In plants, pathogen effector-triggered immunity (ETI) often leads to programmed cell death, which is restricted by NPR1, an activator of systemic acquired resistance. However, the biochemical ...activities of NPR1 enabling it to promote defense and restrict cell death remain unclear. Here we show that NPR1 promotes cell survival by targeting substrates for ubiquitination and degradation through formation of salicylic acid-induced NPR1 condensates (SINCs). SINCs are enriched with stress response proteins, including nucleotide-binding leucine-rich repeat immune receptors, oxidative and DNA damage response proteins, and protein quality control machineries. Transition of NPR1 into condensates is required for formation of the NPR1-Cullin 3 E3 ligase complex to ubiquitinate SINC-localized substrates, such as EDS1 and specific WRKY transcription factors, and promote cell survival during ETI. Our analysis of SINCs suggests that NPR1 is centrally integrated into the cell death or survival decisions in plant immunity by modulating multiple stress-responsive processes in this quasi-organelle.
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•NPR1 promotes ubiquitination of cytoplasmic proteins upon SA induction•SA-induced NPR1 condensates (SINCs) in cytoplasm are enriched with stress proteins•SINC induction facilitates formation of the NPR1-Cullin 3 E3 ubiquitin ligase complex•SINC is a hub in promoting plant cell survival against biotic and abiotic stresses
The immune regulator NPR1 promotes defense and restricts cell death by forming condensates that target specific substrates for degradation in response to salicylic acid signaling.
Salicylic acid (SA) is a very simple phenolic compound (a C
H
O
compound composed of an aromatic ring, one carboxylic and a hydroxyl group) and this simplicity contrasts with its high versatility and ...the involvement of SA in several plant processes either in optimal conditions or in plants facing environmental cues, including heavy metal (HM) stress. Nowadays, a huge body of evidence has unveiled that SA plays a pivotal role as plant growth regulator and influences intra- and inter-plant communication attributable to its methyl ester form, methyl salicylate, which is highly volatile. Under stress, including HM stress, SA interacts with other plant hormones (e.g., auxins, abscisic acid, gibberellin) and promotes the stimulation of antioxidant compounds and enzymes thereby alerting HM-treated plants and helping in counteracting HM stress. The present literature survey reviews recent literature concerning the roles of SA in plants suffering from HM stress with the aim of providing a comprehensive picture about SA and HM, in order to orientate the direction of future research on this topic.
Salicylic acid (SA) is a phytohormone that plays important roles in many aspects of plant life, notably in plant defenses against pathogens. Key mechanisms of SA signal transduction pathways have now ...been uncovered. Even though details are still missing, we understand how SA production is regulated and which molecular machinery is implicated in the control of downstream transcriptional responses. The NPR1 pathway has been described to play the main role in SA transduction. However, the mode of SA perception is unclear. NPR1 protein has been shown to bind SA. Nevertheless, NPR1 action requires upstream regulatory events (such as a change in cell redox status). Besides, a number of SA-induced responses are independent from NPR1. This shows that there is more than one way for plants to perceive SA. Indeed, multiple SA-binding proteins of contrasting structures and functions have now been identified. Yet, all of these proteins can be considered as candidate SA receptors and might have a role in multinodal (decentralized) SA input. This phenomenon is unprecedented for other plant hormones and is a point of discussion of this review.
Nonexpressor of pathogenesis-related genes 1 (NPR1) was discovered in Arabidopsis as an activator of salicylic acid (SA)-mediated immune responses nearly 30 years ago. How NPR1 confers resistance ...against a variety of pathogens and stresses has been extensively studied; however, only in recent years have the underlying molecular mechanisms been uncovered, particularly NPR1’s role in SA-mediated transcriptional reprogramming, stress protein homeostasis, and cell survival. Structural analyses ultimately defined NPR1 and its paralogs as SA receptors. The SA-bound NPR1 dimer induces transcription by bridging two TGA transcription factor dimers, forming an enhanceosome. Moreover, NPR1 orchestrates its multiple functions through the formation of distinct nuclear and cytoplasmic biomolecular condensates. Furthermore, NPR1 plays a central role in plant health by regulating the crosstalk between SA and other defense and growth hormones. In this review, we focus on these recent advances and discuss how NPR1 can be utilized to engineer resistance against biotic and abiotic stresses.
Although NPR1 was discovered three decades ago, we are only at the beginning of uncovering the full scope of its activities in plant immunity. Here, we summarize NPR1’s function and discuss how the new cellular and structural information on the protein could be utilized for engineering disease resistance in plants.
Salicylic acid (SA) is a plant hormone that is critical for resistance to pathogens
. The NPR proteins have previously been identified as SA receptors
, although how they perceive SA and coordinate ...hormonal signalling remain unknown. Here we report the mapping of the SA-binding core of Arabidopsis thaliana NPR4 and its ligand-bound crystal structure. The SA-binding core domain of NPR4 refolded with SA adopts an α-helical fold that completely buries SA in its hydrophobic core. The lack of a ligand-entry pathway suggests that SA binding involves a major conformational remodelling of the SA-binding core of NPR4, which we validated using hydrogen-deuterium-exchange mass spectrometry analysis of the full-length protein and through SA-induced disruption of interactions between NPR1 and NPR4. We show that, despite the two proteins sharing nearly identical hormone-binding residues, NPR1 displays minimal SA-binding activity compared to NPR4. We further identify two surface residues of the SA-binding core, the mutation of which can alter the SA-binding ability of NPR4 and its interaction with NPR1. We also demonstrate that expressing a variant of NPR4 that is hypersensitive to SA could enhance SA-mediated basal immunity without compromising effector-triggered immunity, because the ability of this variant to re-associate with NPR1 at high levels of SA remains intact. By revealing the structural mechanisms of SA perception by NPR proteins, our work paves the way for future investigation of the specific roles of these proteins in SA signalling and their potential for engineering plant immunity.
WRKY transcription factors (TFs) have been mainly associated with plant defense, but recent studies have suggested additional roles in the regulation of other physiological processes. Here, we ...explored the possible contribution of two related group III WRKY TFs, WRKY70 and WRKY54, to osmotic stress tolerance. These TFs are positive regulators of plant defense, and co-operate as negative regulators of salicylic acid (SA) biosynthesis and senescence.
We employed single and double mutants of wrky54 and wrky70, as well as a WRKY70 overexpressor line, to explore the role of these TFs in osmotic stress (polyethylene glycol) responses. Their effect on gene expression was characterized by microarrays and verified by quantitative PCR. Stomatal phenotypes were assessed by water retention and stomatal conductance measurements.
The wrky54wrky70 double mutants exhibited clearly enhanced tolerance to osmotic stress. However, gene expression analysis showed reduced induction of osmotic stress-responsive genes in addition to reduced accumulation of the osmoprotectant proline. By contrast, the enhanced tolerance was correlated with improved water retention and enhanced stomatal closure.
These findings demonstrate that WRKY70 and WRKY54 co-operate as negative regulators of stomatal closure and, consequently, osmotic stress tolerance in Arabidopsis, suggesting that they have an important role, not only in plant defense, but also in abiotic stress signaling.
The phytohormone salicylic acid (SA) plays essential roles in biotic and abiotic responses, plant development, and leaf senescence. 2,5-Dihydroxybenzoic acid (2,5-DHBA or gentisic acid) is one of the ...most commonly occurring aromatic acids in green plants and is assumed to be generated from SA, but the enzymes involved in its production remain obscure. DMR6 (Downy Mildew Resistant6; At5g24530) has been proven essential in plant immunity of Arabidopsis (Arabidopsis thaliana), but its biochemical properties are not well understood. Here, we report the discovery and functional characterization of DMR6 as a salicylic acid 5-hydroxylase (S5H) that catalyzes the formation of 2,5-DHBA by hydroxylating SA at the C5 position of its phenyl ring in Arabidopsis. S5H/DMR6 specifically converts SA to 2,5-DHBA in vitro and displays higher catalytic efficiency (K
cat/K
m = 4.96 × 10⁴ M⁻¹ s⁻¹) than the previously reported S3H (K
cat/K
m = 6.09 × 10³ M⁻¹ s⁻¹) for SA. Interestingly, S5H/DMR6 displays a substrate inhibition property that may enable automatic control of its enzyme activities. The s5h mutant and s5hs3h double mutant overaccumulate SA and display phenotypes such as a smaller growth size, early senescence, and a loss of susceptibility to Pseudomonas syringae pv tomato DC3000. S5H/DMR6 is sensitively induced by SA/pathogen treatment and is expressed widely from young seedlings to senescing plants, whereas S3H is more specifically expressed at themature and senescing stages. Collectively, our results disclose the identity of the enzyme required for 2,5-DHBA formation and reveal a mechanism by which plants fine-tune SA homeostasis by mediating SA 5-hydroxylation.
In recent years, numerous studies have shown that conversion of conventional drugs in ionic liquid (IL) formulation could be a successful strategy to improve their physicochemical properties or ...suggest a new route of administration. We report the synthesis and detailed characterization of eight salicylic acid-based ILs (SA-ILs) containing cation non-polar or aromatic amino acid esters. Using in vitro assays, we preliminary evaluated the therapeutic potency of the novel SA-ILs. We observed that conversion of the SA into ionic liquids led to a decrease in its cytotoxicity toward NIH/3T3 murine embryo fibroblasts and human HaCaT keratinocytes. It should be mentioned is that all amino acid alkyl ester salicylates AAORSA inhibit the production of the proinflammatory cytokine IL-6 in LPS-stimulated keratinocytes. Moreover, keratinocytes, pretreated with PheOMeSA and PheOPrSA seem to be protected from LPS-induced inflammation. Finally, the novel compounds exhibit a similar binding affinity to bovine serum albumin (BSA) as the parent SA, suggesting a similar pharmacokinetic profile. These preliminary results indicate that SA-ILs, especially those with PheOMe, PheOPr, and ValOiPr cation, have the potential to be further investigated as novel topical agents for chronic skin diseases such as psoriasis and acne vulgaris.
Salicylic acid (SA) is a class of trace pollutants widely presented in the environment belonged to pharmaceuticals and personal care products. It is difficult to remove SA by the traditional ...treatment processes because of its toxicity. In this paper, the degradation of SA by Mn-loaded Cu/Fe particle electrodes was studied. Firstly, the particle electrodes were prepared by impregnation-roasting method and then characterized by SEM, XRF and XRD. The diffraction peaks of Fe2O3 and CuO in the XRD patterns of the particle electrodes which had the dense spherical particles were significantly increased and the content of CuO and Fe2O3 increased by 1.9% and 3.6% respectively. Secondly, single factor experiments were carried out under conditions of cell voltage, electrolyte concentration, pH, HRT, inter-electrode distance and initial pollutant concentration. Under the optimum conditions of all the factors, the degradation rate of SA reached 76.9%. Then, HPLC and GCMS were employed to deduce the degradation pathways of SA by the TDE with Mn-particle electrodes (Mn-PETDE). Under the action of •OH, SA underwent decarboxylation and substitution reactions and then mineralized after the ring-opening reaction. All results demonstrated that this Mn-PETDE was effective for degradation of SA.
•Particle electrodes were used by manganese slag.•Getting the optimal condition by single factor experiments.•Mn-PETDE had a high efficient degradation performance to salicylic acid.•The degradation pathway of salicylic acid was proved through HPLC and GC-MS.
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