of the infection cycle, as well as the induction of cell death responses mediated by helper NLRs. Early events in this process involve recognition of the activation of the R gene response by various chaperones and the transport of these complexes to the sites of subsequent events. These events include activation of several kinase cascade pathways, and the syntheses of two master transcriptional regulators, EDS1 and NPR1, as well as the phytohormones salicylic acid, jasmonic acid, and ethylene. The phytohormones, which transit from a primed, resting states to active states, regulate the remainder of the defense signaling pathways, both directly and by crosstalk with each other. This regulation results in the turnover of various suppressors of downstream events and the synthesis of various transcription factors that cooperate and/or compete to induce or suppress transcription of either other regulatory proteins, or plant effector molecules. This network of interactions results in the production of defense effectors acting alone or together with cell death in the infected region, with or without the further activation of non-specific, long-distance resistance. Here, we review the current state of knowledge regarding these processes and the components of the local responses, their interactions, regulation, and crosstalk.

Cucumis sativus CsbZIP90 suppresses Podosphaera xanthii resistance by modulating reactive oxygen species

Resistance to disease in plants requires the coordinated action of multiple functionally related genes, as it is difficult to improve disease resistance with a single functional gene. Therefore, the use of transcription factors to regulate the expression of multiple resistance genes to improve disease resistance has become a recent focus in the field of gene research. The basic leucine zipper (bZIP) transcription factor family plays vital regulatory roles in processes, such as plant growth and development and the stress response. In our previous study, CsbZIP90 (Cucsa.134370) was involved in the defense response of cucumber to Podosphaera xanthii, but the relationship between cucumber and resistance to powdery mildew remained unclear. Herein, we detected the function of CsbZIP90 in response to P. xanthii. CsbZIP90 was localized to the cytoplasm and nucleus, and its expression was significantly induced during P. xanthii attack. Transient overexpression of CsbZIP90 in cucumber cotyledons resulted in decreased resistance to P. xanthii, while silencing CsbZIP90 increased resistance to P. xanthii. CsbZIP90 negatively regulated the expression of reactive oxygen species (ROS)-related genes and activities of ROS-related kinases. Taken together, our results show that CsbZIP90 suppresses P. xanthi resistance by modulating ROS. This study will provide target genes for breeding cucumbers resistant to P. xanthii.

Plasma membrane association and resistosome formation of plant helper immune receptors

Intracellular plant immune receptors, termed NLRs (Nucleotide-binding Leucine-rich repeat Receptors), confer effector-triggered immunity. Sensor NLRs are responsible for pathogen effector recognition. Helper NLRs function downstream of sensor NLRs to transduce signaling and induce cell death and immunity. Activation of sensor NLRs that contain TIR (Toll/interleukin-1receptor) domains generates small molecules that induce an association between a downstream heterodimer signalosome of EDS1 (EnhancedDisease Susceptibility 1)/SAG101 (Senescence-AssociatedGene 101) and the helper NLR of NRG1 (NRequired Gene 1). Autoactive 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 are not well characterized. We demonstrate that helper NLRs require positively charged residues in their N-terminal domains for phospholipid binding and PM association before and after activation, despite oligomerization and conformational changes that accompany activation. We demonstrate that effector activation of a TIR-containing sensor NLR induces NRG1 oligomerization at the PM and that the cytoplasmic pool of EDS1/SAG101 is critical for cell death function. EDS1/SAG101 cannot be detected in the oligomerized NRG1 resistosome, suggesting that additional unknown triggers might be required to induce the dissociation of EDS1/SAG101 from the previously described NRG1/EDS1/SAG101 heterotrimer before subsequent NRG1 oligomerization. Alternatively, the conformational changes resulting from NRG1 oligomerization abrogate the interface for EDS1/SAG101 association. Our data provide observations regarding dynamic PM association during helper NLR activation and underpin an updated model for effector-induced NRG1 resistosome formation.

Plant immunity in soybean: progress, strategies, and perspectives

Soybean (Glycine max) is one of the most important commercial crops worldwide. Soybean hosts diverse microbes, including pathogens that may cause diseases and symbionts that contribute to nitrogen fixation. Study on soybean-microbe interactions to understand pathogenesis, immunity, and symbiosis represents an important research direction toward plant protection in soybean. In terms of immune mechanisms, current research in soybean lags far behind that in the model plants Arabidopsis and rice. In this review, we summarized the shared and unique mechanisms involved in the two-tiered plant immunity and the virulence function of pathogen effectors between soybean and Arabidopsis, providing a molecular roadmap for future research on soybean immunity. We also discussed disease resistance engineering and future perspectives in soybean.

TIR enzymatic functions: signaling molecules and receptor mechanisms

The evolutionarily conserved Toll/Interleukin-1 Receptor (TIR) domains across kingdoms of prokaryotes, plants, and animals play critical roles in innate immunity. Recent studies have revealed the enzymatic functions of TIRs, the structural bases of TIRs as holoenzymes, and the identity of TIR-generated small signaling molecules and their receptors, which significantly advanced our understanding on TIR-mediated immune signaling pathways. We reviewed the most up-to-date findings in TIR enzymatic functions from the perspectives of signaling molecules and receptor mechanisms.

The Nucleotide Revolution: Immunity at the Intersection of Toll/Interleukin-1 Receptor Domains, Nucleotides, and Ca2

The discovery of the enzymatic activity of the toll/interleukin-1 receptor (TIR) domain protein SARM1 five years ago preceded a flood of discoveries regarding the nucleotide substrates and products of TIR domains in plants, animals, bacteria, and archaea. These discoveries into the activity of TIR domains coincide with major advances in understanding the structure and mechanisms of NOD-like receptors and the mutual dependence of pattern recognition receptor- and effector-triggered immunity (PTI and ETI, respectively) in plants. It is quickly becoming clear that TIR domains and TIR-produced nucleotides are ancestral signaling molecules that modulate immunity and that their activity is closely associated with Ca²⁺ signaling. TIR domain research now bridges the separate disciplines of molecular plant- and animal-microbe interactions, neurology, and prokaryotic immunity. A cohesive framework for understanding the role of enzymatic TIR domains in diverse organisms will help unite the research of these disparate fields. Here, we review known products of TIR domains in plants, animals, bacteria, and archaea and use context gained from animal and prokaryotic TIR domain systems to present a model for TIR domains, nucleotides, and Ca²⁺ at the intersection of PTI and ETI in plant immunity. [Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Advances in Fungal Elicitor-Triggered Plant Immunity

There is an array of pathogenic fungi in the natural environment of plants, which produce some molecules including pathogen-associated molecular patterns (PAMPs) and effectors during infection. These molecules, which can be recognized by plant specific receptors to activate plant immunity, including PTI (PAMP-triggered immunity) and ETI (effector-triggered immunity), are called elicitors. Undoubtedly, identification of novel fungal elicitors and their plant receptors and comprehensive understanding about fungal elicitor-triggered plant immunity will be of great significance to effectively control plant diseases. Great progress has occurred in fungal elicitor-triggered plant immunity, especially in the signaling pathways of PTI and ETI, in recent years. Here, recent advances in fungal elicitor-triggered plant immunity are summarized and their important contribution to the enlightenment of plant disease control is also discussed.

Ferroptosis, necroptosis, and pyroptosis in the occurrence and development of ovarian cancer

Ovarian cancer (OC) is one of the most common malignancies that causes death in women and is a heterogeneous disease with complex molecular and genetic changes. Because of the relatively high recurrence rate of OC, it is crucial to understand the associated mechanisms of drug resistance and to discover potential target for rational targeted therapy. Cell death is a genetically determined process. Active and orderly cell death is prevalent during the development of living organisms and plays a critical role in regulating life homeostasis. Ferroptosis, a novel type of cell death discovered in recent years, is distinct from apoptosis and necrosis and is mainly caused by the imbalance between the production and degradation of intracellular lipid reactive oxygen species triggered by increased iron content. Necroptosis is a regulated non-cysteine protease–dependent programmed cell necrosis, morphologically exhibiting the same features as necrosis and occurring via a unique mechanism of programmed cell death different from the apoptotic signaling pathway. Pyroptosis is a form of programmed cell death that is characterized by the formation of membrane pores and subsequent cell lysis as well as release of pro-inflammatory cell contents mediated by the abscisin family. Studies have shown that ferroptosis, necroptosis, and pyroptosis are involved in the development and progression of a variety of diseases, including tumors. In this review, we summarized the recent advances in ferroptosis, necroptosis, and pyroptosis in the occurrence, development, and therapeutic potential of OC.