Persulfidation proteome reveals the regulation of protein function by hydrogen sulfide in diverse biological processes in Arabidopsis

Hydrogen sulfide mechanism of action in plants; from interaction with regulatory molecules to persulfidation of proteins

Hydrogen sulfide (H2S), previously known as a toxic gas, is currently considered one of the most important gaseous transmitters in plants. This novel signaling molecule has been determined to play notable roles in plant growth, development, and maturation. In addition, pharmacological and genetic evidence indicated that this regulatory molecule effectively ameliorates various plant stress conditions. H2S is involved in these processes by changing gene expression, enzyme activities, and metabolite concentrations. During its regulatory function, H2S interacts with other signaling pathways such as hydrogen peroxide (H2O2), nitric oxide (NO), Ca2+, carbon monoxide (CO), phosphatidic acid (PA), phytohormones, etc. The H2S mechanism of action may depend on the persulfidation post-translational modification (PTM), which attacks the cysteine (Cys) residues on the target proteins and changes their structure and activities. This review summarized H2S biosynthesis pathways, its role in sulfide state, and its donors in plant biology. We also discuss recent progress in the research on the interactions of H2S with other signaling molecules, as well as the role of persulfidation in modulating various plant reactions.

New role for thioredoxins in plants: Implication of TRXo1 in protein depersulfidation

Persulfidation, a posttranslational modification of cysteines to persulfides, is the best characterized molecular mechanism of H2S signaling. This study is focused on new functions for thioredoxins (TRXs) in plants beyond those of thiol disulfide (S-S) exchange, including the regulation of protein persulfidation as it has been described in animal systems. To elucidate the impact of TRXo1 deficiency on the protein persulfidation pattern in plants of Arabidopsis thaliana L. wild type (WT) and two Attrxo1 T-DNA insertion mutants grown under non stress conditions, a quantitative proteomic approach was performed. The proteomic analysis revealed a higher number of proteins that were more persulfidated in the mutants compared to WT plants, suggesting a role for TRXo1 in protein depersulfidation. Interestingly, most of the differentially persulfidated proteins were located in the chloroplast, implying a coordination between chloroplast H2S-dependent persulfidation and mitochondrial TRXo1 depersulfidation. Among the differentially persulfidated proteins located in mitochondria, the antioxidant enzymes sAPX, DHAR1 and MDAR6 were selected for further studies. The effect of H2S-dependent persulfidation on their enzymatic activities and its reversibility by the NADPH/thioredoxin reductase (NTRB)/TRXo1 system was analyzed, as well as their persulfidation levels were quantified. Sulfide treatment brought about increases in the activity levels of the enzymes, that match with a raise on the persulfidation levels. Interestingly, both activations declining after treatment with the thioredoxin system, indicate the regulation of their persulfidation by TRXo1. These results point to a positive effect of persulfidation on the enzymatic activities and also to a new depersulfidase activity for TRXo1. All together these results give a new insight of the mechanism of elimination of -SSH groups in plants exerted by TRXo1, and the involvement of a redox regulation on the protein persulfidation.

Hydrogen sulfide-induced barley resilience to drought and salinity through protein persulfidation

Barley (Hordeum vulgare) is a widely cultivated cereal crops, and its production is increasingly threatened by environmental stresses such as drought and salinity. Hydrogen sulfide is established as a signaling molecule that promotes tolerance to plant stress throught persulfidation, a post-translational modification of cysteine residues in proteins. The purpose of this study is to explore the impact of NaHS (sulfide donor) pretreatment on barley plants in enhancing tolerance to drought and salinity stresses, and determine if persulfidation is involved. In pretreated-plants, phenotypical traits and pigment contents showed an improvement in the survival of the plants under stress conditions. Quantification of stress-markers such as anthocyanin, proline, and reactive oxygen species also showed significant decreased contents in pretreated compared to untreated plants. In addition, the accumulation of amino acids under drought stress was significantly reduced when plants were pretreated with NaHS. Similarly, the increase of ABA content as a typical drought response was reduced in the pretreated plants. When plants are exposed to salt stress, the Na+/K+ ratio was maintained low in NaHS-pretreated plants, by increasing K+ levels. The sulfide ameliorative effect to salt was also observed during germination in previously NaHS-soaked seeds. Our findings suggest that sulfide pretreatment prepares barely plants to better deal with drought and salinity. Moreover, persulfidation was analyzed under all conditions, exhibiting enhanced levels under stress when plants were pretreated with NaHS. Our findings indicate that sulfide pretreatment induces a previous state in barley to respond more efficiently to stress and propose persulfidation is the underlying mechanism.

Hydrogen sulfide enhances cadmium tolerance in oilseed rape roots by augmenting glutathione-mediated antioxidant defense and ROS homeostasis

Hydrogen sulfide (H2S) plays a crucial role in regulating plant development and stress responses. Here, the potential role of H2S in enhancing cadmium (Cd) tolerance by modulating the antioxidant defense system and reactive oxygen species (ROS) homeostasis was investigated. The results shown that Cd (II) exposure significantly inhibited the growth and chlorophyll content of rapeseed seedlings. Optimal exogenous sodium hydrosulfide (NaHS; 50 μM) pretreatment markedly alleviated Cd-induced growth inhibition, chlorosis, and root morphology in contrast to increased Cd accumulation in the roots. The DW of the leaves and roots, and the total chlorophyll content increased by 23.8 %, 21.4 % and 114.8 %, respectively. Cd (II)-induced oxidative damage was significantly ameliorated by NaHS application through the reduction of hydrogen peroxide (H2O2) and superoxide (O2•-) accumulation, which were up to 47.3 % and 67.6 %, respectively. Moreover, exogenous NaHS elevated the glutathione (GSH) content and GSH/glutathione disulfide (GSSG) ratio in Cd-stressed roots from 21.9 - 33.3 % and 39.3-87.4 %, respectively. The activity of antioxidant enzymes, with the exception of ascorbate peroxidase, was further elevated by NaHS application. These results suggest that H2S enhances Cd tolerance by augmenting GSH pools and activating antioxidant enzymes to control reactive oxygen species (ROS) homeostasis, thereby ameliorating Cd-induced oxidative stress in rapeseed seedling roots.

Hydrogen Sulphide: A Key Player in Plant Development and Stress Resilience

Based on the research conducted so far, hydrogen sulphide (H2S) plays a crucial role in the development and stress resilience of plants. H2S, which acts as a signalling molecule, responds to different stresses such as heavy metals, drought, and salinity, and it regulates various aspects of plant growth and development including seed germination, root development, stomatal movement, flowering, and fruit ripening. Additionally, H2S is involved in mediating legume-Rhizobium symbiosis signalling. It modulates plant responses to external environmental stimuli by interacting with other signalling molecules like phytohormones, nitric oxide, and reactive oxygen species. Furthermore, H2S exerts these regulations since it can modify protein functions through a reversible thiol-based oxidative posttranslational modification called persulfidation, particularly in stress response and developmental processes. As a result, H2S is recognised as an important emerging signalling molecule with multiple roles in plants. Research in this field holds promise for engineering stress tolerance in crops and may lead to potential biotechnological applications in agriculture and environmental management.

Intranasal Administrations of AP39-Loaded Liposomes Selectively Deliver H2S to Neuronal Mitochondria to Protect Neonatal Hypoxia-Ischemia by Targeting ERK1/2 and Caspase-1

Mitochondrial dysfunction contributes to the pathology of hypoxia-ischemia (HI) brain damage by aberrant production of ROS. Hydrogen sulfide (H2S) has been demonstrated to exert neuroprotective effects through antioxidant mechanisms. However, the diffusion of H2S in vivo is not specifically targeted and may even be systemically toxic. In this study, based on mitochondria-targeted H2S donor AP39, we fabricated liposomes encapsulating AP39 (AP39@Lip) via intranasal delivery to improve functional recovery after HI brain injury. This study presents that intranasal administration of AP39@Lip was capable of attenuating acute brain injury by inhibiting mitochondrial dysfunction, apoptosis, neuroinflammation, and ROS production in the lesional cortex 3 days after HI brain injury. Similarly, AP39@Lip was observed to restore both short- and long-term function following HI injury without obvious toxicity. Mechanistically, the therapeutic effects of AP39@Lip mainly relied on its colocalization with neuronal mitochondria 24 h after administration and reversed H2S levels in the lesional cortex. Moreover, molecular docking and cellular thermal shift assay suggest that AP39 inhibited the activation of ERK1/2 and caspase-1 by directly binding to ERK1/2 or caspase-1. These results indicate that intranasal administration of AP39@Lip selectively delivered H2S to neuronal mitochondria and mitigated mitochondrial damage following HI insult by targeting ERK1/2 and caspase-1.

Dual Roles of Reducing Systems in Protein Persulfidation and Depersulfidation

The oxidative modification of specific cysteine residues to persulfides is thought to be the main way by which hydrogen sulfide (H2S) exerts its biological and signaling functions. Therefore, protein persulfidation represents an important thiol-switching mechanism as other reversible redox post-translational modifications. Considering their reductase activity but also their connections with proteins that generate H2S and its related molecules, the glutaredoxin (GRX) and thioredoxin (TRX)-reducing systems have potential dual roles in both protein persulfidation and depersulfidation. In this review, we will first focus on recent advances describing the physiological pathways leading to protein persulfidation before discussing the dual roles of the physiological TRX and glutathione/GRX-reducing systems in protein persulfidation/depersulfidation.

Oxidative post-translational modifications of plant antioxidant systems under environmental stress

Plants are often subject to environmental challenges posed by abiotic and biotic stresses, which are increasing under the current climate change conditions, provoking a loss in crop yield worldwide. Plants must cope with adverse situations such as increasing temperatures, air pollution or loss of agricultural land due to salinity, drought, contamination, and pathogen attacks, among others. Plants under stress conditions increase the production of reactive oxygen-, nitrogen-, and sulphur species (ROS/RNS/RSS), whose concentrations must be tightly regulated. The enzymatic antioxidant system and metabolites are in charge of their control to avoid their deleterious effects on cellular components, allowing their participation in signalling events. As signalling molecules, reactive species are involved in plant responses to the environment through post-translational modifications (PTMs) of proteins, which, in turn, may regulate the structure, function, and location of the antioxidant proteins by oxidative/nitrosative/persulfure modifications of different amino acid residues. In this review, we examine the different effects of these post-translational modifications, which are emerging as a fine-tuned point of control of the antioxidant systems involved in plant responses to climate change, a growing threat to crop production.

The role of gasotransmitter hydrogen sulfide in plant cadmium stress responses

Cadmium (Cd) is a toxic heavy metal that poses a significant risk to both plant growth and human health. To mitigate or lessen Cd toxicity, plants have evolved a wide range of sensing and defense strategies. The gasotransmitter hydrogen sulfide (H2S) is involved in plant responses to Cd stress and exhibits a crucial role in modulating Cd tolerance through a well-orchestrated interaction with several signaling pathways. Here, we review potential experimental approaches to manipulate H2S signals, concluding that research on another gasotransmitter, namely nitric oxide (NO), serves as a good model for research on H2S. Additionally, we discuss potential strategies to leverage H2S-reguated Cd tolerance to improve plant performance under Cd stress.

Genome-Wide In Silico Analysis of 1-Aminocyclopropane-1-carboxylate oxidase (ACO) Gene Family in Rice (Oryza sativa L.)

The plant hormone ethylene elicits crucial regulatory effects on plant growth, development, and stress resistance. As the enzyme that catalyzes the final step of ethylene biosynthesis, 1-Aminocyclopropane-1-carboxylic acid oxidase (ACO) plays a key role in precisely controlling ethylene production. However, the functional characterization of the ACO gene family in rice remains largely unexplored. In this study, we performed a phylogenetic analysis of seven OsACO genes (OsACO1-OsACO7), which were classified into three subfamilies (Types I, II, and III). The members within the same clades exhibited similar tertiary structures and conserved protein motifs. We conducted inter/intraspecies covariance assays of OsACOs to elucidate their evolutionary and duplication events. Numerous cis-acting elements identified in OsACO promoter regions are associated with development, hormonal stimuli, and environmental responses. The expression assay by RT-qPCR revealed that OsACO genes exhibited tissue-specific expression and were significantly altered under various abiotic stresses, indicating their potential involvement in these processes regulated at the transcriptional level. Additionally, we predicted candidate-targeting miRNAs and identified putative cysteine sites of S-nitrosylation (SNO) and S-sulfhydration (SSH) in OsACOs, providing insights into their post-transcriptional and post-translational regulatory mechanisms. These findings pave the way for the further investigation of OsACO functions and their potential applications in improving rice growth and stress resilience by modulating ethylene biosynthesis.

Functional interaction of melatonin with gasotransmitters and ROS in plant adaptation to abiotic stresses

Melatonin is considered a multifunctional stress metabolite and a novel plant hormone affecting seed germination, root architecture, circadian rhythms, leaf senescence, and fruit ripening. Melatonin functions related to plant adaptation to stress stimuli of various natures are considered especially important. One of the key components of melatonin's stress-protective action is its ability to neutralise reactive oxygen species (ROS) and reactive nitrogen species directly. However, many of its effects are related to its involvement in the signalling network of plant cells and its influence on the expression of a large number of genes important for adaptation to adverse factors. Insights into the functional relationships of melatonin with gasotransmitters (GT) - gaseous molecules performing signalling functions - are still emerging. This review has analysed and summarised the experimental data that testify to the participation of the main GTs - nitric oxide, hydrogen sulfide, and carbon monoxide - in the implementation of the protective effect of melatonin when plants are exposed to abiotic stimuli of various nature. In addition, modulation by melatonin of one of the most important components in the action of GTs and ROS - post-translational modifications of proteins and the influence of ROS and GTs on melatonin synthesis in plants under stress conditions and the specific physiological effects of exogenous melatonin and GTs have been reviewed. Finally, the prospects of the GTs' practical application to achieve synergistic stress-protective effects on plants have been considered.

Rhizobia cystathionine γ-lyase-derived H2S delays nodule senescence in soybean

Hydrogen sulfide (H2S) is required for optimal establishment of soybean (Glycine max)-Sinorhizobium fredii symbiotic interaction, yet its role in regulating the nitrogen fixation-senescence transition remains poorly understood. A S. fredii cystathionine γ-lyase (CSE) mutant deficient in H2S synthesis showed early nodule senescence characterized by reduced nitrogenase activity, structural changes in nodule cells, and accelerated bacteroid death. In parallel, the CSE mutant facilitated the generation of reactive oxygen species (ROS) and elicited antioxidant responses. We observed that H2S-mediated persulfidation of cysteine C31/C80 in ascorbate peroxidase (APX) and C32 in APX2-modulated enzyme activity, thereby participating in hydrogen peroxide (H2O2) detoxification and delaying nodule senescence. Comparative transcriptomic analysis revealed a significant upregulation of GmMYB128, an MYB transcription factor (TF), in the CSE mutant nodules. Functional analysis through overexpression and RNAi lines of GmMYB128 demonstrated its role as a positive regulator in nodule senescence. MYB128-OE inoculated with the CSE mutant strain exhibited a reduction in nitrogenase activity and a significant increase in DD15 expression, both of which were mitigated by NaHS addition. Changes at the protein level encompassed the activation of plant defenses alongside turnover in carbohydrates and amino acids. Our results suggest that H2S plays an important role in maintaining efficient symbiosis and preventing premature senescence of soybean nodules.

Hydrogen sulphide alleviates root growth inhibition induced by phosphate starvation

Phosphorus (P) has crucial roles in plant growth and development. Hydrogen sulphide (H2S) has multiple functions in plants, particularly having the ability to promote tolerance to a variety of adversity stresses. However, it is unclear whether H2S has a function when plants suffer Pi-deficiency stress. DES1, encoding L-cysteine desulfhydrase1, is a crucial source of H2S in Arabidopsis thaliana by catalysing the substrate L-cysteine. Under phosphate starvation, the des1 mutant had a significantly shorter primary root length than the wild-type Col-0, and exogenous application of H2S donor NaHS could compensate for the root growth-sensitive phenotype. In contrast, the transgenic lines DES1ox overexpressing DES1 exhibited less sensitivity to phosphate starvation in terms of longer roots compared to the Col-0. These results demonstrate that H2S is involved in the regulation of Arabidopsis root growth under phosphate starvation. Moreover, using quantitative real-time polymerase chain reaction experiments to analyse the changes in genes induced by phosphate starvation in des1 mutant and Col-0, we screened to find that the expression of the Sulfoquinovosyl diacylglycerol 1 (SQD1) gene was significantly downregulated in the des1 mutant. Consistently, exogenous H2S significantly promoted SQD1 expression levels in roots of Col-0. Taken together, we demonstrate that DES1-mediated H2S participates in alleviating root growth inhibition by promoting the expression of SQD1 under Pi starvation.

Hydrogen sulfide and ethylene regulate photosynthesis, sugar metabolism, and tolerance to heat stress in the presence of sulfur in rice

Heat stress impacts photosynthesis and carbohydrate metabolism, challenging food security. To comprehend the mechanisms of thermotolerance, we examined the role of ethylene (ET) and hydrogen sulfide (H2S) with or without sulfur (S) in rice (Oryza sativa L.). Both ET and H2S promoted heat stress tolerance more conspicuously in the presence of S, restoring the balance between carbon assimilation and utilization. The enhanced photosynthesis in ET and H2S-treated plants under heat stress was linked with increased relative expression of Rubisco subunits rbcS and rbcL and carbohydrate metabolizing, including Sucrose Synthase 2 (SuSy2) and Sucrose transport 1 (SUT1). Notably, the H2S application showed the highest increase of 2.3, 3.2, 3.0, and 2.4-fold expression of the rbcS, rbcL, SuSy2, and SUT1, respectively, compared to the heat stress alone. The application of H2S with S more prominently increased starch content, total soluble sugar, and soluble invertase activity by 59.3%, 35.7%, and 25.9%, and also activity of soluble starch synthase and granule-bound starch synthase by 47.2% and 32.8%, respectively, compared to heat-stressed plants. The treatment (H2S plus S) elevated cysteine and GSH content and the activity of the antioxidant enzymes to maintain cellular redox potential under heat stress. These observed tolerance responses were less pronounced in plants treated with hypotaurine (HT; H2S scavenger) than those treated with norbornadiene (NBD; ET inhibitor), underscoring the superior role of H2S over ET in mitigating heat stress. The present study's findings explain that H2S is crucial for the ET-mediated response in augmenting photosynthesis and heat stress tolerance in rice.

Molecular regulation by H2S of antioxidant and glucose metabolism in cold-sensitive Capsicum

BACKGROUND

Cold is an important environmental limiting factor affecting plant yield and quality. Capsicum (chili pepper), a tropical and subtropical vegetable crop, is extremely sensitive to cold. Although H2S is an important signaling regulator in the responses of plant growth and development to abiotic stress, few studies have examined its effects on cold-sensitive capsicum varieties. Through biotechnology methods to enhance the cold resistance of peppers, to provide some reference for pepper breeding, investigated molecular regulation by H2S of responses to cold stress in cold-sensitive capsicum plants, via physiological and transcriptomic analyses.

RESULTS

In capsicum seedlings, exogenous H2S enhanced relative electrical conductivity (REC) and levels of malondialdehyde (MDA) under cold stress, maintained membrane integrity, increased the activity of enzymatic and non-enzymatic antioxidants, balanced reactive oxygen species levels (O2·- and H2O2), and improved photosynthesis, mitigating the damage caused by cold. In addition, 416 differentially expressed genes (DEGs) were involved in the response to cold stress after H2S treatment. These DEGs were mainly enriched in the ascorbate-glutathione and starch-sucrose metabolic pathways and plant hormone signal-transduction pathways. Exogenous H2S altered the expression of key enzyme-encoding genes such as GST, APX, and MDHAR in the ascorbate-glutathione metabolism pathway, as well as that of regulatory genes for stimulatory hormones (auxin, cytokinins, and gibberellins) and inhibitory hormones (including jasmonate and salicylic acid) in the plant hormone signal-transduction pathway, helping to maintain the energy supply and intracellular metabolic stability under cold stress.

CONCLUSIONS

These findings reveal that exogenous H2S improves cold tolerance in cold-sensitive capsicum plants, elucidating the molecular mechanisms underlying its responses to cold stress. This study provides a theoretical basis for exploring and improving cold tolerance in capsicum plants.

Protein persulfidation in plants: mechanisms and functions beyond a simple stress response

Posttranslational modifications (PTMs) can modulate the activity, localization and interactions of proteins and (re)define their biological function. Understanding how changing environments can alter cellular processes thus requires detailed knowledge about the dynamics of PTMs in time and space. A PTM that gained increasing attention in the last decades is protein persulfidation, where a cysteine thiol (-SH) is covalently bound to sulfane sulfur to form a persulfide (-SSH). The precise cellular mechanisms underlying the presumed persulfide signaling in plants are, however, only beginning to emerge. In the mitochondrial matrix, strict regulation of persulfidation and H2S homeostasis is of prime importance for maintaining mitochondrial bioenergetic processes because H2S is a highly potent poison for cytochrome c oxidase. This review summarizes the current knowledge about protein persulfidation and corresponding processes in mitochondria of the model plant Arabidopsis. These processes will be compared to the respective processes in non-plant models to underpin similarities or highlight apparent differences. We provide an overview of mitochondrial pathways that contribute to H2S and protein persulfide generation and mechanisms for H2S fixation and de-persulfidation. Based on current proteomic data, we compile a plant mitochondrial persulfidome and discuss how persulfidation may regulate protein function.

Mitochondrial ß-Cyanoalanine Synthase Participates in flg22-Induced Stomatal Immunity

Plants regulate gas exchange with the environment and modulate transpirational water flow through guard cells, which set the aperture of the stomatal pores. External and internal stimuli are detected by guard cells and integrated into a signalling network that modulate turgor pressure and, hence, pore size. Pathogen-associated molecular patterns are among the stimuli that induce stomatal closure, to prevent pathogen entry through the pores, and this response, also referred to as stomatal immunity, is one of the hallmarks of PAMP-triggered immunity. While reactive oxygen species (ROS)-mediated signalling plays a key role in stomatal immunity, also the gasotransmitter hydrogen sulphide (H2S) interacts with key components of the guard cell signalling network to induce stomatal closure. While the role of H2S, produced by the main cytosolic source L-cysteine desulfhydrase 1, has been already investigated, there are additional enzymatic sources that synthesize H2S in different subcellular compartments. Their function has remained enigmatic, however. In this work, we elucidate the involvement of the mitochondrial H2S source, β-cyanoalanine synthase CAS-C1, on stomatal immunity induced by the bacterial PAMP flagellin (flg22). We show that cas-c1 plants are impaired to induce flg22-triggered stomatal closure and apoplastic ROS production, while they are more susceptible to bacterial surface inoculation. Moreover, mitochondrial H2S donor AP39 induced stomatal closure in an RBOHD-dependent manner, while depletion of endogenous H2S, impaired RBOHD-mediated apoplastic ROS production. In addition, pharmacological disruption of mitochondrial electron transport chain activity, affected stomatal closure produced by flg22, indicating its participation in the stomatal immunity response. Our findings add evidence to the emerging realization that intracellular organelles play a decisive role in orchestrating stomatal signalling and immune responses and suggest that mitochondrial-derived H2S is an important player of the stomatal immunity signalling network.

Post-Translational Modifications to Cysteine Residues in Plant Proteins and Their Impact on the Regulation of Metabolism and Signal Transduction

Cys is one of the least abundant amino acids in proteins. However, it is often highly conserved and is usually found in important structural and functional regions of proteins. Its unique chemical properties allow it to undergo several post-translational modifications, many of which are mediated by reactive oxygen, nitrogen, sulfur, or carbonyl species. Thus, in addition to their role in catalysis, protein stability, and metal binding, Cys residues are crucial for the redox regulation of metabolism and signal transduction. In this review, we discuss Cys post-translational modifications (PTMs) and their role in plant metabolism and signal transduction. These modifications include the oxidation of the thiol group (S-sulfenylation, S-sulfinylation and S-sulfonylation), the formation of disulfide bridges, S-glutathionylation, persulfidation, S-cyanylation S-nitrosation, S-carbonylation, S-acylation, prenylation, CoAlation, and the formation of thiohemiacetal. For each of these PTMs, we discuss the origin of the modifier, the mechanisms involved in PTM, and their reversibility. Examples of the involvement of Cys PTMs in the modulation of protein structure, function, stability, and localization are presented to highlight their importance in the regulation of plant metabolic and signaling pathways.

Persulfidation and phosphorylation of transcription factor SlWRKY6 differentially regulate tomato fruit ripening

Cysteine desulfhydrase catalyses the generation of the signaling molecule hydrogen sulfide (H2S) in plants. In this study, we found that H2S can inhibit tomato (Solanum lycopersicum) fruit ripening and SlWRKY6 undergoes differential protein persulfidation in SlLCD1-overexpressing leaves. Then, further study indicated that SlWRKY6 could be persulfidated by H2S at Cys396. By construction of slwrky6 mutants and SlWRKY6-OE lines, we found that SlWRKY6 positively regulates leaf senescence and fruit ripening by activating the transcription of ripening-related genes STAYGREEN 1 (SlSGR1) and Senescence-Associated Gene 12 (SlSAG12). In addition, SlWRKY6 interacted with kinase SlMAPK4 and was phosphorylated at Ser33. Dual-luciferase transient expression assays and electrophoretic mobility shift assays indicated that SlWRKY6 persulfidation attenuated its transcriptional regulation of target genes SlSGR1 and SlSAG12, whereas SlWRKY6 phosphorylation by SlMAPK4 activated the transcription of target genes to promote fruit ripening. Moreover, we provided evidence that SlWRKY6 persulfidation attenuated its SlMAPK4-mediated phosphorylation to inhibit tomato fruit ripening. By transient expression of SlWRKY6, SlWRKY6C396A, SlWRKY6S33A, and SlWRKY6S33D in slwrky6 fruits, we found that SlWRKY6 persulfidation attenuated the expression of SlSGR1 and SlSAG12 thereby delaying tomato fruit ripening, while SlWRKY6 phosphorylation increased the expression of target genes. As tomato fruits ripened, endogenous H2S production decreased, while SlMAPK4 expression increased. Therefore, our findings reveal a model in which SlWRKY6 persulfidation due to higher endogenous H2S levels in un-ripened fruit inhibits its ability to activate SlSGR1 and SlSAG12 expression, while SlWRKY6 phosphorylation by SlMAPK4 activates its transcriptional activity, thereby promoting tomato fruit ripening.

Analysis of sulfide signaling in rice highlights specific drought responses

Hydrogen sulfide regulates essential plant processes, including adaptation responses to stress situations, and the best characterized mechanism of action of sulfide consists of the post-translational modification of persulfidation. In this study, we reveal the first persulfidation proteome described in rice including 3443 different persulfidated proteins that participate in a broad range of biological processes and metabolic pathways. In addition, comparative proteomics revealed specific proteins involved in sulfide signaling during drought responses. Several proteins are involved in the maintenance of cellular redox homeostasis, the tricarboxylic acid cycle and energy-related pathways, and ion transmembrane transport and cellular water homeostasis, with the aquaporin family showing the highest differential levels of persulfidation. We revealed that water transport activity is regulated by sulfide which correlates with an increasing level of persulfidation of aquaporins. Our findings emphasize the impact of persulfidation on total ATP levels, fatty acid composition, levels of reactive oxygen species, antioxidant enzymatic activities, and relative water content. Interestingly, the role of persulfidation in aquaporin transport activity as an adaptation response in rice differs from current knowledge of Arabidopsis, which highlights the distinct role of sulfide in improving rice tolerance to drought.

NADPH oxidase-mediated sulfenylation of cysteine derivatives regulates plant immunity

Reactive oxygen species (ROS) are rapidly generated during plant immune responses by respiratory burst oxidase homolog (RBOH), which is a plasma membrane-localized NADPH oxidase. Although regulatory mechanisms of RBOH activity have been well documented, the ROS-mediated downstream signaling is unclear. We here demonstrated that ROS sensor proteins play a central role in ROS signaling via oxidative post-translational modification of cysteine residues, sulfenylation. To detect protein sulfenylation, we used dimedone, which specifically and irreversibly binds to sulfenylated proteins. The sulfenylated proteins were labeled by dimedone in Nicotiana benthamiana leaves, and the conjugates were detected by immunoblot analyses. In addition, a reductant dissociated H2O2-induced conjugates, suggesting that cysteine persulfide and/or polysulfides are involved in sulfenylation. These sulfenylated proteins were continuously increased during both pattern-triggered immunity (PTI) and effector-triggered immunity (ETI) in a RBOH-dependent manner. Pharmacological inhibition of ROS sensor proteins by dimedone perturbated cell death, ROS accumulation induced by INF1 and MEK2DD, and defense against fungal pathogens. On the other hand, Rpi-blb2-mediated ETI responses were enhanced by dimedone. These results suggest that the sulfenylation of cysteine and its derivatives in various ROS sensor proteins are important events downstream of the RBOH-dependent ROS burst to regulate plant immune responses.

The role of redox-active small molecules and oxidative protein post-translational modifications in seed aging

Seed vigor is a crucial indicator of seed quality. Variations in seed vigor are closely associated with seed properties and storage conditions. The vigor of mature seeds progressively declines during storage, which is called seed deterioration or aging. Seed aging induces a cascade of cellular damage, including impaired subcellular structures and macromolecules, such as lipids, proteins, and DNA. Reactive oxygen species (ROS) act as signaling molecules during seed aging causing oxidative damage and triggering programmed cell death (PCD). Mitochondria are the main site of ROS production and change morphology and function before other organelles during aging. The roles of other small redox-active molecules in regulating cell and seed vigor, such as nitric oxide (NO) and hydrogen sulfide (H2S), were identified later. ROS, NO, and H2S typically regulate protein function through post-translational modifications (PTMs), including carbonylation, S-glutathionylation, S-nitrosylation, and S-sulfhydration. These signaling molecules as well as the PTMs they induce interact to regulate cell fate and seed vigor. This review was conducted to describe the physiological changes and underlying molecular mechanisms that in seed aging and provides a comprehensive view of how ROS, NO, and H2S affect cell death and seed vigor.

Post-Translational Modification of WRKY Transcription Factors

Post-translational modifications (PTMs) of proteins are involved in numerous biological processes, including signal transduction, cell cycle regulation, growth and development, and stress responses. WRKY transcription factors (TFs) play significant roles in plant growth, development, and responses to both biotic and abiotic stresses, making them one of the largest and most vital TF families in plants. Recent studies have increasingly highlighted the importance of PTMs of WRKY TFs in various life processes. This review focuses on the recent advancements in understanding the phosphorylation and ubiquitination of WRKY TFs, particularly their roles in resistance to biotic and abiotic stresses and in plant growth and development. Future research directions and prospects in this field are also discussed.

Copper Is Accumulated as Copper Sulfide Particles, and Not Bound to Glutathione, Phytochelatins or Metallothioneins, in the Marine Alga Ulva compressa (Chlorophyta)

To analyze the mechanism of copper accumulation in the marine alga Ulva compressa, it was cultivated with 10 μM of copper, with 10 μM of copper and increasing concentrations of a sulfide donor (NaHS) for 0 to 7 days, and with 10 μM of copper and a concentration of the sulfide acceptor (hypotaurine) for 5 days. The level of intracellular copper was determined as well as the level of glutathione (GSH) and phytochelatins (PCs) and the expression of metallothioneins (UcMTs). The level of intracellular copper in the algae treated with copper increased at day 1, slightly increased until day 5 and remained unchanged until day 7. The level of copper in the algae cultivated with copper and 100 or 200 μM of NaHS continuously increased until day 7 and the copper level was higher in the algae cultivated with 200 μM of NaHS compared to 100 μM of NaHS. In contrast, the level of intracellular copper decreased in the algae treated with copper and hypotaurine. The level of intracellular copper did not correlate with the level of GSH or with the expression of UcMTs, and PCs were not detected in response to copper, or copper and NaHS. Algae treated with copper and with copper and 200 μM of NaHS for 5 days were visualized by TEM and the elemental composition of electrondense particles was analyzed by EDXS. The algae treated with copper showed electrondense particles containing copper and sulfur, but not nitrogen, and they were mainly located in the chloroplast, but also in the cytoplasm. The algae treated with copper and NaHS showed a higher level of electrondense particles containing copper and sulfur, but not nitrogen, and they were located in the chloroplast, and in the cytoplasm. Thus, copper is accumulated as copper sulfide insoluble particles, and not bound to GSH, PCs or UcMTs, in the marine alga U. compressa.

The Molecular Frequency, Conservation and Role of Reactive Cysteines in Plant Lipid Metabolism

Cysteines (Cys) are chemically reactive amino acids containing sulfur that play diverse roles in plant biology. Recent proteomics investigations in Arabidopsis thaliana have revealed the presence of thiol post-translational modifications (PTMs) in several Cys residues. These PTMs are presumed to impact protein structure and function, yet mechanistic data regarding the specific Cys susceptible to modification and their biochemical relevance remain limited. To help address these limitations, we have conducted a wide-ranging analysis by integrating published datasets encompassing PTM proteomics (comparing S-sulfenylation, persulfidation, S-nitrosylation and S-acylation), genomics and protein structures, with a specific focus on proteins involved in plant lipid metabolism. The prevalence and distribution of modified Cys residues across all analyzed proteins is diverse and multifaceted. Nevertheless, by combining an evaluation of sequence conservation across 100+ plant genomes with AlphaFold-generated protein structures and physicochemical predictions, we have unveiled structural propensities associated with Cys modifications. Furthermore, we have identified discernible patterns in lipid biochemical pathways enriched with Cys PTMs, notably involving beta-oxidation, jasmonic acid biosynthesis, fatty acid biosynthesis and wax biosynthesis. These collective findings provide valuable insights for future investigations targeting the mechanistic foundations of Cys modifications and the regulation of modified proteins in lipid metabolism and other metabolic pathways.

Metabolic and Functional Interactions of H2S and Sucrose in Maize Thermotolerance through Redox Homeodynamics

Hydrogen sulfide (H2S) is a novel gasotransmitter. Sucrose (SUC) is a source of cellular energy and a signaling molecule. Maize is the third most common food crop worldwide. However, the interaction of H2S and SUC in maize thermotolerance is not widely known. In this study, using maize seedlings as materials, the metabolic and functional interactions of H2S and SUC in maize thermotolerance were investigated. The data show that under heat stress, the survival rate and tissue viability were increased by exogenous SUC, while the malondialdehyde content and electrolyte leakage were reduced by SUC, indicating SUC could increase maize thermotolerance. Also, SUC-promoted thermotolerance was enhanced by H2S, while separately weakened by an inhibitor (propargylglycine) and a scavenger (hypotaurine) of H2S and a SUC-transport inhibitor (N-ethylmaleimide), suggesting the interaction of H2S and SUC in the development of maize thermotolerance. To establish the underlying mechanism of H2S-SUC interaction-promoted thermotolerance, redox parameters in mesocotyls of maize seedlings were measured before and after heat stress. The data indicate that the activity and gene expression of H2S-metabolizing enzymes were up-regulated by SUC, whereas H2S had no significant effect on the activity and gene expression of SUC-metabolizing enzymes. In addition, the activity and gene expression of catalase, glutathione reductase, ascorbate peroxidase, peroxidase, dehydroascorbate reductase, monodehydroascorbate reductase, and superoxide dismutase were reinforced by H2S, SUC, and their combination under non-heat and heat conditions to varying degrees. Similarly, the content of ascorbic acid, flavone, carotenoid, and polyphenol was increased by H2S, SUC, and their combination, whereas the production of superoxide radicals and the hydrogen peroxide level were impaired by these treatments to different extents. These results imply that the metabolic and functional interactions of H2S and sucrose signaling exist in the formation of maize thermotolerance through redox homeodynamics. This finding lays the theoretical basis for developing climate-resistant maize crops and improving food security.

Persulfidome of Sweet Pepper Fruits during Ripening: The Case Study of Leucine Aminopeptidase That Is Positively Modulated by H2S

Protein persulfidation is a thiol-based oxidative posttranslational modification (oxiPTM) that involves the modification of susceptible cysteine thiol groups present in peptides and proteins through hydrogen sulfide (H2S), thus affecting their function. Using sweet pepper (Capsicum annuum L.) fruits as a model material at different stages of ripening (immature green and ripe red), endogenous persulfidated proteins (persulfidome) were labeled using the dimedone switch method and identified using liquid chromatography and mass spectrometry analysis (LC-MS/MS). A total of 891 persulfidated proteins were found in pepper fruits, either immature green or ripe red. Among these, 370 proteins were exclusively present in green pepper, 237 proteins were exclusively present in red pepper, and 284 proteins were shared between both stages of ripening. A comparative analysis of the pepper persulfidome with that described in Arabidopsis leaves allowed the identification of 25% of common proteins. Among these proteins, glutathione reductase (GR) and leucine aminopeptidase (LAP) were selected to evaluate the effect of persulfidation using an in vitro approach. GR activity was unaffected, whereas LAP activity increased by 3-fold after persulfidation. Furthermore, this effect was reverted through treatment with dithiothreitol (DTT). To our knowledge, this is the first persulfidome described in fruits, which opens new avenues to study H2S metabolism. Additionally, the results obtained lead us to hypothesize that LAP could be involved in glutathione (GSH) recycling in pepper fruits.

Mining proteomes for zinc finger persulfidation

Hydrogen sulfide (H2S) is an endogenous gasotransmitter that signals via persulfidation. There is evidence that the cysteine residues of certain zinc finger (ZF) proteins, a common type of cysteine rich protein, are modified to persulfides by H2S. To determine how frequently ZF persulfidation occurs in cells and identify the types of ZFs that are persulfidated, persulfide specific proteomics data were evaluated. 22 datasets from 16 studies were analyzed via a meta-analysis approach. Persulfidated ZFs were identified in a range of eukaryotic species, including Homo sapiens, Mus musculus, Rattus norvegicus, Arabidopsis thaliana, and Emiliania huxley (single-celled phytoplankton). The types of ZFs identified for each species encompassed all three common ZF ligand sets (4-cysteine, 3-cysteine-1-histidine, and 2-cysteine-2-hisitidine), indicating that persulfidation of ZFs is broad. Overlap analysis between different species identified several common ZFs. GO and KEGG analysis identified pathway enrichment for ubiquitin-dependent protein catabolic process and viral carcinogenesis. These collective findings support ZF persulfidation as a wide-ranging PTM that impacts all classes of ZFs.

Gene regulatory networks underlying sulfate deficiency responses in plants

Sulfur (S) is an essential macronutrient for plants and its availability in soils is an important determinant for growth and development. Current regulatory policies aimed at reducing industrial S emissions together with changes in agronomical practices have led to a decline in S contents in soils worldwide. Deficiency of sulfate-the primary form of S accessible to plants in soil-has adverse effects on both crop yield and nutritional quality. Hence, recent research has increasingly focused on unraveling the molecular mechanisms through which plants detect and adapt to a limiting supply of sulfate. A significant part of these studies involves the use of omics technologies and has generated comprehensive catalogs of sulfate deficiency-responsive genes and processes, principally in Arabidopsis together with a few studies centering on crop species such as wheat, rice, or members of the Brassica genus. Although we know that sulfate deficiency elicits an important reprogramming of the transcriptome, the transcriptional regulators orchestrating this response are not yet well understood. In this review, we summarize our current knowledge of gene expression responses to sulfate deficiency and recent efforts towards the identification of the transcription factors that are involved in controlling these responses. We further compare the transcriptional response and putative regulators between Arabidopsis and two important crop species, rice and tomato, to gain insights into common mechanisms of the response to sulfate deficiency.

Persulfidation of plant and bacteroid proteins is involved in legume nodule development and senescence

Legumes establish symbiosis with rhizobia, forming nitrogen-fixing nodules. The central role of reactive oxygen species (ROS) and reactive nitrogen species (RNS) in nodule biology has been clearly established. Recently, hydrogen sulfide (H2S) and other reactive sulfur species (RSS) have emerged as novel signaling molecules in animals and plants. A major mechanism by which ROS, RNS, and RSS fulfil their signaling role is the post-translational modification of proteins. To identify possible functions of H2S in nodule development and senescence, we used the tag-switch method to quantify changes in the persulfidation profile of common bean (Phaseolus vulgaris) nodules at different developmental stages. Proteomic analyses indicate that persulfidation plays a regulatory role in plant and bacteroid metabolism and senescence. The effect of a H2S donor on nodule functioning and on several proteins involved in ROS and RNS homeostasis was also investigated. Our results using recombinant proteins and nodulated plants support a crosstalk among H2S, ROS, and RNS, a protective function of persulfidation on redox-sensitive enzymes, and a beneficial effect of H2S on symbiotic nitrogen fixation. We conclude that the general decrease of persulfidation levels observed in plant proteins of aging nodules is one of the mechanisms that disrupt redox homeostasis leading to senescence.

Elucidating the intricacies of the H2S signaling pathway in gasotransmitters: Highlighting the regulation of plant thiocyanate detoxification pathways

In recent decades, there has been increasing interest in elucidating the role of sulfur-containing compounds in plant metabolism, particularly emphasizing their function as signaling molecules. Among these, thiocyanate (SCN-), a compound imbued with sulfur and nitrogen, has emerged as a significant environmental contaminant frequently detected in irrigation water. This compound is known for its potential to adversely impact plant growth and agricultural yield. Although adopting exogenous SCN- as a nitrogen source in plant cells has been the subject of thorough investigation, the fate of sulfur resulting from the assimilation of exogenous SCN- has not been fully explored. There is burgeoning curiosity in probing the fate of SCN- within plant systems, especially considering the possible generation of the gaseous signaling molecule, hydrogen sulfide (H2S) during the metabolism of SCN-. Notably, the endogenous synthesis of H2S occurs predominantly within chloroplasts, the cytosol, and mitochondria. In contrast, the production of H2S following the assimilation of exogenous SCN- is explicitly confined to chloroplasts and mitochondria. This phenomenon indicates complex interplay and communication among various subcellular organelles, influencing signal transduction and other vital physiological processes. This review, augmented by a small-scale experimental study, endeavors to provide insights into the functional characteristics of H2S signaling in plants subjected to SCN--stress. Furthermore, a comparative analysis of the occurrence and trajectory of endogenous H2S and H2S derived from SCN--assimilation within plant organisms was performed, providing a focused lens for a comprehensive examination of the multifaceted roles of H2S in rice plants. By delving into these dimensions, our objective is to enhance the understanding of the regulatory mechanisms employed by the gasotransmitter H2S in plant adaptations and responses to SCN--stress, yielding invaluable insights into strategies for plant resilience and adaptive capabilities.

Exogenous hydrogen sulphide promotes plant flowering through the Arabidopsis splicing factor AtU2AF65a

Alternative splicing (AS) is an important regulatory mode at the post-transcriptional level, through which many flowering genes regulate floral transition by producing multiple transcripts, and splicing factors have essential roles in this process. Hydrogen sulphide (H2S) is a newly found gasotransmitter that has critical physiological roles in plants, and one of its potential modes of action is via persulfidation of target proteins at specific cysteine sites. Previously, it has been shown that both the splicing factor AtU2AF65a and H2S are involved in the regulation of plant flowering. This study found that, in Arabidopsis, the promoting effect of H2S on flowering was abolished in atu2af65a-4 mutants. Transcriptome analyses showed that when AtU2AF65a contained mutations, the regulatory function of H2S during the AS of many flowering genes (including SPA1, LUH, LUG and MAF3) was inhibited. The persulfidation assay showed that AtU2AF65a can be persulfidated by H2S, and the RNA immunoprecipitation data indicated that H2S could alter the binding affinity of AtU2AF65a to the precursor messenger RNA of the above-mentioned flowering genes. Overall, our results suggest that H2S may regulate the AS of flowering-related genes through persulfidation of splicing factor AtU2AF65a and thus lead to early flowering in plants.

Sulfate Availability and Hormonal Signaling in the Coordination of Plant Growth and Development

Sulfur (S), one of the crucial macronutrients, plays a pivotal role in fundamental plant processes and the regulation of diverse metabolic pathways. Additionally, it has a major function in plant protection against adverse conditions by enhancing tolerance, often interacting with other molecules to counteract stresses. Despite its significance, a thorough comprehension of how plants regulate S nutrition and particularly the involvement of phytohormones in this process remains elusive. Phytohormone signaling pathways crosstalk to modulate growth and developmental programs in a multifactorial manner. Additionally, S availability regulates the growth and development of plants through molecular mechanisms intertwined with phytohormone signaling pathways. Conversely, many phytohormones influence or alter S metabolism within interconnected pathways. S metabolism is closely associated with phytohormones such as abscisic acid (ABA), auxin (AUX), brassinosteroids (BR), cytokinins (CK), ethylene (ET), gibberellic acid (GA), jasmonic acid (JA), salicylic acid (SA), and strigolactones (SL). This review provides a summary of the research concerning the impact of phytohormones on S metabolism and, conversely, how S availability affects hormonal signaling. Although numerous molecular details are yet to be fully understood, several core signaling components have been identified at the crossroads of S and major phytohormonal pathways.

Plant Life with and without Oxygen: A Metabolomics Approach

Oxygen deficiency is an environmental challenge which affects plant growth, the development and distribution in land and aquatic ecosystems, as well as crop yield losses worldwide. The capacity to exist in the conditions of deficiency or the complete lack of oxygen depends on a number of anatomic, developmental and molecular adaptations. The lack of molecular oxygen leads to an inhibition of aerobic respiration, which causes energy starvation and the acceleration of glycolysis passing into fermentations. We focus on systemic metabolic alterations revealed with the different approaches of metabolomics. Oxygen deprivation stimulates the accumulation of glucose, pyruvate and lactate, indicating the acceleration of the sugar metabolism, glycolysis and lactic fermentation, respectively. Among the Krebs-cycle metabolites, only the succinate level increases. Amino acids related to glycolysis, including the phosphoglycerate family (Ser and Gly), shikimate family (Phe, Tyr and Trp) and pyruvate family (Ala, Leu and Val), are greatly elevated. Members of the Asp family (Asn, Lys, Met, Thr and Ile), as well as the Glu family (Glu, Pro, Arg and GABA), accumulate as well. These metabolites are important members of the metabolic signature of oxygen deficiency in plants, linking glycolysis with an altered Krebs cycle and allowing alternative pathways of NAD(P)H reoxidation to avoid the excessive accumulation of toxic fermentation products (lactate, acetaldehyde, ethanol). Reoxygenation induces the downregulation of the levels of major anaerobically induced metabolites, including lactate, succinate and amino acids, especially members of the pyruvate family (Ala, Leu and Val), Tyr and Glu family (GABA and Glu) and Asp family (Asn, Met, Thr and Ile). The metabolic profiles during native and environmental hypoxia are rather similar, consisting in the accumulation of fermentation products, succinate, fumarate and amino acids, particularly Ala, Gly and GABA. The most intriguing fact is that metabolic alterations during oxidative stress are very much similar, with plant response to oxygen deprivation but not to reoxygenation.

Untargeted polysulfide omics analysis of alternations in polysulfide production during the germination of broccoli sprouts

Higher consumption of broccoli (Brassica oleracea var. italica) is associated with a reduced risk of cardiometabolic diseases, neurological disorders, diabetes, and cancer. Broccoli is rich in various phytochemicals, including glucosinolates, and isothiocyanates. Moreover, it has recently reported the endogenous production of polysulfides, such as cysteine hydropersulfide (CysS2H) and glutathione hydropersulfide (GS2H), in mammals including humans, and that these bioactive substances function as potent antioxidants and important regulators of redox signaling in vivo. However, few studies have focused on the endogenous polysulfide content of broccoli and the impact of germination on the polysulfide content and composition in broccoli. In this study, we investigated the alternations in polysulfide biosynthesis in broccoli during germination by performing untargeted polysulfide omics analysis and quantitative targeted polysulfide metabolomics through liquid chromatography-electrospray ionization-tandem mass spectrometry. We also performed 2,2-diphenyl-1-picrylhydrazyl radical-scavenging assay to determine the antioxidant properties of the polysulfides. The results revealed that the total polysulfide content of broccoli sprouts significantly increased during germination and growth; CysS2H and cysteine hydrotrisulfide were the predominant organic polysulfide metabolites. Furthermore, we determined that novel sulforaphane (SFN) derivatives conjugated with CysS2H and GS2H were endogenously produced in the broccoli sprouts, and the novel SFN conjugated with CysS2H exhibited a greater radical scavenging capacity than SFN and cysteine. These results suggest that the abundance of polysulfides in broccoli sprouts contribute to their health-promoting properties. Our findings have important biological implications for the development of novel pharmacological targets for the health-promoting effects of broccoli sprouts in humans.

Transcriptional and post-translational regulation of plant autophagy

In response to changing environmental conditions, plants activate cellular responses to enable them to adapt. One such response is autophagy, in which cellular components, for example proteins and organelles, are delivered to the vacuole for degradation. Autophagy is activated by a wide range of conditions, and the regulatory pathways controlling this activation are now being elucidated. However, key aspects of how these factors may function together to properly modulate autophagy in response to specific internal or external signals are yet to be discovered. In this review we discuss mechanisms for regulation of autophagy in response to environmental stress and disruptions in cell homeostasis. These pathways include post-translational modification of proteins required for autophagy activation and progression, control of protein stability of the autophagy machinery, and transcriptional regulation, resulting in changes in transcription of genes involved in autophagy. In particular, we highlight potential connections between the roles of key regulators and explore gaps in research, the filling of which can further our understanding of the autophagy regulatory network in plants.

Photorespiration: regulation and new insights on the potential role of persulfidation

Photorespiration has been considered a 'futile' cycle in C3 plants, necessary to detoxify and recycle the metabolites generated by the oxygenating activity of Rubisco. However, several reports indicate that this metabolic route plays a fundamental role in plant metabolism and constitutes a very interesting research topic. Many open questions still remain with regard to photorespiration. One of these questions is how the photorespiratory process is regulated in plants and what factors contribute to this regulation. In this review, we summarize recent advances in the regulation of the photorespiratory pathway with a special focus on the transcriptional and post-translational regulation of photorespiration and the interconnections of this process with nitrogen and sulfur metabolism. Recent findings on sulfide signaling and protein persulfidation are also described.

Persulfidation maintains cytosolic G6PDs activity through changing tetrameric structure and competing cysteine sulfur oxidation under salt stress in Arabidopsis and tomato

Glucose-6-phosphate dehydrogenases (G6PDs) are essential regulators of cellular redox. Hydrogen sulfide (H2 S) is a small gasotransmitter that improves plant adaptation to stress; however, its role in regulating G6PD oligomerization to resist oxidative stress remains unknown in plants. Persulfidation of cytosolic G6PDs was analyzed by mass spectrometry (MS). The structural change model of AtG6PD6 homooligomer was built by chemical cross-linking coupled with mass spectrometry (CXMS). We isolated AtG6PD6C159A and SlG6PDCC155A transgenic lines to confirm the in vivo function of persulfidated sites with the g6pd5,6 background. Persulfidation occurs at Arabidopsis G6PD6 Cystine (Cys)159 and tomato G6PDC Cys155, leading to alterations of spatial distance between lysine (K)491-K475 from 42.0 Å to 10.3 Å within the G6PD tetramer. The structural alteration occurs in the structural NADP+ binding domain, which governs the stability of G6PD homooligomer. Persulfidation enhances G6PD oligomerization, thereby increasing substrate affinity. Under high salt stress, cytosolic G6PDs activity was inhibited due to oxidative modifications. Persulfidation protects these specific sites and prevents oxidative damage. In summary, H2 S-mediated persulfidation promotes cytosolic G6PD activity by altering homotetrameric structure. The cytosolic G6PD adaptive regulation with two kinds of protein modifications at the atomic and molecular levels is critical for the cellular stress response.

Regulation of V-ATPase by Jasmonic Acid: Possible Role of Persulfidation

Vacuolar H+-translocating ATPase (V-ATPase) is a proton pump crucial for plant growth and survival. For this reason, its activity is tightly regulated, and various factors, such as signaling molecules and phytohormones, may be involved in this process. The aim of this study was to explain the role of jasmonic acid (JA) in the signaling pathways responsible for the regulation of V-ATPase in cucumber roots and its relationship with other regulators of this pump, i.e., H2S and H2O2. We analyzed several aspects of the JA action on the enzyme, including transcriptional regulation, modulation of protein levels, and persulfidation of selected V-ATPase subunits as an oxidative posttranslational modification induced by H2S. Our results indicated that JA functions as a repressor of V-ATPase, and its action is related to a decrease in the protein amount of the A and B subunits, the induction of oxidative stress, and the downregulation of the E subunit persulfidation. We suggest that both H2S and H2O2 may be downstream components of JA-dependent negative proton pump regulation. The comparison of signaling pathways induced by two negative regulators of the pump, JA and cadmium, revealed that multiple pathways are involved in the V-ATPase downregulation in cucumber roots.

Regulation of Mitochondrial Respiration by Hydrogen Sulfide

Hydrogen sulfide (H2S), the third gasotransmitter, has positive roles in animals and plants. Mitochondria are the source and the target of H2S and the regulatory hub in metabolism, stress, and disease. Mitochondrial bioenergetics is a vital process that produces ATP and provides energy to support the physiological and biochemical processes. H2S regulates mitochondrial bioenergetic functions and mitochondrial oxidative phosphorylation. The article summarizes the recent knowledge of the chemical and biological characteristics, the mitochondrial biosynthesis of H2S, and the regulatory effects of H2S on the tricarboxylic acid cycle and the mitochondrial respiratory chain complexes. The roles of H2S on the tricarboxylic acid cycle and mitochondrial respiratory complexes in mammals have been widely studied. The biological function of H2S is now a hot topic in plants. Mitochondria are also vital organelles regulating plant processes. The regulation of H2S in plant mitochondrial functions is gaining more and more attention. This paper mainly summarizes the current knowledge on the regulatory effects of H2S on the tricarboxylic acid cycle (TCA) and the mitochondrial respiratory chain. A study of the roles of H2S in mitochondrial respiration in plants to elucidate the botanical function of H2S in plants would be highly desirable.

Sulfide promotes tolerance to drought through protein persulfidation in Arabidopsis

Hydrogen sulfide (H2S) is a signaling molecule that regulates essential plant processes. In this study, the role of H2S during drought was analysed, focusing on the underlying mechanism. Pretreatments with H2S before imposing drought on plants substantially improved the characteristic stressed phenotypes under drought and decreased the levels of typical biochemical stress markers such as anthocyanin, proline, and hydrogen peroxide. H2S also regulated drought-responsive genes and amino acid metabolism, and repressed drought-induced bulk autophagy and protein ubiquitination, demonstrating the protective effects of H2S pretreatment. Quantitative proteomic analysis identified 887 significantly different persulfidated proteins between control and drought stress plants. Bioinformatic analyses of the proteins more persulfidated in drought revealed that the most enriched biological processes were cellular response to oxidative stress and hydrogen peroxide catabolism. Protein degradation, abiotic stress responses, and the phenylpropanoid pathway were also highlighted, suggesting the importance of persulfidation in coping with drought-induced stress. Our findings emphasize the role of H2S as a promoter of enhanced tolerance to drought, enabling plants to respond more rapidly and efficiently. Furthermore, the main role of protein persulfidation in alleviating reactive oxygen species accumulation and balancing redox homeostasis under drought stress is highlighted.

Mapping Pregnancy-dependent Sulfhydrome Unfolds Diverse Functions of Protein Sulfhydration in Human Uterine Artery

Uterine artery (UA) hydrogen sulfide (H2S) production is augmented in pregnancy and, on stimulation by systemic/local vasodilators, contributes to pregnancy-dependent uterine vasodilation; however, how H2S exploits this role is largely unknown. S-sulfhydration converts free thiols to persulfides at reactive cysteine(s) on targeted proteins to affect the entire proteome posttranslationally, representing the main route for H2S to elicit its function. Here, we used Tag-Switch to quantify changes in sulfhydrated (SSH-) proteins (ie, sulfhydrome) in H2S-treated nonpregnant and pregnant human UA. We further used the low-pH quantitative thiol reactivity profiling platform by which paired sulfhydromes were subjected to liquid chromatography tandem mass spectrometry-based peptide sequencing to generate site (cysteine)-specific pregnancy-dependent H2S-responsive human UA sulfhydrome. Total levels of sulfhydrated proteins were significantly greater in pregnant vs nonpregnant human UA and further stimulated by treatment with sodium hydrosulfide. We identified a total of 360 and 1671 SSH-peptides from 480 and 1186 SSH-proteins in untreated and sodium hydrosulfide-treated human UA, respectively. Bioinformatics analyses identified pregnancy-dependent H2S-responsive human UA SSH peptides/proteins, which were categorized to various molecular functions, pathways, and biological processes, especially vascular smooth muscle contraction/relaxation. Pregnancy-dependent changes in these proteins were rectified by immunoblotting of the Tag-Switch labeled SSH proteins. Low-pH quantitative thiol reactivity profiling failed to identify low abundance SSH proteins such as KATP channels in human UA; however, immunoblotting of Tag-Switch-labeled SSH proteins identified pregnancy-dependent upregulation of SSH-KATP channels without altering their total proteins. Thus, comprehensive analyses of human UA sulfhydromes influenced by endogenous and exogenous H2S inform novel roles of protein sulfhydration in uterine hemodynamics regulation.

The Modulation of Sucrose Nonfermenting 1-Related Protein Kinase 2.6 State by Persulfidation and Phosphorylation: Insights from Molecular Dynamics Simulations

SnRK2.6 (SUCROSE NONFERMENTING 1-RELATED PROTEIN KINASE2.6) has been characterized as a molecular switch for the intracellular abscisic acid (ABA) signal-transduction pathway. Normally, SnRK2.6 is kept in an "off" state, forming a binary complex with protein phosphatase type 2Cs (PP2Cs). Upon stressful conditions, SnRK2.6 turns into an "on" state by its release from PP2Cs and then phosphorylation at Ser175. However, how the "on" and "off" states for SnRK2.6 are fine-tuned, thereby controlling the initiation and braking processes of ABA signaling, is still largely unclear. SnRK2.6 activity was tightly regulated through protein post-translational modifications (PTM), such as persulfidation and phosphorylation. Taking advantage of molecular dynamics simulations, our results showed that Cys131/137 persulfidation on SnRK2.6 induces destabilized binding and weakened interactions between SnRK2.6 and HAB1 (HYPERSENSITIVE TO ABA1), an important PP2C family protein. This unfavorable effect on the association of the SnRK2.6-HAB1 complex suggests that persulfidation functions are a positive regulator of ABA signaling initiation. In addition, Ser267 phosphorylation in persulfidated SnRK2.6 renders a stable physical association between SnRK2.6 and HAB1, a key characterization for SnRK2.6 inhibition. Rather than Ser175, HAB1 cannot dephosphorylate Ser267 in SnRK2.6, which implies that the retained phosphorylation status of Ser267 could ensure that the activated SnRK2.6 reforms the binary complex to cease ABA signaling. Taken together, our findings expand current knowledge concerning the regulation of persulfidation and phosphorylation on the state transition of SnRK2.6 and provide insights into the fine-tuned mechanism of ABA signaling.

Signal Mediators in the Implementation of Jasmonic Acid's Protective Effect on Plants under Abiotic Stresses

Plant cells respond to stress by activating signaling and regulatory networks that include plant hormones and numerous mediators of non-hormonal nature. These include the universal intracellular messenger calcium, reactive oxygen species (ROS), gasotransmitters, small gaseous molecules synthesized by living organisms, and signal functions such as nitrogen monoxide (NO), hydrogen sulfide (H₂S), carbon monoxide (CO), and others. This review focuses on the role of functional linkages of jasmonic acid and jasmonate signaling components with gasotransmitters and other signaling mediators, as well as some stress metabolites, in the regulation of plant adaptive responses to abiotic stressors. Data on the involvement of NO, H₂S, and CO in the regulation of jasmonic acid formation in plant cells and its signal transduction were analyzed. The possible involvement of the protein components of jasmonate signaling in stress-protective gasotransmitter effects is discussed. Emphasis is placed on the significance of the functional interaction between jasmonic acid and signaling mediators in the regulation of the antioxidant system, stomatal apparatus, and other processes important for plant adaptation to abiotic stresses.

Emerging Chemical Biology of Protein Persulfidation

Significance: Protein persulfidation (the formation of RSSH), an evolutionarily conserved oxidative posttranslational modification in which thiol groups in cysteine residues are converted into persulfides, has emerged as one of the main mechanisms through which hydrogen sulfide (H2S) conveys its signaling. Recent Advances: New methodological advances in persulfide labeling started unraveling the chemical biology of this modification and its role in (patho)physiology. Some of the key metabolic enzymes are regulated by persulfidation. RSSH levels are important for the cellular defense against oxidative injury, and they decrease with aging, leaving proteins vulnerable to oxidative damage. Persulfidation is dysregulated in many diseases. Critical Issues: A relatively new field of signaling by protein persulfidation still has many unanswered questions: the mechanism(s) of persulfide formation and transpersulfidation and the identification of "protein persulfidases," the improvement of methods to monitor RSSH changes and identify protein targets, and understanding the mechanisms through which this modification controls important (patho)physiological functions. Future Directions: Deep mechanistic studies using more selective and sensitive RSSH labeling techniques will provide high-resolution structural, functional, quantitative, and spatiotemporal information on RSSH dynamics and help with better understanding how H2S-derived protein persulfidation affects protein structure and function in health and disease. This knowledge could pave the way for targeted drug design for a wide variety of pathologies. Antioxid. Redox Signal. 39, 19-39.

Silencing of SbPPCK1-3 Negatively Affects Development, Stress Responses and Productivity in Sorghum

Phosphoenolpyruvate carboxylase (PEPC) plays central roles in photosynthesis, respiration, amino acid synthesis, and seed development. PEPC is regulated by different post-translational modifications. Between them, the phosphorylation by PEPC-kinase (PEPCk) is widely documented. In this work, we simultaneously silenced the three sorghum genes encoding PEPCk (SbPPCK1-3) by RNAi interference, obtaining 12 independent transgenic lines (Ppck1-12 lines), showing different degrees of SbPPCK1-3 silencing. Among them, two T2 homozygous lines (Ppck-2 and Ppck-4) were selected for further evaluation. Expression of SbPPCK1 was reduced by 65% and 83% in Ppck-2 and Ppck-4 illuminated leaves, respectively. Expression of SbPPCK2 was higher in roots and decreased by 50% in Ppck-2 and Ppck-4 in this tissue. Expression of SbPPCK3 was low and highly variable. Despite the incomplete gene silencing, it decreased the degree of phosphorylation of PEPC in illuminated leaves, P-deficient plants, and NaCl-treated plants. Both leaves and seeds of Ppck lines had altered metabolic profiles and a general decrease in amino acid content. In addition, Ppck lines showed delayed flowering, and 20% of Ppck-4 plants did not produce flowers at all. The total amount of seeds was lowered by 50% and 36% in Ppck-2 and Ppck-4 lines, respectively. The quality of seeds was lower in Ppck lines: lower amino acid content, including Lys, and higher phytate content. These data confirm the relevance of the phosphorylation of PEPC in sorghum development, stress responses, yield, and quality of seeds.

NADP-Dependent Malic Enzyme Genes in Sweet Pepper Fruits: Involvement in Ripening and Modulation by Nitric Oxide (NO)

NADPH is an indispensable cofactor in a wide range of physiological processes that is generated by a family of NADPH dehydrogenases, of which the NADP-dependent malic enzyme (NADP-ME) is a member. Pepper (Capsicum annuum L.) fruit is a horticultural product consumed worldwide that has great nutritional and economic relevance. Besides the phenotypical changes that pepper fruit undergoes during ripening, there are many associated modifications at transcriptomic, proteome, biochemical and metabolic levels. Nitric oxide (NO) is a recognized signal molecule with regulatory functions in diverse plant processes. To our knowledge, there is very scarce information about the number of genes encoding for NADP-ME in pepper plants and their expression during the ripening of sweet pepper fruit. Using a data mining approach to evaluate the pepper plant genome and fruit transcriptome (RNA-seq), five NADP-ME genes were identified, and four of them, namely CaNADP-ME2 to CaNADP-ME5, were expressed in fruit. The time course expression analysis of these genes during different fruit ripening stages, including green immature (G), breaking point (BP) and red ripe (R), showed that they were differentially modulated. Thus, while CaNADP-ME3 and CaNADP-ME5 were upregulated, CaNADP-ME2 and CaNADP-ME4 were downregulated. Exogenous NO treatment of fruit triggered the downregulation of CaNADP-ME4. We obtained a 50-75% ammonium-sulfate-enriched protein fraction containing CaNADP-ME enzyme activity, and this was assayed via non-denaturing polyacrylamide gel electrophoresis (PAGE). The results allow us to identify four isozymes designated from CaNADP-ME I to CaNADP-ME IV. Taken together, the data provide new pieces of information on the CaNADP-ME system with the identification of five CaNADP-ME genes and how the four genes expressed in pepper fruits are modulated during ripening and exogenous NO gas treatment.

H2 S works synergistically with rhizobia to modify photosynthetic carbon assimilation and metabolism in nitrogen-deficient soybeans

Hydrogen sulfide (H₂ S) performs a crucial role in plant development and abiotic stress responses by interacting with other signalling molecules. However, the synergistic involvement of H₂ S and rhizobia in photosynthetic carbon (C) metabolism in soybean (Glycine max) under nitrogen (N) deficiency has been largely overlooked. Therefore, we scrutinised how H₂ S drives photosynthetic C fixation, utilisation, and accumulation in soybean-rhizobia symbiotic systems. When soybeans encountered N deficiency, organ growth, grain output, and nodule N-fixation performance were considerably improved owing to H₂ S and rhizobia. Furthermore, H₂ S collaborated with rhizobia to actively govern assimilation product generation and transport, modulating C allocation, utilisation, and accumulation. Additionally, H₂ S and rhizobia profoundly affected critical enzyme activities and coding gene expressions implicated in C fixation, transport, and metabolism. Furthermore, we observed substantial effects of H₂ S and rhizobia on primary metabolism and C-N coupled metabolic networks in essential organs via C metabolic regulation. Consequently, H₂ S synergy with rhizobia inspired complex primary metabolism and C-N coupled metabolic pathways by directing the expression of key enzymes and related coding genes involved in C metabolism, stimulating effective C fixation, transport, and distribution, and ultimately improving N fixation, growth, and grain yield in soybeans.

The glutathione-dependent alarm triggers signalling responses involved in plant acclimation to cadmium

Cadmium (Cd) uptake from polluted soils inhibits plant growth and disturbs physiological processes, at least partly due to disturbances in the cellular redox environment. Although the sulfur-containing antioxidant glutathione is important in maintaining redox homeostasis, its role as an antioxidant can be overruled by its involvement in Cd chelation as a phytochelatin precursor. Following Cd exposure, plants rapidly invest in phytochelatin production, thereby disturbing the redox environment by transiently depleting glutathione concentrations. Consequently, a network of signalling responses is initiated, in which the phytohormone ethylene is an important player involved in the recovery of glutathione levels. Furthermore, these responses are intricately connected to organellar stress signalling and autophagy, and contribute to cell fate determination. In general, this may pave the way for acclimation (e.g. restoration of glutathione levels and organellar homeostasis) and plant tolerance in the case of mild stress conditions. This review addresses connections between these players and discusses the possible involvement of the gasotransmitter hydrogen sulfide in plant acclimation to Cd exposure.

Thioredoxin TRXo1 is involved in ABA perception via PYR1 redox regulation

Abscisic acid (ABA) plays a fundamental role in plant growth and development processes such as seed germination, stomatal response or adaptation to stress, amongst others. Increases in the endogenous ABA content is recognized by specific receptors of the PYR/PYL/RCAR family that are coupled to a phosphorylation cascade targeting transcription factors and ion channels. Just like other receptors of the family, nuclear receptor PYR1 binds ABA and inhibits the activity of type 2C phosphatases (PP2Cs), thus avoiding the phosphatase-exerted inhibition on SnRK2 kinases, positive regulators which phosphorylate targets and trigger ABA signalling. Thioredoxins (TRXs) are key components of cellular redox homeostasis that regulate specific target proteins through a thiol-disulfide exchange, playing an essential role in redox homeostasis, cell survival, and growth. In higher plants, TRXs have been found in almost all cellular compartments, although its presence and role in nucleus has been less studied. In this work, affinity chromatography, Dot-blot, co-immunoprecipitation, and bimolecular fluorescence complementation assays allowed us to identify PYR1 as a new TRXo1 target in the nucleus. Studies on recombinant HisAtPYR1 oxidation-reduction with wild type and site-specific mutagenized forms showed that the receptor underwent redox regulation involving changes in the oligomeric state in which Cys³⁰ and Cys⁶⁵ residues were implied. TRXo1 was able to reduce previously-oxidized inactive PYR1, thus recovering its capacity to inhibit HAB1 phosphatase. In vivo PYR1 oligomerization was dependent on the redox state, and a differential pattern was detected in KO and over-expressing Attrxo1 mutant plants grown in the presence of ABA compared to WT plants. Thus, our findings suggest the existence of a redox regulation of TRXo1 on PYR1 that may be relevant for ABA signalling and had not been described so far.