HPCA1 is required for systemic reactive oxygen species and calcium cell-to-cell signaling and plant acclimation to stress

Ca2+-dependent H2O2 response in roots and leaves of barley - a transcriptomic investigation

BACKGROUND

Ca2+ and H2O2 are second messengers that regulate a wide range of cellular events in response to different environmental and developmental cues. In plants, stress-induced H2O2 has been shown to initiate characteristic Ca2+ signatures; however, a clear picture of the molecular connection between H2O2-induced Ca2+ signals and H2O2-induced cellular responses is missing, particularly in cereal crops such as barley. Here, we employed RNA-seq analyses to identify transcriptome changes in roots and leaves of barley after H2O2 treatment under conditions that inhibited the formation of cytosolic Ca2+ transients. To that end, plasma membrane Ca2+ channels were blocked by LaCl3 application prior to stimulation of barley tissues with H2O2.

RESULTS

We examined the expression patterns of 4246 genes that had previously been shown to be differentially expressed upon H2O2 application. Here, we further compared their expression between H2O2 and LaCl3 + H2O2 treatment. Genes showing expression patterns different to the previous study were considered to be Ca2+-dependent H2O2-responsive genes. These genes, numbering 331 in leaves and 1320 in roots, could be classified in five and four clusters, respectively. Expression patterns of several genes from each cluster were confirmed by RT-qPCR. We furthermore performed a network analysis to identify potential regulatory paths from known Ca2+-related genes to the newly identified Ca2+-dependent H2O2 responsive genes, using the recently described Stress Knowledge Map. This analysis indicated several transcription factors as key points of the responses mediated by the cross-talk between H2O2 and Ca2+.

CONCLUSION

Our study indicates that about 70% of the H2O2-responsive genes in barley roots require a transient increase in cytosolic Ca2+ concentrations for alteration in their transcript abundance, whereas in leaves, the Ca2+ dependency was much lower at about 33%. Targeted gene analysis and pathway modeling identified not only known components of the Ca2+ signaling cascade in plants but also genes that are not yet connected to stimuli-associated signaling. Potential key transcription factors identified in this study can be further analyzed in barley and other crops to ultimately disentangle the underlying mechanisms of H2O2-associated signal transduction mechanisms. This could aid breeding for improved stress resistance to optimize performance and productivity under increasing climate challenges.

Integrating proteomics and metabolomics to elucidate the regulatory mechanisms of pimpled egg production in chickens: Multi-omics analysis of the mechanism of pimpled egg formation

Eggshells not only protect the contents of the egg from external damage but are also a key factor influencing consumer choice, second only to price. In the later stages of egg production, the incidence of pimpled eggs significantly increases, severely affecting the hatchability and food safety of the eggs. This study compares the differences in the uterine proteomes and metabolomes of hens producing pimpled eggs and those producing normal eggs, aiming to identify the proteins and metabolites that may play a crucial role in the formation of pimpled eggs. A total of 242 differentially expressed proteins (DEPs) were identified in uterine tissue, of which 116 were upregulated and 126 were downregulated. Enrichment analysis revealed that the DEPs were enriched in pathways related to ion transport, energy metabolism, and immune responses. The study found that in the normal eggs (NE) group, HCO₃⁻ was predominantly transported via SLC4A1, although other transport pathways may also play a role. In contrast, in the pimpled eggs (PE) group, bicarbonate ions (HCO₃⁻) was primarily transported through SLC4A4. Additionally, a total of 44 differentially metabolites (DMs) were identified in the uterus, with 5'-Adenylic acid (ATP) being significantly downregulated in the PE group. The ions and matrix proteins required for eggshell formation are transported from uterine cells to the uterine fluid against a concentration gradient, a process that consumes a substantial amount of energy. The decrease in ATP concentration in the PE group may be a significant factor influencing the formation of pimpled eggs. Subsequently, we found that the DEPs and DMs were jointly enriched in several signaling pathways, including the FoxO signaling pathway related to energy metabolism, nicotinate and nicotinamide metabolism, and tryptophan metabolism associated with immune response. Notably, the DMs involved in these signaling pathways were all downregulated in the PE group. Our research findings indicate that SLC4A1, SLC4A2, and ATP2B4 (DEPs), along with 5'-adenylic acid and trigonelline (DMs), influence the formation of eggshells through mechanisms related to energy metabolism, ion transport, and immune response. These DEPs and DMs may serve as potential biomarkers for the genetic improvement of eggshell quality.

Orchestrating ROS regulation: coordinated post-translational modification switches in NADPH oxidases

Reactive oxygen species (ROS) are among the most important signaling molecules, playing a significant role in plant growth, development, and responses to various environmental stresses. Respiratory burst oxidase homologs (RBOHs) are key enzymes in ROS production. Plants tightly regulate the activation and deactivation of RBOHs through various post-translational modifications (PTMs), including phosphorylation, ubiquitination, S-nitrosylation, and persulfidation. These PTMs fine-tune ROS production, ensuring normal plant growth and development while facilitating rapid responses to abiotic and biotic stresses. This review discusses the effects of different PTMs on RBOH function and their biological relevance. Additionally, we examine the evolutionary conservation of PTM sites and emphasize the complex interplay between multiple PTMs regulating RBOHs.

Consecutive oxidative stress in CATALASE2-deficient Arabidopsis negatively regulates Glycolate Oxidase1 activity through S-nitrosylation

Glycolate oxidase (GOX) is a crucial enzyme of photorespiration involving carbon metabolism and stress responses. It is poorly understood, however, how its activities are modulated in response to oxidative stress elicited by various environmental cues. Analysis of Arabidopsis catalase-defective mutant cat2 revealed that the GOX activities were gradually repressed during the growth, which were accompanied by decreased salicylic acid (SA)-dependent cell death, suggesting photorespiratory H2O2 may entrain negative feedback regulation of GOX in an age-dependent manner. Intriguingly, a loss-of-function mutation in GLYCOLATE OXIDASE1 (GOX1) rather than in GOX2 and GOX3 attenuated the SA responses of cat2. We found that GOX1 is S-nitrosylated at Cys-343 during consecutive oxidative stress in the cat2 mutant. Subsequently, increased GOX1-SNO formations may contribute to progressively decreased GOX activities and then compromised photorespiratory H2O2 flux, which forms a negative feedback loop limiting the amplified activation of SA-dependent defence responses. Together, the data reveal that GOX S-nitrosylation is involved in the crosstalk between photorespiratory H2O2 and NO signalling in the fine-tuning regulation of oxidative stress responses and further highlight that NO-based S-nitrosylation acts as an on-off switch for ROS homeostasis.

Plant extracellular vesicles contribute to the amplification of immune signals during systemic acquired resistance

KEY MESSAGE

Plant extracellular vesicles play a role in systemic acquired resistance by facilitating the transmission of immune signals between plant cells. Extracellular vesicles (EVs) play a critical role in facilitating the transfer of nucleic acids and proteins between plants and pathogens. However, the involvement of plant EVs in intercellular communication and their contribution to the regulation of physiological and pathological conditions in plants remains unclear. In this study, we isolated EVs from the apoplast of Arabidopsis plants induced by systemic acquired resistance (SAR) and conducted proteomic and physiological analyses to investigate the role of EVs in SAR. The results demonstrated that plant cells are capable of internalizing EVs, and EV secretion was enhanced in SAR-induced plants. EVs isolated from SAR-induced plants effectively inhibited the spore production of Botrytis cinerea, activated the transcription of several SAR marker genes, and improved plant resistance to Pseudomonas syringae pv. tomato DC3000 (Pst DC3000). Several proteins associated with defense responses were enriched in EVs upon SAR induction. Among these, the receptor-like kinase H2O2-Induced Ca2+ Increase 1 (HPCA1) was identified as a crucial component in SAR. In addition, plant EVs contained numerous proteins involved in the transmission of signals related to pathogen-associated molecular patterns-triggered immunity (PTI) and effector-triggered immunity (ETI). Our findings suggest that plant EVs are functionally involved in the propagation of SAR signals and may play diverse roles in plant immune responses.

Calcium signaling in hypoxic response

Plants can experience a lack of oxygen due to environmental conditions, such as flooding events or intense microbial blooms in the soil, and from their own metabolic activities. The associated limit on aerobic respiration can be fatal. Therefore, plants have evolved sensing systems that monitor oxygen levels and trigger a suite of metabolic, physiologic, and developmental responses to endure, or potentially escape, these oxygen-limiting conditions. Low oxygen stress has long been known to trigger changes in cytosolic Ca2+ levels in plants, and recent work has seen some major steps forward in characterizing these events as part of a Ca2+-based signaling system through (1) defining how hypoxia may trigger and then shape the dynamics of these Ca2+ signals, and (2) identifying a host of the downstream elements that allow Ca2+ to regulate a wide-ranging network of hypoxia responses. Calcium transporters such as the CAX family of Ca2+/H+ antiporters at the tonoplast have emerged as important components of the system that forms hypoxia-related Ca2+ signals. Downstream lies a web of Ca2+-responsive proteins such as the calmodulin like proteins, Ca2+-dependent kinases, and the calcineurin-B like proteins along with their interacting kinases. A host of other regulators such as reactive oxygen species and lipid-mediated signals then act in parallel to the Ca2+-dependent events to closely control and coordinate the myriad responses that characterize the plant's low oxygen response.

ROS, an Important Plant Growth Regulator in Root Growth and Development: Functional Genes and Mechanism

Roots are fundamental to the growth, development, and survival of plants. Beyond anchoring the plant, roots absorb water and nutrients, supporting the plant's ability to grow and function normally. Root systems, originating from the apical meristem, exhibit significant diversity depending on the plant species. ROS are byproducts of aerobic metabolism, present in both above- and below-ground plant tissues. While ROS were once considered merely harmful byproducts of oxygen metabolism, they are now recognized as critical signaling molecules that regulate plant growth and development. Under stress conditions, plants produce elevated levels of ROS, which can inhibit growth. However, moderate ROS levels act as signals that integrate various regulatory pathways, contributing to normal plant development. However, there is still a lack of comprehensive and systematic research on how ROS precisely regulate root growth and development. This review provides an overview of ROS production pathways and their regulatory mechanisms in plants, with a particular focus on their influence on root development.

Excess iron accumulation affects maize endosperm development by inhibiting starch synthesis and inducing DNA damage

Iron (Fe) storage in cereal seeds is the principal source of dietary Fe for humans. In maize (Zea mays), the accumulation of Fe in seeds is known to be negatively correlated with crop yield. Hence, it is essential to understand the underlying mechanism, which is crucial for developing and breeding maize cultivars with high yields and high Fe concentrations in the kernels. Here, through the successful application of in vitro kernel culture, we demonstrated that excess Fe supply in the medium caused the kernel to become collapsed and lighter in color, consistent with those found in yellow strip like 2 (ysl2, a small kernel mutant), implicated a crucial role of Fe concentration in kernel development. Indeed, over-accumulation of Fe in endosperm inhibited the abundance and activity of ADP-glucose pyrophosphorylase (AGPase) and the kernel development defect was alleviated by overexpression of Briittle 2 (Bt2, encoding a small subunit of AGPase) in ysl2 mutant. Imaging and quantitative analyses of reactive oxygen species (ROS) and cell death showed that Fe stress-induced ROS burst and severe DNA damage in endosperm cells. In addition, we have successfully identified candidate genes that are associated with iron homeostasis within the kernel, as well as upstream transcription factors that regulate ZmYSL2 by yeast one-hybrid screening. Collectively, our study will provide insights into the molecular mechanism of Fe accumulation-regulated seed development and promote the future efficient application of Fe element in corn improvement.

Exogenous Calcium Enhances Castor Tolerance to Saline-Alkaline Stress by Regulating Antioxidant Enzyme Activity and Activating Ca2+ and ROS Signaling Crosstalk

Saline-alkaline stress is a major factor limiting agricultural development, with calcium (Ca2+) playing a role in regulating plant tolerance through multiple signaling pathways. However, the specific mechanisms by which Ca2+ mediates saline-alkaline stress tolerance at the molecular level remain incompletely understood. This study investigates the effects of exogenous Ca2+ application on enhancing plant tolerance to saline-alkaline stress, focusing on its impact on the antioxidant system and Ca2+ and reactive oxygen species (ROS) signaling pathways. Through physiological assays and transcriptomic analyses, we evaluated oxidative damage markers, antioxidant enzyme activities, and the expression of key Ca2+ and ROS signaling genes. The results showed that saline-alkaline stress significantly elevated ROS levels, which led to increased membrane lipid peroxidation and induced upregulation of antioxidant response elements in castor roots. Exogenous calcium treatment reduced ROS accumulation by increasing superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities and decreasing malondialdehyde (MDA) levels, demonstrating a marked improvement in the antioxidant system. Transcriptomic analysis identified CAT2 (LOC107261240) as the primary target gene associated with increased CAT activity in response to exogenous calcium. Additionally, the upregulation of specific Ca2+ channels, Ca2+ sensors, ROS receptors, and antioxidant-related genes with calcium treatment highlights the critical role of Ca2+-ROS signaling crosstalk in enhancing stress tolerance. Protein-protein interaction analysis identified APX3 and other hub genes involved in Ca2+-ROS signaling transduction and the regulation of antioxidant activity. These findings enhance our understanding of calcium's complex regulatory roles in plant abiotic stress responses, offering new theoretical insights for improving crop resilience in agriculture.

ROS as Signaling Molecules to Initiate the Process of Plant Acclimatization to Abiotic Stress

During their life cycle, plants constantly respond to environmental changes. Abiotic stressors affect the photosynthetic and respiratory processes of plants. Reactive oxygen species (ROS) are produced during aerobic metabolism and play an important role as regulatory mediators in signaling processes, activating the plant's protective response to abiotic stress and restoring "oxidation-reduction homeostasis". Cells develop normally if the rates of ROS production and the ability to neutralize them are balanced. To implement oxidation-reduction signaling, this balance must be disrupted either by an increase in ROS concentration or a decrease in the activity of one or more antioxidant systems. Under abiotic stress, plants accumulate excessive amounts of ROS, and if the ROS content exceeds the threshold amount dangerous for living organisms, it can lead to damage to all major cellular components. Adaptive resistance of plants to abiotic stressors depends on a set of mechanisms of adaptation to them. The accumulation of ROS in the cell depends on the type of abiotic stress, the strength of its impact on the plant, the duration of its impact, and the recovery period. The aim of this review is to provide a general understanding of the processes occurring during ROS homeostasis in plants, oxidation-reduction processes in cellular compartments in response to abiotic stress, and the participation of ROS in signaling processes activating adaptation processes to abiotic stress.

Real-time live imaging of cytosolic hydrogen peroxide and Ca2+ of Marchantia polymorpha gemmalings reveal immediate initial responses of plant cells triggered by nonthermal plasma irradiation

Cold atmospheric pressure plasma generators capable of generating plasma under normal pressure and temperature conditions have recently been developed, and their biological applications have been extensively studied. Plasma irradiation has been reported to affect plant germination and growth; however, the molecular mechanism underlying these effects and initial cellular responses to plasma irradiation remains poorly understood. To unravel the molecular and cellular mechanisms underlying the effects of plasma irradiation on plants, we have been establishing novel experimental systems using a model liverwort Marchantia polymorpha. We here focused on the initial responses of plant cells to plasma irradiation. To investigate immediate cellular responses following plasma irradiation, we developed a new plasma device that allows irradiation under a microscope. Through integration with live fluorescence imaging, we established an experimental setup to track, the dynamics of intracellular concentration of H2O2 and Ca2+ as representative initial cellular responses. We revealed that plasma irradiation induced a rapid and transient increase in intracellular concentration of H2O2 and Ca2+ in Marchantia gemmalings. Pharmacological analyses suggested that the long-lived reactive species, H2O2, generated by the plasma generator was directly delivered into the plant cells. Competitive inhibitors of Ca2+ channels abolished the Ca2+ rise, suggesting that plasma irradiation immediately activate plasma membrane Ca2+ channel(s) to induce Ca2+ influx. Importantly, this study marks the inaugural demonstration of real-time monitoring of cytosolic H2O2 and Ca2+ dynamics in plants, triggered by plasma irradiation.

Interorgan, intraorgan and interplant communication mediated by nitric oxide and related species

Plant survival to a potential plethora of diverse environmental insults is underpinned by coordinated communication amongst organs to help shape effective responses to these environmental challenges at the whole plant level. This interorgan communication is supported by a complex signal network that regulates growth, development and environmental responses. Nitric oxide (NO) has emerged as a key signalling molecule in plants. However, its potential role in interorgan communication has only recently started to come into view. Direct and indirect evidence has emerged supporting that NO and related species (S-nitrosoglutathione, nitro-linolenic acid) are mobile interorgan signals transmitting responses to stresses such as hypoxia and heat. Beyond their role as mobile signals, NO and related species are involved in mediating xylem development, thus contributing to efficient root-shoot communication. Moreover, NO and related species are regulators in intraorgan systemic defence responses aiming an effective, coordinated defence against pathogens. Beyond its in planta signalling role, NO and related species may act as ex planta signals coordinating external leaf-to-leaf, root-to-leaf but also plant-to-plant communication. Here, we discuss these exciting developments and emphasise how their manipulation may provide novel strategies for crop improvement.

Understanding the mechanobiology of phytoacoustics through molecular Lens: Mechanisms and future perspectives

BACKGROUND

How plants emit, perceive, and respond to sound vibrations (SVs) is a long-standing question in the field of plant sensory biology. In recent years, there have been numerous studies on how SVs affect plant morphological, physiological, and biochemical traits related to growth and adaptive responses. For instance, under drought SVs navigate plant roots towards water, activate their defence responses against stressors, and increase nectar sugar in response to pollinator SVs. Also, plants emit SVs during stresses which are informative in terms of ecological and adaptive perspective. However, the molecular mechanisms underlying the SV perception and emission in plants remain largely unknown. Therefore, deciphering the complexity of plant-SV interactions and identifying bonafide receptors and signaling players will be game changers overcoming the roadblocks in phytoacoustics.

AIM OF REVIEW

The aim of this review is to provide an overview of recent developments in phytoacoustics. We primarily focuss on SV signal perception and transduction with current challenges and future perspectives.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Timeline breakthroughs in phytoacoustics have constantly shaped our understanding and belief that plants may emit and respond to SVs like other species. However, unlike other plant mechanostimuli, little is known about SV perception and signal transduction. Here, we provide an update on phytoacoustics and its ecological importance. Next, we discuss the role of cell wall receptor-like kinases, mechanosensitive channels, intracellular organelle signaling, and other key players involved in plant-SV receptive pathways that connect them. We also highlight the role of calcium (Ca2+), reactive oxygen species (ROS), hormones, and other emerging signaling molecules in SV signal transduction. Further, we discuss the importance of molecular, biophysical, computational, and live cell imaging tools for decoding the molecular complexity of acoustic signaling in plants. Finally, we summarised the role of SV priming in plants and discuss how SVs could modulate plant defense and growth trade-offs during other stresses.

Abscisic acid-induced H2O2 production positively regulates the activity of SAPK8/9/10 through oxidation of the type one protein phosphatase OsPP47

Subclass III sucrose nonfermenting1-related protein kinase 2s (SnRK2s) are positive regulators of abscisic acid (ABA) signaling and abiotic stress responses. However, the underlying activation mechanisms of osmotic stress/ABA-activated protein kinase 8/9/10 (SAPK8/9/10) of rice (Oryza sativa) subclass III SnRK2s in ABA signaling remain to be elucidated. In this study, we employed biochemical, molecular biology, cell biology, and genetic approaches to identify the molecular mechanism by which OsPP47, a type one protein phosphatase in rice, regulates SAPK8/9/10 activity in ABA signaling. We found that OsPP47 not only physically interacted with SAPK8/9/10 but also interacted with ABA receptors PYLs. OsPP47 negatively regulated ABA sensitivity in seed germination and root growth. In the absence of ABA, OsPP47 directly inactivated SAPK8/9/10 by dephosphorylation. In the presence of ABA, ABA-bound OsPYL2 formed complexes with OsPP47 and inhibited its phosphatase activity, partially releasing the inhibition of SAPK8/9/10. SAPK8/9/10-mediated H2O2 production inhibited OsPP47 activity by oxidizing Cys-116 and Cys-256 to form OsPP47 oligomers, resulting in not only preventing the OsPP47-SAPK8/9/10 interaction but also blocking the inhibition of SAPK8/9/10 activity by OsPP47. Our results reveal novel pathways for the inhibition of SAPK8/9/10 in the basal state and for the activation of SAPK8/9/10 induced by ABA in rice.

Redox regulation of meristem quiescence: outside/in

Quiescence is an essential property of meristematic cells, which restrains the cell cycle while retaining the capacity to divide. This crucial process not only facilitates life-long tissue homeostasis and regenerative capacity but also provides protection against adverse environmental conditions, enabling cells to conserve the proliferative potency while minimizing DNA damage. As a survival attribute, quiescence is inherently regulated by the products of aerobic life, in particular reactive oxygen species (ROS) and the redox (reduction/oxidation) mechanisms that plant have evolved to channel these into pervasive signals. Adaptive responses allow quiescent cells to compensate for reduced oxygen tension (hypoxia) in a reversible manner, while the regulated production of the superoxide anion (O2·-) facilitates cell division and the maintenance of stem cells. Here we discuss the role of ROS and redox reactions in the control of the quiescent state in plant meristems, and how this process is integrated with cellular energy and hormone biochemistry. We consider the pathways that sense and transmit redox signals with a focus on the central significance of redox regulation in the mitochondria and nucleus, which is a major regulator of quiescence in meristems. We discuss recent studies that suggest that ROS are a critical component of the feedback loops that control stem cell identity and fate, and suggest that the ROS/hypoxia interface is an important 'outside/in' positional cue for plant cells, particularly in meristems.

Crosstalk of methylglyoxal and calcium signaling in maize (Zea mays L.) thermotolerance through methylglyoxal-scavenging system

Methylglyoxal (MG) and calcium ion (Ca2+) can increase multiple-stress tolerance including plant thermotolerance. However, whether crosstalk of MG and Ca2+ exists in the formation of maize thermotolerance and underlying mechanism still remain elusive. In this paper, maize seedlings were irrigated with MG and calcium chloride alone or in combination, and then exposed to heat stress (HS). The results manifested that, compared with the survival percentage (SP, 45.3%) of the control seedlings, the SP of MG and Ca2+ alone or in combination was increased to 72.4%, 74.2%, and 83.4% under HS conditions, indicating that Ca2+ and MG alone or in combination could upraise seedling thermotolerance. Also, the MG-upraised SP was separately weakened to 42.2%, 40.3%, 52.1%, and 39.4% by Ca2+ chelator (ethylene glycol tetraacetic acid, EGTA), plasma membrane Ca2+ channel blocker (lanthanum chloride, LaCl3), intracellular Ca2+ channel blocker (neomycin, NEC), and calmodulin (CaM) antagonist (trifluoperazine, TFP). However, significant effect of MG scavengers N-acetylcysteine (NAC) and aminoguanidine (AG) on Ca2+-induced thermotolerance was not observed. Similarly, an endogenous Ca2+ level in seedlings was increased by exogenous MG under non-HS and HS conditions, while exogenous Ca2+ had no significant effect on endogenous MG. These data implied that Ca2+ signaling, at least partly, mediated MG-upraised thermotolerance in maize seedlings. Moreover, the activity and gene expression of glyoxalase system (glyoxalase I, glyoxalase II, and glyoxalase III) and non-glyoxalase system (MG reductase, aldehyde reductase, aldo-keto reductase, and lactate dehydrogenase) were up-regulated to a certain extent by Ca2+ and MG alone in seedlings under non-HS and HS conditions. The up-regulated MG-scavenging system by MG was enhanced by Ca2+, while impaired by EGTA, LaCl3, NEC, or TFP. These data suggest that the crosstalk of MG and Ca2+ signaling in maize thermotolerance through MG-scavenging system. These findings provided a theoretical basis for breeding climate-resilient maize crop and developing smart agriculture.

Rapid plant-to-plant systemic signaling via a Cuscuta bridge

Two plants connected via a Cuscuta bridge exchange rapid systemic calcium, electric, and reactive oxygen species signals, suggesting that Cuscuta may have beneficial effects to host plants.

Small size, big impact: Small molecules in plant systemic immune signaling

Plants produce diverse small molecules rapidly in response to localized pathogenic attack. Some of the molecules are able to migrate systemically as mobile signals, leading to the immune priming that protects the distal tissues against future infections by a broad-spectrum of invaders. Such form of defense is unique in plants and is known as systemic acquired resistance (SAR). There are many small molecules identified so far with important roles in the systemic immune signaling, some may have the potential to act as the mobile systemic signal in SAR establishment. Here, we summarize the recent advances in SAR research, with a focus on the role and mechanisms of different small molecules in systemic immune signaling.

Reactive Byproducts of Plant Redox Metabolism and Protein Functions

Living organisms exhibit an impressive ability to expand the basic information encoded in their genome, specifically regarding the structure and function of protein. Two basic strategies are employed to increase protein diversity and functionality: alternative mRNA splicing and post-translational protein modifications (PTMs). Enzymatic regulation is responsible for the majority of the chemical reactions occurring within living cells. However, plants redox metabolism perpetually generates reactive byproducts that spontaneously interact with and modify biomolecules, including proteins. Reactive carbonyls resulted from the oxidative metabolism of carbohydrates and lipids carbonylate proteins, leading to the latter inactivation and deposition in the form of glycation and lipoxidation end products. The protein nitrosylation caused by reactive nitrogen species plays a crucial role in plant morphogenesis and stress reactions. The redox state of protein thiol groups modified by reactive oxygen species is regulated through the interplay of thioredoxins and glutaredoxins, thereby influencing processes such as protein folding, enzyme activity, and calcium and hormone signaling. This review provides a summary of the PTMs caused by chemically active metabolites and explores their functional consequences in plant proteins.

New insights into plasmodesmata: complex 'protoplasmic connecting threads'

Intercellular communication in plants, as in other multicellular organisms, allows cells in tissues to coordinate their responses for development and in response to environmental stimuli. Much of this communication is facilitated by plasmodesmata (PD), consisting of membranes and cytoplasm, that connect adjacent cells to each other. PD have long been viewed as passive conduits for the movement of a variety of metabolites and molecular cargoes, but this perception has been changing over the last two decades or so. Research from the last few years has revealed the importance of PD as signaling hubs and as crucial players in hormone signaling. The adoption of advanced biochemical approaches, molecular tools, and high-resolution imaging modalities has led to several recent breakthroughs in our understanding of the roles of PD, revealing the structural and regulatory complexity of these 'protoplasmic connecting threads'. We highlight several of these findings that we think well illustrate the current understanding of PD as functioning at the nexus of plant physiology, development, and acclimation to the environment.

H2O2 sulfenylates CHE, linking local infection to the establishment of systemic acquired resistance

In plants, a local infection can lead to systemic acquired resistance (SAR) through increased production of salicylic acid (SA). For many years, the identity of the mobile signal and its direct transduction mechanism for systemic SA synthesis in initiating SAR have been debated. We found that in Arabidopsis thaliana, after a local infection, the conserved cysteine residue of the transcription factor CCA1 HIKING EXPEDITION (CHE) undergoes sulfenylation in systemic tissues, which enhances its binding to the promoter of the SA-synthesis gene ISOCHORISMATE SYNTHASE1 (ICS1) and increases SA production. Furthermore, hydrogen peroxide (H2O2) produced through NADPH oxidases is the mobile signal that sulfenylates CHE in a concentration-dependent manner. Accumulation of SA and the previously reported signal molecules, such as N-hydroxypipecolic acid (NHP), then form a signal amplification loop to establish SAR.

Exploring the puzzle of reactive oxygen species acting on root hair cells

Reactive oxygen species (ROS) are essential signaling molecules that enable cells to respond rapidly to a range of stimuli. The ability of plants to recognize various stressors, incorporate a variety of environmental inputs, and initiate stress-response networks depends on ROS. Plants develop resilience and defensive systems as a result of these processes. Root hairs are central components of root biology since they increase the surface area of the root, anchor it in the soil, increase its ability to absorb water and nutrients, and foster interactions between microorganisms. In this review, we specifically focused on root hair cells and we highlighted the identification of ROS receptors, important new regulatory hubs that connect ROS production, transport, and signaling in the context of two hormonal pathways (auxin and ethylene) and under low temperature environmental input related to nutrients. As ROS play a crucial role in regulating cell elongation rates, root hairs are rapidly gaining traction as a very valuable single plant cell model for investigating ROS homeostasis and signaling. These promising findings might soon facilitate the development of plants and roots that are more resilient to environmental stressors.

Redox signaling and oxidative stress in systemic acquired resistance

Plants fully depend on their immune systems to defend against pathogens. Upon pathogen attack, plants not only activate immune responses at the infection site but also trigger a defense mechanism known as systemic acquired resistance (SAR) in distal systemic tissues to prevent subsequent infections by a broad-spectrum of pathogens. SAR is induced by mobile signals produced at the infection site. Accumulating evidence suggests that reactive oxygen species (ROS) play a central role in SAR signaling. ROS burst at the infection site is one of the earliest cellular responses following pathogen infection and can spread to systemic tissues through membrane-associated NADPH oxidase-dependent relay production of ROS. It is well known that ROS ignite redox signaling and, when in excess, cause oxidative stress, damaging cellular components. In this review, we summarize current knowledge on redox regulation of several SAR signaling components. We discuss the ROS amplification loop in systemic tissues involving multiple SAR mobile signals. Moreover, we highlight the essential role of oxidative stress in generating SAR signals including azelaic acid and extracellular NAD(P) [eNAD(P)]. Finally, we propose that eNAD(P) is a damage-associated molecular pattern serving as a converging point of SAR mobile signals in systemic tissues.

Superoxide signalling and antioxidant processing in the plant nucleus

The superoxide anion radical (O2·-) is a one-electron reduction product of molecular oxygen. Compared with other forms of reactive oxygen species (ROS), superoxide has limited reactivity. Nevertheless, superoxide reacts with nitric oxide, ascorbate, and the iron moieties of [Fe-S] cluster-containing proteins. Superoxide has largely been neglected as a signalling molecule in the plant literature in favour of the most stable ROS form, hydrogen peroxide. However, superoxide can accumulate in plant cells, particularly in meristems, where superoxide dismutase activity and ascorbate accumulation are limited (or absent), or when superoxide is generated within the lipid environment of membranes. Moreover, oxidation of the nucleus in response to environmental stresses is a widespread phenomenon. Superoxide is generated in many intracellular compartments including mitochondria, chloroplasts, and on the apoplastic/cell wall face of the plasma membrane. However, nuclear superoxide production and functions remain poorly documented in plants. Accumulating evidence suggests that the nuclear pools of antioxidants such as glutathione are discrete and separate from the cytosolic pools, allowing compartment-specific signalling in the nucleus. We consider the potential mechanisms of superoxide generation and targets in the nucleus, together with the importance of antioxidant processing in regulating superoxide signalling.

Redox regulation of epigenetic and epitranscriptomic gene regulatory pathways in plants

Developmental and environmental constraints influence genome expression through complex networks of regulatory mechanisms. Epigenetic modifications and remodelling of chromatin are some of the major actors regulating the dynamic of gene expression. Unravelling the factors relaying environmental signals that induce gene expression reprogramming under stress conditions is an important and fundamental question. Indeed, many enzymes involved in epigenetic and chromatin modifications are regulated by redox pathways, through post-translational modifications of proteins or by modifications of the flux of metabolic intermediates. Such modifications are potential hubs to relay developmental and environmental changes for gene expression reprogramming. In this review, we provide an update on the interaction between major redox mediators, such as reactive oxygen and nitrogen species and antioxidants, and epigenetic changes in plants. We detail how redox status alters post-translational modifications of proteins, intracellular epigenetic and epitranscriptional modifications, and how redox regulation interplays with DNA methylation, histone acetylation and methylation, miRNA biogenesis, and chromatin structure and remodelling to reprogram genome expression under environmental constraints.

Functional analysis of reactive oxygen species-driven stress systemic signalling, interplay and acclimation

Reactive oxygen species (ROS) play a critical role in plant development and stress responses, acting as key components in rapid signalling pathways. The 'ROS wave' triggers essential acclimation processes, ultimately ensuring plant survival under diverse challenges. This review explores recent advances in understanding the composition and functionality of the ROS wave within plant cells. During their initiation and propagation, ROS waves interact with other rapid signalling pathways, hormones and various molecular compounds. Recent research sheds light on the intriguing lack of a rigid hierarchy governing these interactions, highlighting a complex interplay between diverse signals. Notably, ROS waves culminate in systemic acclimation, a crucial outcome for enhanced stress tolerance. This review emphasizes the versatility of ROS, which act as flexible players within a network of short- and long-term factors contributing to plant stress resilience. Unveiling the intricacies of these interactions between ROS and various signalling molecules holds immense potential for developing strategies to augment plant stress tolerance, contributing to improved agricultural practices and overall ecosystem well-being.

The redox code of plants

Central metabolism is organised through high-flux, Nicotinamide Adenine Dinucleotide (NAD+/NADH) and NADP+/NADPH systems operating at near equilibrium. As oxygen is indispensable for aerobic organisms, these systems are also linked to the levels of reactive oxygen species, such as H2O2, and through H2O2 to the regulation of macromolecular structures and activities, via kinetically controlled sulphur switches in the redox proteome. Dynamic changes in H2O2 production, scavenging and transport, associated with development, growth and responses to the environment are, therefore, linked to the redox state of the cell and regulate cellular function. These basic principles form the 'redox code' of cells and were first defined by D. P. Jones and H. Sies in 2015. Here, we apply these principles to plants in which recent studies have shown that they can also explain cell-to-cell and even plant-to-plant signalling processes. The redox code is, therefore, an integral part of biological systems and can be used to explain multiple processes in plants at the subcellular, cellular, tissue, whole organism and perhaps even community and ecosystem levels. As the environmental conditions on our planet are worsening due to global warming, climate change and increased pollution levels, new studies are needed applying the redox code of plants to these changes.

Root-derived long-distance signals trigger ABA synthesis and enhance drought resistance in Arabidopsis

Vascular plants have evolved intricate long-distance signaling mechanisms to cope with environmental stress, with reactive oxygen species (ROS) emerging as pivotal systemic signals in plant stress responses. However, the exact role of ROS as root-to-shoot signals in the drought response has not been determined. In this study, we reveal that compared with wild-type plants, ferric reductase defective 3 (frd3) mutants exhibit enhanced drought resistance concomitant with elevated NINE-CIS-EPOXYCAROTENOID DIOXYGENASE 3 (NCED3) transcript levels and abscisic acid (ABA) contents in leaves as well as increased hydrogen peroxide (H2O2) levels in roots and leaves. Grafting experiments distinctly illustrate that drought resistance can be conferred by the frd3 rootstock regardless of the scion genotype, indicating that long-distance signals originating from frd3 roots promote an increase in ABA levels in leaves. Intriguingly, the drought resistance conferred by the frd3 mutant rootstock is weakened by the CAT2-overexpressing scion, suggesting that H2O2 may be involved in long-distance signaling. Moreover, the results of comparative transcriptome and proteome analyses support the drought resistance phenotype of the frd3 mutant. Taken together, our findings substantiate the notion that frd3 root-derived long-distance signals trigger ABA synthesis in leaves and enhance drought resistance, providing new evidence for root-to-shoot long-distance signaling in the drought response of plants.

Aquaporins: a vital nexus in H2O2-gasotransmitter signaling

Land plants have evolved with a complex mechanism of water uptake facilitated by the activity of aquaporins under normal and challenging environments. However, we lack a clear understanding of its interactions with reactive oxygen species, particularly hydrogen peroxide (H2O2) and the gasotransmitters nitric oxide (NO) and hydrogen sulfide (H2S), under oxidative stress. Here, we assess the crosstalk of aquaporin function, H2O2 homeostasis, and NO-H2S signaling in plants and provide a computational prediction of cysteine-based oxidative post-translational modifications (oxiPTMs) in plant aquaporins. We propose that aquaporin activity could be regulated by three major oxiPTMs, S-nitrosation, S-sulfenylation, and persulfidation, mediated by NO, H2O2, and H2S, respectively. Therefore, aquaporins might be key players in the gasotransmitter-mediated long-distance oxidative stress signals in plant cells.

ROS are universal cell-to-cell stress signals

The interplay between reactive oxygen species (ROS) and the redox state of cells is deeply rooted in the biology of almost all organisms, regulating development, growth, and responses to the environment. Recent studies revealed that the ROS levels and redox state of one cell can be transmitted, as an information 'state' or 'currency', to other cells and spread by cell-to-cell communication within an entire community of cells or an organism. Here, we discuss the different pathways that mediate cell-to-cell signaling in plants, their hierarchy, and the different mechanisms that transmit ROS/redox signaling between different cells. We further hypothesize that ROS/redox signaling between different organisms could play a key role within the 'one world' principle, impacting human health and our future.

Whole transcriptome sequencing reveals key genes and ceRNA regulatory networks associated with pimpled eggs in hens

Eggshell is one of the most important indicators of egg quality, and due to low shell strength, pimple eggs (PE) are more susceptible to breakage, thus causing huge economic losses to the egg industry. At the current time, the molecular mechanisms that regulate the formation of pimple eggs are poorly understood. In this study, uterine tissues of PE-laying hens (n = 8) and normal egg (NE) -laying hens (n = 8) were analyzed by whole transcriptome sequencing, and a total of 619 differentially expressed mRNAs (DE mRNAs), 122 differentially expressed lncRNAs (DE lncRNAs) and 21 differentially expressed miRNAs (DE miRNAs) were obtained. Based on the targeting relationship among DE mRNAs, DE lncRNAs and DE miRNAs, we constructed a competitive endogenous RNA (ceRNA) network including 12 DE miRNAs, 19 DE lncRNAs, and 128 DE mRNAs. Considering the large amount of information contained in the network, we constructed a smaller ceRNA network to better understand the complex mechanisms of pimple egg formation. The smaller ceRNA network network contains 7 DE lncRNAs (LOC107056551, LOC121109367, LOC121108909, LOC121108862, LOC112530033, LOC121113165, LOC107054145), 5 DE miRNAs (gga-miR-6568-3p, gga-miR-31-5p, gga-miR-18b-3p, gga-miR-1759-3p, gga-miR-12240-3p) and 7 DE mRNAs (CABP1, DNAJC5, HCN3, HPCA, IBSP, KCNT1, OTOP3), and these differentially expressed genes may play key regulatory roles in the formation of pimpled eggs in hens. This study provides the overall expression profiles of mRNAs, lncRNAs and miRNAs in the uterine tissues of hens, which provides a theoretical basis for further research on the molecular mechanisms of pimpled egg formation, and has potential applications in improving eggshell quality.

The ascorbate-glutathione cycle coming of age

Concepts regarding the operation of the ascorbate-glutathione cycle and the associated water/water cycle in the processing of metabolically generated hydrogen peroxide and other forms of reactive oxygen species (ROS) are well established in the literature. However, our knowledge of the functions of these cycles and their component enzymes continues to grow and evolve. Recent insights include participation in the intrinsic environmental and developmental signalling pathways that regulate plant growth, development, and defence. In addition to ROS processing, the enzymes of the two cycles not only support the functions of ascorbate and glutathione, they also have 'moonlighting' functions. They are subject to post-translational modifications and have an extensive interactome, particularly with other signalling proteins. In this assessment of current knowledge, we highlight the central position of the ascorbate-glutathione cycle in the network of cellular redox systems that underpin the energy-sensitive communication within the different cellular compartments and integrate plant signalling pathways.

Evolutionary insights into strategy shifts for the safe and effective accumulation of ascorbate in plants

Plants accumulate high concentrations of ascorbate, commonly in their leaves, as a redox buffer. While ascorbate levels have increased during plant evolution, the mechanisms behind this phenomenon are unclear. Moreover, has the increase in ascorbate concentration been achieved without imposing any detrimental effects on the plants? In this review, we focus on potential transitions in two regulatory mechanisms related to ascorbate biosynthesis and the availability of cellular dehydroascorbate (DHA) during plant evolution. The first transition might be that the trigger for the transcriptional induction of VTC2, which encodes the rate-limiting enzyme in ascorbate biosynthesis, has shifted from oxidative stress (in green algae) to light/photosynthesis (in land plants), probably enabling the continuous accumulation of ascorbate under illumination. This could serve as a preventive system against the unpredictable occurrence of oxidative stress. The second transition might be that DHA-degrading enzymes, which protect cells from the highly reactive DHA in green algae and mosses, have been lost in ferns or flowering plants. Instead, flowering plants may have increased glutathione concentrations to reinforce the DHA reduction capacity, possibly allowing ascorbate accumulation and avoiding the toxicity of DHA. These potential transitions may have contributed to strategies for plants' safe and effective accumulation of ascorbate.

Transcriptome Analysis for Salt-Responsive Genes in Two Different Alfalfa (Medicago sativa L.) Cultivars and Functional Analysis of MsHPCA1

Alfalfa (Medicago sativa L.) is an important forage legume and soil salinization seriously affects its growth and yield. In a previous study, we identified a salt-tolerant variety 'Gongnong NO.1' and a salt-sensitive variety 'Sibeide'. To unravel the molecular mechanism involved in salt stress, we conducted transcriptomic analysis on these two cultivars grown under 0 and 250 mM NaCl treatments for 0, 12, and 24 h. Totals of 336, and 548 differentially expressed genes (DEGs) in response to NaCl were, respectively, identified in the 'Gongnong NO.1' and 'Sibeide' varieties. The Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) pathway enrichment analysis showed that the DEGs were classified in carbohydrate metabolism, energy production, transcription factor, and stress-associated pathway. Expression of MsHPCA1, encoding a putative H2O2 receptor, was responsive to both NaCl and H2O2 treatment. MsHPCA1 was localized in cell membrane and overexpression of MsHPCA1 in alfalfa increased salt tolerance and H2O2 content. This study will provide new gene resources for the improvement in salt tolerance in alfalfa and legume crops, which has important theoretical significance and potential application value.

Propagation of a rapid cell-to-cell H2O2 signal over long distances in a monolayer of cardiomyocyte cells

Cell-to-cell communication plays a cardinal role in the biology of multicellular organisms. H2O2 is an important cell-to-cell signaling molecule involved in the response of mammalian cells to wounding and other stimuli. We previously identified a signaling pathway that transmits wound-induced cell-to-cell H2O2 signals within minutes over long distances, measured in centimeters, in a monolayer of cardiomyocytes. Here we report that this long-distance H2O2 signaling pathway is accompanied by enhanced accumulation of cytosolic H2O2 and altered redox state in cells along its path. We further show that it requires the production of superoxide, as well as the function of gap junctions, and that it is accompanied by changes in the abundance of hundreds of proteins in cells along its path. Our findings highlight the existence of a unique and rapid long-distance H2O2 signaling pathway that could play an important role in different inflammatory responses, wound responses/healing, cardiovascular disease, and/or other conditions.

The function of sphingolipids in membrane trafficking and cell signaling in plants, in comparison with yeast and animal cells

Sphingolipids are essential membrane components involved in a wide range of cellular, developmental and signaling processes. Sphingolipids are so essential that knock-out mutation often leads to lethality. In recent years, conditional or weak allele mutants as well as the broadening of the pharmacological catalog allowed to decipher sphingolipid function more precisely in a less invasive way. This review intends to provide a discussion and point of view on the function of sphingolipids with a main focus on endomembrane trafficking, Golgi-mediated protein sorting, cell polarity, cell-to-cell communication and cell signaling at the plasma membrane. While our main angle is the plant field research, we will constantly refer to and compare with the advances made in the yeast and animal field. In this review, we will emphasize the role of sphingolipids not only as a membrane component, but also as a key player at a center of homeostatic regulatory networks involving direct or indirect interaction with other lipids, proteins and ion fluxes.

Systemic stomatal responses in plants: Coordinating development, stress, and pathogen defense under a changing climate

To successfully survive, develop, grow and reproduce, multicellular organisms must coordinate their molecular, physiological, developmental and metabolic responses among their different cells and tissues. This process is mediated by cell-to-cell, vascular and/or volatile communication, and involves electric, chemical and/or hydraulic signals. Within this context, stomata serve a dual role by coordinating their responses to the environment with their neighbouring cells at the epidermis, but also with other stomata present on other parts of the plant. As stomata represent one of the most important conduits between the plant and its above-ground environment, as well as directly affect photosynthesis, respiration and the hydraulic status of the plant by controlling its gas and vapour exchange with the atmosphere, coordinating the overall response of stomata within and between different leaves and tissues plays a cardinal role in plant growth, development and reproduction. Here, we discuss different examples of local and systemic stomatal coordination, the different signalling pathways that mediate them, and the importance of systemic stomatal coordination to our food supply, ecosystems and weather patterns, under our changing climate. We further discuss the potential biotechnological implications of regulating systemic stomatal responses for enhancing agricultural productivity in a warmer and CO2 -rich environment.

Calcium-Mediated Modulation of GC Switch Regulates Peroxisomal H2O2 Levels in Response to Wounding in Plants

Ca2+ and H2O2 interact with each other to regulate plant systemic responses. However, their precise mechanism is not fully understood. A recent study revealed that the Ca2+ regulates the glycolate oxidase-catalase (GC) switch-mediated photorespiratory H2O2 during wounding. Glutamate-receptor-like (GLR) Ca2+ channels (GLR 3.3 and GLR3.6) are responsible for Ca2+ influx during injury for regulation of the GC switch. Mechanical injury quickly shifts the GC switch to a highly interactive state in the systemic leaves that ultimately results in the reduced peroxisomal H2O2. However, the mechanism of H2O2 reduction in peroxisome remains elusive.

Reactive oxygen species: Multidimensional regulators of plant adaptation to abiotic stress and development

Reactive oxygen species (ROS) are produced as undesirable by-products of metabolism in various cellular compartments, especially in response to unfavorable environmental conditions, throughout the life cycle of plants. Stress-induced ROS production disrupts normal cellular function and leads to oxidative damage. To cope with excessive ROS, plants are equipped with a sophisticated antioxidative defense system consisting of enzymatic and non-enzymatic components that scavenge ROS or inhibit their harmful effects on biomolecules. Nonetheless, when maintained at relatively low levels, ROS act as signaling molecules that regulate plant growth, development, and adaptation to adverse conditions. Here, we provide an overview of current approaches for detecting ROS. We also discuss recent advances in understanding ROS signaling, ROS metabolism, and the roles of ROS in plant growth and responses to various abiotic stresses.

Green leaf volatiles co-opt proteins involved in molecular pattern signalling in plant cells

The green leaf volatiles (GLVs) Z-3-hexen-1-ol (Z3-HOL) and Z-3-hexenyl acetate (Z3-HAC) are airborne infochemicals released from damaged plant tissues that induce defenses and developmental responses in receiver plants, but little is known about their mechanism of action. We found that Z3-HOL and Z3-HAC induce similar but distinctive physiological and signaling responses in tomato seedlings and cell cultures. In seedlings, Z3-HAC showed a stronger root growth inhibition effect than Z3-HOL. In cell cultures, the two GLVs induced distinct changes in MAP kinase (MAPK) activity and proton fluxes as well as rapid and massive changes in the phosphorylation status of proteins within 5 min. Many of these phosphoproteins are involved in reprogramming the proteome from cellular homoeostasis to stress and include pattern recognition receptors, a receptor-like cytoplasmic kinase, MAPK cascade components, calcium signaling proteins and transcriptional regulators. These are well-known components of damage-associated molecular pattern (DAMP) signaling pathways. These rapid changes in the phosphoproteome may underly the activation of defense and developmental responses to GLVs. Our data provide further evidence that GLVs function like DAMPs and indicate that GLVs coopt DAMP signaling pathways.

A general concept of quantitative abiotic stress sensing

Plants often encounter stress in their environment. For appropriate responses to particular stressors, cells rely on sensory mechanisms that detect emerging stress. Considering sensor and signal amplification characteristics, a single sensor system hardly covers the entire stress range encountered by plants (e.g., salinity, drought, temperature stress). A dual system comprising stress-specific sensors and a general quantitative stress sensory system is proposed to enable the plant to optimize its response. The quantitative stress sensory system exploits the redox and reactive oxygen species (ROS) network by altering the oxidation and reduction rates of individual redox-active molecules under stress impact. The proposed mechanism of quantitative stress sensing also fits the requirement of dealing with multifactorial stress conditions.

Ca2+/calmodulin-mediated desensitization of glutamate receptors shapes plant systemic wound signalling and anti-herbivore defence

Plants rely on systemic signalling mechanisms to establish whole-body defence in response to insect and nematode attacks. GLUTAMATE RECEPTOR-LIKE (GLR) genes have been implicated in long-distance transmission of wound signals to initiate the accumulation of the defence hormone jasmonate (JA) at undamaged distal sites. The systemic signalling entails the activation of Ca2+-permeable GLR channels by wound-released glutamate, triggering membrane depolarization and cytosolic Ca2+ influx throughout the whole plant. The systemic electrical and calcium signals rapidly dissipate to restore the resting state, partially due to desensitization of the GLR channels. Here we report the discovery of calmodulin-mediated, Ca2+-dependent desensitization of GLR channels, revealing a negative feedback loop in the orchestration of plant systemic wound responses. A CRISPR-engineered GLR3.3 allele with impaired desensitization showed prolonged systemic electrical signalling and Ca2+ waves, leading to enhanced plant defence against herbivores. Moreover, this Ca2+/calmodulin-mediated desensitization of GLR channels is a highly conserved mechanism in plants, providing a potential target for engineering anti-herbivore defence in crops.

S-nitrosylation switches the Arabidopsis redox sensor protein, QSOX1, from an oxidoreductase to a molecular chaperone under heat stress

The Arabidopsis quiescin sulfhydryl oxidase 1 (QSOX1) thiol-based redox sensor has been identified as a negative regulator of plant immunity. Here, we have found that small molecular weight proteins of QSOX1 were converted to high molecular weight (HMW) complexes upon exposure to heat stress and that this was accompanied by a switch in QSOX1 function from a thiol-reductase to a molecular chaperone. Plant treatment with S-nitrosoglutathione (GSNO), which causes nitrosylation of cysteine residues (S-nitrosylation), but not with H2O2, induced HMW QSOX1 complexes. Thus, functional switching of QSOX1 is induced by GSNO treatment. Accordingly, simultaneous treatment of plants with heat shock and GSNO led to a significant increase in QSOX1 chaperone activity by increasing its oligomerization. Consequently, transgenic Arabidopsis overexpressing QSOX1 (QSOX1OE) showed strong resistance to heat shock, whereas qsox1 knockout plants exhibited high sensitivity to heat stress. Plant treatment with GSNO under heat stress conditions increased their resistance to heat shock. We conclude that S-nitrosylation allows the thiol-based redox sensor, QSOX1, to respond to various external stresses in multiple ways.

Small holes, big impact: Stomata in plant-pathogen-climate epic trifecta

The regulation of stomatal aperture opening and closure represents an evolutionary battle between plants and pathogens, characterized by adaptive strategies that influence both plant resistance and pathogen virulence. The ongoing climate change introduces further complexity, affecting pathogen invasion and host immunity. This review delves into recent advances on our understanding of the mechanisms governing immunity-related stomatal movement and patterning with an emphasis on the regulation of stomatal opening and closure dynamics by pathogen patterns and host phytocytokines. In addition, the review explores how climate changes impact plant-pathogen interactions by modulating stomatal behavior. In light of the pressing challenges associated with food security and the unpredictable nature of climate changes, future research in this field, which includes the investigation of spatiotemporal regulation and engineering of stomatal immunity, emerges as a promising avenue for enhancing crop resilience and contributing to climate control strategies.

CPK12 and Ca2+-mediated hypoxia signaling

Hypoxia triggers reactive oxygen species (ROS)-induced elevation in cytoplasmic calcium (Ca2+) in the plant cells. Calcium-dependent protein kinase 12 (CPK12) acts as a sensor to recognize the Ca2+ signature and is activated by autophosphorylation. Then, the CPK12 moves into the nucleus with the help of phosphatidic acid (PA) and phosphorylates ERF-VII family proteins that activate hypoxia signaling and response. The study provides a novel mechanism of hypoxia signaling in plants. Moreover, the mechanism of hypoxia-specific Ca2+ signature generation remains elusive.

Propagation of a rapid cell-to-cell H 2 O 2 signal over long distances in a monolayer of cardiomyocyte cells

Cell-to-cell communication plays a cardinal role in the biology of multicellular organisms. H 2 O 2 is an important cell-to-cell signaling molecule involved in the response of mammalian cells to wounding and other stimuli. We previously identified a signaling pathway that transmits wound-induced cell-to-cell H 2 O 2 signals within minutes over long distances, measured in centimeters, in a monolayer of cardiomyocytes. Here we report that this long-distance H 2 O 2 signaling pathway is accompanied by enhanced accumulation of cytosolic H 2 O 2 and altered redox state in cells along its path. We further show that it requires the production of superoxide, as well as the function of gap junctions, and that it is accompanied by changes in the abundance of hundreds of proteins in cells along its path. Our findings highlight the existence of a unique and rapid long-distance H 2 O 2 signaling pathway that could play an important role in different inflammatory responses, wound responses/healing, cardiovascular disease, and/or other conditions.

Highlights

Wounding induces an H 2 O 2 cell-to-cell signal in a monolayer of cardiomyocytes. The cell-to-cell signal requires H 2 O 2 and O 2 · - accumulation along its path. The signal propagates over several centimeters changing the redox state of cells.Changes in the abundance of hundreds of proteins accompanies the signal.The cell-to-cell signal requires paracrine and juxtacrine signaling.

Wounding induces a peroxisomal H2 O2 decrease via glycolate oxidase-catalase switch dependent on glutamate receptor-like channel-supported Ca2+ signaling in plants

Sensing of environmental challenges, such as mechanical injury, by a single plant tissue results in the activation of systemic signaling, which attunes the plant's physiology and morphology for better survival and reproduction. As key signals, both calcium ions (Ca2+ ) and hydrogen peroxide (H2 O2 ) interplay with each other to mediate plant systemic signaling. However, the mechanisms underlying Ca2+ -H2 O2 crosstalk are not fully revealed. Our previous study showed that the interaction between glycolate oxidase and catalase, key enzymes of photorespiration, serves as a molecular switch (GC switch) to dynamically modulate photorespiratory H2 O2 fluctuations via metabolic channeling. In this study, we further demonstrate that local wounding induces a rapid shift of the GC switch to a more interactive state in systemic leaves, resulting in a sharp decrease in peroxisomal H2 O2 levels, in contrast to a simultaneous outburst of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-derived apoplastic H2 O2 . Moreover, the systemic response of the two processes depends on the transmission of Ca2+ signaling, mediated by glutamate-receptor-like Ca2+ channels 3.3 and 3.6. Mechanistically, by direct binding and/or indirect mediation by some potential biochemical sensors, peroxisomal Ca2+ regulates the GC switch states in situ, leading to changes in H2 O2 levels. Our findings provide new insights into the functions of photorespiratory H2 O2 in plant systemic acclimation and an optimized systemic H2 O2 signaling via spatiotemporal interplay between the GC switch and NADPH oxidases.

Rapid systemic responses of Arabidopsis to waterlogging stress

Waterlogging stress (WLS) negatively impacts the growth and yield of crops resulting in heavy losses to agricultural production. Previous studies have revealed that WLS induces a systemic response in shoots that is partially dependent on the plant hormones ethylene and abscisic acid. However, the role of rapid cell-to-cell signaling pathways, such as the reactive oxygen species (ROS) and calcium waves, in systemic responses of plants to WLS is unknown at present. Here, we reveal that an abrupt WLS treatment of Arabidopsis (Arabidopsis thaliana) plants growing in peat moss triggers systemic ROS and calcium wave responses and that the WLS-triggered ROS wave response of Arabidopsis is dependent on the ROS-generating RESPIRATORY BURST OXIDASE HOMOLOG D (RBOHD), calcium-permeable channels GLUTAMATE-LIKE RECEPTOR 3.3 and 3.6 (GLR3.3 and GLR3.6), and aquaporin PLASMA MEMBRANE INTRINSIC PROTEIN 2;1 (PIP2;1) proteins. We further show that WLS is accompanied by a rapid systemic transcriptomic response that is evident as early as 10 min following waterlogging initiation, includes many hypoxia-response transcripts, and is partially dependent on RBOHD. Interestingly, the abrupt WLS of Arabidopsis resulted in the triggering of a rapid hydraulic wave response and the transient opening of stomata on leaves. In addition, it induced in plants a heightened state of tolerance to a subsequent submergence stress. Taken together, our findings reveal that the initiation of WLS in plants is accompanied by rapid systemic physiological and transcriptomic responses that involve the ROS, calcium, and hydraulic waves, as well as the induction of hypoxia acclimation mechanisms in systemic tissues.

Extra- and intranuclear heat perception and triggering mechanisms in plants

The escalating impact of global warming on crop yield and quality poses a significant threat to future food supplies. Breeding heat-resistant crop varieties holds promise, but necessitates a deeper understanding of the molecular mechanisms underlying plant heat tolerance. Recent studies have shed light on the initial events of heat perception in plants. In this review, we provide a comprehensive summary of the recent progress made in unraveling the mechanisms of heat perception and response in plants. Calcium ion (Ca2+), hydrogen peroxide (H2O2), and nitric oxide (NO) have emerged as key participants in heat perception. Furthermore, we discuss the potential roles of the NAC transcription factor NTL3, thermo-tolerance 3.1 (TT3.1), and Target of temperature 3 (TOT3) as thermosensors associated with the plasma membrane. Additionally, we explore the involvement of cytoplasmic HISTONE DEACETYLASE 9 (HDA9), mRNA encoding the phytochrome-interacting factor 7 (PIF7), and chloroplasts in mediating heat perception. This review also highlights the role of intranuclear transcriptional condensates formed by phytochrome B (phyB), EARLY FLOWERING 3 (ELF3), and guanylate-binding protein (GBP)-like GTPase 3 (GBPL3) in heat perception. Finally, we raise the unresolved questions in the field of heat perception that require further investigation in the future.