The Calcineurin B-like calcium sensors CBL1 and CBL9 together with their interacting protein kinase CIPK26 regulate the Arabidopsis NADPH oxidase RBOHF

The role of CBL-CIPK signaling in plant responses to biotic and abiotic stresses

Plants have a variety of regulatory mechanisms to perceive, transduce, and respond to biotic and abiotic stress. One such mechanism is the calcium-sensing CBL-CIPK system responsible for the sensing of specific stressors, such as drought or pathogens. CBLs perceive and bind Calcium (Ca2+) in response to stress and then interact with CIPKs to form an activated complex. This leads to the phosphorylation of downstream targets, including transporters and ion channels, and modulates transcription factor levels and the consequent levels of stress-associated genes. This review describes the mechanisms underlying the response of the CBL-CIPK pathway to biotic and abiotic stresses, including regulating ion transport channels, coordinating plant hormone signal transduction, and pathways related to ROS signaling. Investigation of the function of the CBL-CIPK pathway is important for understanding plant stress tolerance and provides a promising avenue for molecular breeding.

Integrative regulatory mechanisms of stomatal movements under changing climate

Global climate change-caused drought stress, high temperatures and other extreme weather profoundly impact plant growth and development, restricting sustainable crop production. To cope with various environmental stimuli, plants can optimize the opening and closing of stomata to balance CO2 uptake for photosynthesis and water loss from leaves. Guard cells perceive and integrate various signals to adjust stomatal pores through turgor pressure regulation. Molecular mechanisms and signaling networks underlying the stomatal movements in response to environmental stresses have been extensively studied and elucidated. This review focuses on the molecular mechanisms of stomatal movements mediated by abscisic acid, light, CO2 , reactive oxygen species, pathogens, temperature, and other phytohormones. We discussed the significance of elucidating the integrative mechanisms that regulate stomatal movements in helping design smart crops with enhanced water use efficiency and resilience in a climate-changing world.

The WRKY46-MYC2 module plays a critical role in E-2-hexenal-induced anti-herbivore responses by promoting flavonoid accumulation

Volatile organic compounds (VOCs) play key roles in plant-plant communication, especially in response to pest attack. E-2-hexenal is an important component of VOCs, but it is unclear whether it can induce endogenous plant resistance to insects. Here, we show that E-2-hexenal activates early signaling events in Arabidopsis (Arabidopsis thaliana) mesophyll cells, including an H2O2 burst at the plasma membrane, the directed flow of calcium ions, and an increase in cytosolic calcium concentration. Treatment of wild-type Arabidopsis plants with E-2-hexenal increases their resistance when challenged with the diamondback moth Plutella xylostella L., and this phenomenon is largely lost in the wrky46 mutant. Mechanistically, E-2-hexenal induces the expression of WRKY46 and MYC2, and the physical interaction of their encoded proteins was verified by yeast two-hybrid, firefly luciferase complementation imaging, and in vitro pull-down assays. The WRKY46-MYC2 complex directly binds to the promoter of RBOHD to promote its expression, as demonstrated by luciferase reporter, yeast one-hybrid, chromatin immunoprecipitation, and electrophoretic mobility shift assays. This module also positively regulates the expression of E-2-hexenal-induced naringenin biosynthesis genes (TT4 and CHIL) and the accumulation of total flavonoids, thereby modulating plant tolerance to insects. Together, our results highlight an important role for the WRKY46-MYC2 module in the E-2-hexenal-induced defense response of Arabidopsis, providing new insights into the mechanisms by which VOCs trigger plant defense responses.

Calcineurin B-like protein ZmCBL8-1 promotes salt stress resistance in Arabidopsis

MAIN CONCLUSION

ZmCBL8-1 enhances salt stress tolerance in maize by improving the antioxidant system to neutralize ROS homeostasis and inducing Na+/H+ antiporter gene expressions of leaves. Calcineurin B-like proteins (CBLs) as plant-specific calcium sensors have been explored for their roles in the regulation of abiotic stress tolerance. Further, the functional variations in ZmCBL8, encoding a component of the salt overly sensitive pathway, conferred the salt stress tolerance in maize. ZmCBL8-1 is a transcript of ZmCBL8 found in maize, but its function in the salt stress response is still unclear. The present study aimed to characterize the protein ZmCBL8-1 that was determined to be composed of 194 amino acids (aa) with three conserved EF hands responsible for binding Ca2+. However, a 20-aa fragment was found to be missing from its C-terminus relative to another transcript of ZmCBL8. Results indicated that it harbored a dual-lipid modification motif MGCXXS at its N-terminus and was located on the cell membrane. The accumulation of ZmCBL8-1 transcripts was high in the roots but relatively lower in the leaves of maize under normal condition. In contrast, its expression was significantly decreased in the roots, while increased in the leaves under NaCl treatment. The overexpression of ZmCBL8-1 resulted in higher salt stress resistance of transgenic Arabidopsis in a Ca2+-dependent manner relative to that of the wild type (WT). In ZmCBL8-1-overexpressing plants exposed to NaCl, the contents of malondialdehyde and hydrogen peroxide were decreased in comparison with those in the WT, and the expression of key genes involved in the antioxidant defense system and Na+/H+ antiporter were upregulated. These results suggested that ZmCBL8-1 played a positive role in the response of leaves to salt stress by inducing the expression of Na+/H+ antiporter genes and enhancing the antioxidant system to neutralize the accumulation of reactive oxygen species. These observations further indicate that ZmCBL8-1 confers salt stress tolerance, suggesting that transcriptional regulation of the ZmCBL8 gene is important for salt tolerance.

Calcium binding of AtCBL1: Structural and functional insights

CBL1 is an EF hand Ca2+ binding protein from A. thaliana that is involved in the detection of cellular Ca2+ signals and the downstream signal transmission by interaction with the protein kinase CIPK23. So far, the structure and calcium ion binding affinities of CBL1 remain elusive. In this study it was observed that CBL1 tends to form higher oligomeric states due to an intrinsic hydrophobicity and the presence of the detergent BriJ35 was required for the purification of monomeric and functional protein. Functional insights into the in vitro Ca2+ binding capabilities of CBL1 were obtained by isothermal titration calorimetry (ITC) of the wildtype protein as well as single site EF hand mutants. Based on our results, a binding model of CBL1 for Ca2+in vivo is proposed. Additionally, upon both, ITC measurements and the analysis of an AlphaFold2 model of CBL1, we could gain first insights into the formation of the dimer interface. We could identify an area around EF hand 4 to be relevant for the structural and functional integrity of monomeric CBL1 and likely EF hand 1 to be involved in the dimer interface.

Genome-wide analysis of respiratory burst oxidase homolog gene family in pea (Pisum sativum L.)

Plant respiratory burst oxidase homologs (RBOHs) are key enzymes regulating superoxide production, which is important for plant development and responses to biotic and abiotic stresses. This study aimed to characterize the RBOH gene family in pea (Pisum sativum L.). Seven PsRBOH genes were identified in the pea genome and were phylogenetically clustered into five groups. Collinearity analyses of the RBOHs identified four pairs of orthologs between pea and soybean. The gene structure analysis showed that the number of exons ranged from 6 to 16. Amino acid sequence alignment, conserved domain, and conserved motif analyses showed that all seven PsRBOHs had typical features of plant RBOHs. The expression patterns of PsRBOH genes in different tissues provided suggested their roles in plant growth and organ development. In addition, the expression levels of PsRBOH genes under different abiotic stresses were analyzed via reverse transcription-quantitative polymerase chain reaction (RT-qPCR). The results demonstrated that PsRBOH genes exhibited unique stress-response characteristics, which allowed for functional diversity in response to different abiotic stresses. Furthermore, four PsRBOHs had a high probability of localization in the plasma membrane, and PsRBOH6 was localized to the plasma membrane and endoplasmic reticulum. The results of this study provide valuable information for further functional analysis of pea RBOH genes and their role in plant adaptation to climate-driven environmental constraints.

The Roles of Calcineurin B-like Proteins in Plants under Salt Stress

Salinity stands as a significant environmental stressor, severely impacting crop productivity. Plants exposed to salt stress undergo physiological alterations that influence their growth and development. Meanwhile, plants have also evolved mechanisms to endure the detrimental effects of salinity-induced salt stress. Within plants, Calcineurin B-like (CBL) proteins act as vital Ca2+ sensors, binding to Ca2+ and subsequently transmitting signals to downstream response pathways. CBLs engage with CBL-interacting protein kinases (CIPKs), forming complexes that regulate a multitude of plant growth and developmental processes, notably ion homeostasis in response to salinity conditions. This review introduces the repercussions of salt stress, including osmotic stress, diminished photosynthesis, and oxidative damage. It also explores how CBLs modulate the response to salt stress in plants, outlining the functions of the CBL-CIPK modules involved. Comprehending the mechanisms through which CBL proteins mediate salt tolerance can accelerate the development of cultivars resistant to salinity.

Enhanced Ca2+ binding to EF-hands through phosphorylation of conserved serine residues activates MpRBOHB and chitin-triggered ROS production

NADPH oxidases/RBOHs catalyze apoplastic ROS production and act as key signaling nodes, integrating multiple signal transduction pathways regulating plant development and stress responses. Although RBOHs have been suggested to be activated by Ca2+ binding and phosphorylation by various protein kinases, a mechanism linking Ca2+ binding and phosphorylation in the activity regulation remained elusive. Chitin-triggered ROS production required cytosolic Ca2+ elevation and Ca2+ binding to MpRBOHB in a liverwort Marchantia polymorpha. Heterologous expression analysis of truncated variants revealed that a segment of the N-terminal cytosolic region highly conserved among land plant RBOHs encompassing the two EF-hand motifs is essential for the activation of MpRBOHB. Within the conserved regulatory domain, we have identified two Ser residues whose phosphorylation is critical for the activation in planta. Isothermal titration calorimetry analyses revealed that phosphorylation of the two Ser residues increased the Ca2+ binding affinity of MpRBOHB, while Ca2+ binding is indispensable for the activation, even if the two Ser residues are phosphorylated. Our findings shed light on a mechanism through which phosphorylation potentiates the Ca2+ -dependent activation of MpRBOHB, emphasizing the pivotal role of Ca2+ binding in mediating the Ca2+ and phosphorylation-driven activation of MpRBOHB, which is likely to represent a fundamental mechanism conserved among land plant RBOHs.

ROS interplay between plant growth and stress biology: Challenges and future perspectives

In plants, reactive oxygen species (ROS) have emerged as a multifunctional signaling molecules that modulate diverse stress and growth responses. Earlier studies on ROS in plants primarily focused on its toxicity and ROS-scavenging processes, but recent findings are offering new insights on its role in signal perception and transduction. Further, the interaction of cell wall receptors, calcium channels, HATPase, protein kinases, and hormones with NADPH oxidases (respiratory burst oxidase homologues (RBOHs), provides concrete evidence that ROS regulates major signaling cascades in different cellular compartments related to stress and growth responses. However, at the molecular level there are many knowledge gaps regarding how these players influence ROS signaling and how ROS regulate them during growth and stress events. Furthermore, little is known about how plant sensors or receptors detect ROS under various environmental stresses and induce subsequent signaling cascades. In light of this, we provided an update on the role of ROS signaling in plant growth and stress biology. First, we focused on ROS signaling, its production and regulation by cell wall receptor like kinases. Next, we discussed the interplay between ROS, calcium and hormones, which forms a major signaling trio regulatory network of signal perception and transduction. We also provided an overview on ROS and nitric oxide (NO) crosstalk. Furthermore, we emphasized the function of ROS signaling in biotic, abiotic and mechanical stresses, as well as in plant growth and development. Finally, we conclude by highlighting challenges and future perspectives of ROS signaling in plants that warrants future investigation.

The CBL-CIPK network is involved in the physiological crosstalk between plant growth and stress adaptation

Plants have evolved to deal with different stresses during plant growth, relying on complex interactions or crosstalk between multiple signalling pathways in plant cells. In this sophisticated regulatory network, Ca2+ transients in the cytosol ([Ca2+ ]cyt ) act as major physiological signals to initiate appropriate responses. The CALCINEURIN B-LIKE PROTEIN (CBL)-CBL-INTERACTING PROTEIN KINASE (CIPK) network relays physiological signals characterised by [Ca2+ ]cyt transients during plant development and in response to environmental changes. Many studies are aimed at elucidating the role of the CBL-CIPK network in plant growth and stress responses. This review discusses the involvement of the CBL-CIPK pathways in two levels of crosstalk between plant development and stress adaptation: direct crosstalk through interaction with regulatory proteins, and indirect crosstalk through adaptation of correlated physiological processes that affect both plant development and stress responses. This review thus provides novel insights into the physiological roles of the CBL-CIPK network in plant growth and stress adaptation.

Defense Strategies of Rice in Response to the Attack of the Herbivorous Insect, Chilo suppressalis

Chilo suppressalis is a notorious pest that attacks rice, feeding throughout the entire growth period of rice and posing a serious threat to rice production worldwide. Due to the boring behavior and overlapping generations of C. suppressalis, the pest is difficult to control. Moreover, no rice variety with high resistance to the striped stem borer (SSB) has been found in the available rice germplasm, which also poses a challenge to controlling the SSB. At present, chemical control is widely used in agricultural production to manage the problem, but its effect is limited and it also pollutes the environment. Therefore, developing genetic resistance is the only way to avoid the use of chemical insecticides. This article primarily focuses on the research status of the induced defense of rice against the SSB from the perspective of immunity, in which plant hormones (such as jasmonic acid and ethylene) and mitogen-activated protein kinases (MAPKs) play an important role in the immune response of rice to the SSB. The article also reviews progress in using transgenic technology to study the relationship between rice and the SSB as well as exploring the resistance genes. Lastly, the article discusses prospects for future research on rice's resistance to the SSB.

Genome-wide identification of TaCIPK gene family members in wheat and their roles in host response to Blumeria graminis f. sp. tritici infection

Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is a destructive disease affecting wheat crops worldwide. Functional genes can be activated in response to Bgt inoculations. Calcineurin B-like protein (CBL) together with CBL-interacting protein kinase (CIPK) forms the CBL-CIPK protein complex that participates in Ca2+ sensor kinase-related signaling pathways responding to abiotic and biotic stresses. In this study, we performed a genome-wide screening and identified 27 CIPK subfamilies (123 CIPK transcripts, TaCIPKs) including 55 new and 47 updated TaCIPKs in wheat. Phylogenetic analysis revealed that 123 TaCIPKs could be divided into four groups. Segmental duplications and tandem repeats promoted the expansion of the TaCIPK family. Gene function was further evidenced by differences in gene structure, cis-elements, and protein domains. TaCIPK15-4A was cloned in this study. TaCIPK15-4A contained 17 serine, seven tyrosine, and 15 threonine phosphorylation sites and localized in the plasma membrane and cytoplasm. TaCIPK15-4A expression was induced after Bgt inoculation. Virus-induced gene silencing and overexpression experiments indicated that TaCIPK15-4A could play a positive role in wheat disease resistance to Bgt. Overall, these results provide insights into the role of the TaCIPK gene family in wheat resistance and could be beneficial for further research to prevent Bgt infection.

Coping with the cold: unveiling cryoprotectants, molecular signaling pathways, and strategies for cold stress resilience

Low temperature stress significantly threatens crop productivity and economic sustainability. Plants counter this by deploying advanced molecular mechanisms to perceive and respond to cold stress. Transmembrane proteins initiate these responses, triggering a series of events involving secondary messengers such as calcium ions (Ca2+), reactive oxygen species (ROS), and inositol phosphates. Of these, calcium signaling is paramount, activating downstream phosphorylation cascades and the transcription of cold-responsive genes, including cold-regulated (COR) genes. This review focuses on how plants manage freeze-induced damage through dual strategies: cold tolerance and cold avoidance. Tolerance mechanisms involve acclimatization to decreasing temperatures, fostering gradual accumulation of cold resistance. In contrast, avoidance mechanisms rely on cryoprotectant molecules like potassium ions (K+), proline, glycerol, and antifreeze proteins (AFPs). Cryoprotectants modulate intracellular solute concentration, lower the freezing point, inhibit ice formation, and preserve plasma membrane fluidity. Additionally, these molecules demonstrate antioxidant activity, scavenging ROS, preventing protein denaturation, and subsequently mitigating cellular damage. By forming extensive hydrogen bonds with water molecules, cryoprotectants also limit intercellular water movement, minimizing extracellular ice crystal formation, and cell dehydration. The deployment of cryoprotectants is a key adaptive strategy that bolsters plant resilience to cold stress and promotes survival in freezing environments. However, the specific physiological and molecular mechanisms underlying these protective effects remain insufficiently understood. Therefore, this review underscores the need for further research to elucidate these mechanisms and assess their potential impact on crop productivity and sustainability, contributing to the progressive discourse in plant biology and environmental science.

A novel effector RipBT contributes to Ralstonia solanacearum virulence on potato

Ralstonia solanacearum is one of the most destructive plant-pathogenic bacteria, infecting more than 200 plant species, including potato (Solanum tuberosum) and many other solanaceous crops. R. solanacearum has numerous pathogenicity factors, and type III effectors secreted through type III secretion system (T3SS) are key factors to counteract host immunity. Here, we show that RipBT is a novel T3SS-secreted effector by using a cyaA reporter system. Transient expression of RipBT in Nicotiania benthamiana induced strong cell death in a plasma membrane-localization dependent manner. Notably, mutation of RipBT in R. solanacearum showed attenuated virulence on potato, while RipBT transgenic potato plants exhibited enhanced susceptibility to R. solanacearum. Interestingly, transcriptomic analyses suggest that RipBT may interfere with plant reactive oxygen species (ROS) metabolism during the R. solanacearum infection of potato roots. In addition, the expression of RipBT remarkably suppressed the flg22-induced pathogen-associated molecular pattern-triggered immunity responses, such as the ROS burst. Taken together, RipBT acts as a T3SS effector, promoting R. solanacearum infection on potato and presumably disturbing ROS homeostasis.

Fruit crops combating drought: Physiological responses and regulatory pathways

Drought is a common stress in agricultural production. Thus, it is imperative to understand how fruit crops respond to drought and to develop drought-tolerant varieties. This paper provides an overview of the effects of drought on the vegetative and reproductive growth of fruits. We summarize the empirical studies that have assessed the physiological and molecular mechanisms of the drought response in fruit crops. This review focuses on the roles of calcium (Ca2+) signaling, abscisic acid (ABA), reactive oxygen species signaling, and protein phosphorylation underlying the early drought response in plants. We review the resulting downstream ABA-dependent and ABA-independent transcriptional regulation in fruit crops under drought stress. Moreover, we highlight the positive and negative regulatory mechanisms of microRNAs in the drought response of fruit crops. Lastly, strategies (including breeding and agricultural practices) to improve the drought resistance of fruit crops are outlined.

Soybean Root Transcriptomics: Insights into Sucrose Signaling at the Crossroads of Nutrient Deficiency and Biotic Stress Responses

Soybean (Glycine max) is an important agricultural crop, but nutrient deficiencies frequently limit soybean production. While research has advanced our understanding of plant responses to long-term nutrient deficiencies, less is known about the signaling pathways and immediate responses to certain nutrient deficiencies, such as P_i and Fe deficiencies. Recent studies have shown that sucrose acts as a long-distance signal that is sent in increased concentrations from the shoot to the root in response to various nutrient deficiencies. Here, we mimicked nutrient deficiency-induced sucrose signaling by adding sucrose directly to the roots. To unravel transcriptomic responses to sucrose acting as a signal, we performed Illumina RNA-sequencing of soybean roots treated with sucrose for 20 min and 40 min, compared to non-sucrose-treated controls. We obtained a total of 260 million paired-end reads, mapping to 61,675 soybean genes, some of which are novel (not yet annotated) transcripts. Of these, 358 genes were upregulated after 20 min, and 2416 were upregulated after 40 min of sucrose exposure. GO (gene ontology) analysis revealed a high proportion of sucrose-induced genes involved in signal transduction, particularly hormone, ROS (reactive oxygen species), and calcium signaling, in addition to regulation of transcription. In addition, GO enrichment analysis indicates that sucrose triggers crosstalk between biotic and abiotic stress responses.

SEC14-GOLD protein PATELLIN2 binds IRON-REGULATED TRANSPORTER1 linking root iron uptake to vitamin E

Organisms require micronutrients, and Arabidopsis (Arabidopsis thaliana) IRON-REGULATED TRANSPORTER1 (IRT1) is essential for iron (Fe2+) acquisition into root cells. Uptake of reactive Fe2+ exposes cells to the risk of membrane lipid peroxidation. Surprisingly little is known about how this is avoided. IRT1 activity is controlled by an intracellular variable region (IRT1vr) that acts as a regulatory protein interaction platform. Here, we describe that IRT1vr interacted with peripheral plasma membrane SEC14-Golgi dynamics (SEC14-GOLD) protein PATELLIN2 (PATL2). SEC14 proteins bind lipophilic substrates and transport or present them at the membrane. To date, no direct roles have been attributed to SEC14 proteins in Fe import. PATL2 affected root Fe acquisition responses, interacted with ROS response proteins in roots, and alleviated root lipid peroxidation. PATL2 had high affinity in vitro for the major lipophilic antioxidant vitamin E compound α-tocopherol. Molecular dynamics simulations provided insight into energetic constraints and the orientation and stability of the PATL2-ligand interaction in atomic detail. Hence, this work highlights a compelling mechanism connecting vitamin E with root metal ion transport at the plasma membrane with the participation of an IRT1-interacting and α-tocopherol-binding SEC14 protein.

Abscisic acid increases hydrogen peroxide in mitochondria to facilitate stomatal closure

Abscisic acid (ABA) drives stomatal closure to minimize water loss due to transpiration in response to drought. We examined the subcellular location of ABA-increased accumulation of reactive oxygen species (ROS) in guard cells, which drive stomatal closure, in Arabidopsis (Arabidopsis thaliana). ABA-dependent increases in fluorescence of the generic ROS sensor, dichlorofluorescein (DCF), were observed in mitochondria, chloroplasts, cytosol, and nuclei. The ABA response in all these locations was lost in an ABA-insensitive quintuple receptor mutant. The ABA-increased fluorescence in mitochondria of both DCF- and an H2O2-selective probe, Peroxy Orange 1, colocalized with Mitotracker Red. ABA treatment of guard cells transformed with the genetically encoded H2O2 reporter targeted to the cytoplasm (roGFP2-Orp1), or mitochondria (mt-roGFP2-Orp1), revealed H2O2 increases. Consistent with mitochondrial ROS changes functioning in stomatal closure, we found that guard cells of a mutant with mitochondrial defects, ABA overly sensitive 6 (abo6), have elevated ABA-induced ROS in mitochondria and enhanced stomatal closure. These effects were phenocopied with rotenone, which increased mitochondrial ROS. In contrast, the mitochondrially targeted antioxidant, MitoQ, dampened ABA effects on mitochondrial ROS accumulation and stomatal closure in Col-0 and reversed the guard cell closure phenotype of the abo6 mutant. ABA-induced ROS accumulation in guard cell mitochondria was lost in mutants in genes encoding respiratory burst oxidase homolog (RBOH) enzymes and reduced by treatment with the RBOH inhibitor, VAS2870, consistent with RBOH machinery acting in ABA-increased ROS in guard cell mitochondria. These results demonstrate that ABA elevates H2O2 accumulation in guard cell mitochondria to promote stomatal closure.

Ca2+ deficiency triggers panicle degeneration in rice mediated by Ca2+ /H+ exchanger OsCAX1a

Increasing rice yield has always been one of the primary objectives of rice breeding. However, panicle degeneration often occurs in rice-growing regions and severely curbs rice yield. In this study, we obtained a new apical panicle degeneration mutant, which induces a marked degeneration rate and diminishes the final grain yield. Cellular and physiological analyses revealed that the apical panicle undergoes programmed cell death, accompanied by excessive accumulations of peroxides. Following, the panicle degeneration gene OsCAX1a was identified in the mutant, which was involved in Ca²⁺ transport. Hydroponics assays and Ca²⁺ quantification confirmed that Ca²⁺ transport and distribution to apical tissues were restricted and over-accumulated in the mutant sheath. Ca²⁺ transport between cytoplasm and vacuole was affected, and the reduced Ca²⁺ content in the vacuole and cell wall of the apical panicle and the decreased Ca²⁺ absorption appeared in the mutant. RNA-Seq data indicated that the abnormal CBL (calcineurin b-like proteins) pathway mediated by deficient Ca²⁺ might occur in the mutant, resulting in the burst of ROS and programmed cell death in panicles. Our results explained the key role of OsCAX1a in Ca²⁺ transport and distribution and laid a foundation to further explore the genetic and molecular mechanisms of panicle degeneration in rice.

Characterization of Dendrobium catenatum CBL-CIPK signaling networks and their response to abiotic stress

Dendrobium catenatum is a traditional Chinese medicine listing as rare and endangered due to environmental impacts. But little is known about its stress resistance mechanism. The CBL-CIPK signaling pathway played vital roles in various stress responses. In this study, we identified 9 calcineurin B-like (CBL) genes and 28 CBL-interacting protein kinase (CIPK) genes from D. catenatum. Phylogenetic analysis showed that DcCBL and DcCIPK families could be divided into four and six subgroups, respectively. Members in each subgroup had similar gene structures. Cis-acting element analyses showed that these genes were involved in stress responses and hormone signaling. Spatial expression profiles showed that they were tissue-specific, and expressed lower in vegetative organs than reproductive organs. Gene expression analyses revealed that these genes were involved in drought, heat, cold, and salt responses and depended on abscisic acid (ABA) and salicylic acid (SA) signaling pathways. Furthermore, we cloned 19 DcCIPK genes and 9 DcCBL genes and detected ten interacting CBL-CIPK combinations using yeast two-hybrid system. Finally, we constructed 20 CBL-CIPK signaling pathways based on their expression patterns and interaction relationships. These results established CBL-CIPK signaling pathway responding to abiotic stress and provided a molecular basis for improving D. catenatum stress resistance in the future.

The captivating role of calcium in plant-microbe interaction

Plant immune response is fascinating due to the complete absence of a humoral system. The adaptive immune response in plants relies on the intracellular orchestration of signalling molecules or intermediates associated with transcriptional reprogramming. Plant disease response phenomena largely depend on pathogen recognition, signal perception, and intracellular signal transduction. The pathogens possess specific pathogen-associated molecular patterns (PAMP) or microbe-associated molecular patterns (MAMP), which are first identified by pattern recognition receptors (PRRs) of host plants for successful infection. After successful pathogen recognition, the defence response is initiated within plants. The first line of non-specific defence response is called PAMP-triggered immunity (PTI), followed by the specific robust signalling is called effector-triggered immunity (ETI). Calcium plays a crucial role in both PTI and ETI. The biphasic induction of reactive oxygen species (ROS) is inevitable in any plant-microbe interaction. Calcium ions play crucial roles in the initial oxidative burst and ROS induction. Different pathogens can induce calcium accumulation in the cytosol ([Ca²⁺]_Cyt), called calcium signatures. These calcium signatures further control the diverse defence-responsive proteins in the intracellular milieu. These calcium signatures then activate calcium-dependent protein kinases (CDPKs), calcium calmodulins (CaMs), calcineurin B-like proteins (CBLs), etc., to impart intricate defence signalling within the cell. Decoding this calcium ionic map is imperative to unveil any plant microbe interplay and modulate defence-responsive pathways. Hence, the present review is unique in developing concepts of calcium signature in plants and their subsequent decoding mechanism. This review also intends to articulate early sensing of calcium oscillation, signalling events, and comprehensive mechanistic roles of calcium within plants during pathogenic ingression. This will accumulate and summarize the exciting roles of calcium ions in plant immunity and provide the foundation for future research.

Phytochrome B regulates reactive oxygen signaling during abiotic and biotic stress in plants

Reactive oxygen species (ROS) and the photoreceptor protein phytochrome B (phyB) play a key role in plant acclimation to stress. However, how phyB that primarily functions in the nuclei impacts ROS signaling mediated by respiratory burst oxidase homolog (RBOH) proteins that reside on the plasma membrane, during stress, is unknown. Arabidopsis thaliana and Oryza sativa mutants, RNA-Seq, bioinformatics, biochemistry, molecular biology, and whole-plant ROS imaging were used to address this question. Here, we reveal that phyB and RBOHs function as part of a key regulatory module that controls apoplastic ROS production, stress-response transcript expression, and plant acclimation in response to excess light stress. We further show that phyB can regulate ROS production during stress even if it is restricted to the cytosol and that phyB, respiratory burst oxidase protein D (RBOHD), and respiratory burst oxidase protein F (RBOHF) coregulate thousands of transcripts in response to light stress. Surprisingly, we found that phyB is also required for ROS accumulation in response to heat, wounding, cold, and bacterial infection. Our findings reveal that phyB plays a canonical role in plant responses to biotic and abiotic stresses, regulating apoplastic ROS production, possibly while at the cytosol, and that phyB and RBOHD/RBOHF function in the same regulatory pathway.

Phytochrome B regulates reactive oxygen signaling during abiotic and biotic stress in plants

Reactive oxygen species (ROS) and the photoreceptor protein phytochrome B (phyB) play a key role in plant acclimation to stress. However, how phyB that primarily functions in the nuclei impacts ROS signaling mediated by respiratory burst oxidase homolog (RBOH) proteins that reside on the plasma membrane, during stress, is unknown. Arabidopsis thaliana and Oryza sativa mutants, RNA-Seq, bioinformatics, biochemistry, molecular biology, and whole-plant ROS imaging were used to address this question. Here, we reveal that phyB and RBOHs function as part of a key regulatory module that controls apoplastic ROS production, stress-response transcript expression, and plant acclimation in response to excess light stress. We further show that phyB can regulate ROS production during stress even if it is restricted to the cytosol and that phyB, respiratory burst oxidase protein D (RBOHD), and respiratory burst oxidase protein F (RBOHF) coregulate thousands of transcripts in response to light stress. Surprisingly, we found that phyB is also required for ROS accumulation in response to heat, wounding, cold, and bacterial infection. Our findings reveal that phyB plays a canonical role in plant responses to biotic and abiotic stresses, regulating apoplastic ROS production, possibly while at the cytosol, and that phyB and RBOHD/RBOHF function in the same regulatory pathway.

Comparative transcriptome analysis reveals the regulatory mechanisms of two tropical water lilies in response to cold stress

BACKGROUND

Tropical water lily is an aquatic plant with high ornamental value, but it cannot overwinter naturally at high latitudes. The temperature drop has become a key factor restricting the development and promotion of the industry.

RESULTS

The responses of Nymphaea lotus and Nymphaea rubra to cold stress were analyzed from the perspective of physiology and transcriptomics. Under the cold stress, Nymphaea rubra had obvious leaf edge curling and chlorosis. The degree of peroxidation of its membrane was higher than that of Nymphaea lotus, and the content of photosynthetic pigments also decreased more than that of Nymphaea lotus. The soluble sugar content, SOD enzyme activity and CAT enzyme activity of Nymphaea lotus were higher than those of Nymphaea rubra. This indicated that there were significant differences in the cold sensitivity of the two varieties. GO enrichment and KEGG pathway analysis showed that many stress response genes and pathways were affected and enriched to varying degrees under the cold stress, especially plant hormone signal transduction, metabolic pathways and some transcription factor genes were from ZAT gene family or WKRY gene family. The key transcription factor ZAT12 protein in the cold stress response process has a C₂H₂ conserved domain, and the protein is localized in the nucleus. Under the cold stress, overexpression of the NlZAT12 gene in Arabidopsis thaliana increased the expression of some cold-responsive protein genes. The content of reactive oxygen species and MDA in transgenic Arabidopsis thaliana was lower, and the content of soluble sugar was higher, indicating that overexpression of NlZAT12 can improve the cold tolerance of Arabidopsis thaliana.

CONCLUSION

We demonstrate that ethylene signalling and reactive oxygen species signalling play critical roles in the response of the two cultivars to cold stress. The key gene NlZAT12 for improving cold tolerance was identified. Our study provides a theoretical basis for revealing the molecular mechanism of tropical water lily in response to cold stress.

Salinity-Induced Cytosolic Alkaline Shifts in Arabidopsis Roots Require the SOS Pathway

Plants have evolved elaborate mechanisms to sense, respond to and overcome the detrimental effects of high soil salinity. The role of calcium transients in salinity stress signaling is well established, but the physiological significance of concurrent salinity-induced changes in cytosolic pH remains largely undefined. Here, we analyzed the response of Arabidopsis roots expressing the genetically encoded ratiometric pH-sensor pHGFP fused to marker proteins for the recruitment of the sensor to the cytosolic side of the tonoplast (pHGFP-VTI11) and the plasma membrane (pHGFP-LTI6b). Salinity elicited a rapid alkalinization of cytosolic pH (pHcyt) in the meristematic and elongation zone of wild-type roots. The pH-shift near the plasma membrane preceded that at the tonoplast. In pH-maps transversal to the root axis, the epidermis and cortex had cells with a more alkaline pHcyt relative to cells in the stele in control conditions. Conversely, seedlings treated with 100 mM NaCl exhibited an increased pHcyt in cells of the vasculature relative to the external layers of the root, and this response occurred in both reporter lines. These pHcyt changes were substantially reduced in mutant roots lacking a functional SOS3/CBL4 protein, suggesting that the operation of the SOS pathway mediated the dynamics of pHcyt in response to salinity.

Membrane Proteins in Plant Salinity Stress Perception, Sensing, and Response

Plants have several mechanisms to endure salinity stress. The degree of salt tolerance varies significantly among different terrestrial crops. Proteins at the plant's cell wall and membrane mediate different physiological roles owing to their critical positioning between two distinct environments. A specific membrane protein is responsible for a single type of activity, such as a specific group of ion transport or a similar group of small molecule binding to exert multiple cellular effects. During salinity stress in plants, membrane protein functions: ion homeostasis, signal transduction, redox homeostasis, and solute transport are essential for stress perception, signaling, and recovery. Therefore, comprehensive knowledge about plant membrane proteins is essential to modulate crop salinity tolerance. This review gives a detailed overview of the membrane proteins involved in plant salinity stress highlighting the recent findings. Also, it discusses the role of solute transporters, accessory polypeptides, and proteins in salinity tolerance. Finally, some aspects of membrane proteins are discussed with potential applications to developing salt tolerance in crops.

High temporal-resolution transcriptome landscapes of maize embryo sac and ovule during early seed development

Here we provided a high temporal-resolution transcriptome atlas of maize embryo sac and ovule to reveal the gene activity dynamic during early seed development. The early maize (Zea mays) seed development is initiated from double fertilization in the embryo sac and needs to undergo a highly dynamic and complex development process to form the differentiated embryo and endosperm. Despite the importance of maize seed for food, feed, and biofuel, many regulators responsible for controlling its early development are not known yet. Here, we reported a high temporal-resolution transcriptome atlas of embryo sac and ovule based on 44 time point samples collected within the first four days of seed development. A total of 25,187 genes including 1598 transcription factors (TFs) involved in early seed development were detected. Global comparisons of the expressions of these genes revealed five distinct development stages of early seed, which are mainly related to double fertilization, asymmetric cell division of the zygote, as well as coenocyte formation, cellularization and differentiation in endosperm. We identified 3327 seed-specific genes, which more than one thousand seed-specific genes with main expressions during early seed development were newly identified here, including 859 and 186 genes predominantly expressed in the embryo sac and ovule, respectively. Combined with the published transcriptome data of seed, we uncovered the dominant auxin biosynthesis, transport and signaling related genes at different development stages and subregions of seed. These results are helpful for understanding the genetic control of early seed development.

Parallel repair mechanisms in plants and animals

All organisms have acquired mechanisms for repairing themselves after accidents or lucky escape from predators, but how analogous are these mechanisms across phyla? Plants and animals are distant relatives in the tree of life, but both need to be able to efficiently repair themselves, or they will perish. Both have an outer epidermal barrier layer and a circulatory system that they must protect from infection. However, plant cells are immotile with rigid cell walls, so they cannot raise an animal-like immune response or move away from the insult, as animals can. Here, we discuss the parallel strategies and signalling pathways used by plants and animals to heal their tissues, as well as key differences. A more comprehensive understanding of these parallels and differences could highlight potential avenues to enhance healing of patients' wounds in the clinic and, in a reciprocal way, for developing novel alternatives to agricultural pesticides.

Structure, biochemical function, and signaling mechanism of plant NLRs

To counter pathogen invasion, plants have evolved a large number of immune receptors, including membrane-resident pattern recognition receptors (PRRs) and intracellular nucleotide-binding and leucine-rich repeat receptors (NLRs). Our knowledge about PRR and NLR signaling mechanisms has expanded significantly over the past few years. Plant NLRs form multi-protein complexes called resistosomes in response to pathogen effectors, and the signaling mediated by NLR resistosomes converges on Ca²⁺-permeable channels. Ca²⁺-permeable channels important for PRR signaling have also been identified. These findings highlight a crucial role of Ca²⁺ in triggering plant immune signaling. In this review, we first discuss the structural and biochemical mechanisms of non-canonical NLR Ca²⁺ channels and then summarize our knowledge about immune-related Ca²⁺-permeable channels and their roles in PRR and NLR signaling. We also discuss the potential role of Ca²⁺ in the intricate interaction between PRR and NLR signaling.

Calcium decoders and their targets: The holy alliance that regulate cellular responses in stress signaling

Calcium (Ca²⁺) signaling is versatile communication network in the cell. Stimuli perceived by cells are transposed through Ca²⁺-signature, and are decoded by plethora of Ca²⁺ sensors present in the cell. Calmodulin, calmodulin-like proteins, Ca²⁺-dependent protein kinases and calcineurin B-like proteins are major classes of proteins that decode the Ca²⁺ signature and serve in the propagation of signals to different parts of cells by targeting downstream proteins. These decoders and their targets work together to elicit responses against diverse stress stimuli. Over a period of time, significant attempts have been made to characterize as well as summarize elements of this signaling machinery. We begin with a structural overview and amalgamate the newly identified Ca²⁺ sensor protein in plants. Their ability to bind Ca²⁺, undergo conformational changes, and how it facilitates binding to a wide variety of targets is further embedded. Subsequently, we summarize the recent progress made on the functional characterization of Ca²⁺ sensing machinery and in particular their target proteins in stress signaling. We have focused on the physiological role of Ca²⁺, the Ca²⁺ sensing machinery, and the mode of regulation on their target proteins during plant stress adaptation. Additionally, we also discuss the role of these decoders and their mode of regulation on the target proteins during abiotic, hormone signaling and biotic stress responses in plants. Finally, here, we have enumerated the limitations and challenges in the Ca²⁺ signaling. This article will greatly enable in understanding the current picture of plant response and adaptation during diverse stimuli through the lens of Ca²⁺ signaling.

ROS and calcium oscillations are required for polarized root hair growth

Root hairs are filamentous extensions from epidermis of plant roots with growth limited to the apical dome. Cell expansion undergoes tightly regulated processes, including the coordination between cell wall loosening and cell wall crosslinking, to form the final shape and size. Tip-focused gradients and oscillations of reactive oxygen species (ROS) together with calcium ions (Ca²⁺) as indispensable regulated mechanisms control rapid and polarized elongation of root hair cells. ROS homeostasis mediated by plasma membrane-localized NADPH oxidases, known as respiratory burst oxidase homologues (RBOHs), and class III cell wall peroxidases (PRXs), modulates cell wall properties during cell expansion. The expression levels of RBOHC, an NADPH oxidase that produces ROS, and class III PRXs are directly upregulated by ROOT HAIR DEFECTIVE SIX-LIKE 4 (RSL4), encoding a basic-helix-loop-helix (bHLH) transcription factor, to modulate root hair elongation. Cyclic nucleotide-gated channels (CNGCs), as central regulators of Ca²⁺ oscillations, also regulate root hair extension. Here, we review how the gradients and oscillations of Ca²⁺ and ROS interact to promote the expansion of root hair cells.

Comprehensive identification and expression analyses of the SnRK gene family in Casuarina equisetifolia in response to salt stress

BACKGROUND

Sucrose nonfermenting-1 (SNF1)-related protein kinases (SnRKs) play crucial roles in plant signaling pathways and stress adaptive responses by activating protein phosphorylation pathways. However, there have been no comprehensive studies of the SnRK gene family in the widely planted salt-tolerant tree species Casuarina equisetifolia. Here, we comprehensively analyze this gene family in C. equisetifolia using genome-wide identification, characterization, and profiling of expression changes in response to salt stress.

RESULTS

A total of 26 CeqSnRK genes were identified, which were divided into three subfamilies (SnRK1, SnRK2, and SnRK3). The intron-exon structures and protein‑motif compositions were similar within each subgroup but differed among groups. Ka/Ks ratio analysis indicated that the CeqSnRK family has undergone purifying selection, and cis-regulatory element analysis suggested that these genes may be involved in plant development and responses to various environmental stresses. A heat map was generated using quantitative real‑time PCR (RT-qPCR) data from 26 CeqSnRK genes, suggesting that they were expressed in different tissues. We also examined the expression of all CeqSnRK genes under exposure to different salt concentrations using RT-qPCR, finding that most CeqSnRK genes were regulated by different salt treatments. Moreover, co-expression network analysis revealed synergistic effects among CeqSnRK genes.

CONCLUSIONS

Several CeqSnRK genes (CeqSnRK3.7, CeqSnRK3.16, CeqSnRK3.17) were up-regulated following salt treatment. Among them, CeqSnRK3.16 expression was significantly up-regulated under various salt treatments, identifying this as a candidate gene salt stress tolerance gene. In addition, CeqSnRK3.16 showed significant expression change correlations with multiple genes under salt stress, indicating that it might exhibit synergistic effects with other genes in response to salt stress. This comprehensive analysis will provide a theoretical reference for CeqSnRK gene functional verification and the role of these genes in salt tolerance.

ROS and redox regulation of cell-to-cell and systemic signaling in plants during stress

Stress results in the enhanced accumulation of reactive oxygen species (ROS) in plants, altering the redox state of cells and triggering the activation of multiple defense and acclimation mechanisms. In addition to activating ROS and redox responses in tissues that are directly subjected to stress (termed 'local' tissues), the sensing of stress in plants triggers different systemic signals that travel to other parts of the plant (termed 'systemic' tissues) and activate acclimation and defense mechanisms in them; even before they are subjected to stress. Among the different systemic signals triggered by stress in plants are electric, calcium, ROS, and redox waves that are mobilized in a cell-to-cell fashion from local to systemic tissues over long distances, sometimes at speeds of up to several millimeters per second. Here, we discuss new studies that identified various molecular mechanisms and proteins involved in mediating systemic signals in plants. In addition, we highlight recent studies that are beginning to unravel the mode of integration and hierarchy of the different systemic signals and underline open questions that require further attention. Unraveling the role of ROS and redox in plant stress responses is highly important for the development of climate resilient crops.

The CRK5 and WRKY53 Are Conditional Regulators of Senescence and Stomatal Conductance in Arabidopsis

In Arabidopsis thaliana, cysteine-rich receptor-like kinases (CRKs) constitute a large group of membrane-localized proteins which perceive external stimuli and transduce the signal into the cell. Previous reports based on their loss-of-function phenotypes and expression profile support their role in many developmental and stress-responsive pathways. Our study revealed that one member of this family, CRK5, acts as a negative regulator of leaf aging. Enrichment of the CRK5 promoter region in W-box cis-elements demonstrated that WRKY transcription factors control it. We observed significantly enhanced WRKY53 expression in crk5 and reversion of its early-senescence phenotype in the crk5 wrky53 line, suggesting a negative feedback loop between these proteins antagonistically regulating chlorophyll a and b contents. Yeast-two hybrid assay showed further that CRK5 interacts with several proteins involved in response to water deprivation or calcium signaling, while gas exchange analysis revealed a positive effect of CRK5 on water use efficiency. Consistent with that, the crk5 plants showed disturbed foliar temperature, stomatal conductance, transpiration, and increased susceptibility to osmotic stress. These traits were fully or partially reverted to wild-type phenotype in crk5 wrky53 double mutant. Obtained results suggest that WRKY53 and CRK5 are antagonistic regulators of chlorophyll synthesis/degradation, senescence, and stomatal conductance.

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

Reactive oxygen species (ROS), produced by respiratory burst oxidase homologs (RBOHs) at the apoplast, play a key role in local and systemic cell-to-cell signaling, required for plant acclimation to stress. Here we reveal that the Arabidopsis thaliana leucine-rich-repeat receptor-like kinase H2O2-INDUCED CA2+ INCREASES 1 (HPCA1) acts as a central ROS receptor required for the propagation of cell-to-cell ROS signals, systemic signaling in response to different biotic and abiotic stresses, stress responses at the local and systemic tissues, and plant acclimation to stress, following a local treatment of high light (HL) stress. We further report that HPCA1 is required for systemic calcium signals, but not systemic membrane depolarization responses, and identify the calcium-permeable channel MECHANOSENSITIVE ION CHANNEL LIKE 3, CALCINEURIN B-LIKE CALCIUM SENSOR 4 (CBL4), CBL4-INTERACTING PROTEIN KINASE 26 and Sucrose-non-fermenting-1-related Protein Kinase 2.6/OPEN STOMATA 1 (OST1) as required for the propagation of cell-to-cell ROS signals. In addition, we identify serine residues S343 and S347 of RBOHD (the putative targets of OST1) as playing a key role in cell-to-cell ROS signaling in response to a local application of HL stress. Our findings reveal that HPCA1 plays a key role in mediating and coordinating systemic cell-to-cell ROS and calcium signals required for plant acclimation to stress.

Insight into the regulatory networks underlying the high lipid perennial ryegrass growth under different irradiances

Under favourable conditions, perennial ryegrass (Lolium perenne) engineered to accumulated high lipid (HL) carbon sink in their leaves was previously shown to also enhance photosynthesis and growth. The greater aboveground biomass was found to be diminished in a dense canopy compared to spaced pots. Besides, the underlying genetic regulatory network linking between leaf lipid sinks and these physiological changes remains unknown. In this study, we demonstrated that the growth advantage was not displayed in HL Lolium grown in spaced pots under low lights. Under standard lights, analysis of differentiating transcripts in HL Lolium reveals that the plants had elevated transcripts involved in lipid metabolism, light capturing, photosynthesis, and sugar signalling while reduced expression of genes participating in sugar biosynthesis and transportation. The plants also had altered several transcripts involved in mitochondrial oxidative respiration and redox potential. Many of the above upregulated or downregulated transcript levels were found to be complemented by growing the plants under low light. Overall, this study emphasizes the importance of carbon and energy homeostatic regulatory mechanisms to overall productivity of the HL Lolium through photosynthesis, most of which are significantly impacted by low irradiances.

Regulation of PaRBOH1-mediated ROS production in Norway spruce by Ca2+ binding and phosphorylation

Plant respiratory burst oxidase homologs (RBOHs) are plasma membrane-localized NADPH oxidases that generate superoxide anion radicals, which then dismutate to H₂O₂, into the apoplast using cytoplasmic NADPH as an electron donor. PaRBOH1 is the most highly expressed RBOH gene in developing xylem as well as in a lignin-forming cell culture of Norway spruce (Picea abies L. Karst.). Since no previous information about regulation of gymnosperm RBOHs exist, our aim was to resolve how PaRBOH1 is regulated with a focus on phosphorylation. The N-terminal part of PaRBOH1 was found to contain several putative phosphorylation sites and a four-times repeated motif with similarities to the Botrytis-induced kinase 1 target site in Arabidopsis AtRBOHD. Phosphorylation was indicated for six of the sites in in vitro kinase assays using 15 amino-acid-long peptides for each of the predicted phosphotarget site in the presence of protein extracts of developing xylem. Serine and threonine residues showing positive response in the peptide assays were individually mutated to alanine (kinase-inactive) or to aspartate (phosphomimic), and the wild type PaRBOH1 and the mutated constructs transfected to human kidney embryogenic (HEK293T) cells with a low endogenous level of extracellular ROS production. ROS-producing assays with HEK cells showed that Ca²⁺ and phosphorylation synergistically activate the enzyme and identified several serine and threonine residues that are likely to be phosphorylated including a novel phosphorylation site not characterized in other plant species. These were further investigated with a phosphoproteomic study. Results of Norway spruce, the first gymnosperm species studied in relation to RBOH regulation, show that regulation of RBOH activity is conserved among seed plants.

Natural variations of ZmSRO1d modulate the trade-off between drought resistance and yield by affecting ZmRBOHC-mediated stomatal ROS production in maize

While crop yields have historically increased, drought resistance has become a major concern in the context of global climate change. The trade-off between crop yield and drought resistance is a common phenomenon; however, the underlying molecular modulators remain undetermined. Through genome-wide association study, we revealed that three non-synonymous variants in a drought-resistant allele of ZmSRO1d-R resulted in plasma membrane localization and enhanced mono-ADP-ribosyltransferase activity of ZmSRO1d toward ZmRBOHC, which increased reactive oxygen species (ROS) levels in guard cells and promoted stomatal closure. ZmSRO1d-R enhanced plant drought resilience and protected grain yields under drought conditions, but it led to yield drag under favorable conditions. In contrast, loss-of-function mutants of ZmRBOHC showed remarkably increased yields under well-watered conditions, whereas they showed compromised drought resistance. Interestingly, by analyzing 189 teosinte accessions, we found that the ZmSRO1d-R allele was present in teosinte but was selected against during maize domestication and modern breeding. Collectively, our work suggests that the allele frequency reduction of ZmSRO1d-R in breeding programs may have compromised maize drought resistance while increased yields. Therefore, introduction of the ZmSRO1d-R allele into modern maize cultivars would contribute to food security under drought stress caused by global climate change.

Melatonin as a regulator of plant ionic homeostasis: implications for abiotic stress tolerance

Melatonin is a highly conserved and ubiquitous molecule that operates upstream of a broad array of receptors in animal systems. Since melatonin was discovered in plants in 1995, hundreds of papers have been published revealing its role in plant growth, development, and adaptive responses to the environment. This paper summarizes the current state of knowledge of melatonin's involvement in regulating plant ion homeostasis and abiotic stress tolerance. The major topics covered here are: (i) melatonin's control of H+-ATPase activity and its implication for plant adaptive responses to various abiotic stresses; (ii) regulation of the reactive oxygen species (ROS)-Ca2+ hub by melatonin and its role in stress signaling; and (iii) melatonin's regulation of ionic homeostasis via hormonal cross-talk. We also show that the properties of the melatonin molecule allow its direct scavenging of ROS, thus preventing negative effects of ROS-induced activation of ion channels. The above 'desensitization' may play a critical role in preventing stress-induced K+ loss from the cytosol as well as maintaining basic levels of cytosolic Ca2+ required for optimal cell operation. Future studies should focus on revealing the molecular identity of transporters that could be directly regulated by melatonin and providing a bioinformatic analysis of evolutionary aspects of melatonin sensing and signaling.

A Ca2+-sensor switch for tolerance to elevated salt stress in Arabidopsis

Excessive Na⁺ in soils inhibits plant growth. Here, we report that Na⁺ stress triggers primary calcium signals specifically in a cell group within the root differentiation zone, thus forming a "sodium-sensing niche" in Arabidopsis. The amplitude of this primary calcium signal and the speed of the resulting Ca²⁺ wave dose-dependently increase with rising Na⁺ concentrations, thus providing quantitative information about the stress intensity encountered. We also delineate a Ca²⁺-sensing mechanism that measures the stress intensity in order to mount appropriate salt detoxification responses. This is mediated by a Ca²⁺-sensor-switch mechanism, in which the sensors SOS3/CBL4 and CBL8 are activated by distinct Ca²⁺-signal amplitudes. Although the SOS3/CBL4-SOS2/CIPK24-SOS1 axis confers basal salt tolerance, the CBL8-SOS2/CIPK24-SOS1 module becomes additionally activated only in response to severe salt stress. Thus, Ca²⁺-mediated translation of Na⁺ stress intensity into SOS1 Na⁺/H⁺ antiporter activity facilitates fine tuning of the sodium extrusion capacity for optimized salt-stress tolerance.

H2O2 and Ca2+ Signaling Crosstalk Counteracts ABA to Induce Seed Germination

Seed germination is a critical stage and the first step in the plant’s life cycle. H2O2 and Ca2+ act as important signal molecules in regulating plant growth and development and in providing defense against numerous stresses; however, their crosstalk in modulating seed germination remains largely unaddressed. In the current study, we report that H2O2 and Ca2+ counteracted abscisic acid (ABA) to induce seed germination in melon and Arabidopsis by modulating ABA and gibberellic acid (GA3) balance. H2O2 treatment induced a Ca2+ influx in melon seeds accompanied by the upregulation of cyclic nucleotide-gated ion channel (CNGC) 20, which encodes a plasma membrane Ca2+-permeable channel. However, the inhibition of cytoplasmic free Ca2+ elevation in the melon seeds and Arabidopsis mutant atcngc20 compromised H2O2-induced germination under ABA stress. CaCl2 induced H2O2 accumulation accompanied by the upregulation of respiratory burst oxidase homologue (RBOH) D and RBOHF in melon seeds with ABA pretreatment. However, inhibition of H2O2 accumulation in the melon seeds and Arabidopsis mutant atrbohd and atrbohf abolished CaCl2-induced germination under ABA stress. The current study reveals a novel mechanism in which H2O2 and Ca2+ signaling crosstalk offsets ABA to induce seed germination. H2O2 induces Ca2+ influx, which in turn increases H2O2 accumulation, thus forming a reciprocal positive-regulatory loop to maintain a balance between ABA and GA3 and promote seed germination under ABA stress.

Ethyl Vinyl Ketone Activates K+ Efflux to Regulate Stomatal Closure by MRP4-Dependent eATP Accumulation Working Upstream of H2O2 Burst in Arabidopsis

Plants regulate stomatal mobility to limit water loss and improve pathogen resistance. Ethyl vinyl ketone (evk) is referred to as a reactive electrophilic substance (RES). In this paper, we found that evk can mediate stomatal closure and that evk-induced stomatal closure by increasing guard cell K⁺ efflux. To investigate the role of eATP, and H₂O₂ in evk-regulated K⁺ efflux, we used Arabidopsis wild-type (WT), mutant lines of mrp4, mrp5, dorn1.3 and rbohd/f. Non-invasive micro-test technology (NMT) data showed that evk-induced K⁺ efflux was diminished in mrp4, rbohd/f, and dorn1.3 mutant, which means eATP and H₂O₂ work upstream of evk-induced K⁺ efflux. According to the eATP content assay, evk stimulated eATP production mainly by MRP4. In mrp4 and mrp5 mutant groups and the ABC transporter inhibitor glibenclamide (Gli)-pretreated group, evk-regulated stomatal closure and eATP buildup were diminished, especially in the mrp4 group. According to qRT-PCR and eATP concentration results, evk regulates both relative gene expressions of MRP4/5 and eATP concentration in rbohd/f and WT group. According to the confocal data, evk-induced H₂O₂ production was lower in mrp4, mrp5 mutants, which implied that eATP works upstream of H₂O₂. Moreover, NADPH-dependent H₂O₂ burst is regulated by DORN1. A yeast two-hybrid assay, firefly luciferase complementation imaging assay, bimolecular fluorescence complementation assay, and pulldown assay showed that the interaction between DORN1 and RBOHF can be realized, which means DORN1 may control H₂O₂ burst by regulating RBOHF through interaction. This study reveals that evk-induced stomatal closure requires MRP4-dependent eATP accumulation and subsequent H₂O₂ accumulation to regulate K⁺ efflux.

Comparative Physiological and Transcriptome Analysis Reveal the Molecular Mechanism of Melatonin in Regulating Salt Tolerance in Alfalfa (Medicago sativa L.)

As a high-quality legume forage, alfalfa is restricted by various abiotic stresses during its growth and development. Melatonin is a multifunctional signaling molecule that involves in plant defense against multiple stresses. However, little is known about its downstream signaling pathway and regulatory mechanisms in salt stress of alfalfa. In this study, we investigated the protective effects and key regulatory pathways of melatonin on alfalfa under salt tolerance. The results showed that melatonin promoted the growth of alfalfa seedlings under salt stress, as demonstrated by higher plant height, leaf area, and fresh weight. Melatonin treatment resulted in an increase in the photosynthetic capacity and starch content of alfalfa. Moreover, melatonin decreased cell membrane damage and reactive oxygen species (ROS) accumulation by enhancing antioxidant defense activity under salt stress conditions. Transcriptome sequencing (RNA-seq) analysis revealed that melatonin mainly induced the transcription of genes involved in Ca²⁺ signaling (cyclic nucleotide gated channel, CNGCs; cam modulin/calmodulin-like protein, CAM/CMLs and calcium-dependent protein kinase, CDPKs), starch and sucrose metabolism (α-amylase, AMYs; β-amylase, BAMs; starch synthase, SSs and sucrose synthase, SUSs), plant hormone signal transduction (auxin/indole acetic acid protein, AUX/IAAs; ABA receptor, PYL4; protein phosphatase 2C, PP2Cs; scarecrow-like protein, SCLs and ethylene-responsive transcription factor 1B, ERF1B), and key transcription factors (C3Hs, MYBs, ERFs, and WRKYs). Specifically, we focused on starch and sucrose metabolism and plant hormone signal transduction pathways. The interactions between melatonin and other phytohormones occurred via regulation of the expression of genes involved in hormone signaling pathways. In addition, melatonin increased the contents of endogenous melatonin, auxin, gibberellic acid (GA₃), salicylic acid, brassinosteroids, and ethylene, while decreasing the abscisic acid content under salt stress. In summary, this study established a regulatory network for melatonin-induced key signaling pathways and functional genes under salt stress and provided a theoretical basis for salt tolerance breeding in alfalfa.

Endoplasmic Reticulum Stress and Reactive Oxygen Species in Plants

The endoplasmic reticulum (ER) is a key compartment responsible for protein processing and folding, and it also participates in many signal transduction and metabolic processes. Reactive oxygen species (ROS) are important signaling messengers involved in the redox equilibrium and stress response. A number of abiotic and biotic stresses can trigger the accumulation of unfolded or misfolded proteins and lead to ER stress. In recent years, a number of studies have reported that redox metabolism and ROS are closely related to ER stress. ER stress can benefit ROS generation and even cause oxidative burden in plants, finally leading to oxidative stress depending on the degree of ER stress. Moreover, ER stress activates nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-mediated ROS signaling, increases antioxidant defense mechanisms, and alters the glutathione (GSH) redox state. Meanwhile, the accumulation of ROS plays a special role in inducing the ER stress response. Given these factors, plants have evolved a series of complex regulatory mechanisms to interact with ROS in response to ER stress. In this review, we summarize the perceptions and responses of plant ER stress and oxidative protein folding in the ER. In addition, we analyze the production and signaling of ROS under ER stress in detail in order to provide a theoretical basis for reducing ER stress to improve the crop survival rate in agricultural applications.

Genome-Wide Identification of the Salvia miltiorrhiza SmCIPK Gene Family and Revealing the Salt Resistance Characteristic of SmCIPK13

Members of the CIPK (CBL-interacting protein kinases) gene family play important roles in calcium (Ca²⁺) signaling pathway-regulated plant resistance to abiotic stresses. Salvia miltiorrhiza, which is widely planted and grown in complex and diverse environments, is mainly focused on the transcriptional regulation of enzyme genes related to the biosynthesis of its bioactive components. However, the excavation of the genes related to the resistance of S.miltiorrhiza and the involved signaling pathways have not been deeply studied. In this study, 20 SmCIPK genes were identified and classified into two families and five subfamilies by biochemical means. Sequence characteristics and conserved motif analysis revealed the conservation and difference of SmCIPK protein in plants. Expression pattern analysis showed that SmCIPKs were mainly expressed in flowers and roots, and more than 90% of gene expression was induced by SA (salicylic acid), and MeJA (methyl jasmonate). Furthermore, the expression level of SmCIPK13 could be significantly increased after stress treatment with NaCl. SmCIPK13 expression in yeast reduces sensitivity to salt, while overexpression of it in Arabidopsis has the same effect and was localized in the cytoplasm, cell membrane and nucleus. In conclusion, the identification of the SmCIPK gene family and the functional characterization of the SmCIPK13 gene provides the basis for clarification of key genes in the Ca²⁺ signaling pathway and abiotic stress in S.miltiorrhiza.

Quantitative Analysis for ROS-Producing Activity and Regulation of Plant NADPH Oxidases in HEK293T Cells

Reactive oxygen species (ROS) produced by plant NADPH oxidases, respiratory burst oxidase homologs (RBOHs), play key roles in biotic and abiotic stress responses and development in plants. While properly controlled amounts of ROS function as signaling molecules, excessive accumulation of ROS can cause undesirable side effects due to their ability to oxidize DNA, lipids, and proteins. To limit the damaging consequences of unrestricted ROS accumulation, RBOH activity is tightly controlled by post-translational modifications (PTMs) and protein-protein interactions. In order to analyze these elaborate regulatory mechanisms, it is crucial to quantitatively assess the ROS-producing activity of RBOHs. Given the high endogenous ROS generation in plants, however, it can be challenging in plant cells to measure ROS production derived from specific RBOHs and to analyze the contribution of regulatory events for their activation and inactivation. Here we describe human embryonic kidney 293T (HEK293T) cells as a heterologous expression system and a useful tool to quantitatively monitor ROS production by RBOHs. This system permits the reconstitution of regulatory events to dissect the effects of Ca²⁺, phosphorylation, and protein-protein interactions on RBOH-dependent ROS production.

Thermo-Priming Mediated Cellular Networks for Abiotic Stress Management in Plants

Plants can adapt to different environmental conditions and can survive even under very harsh conditions. They have developed elaborate networks of receptors and signaling components, which modulate their biochemistry and physiology by regulating the genetic information. Plants also have the abilities to transmit information between their different parts to ensure a holistic response to any adverse environmental challenge. One such phenomenon that has received greater attention in recent years is called stress priming. Any milder exposure to stress is used by plants to prime themselves by modifying various cellular and molecular parameters. These changes seem to stay as memory and prepare the plants to better tolerate subsequent exposure to severe stress. In this review, we have discussed the various ways in which plants can be primed and illustrate the biochemical and molecular changes, including chromatin modification leading to stress memory, with major focus on thermo-priming. Alteration in various hormones and their subsequent role during and after priming under various stress conditions imposed by changing climate conditions are also discussed.

The potassium channel GhAKT2bD is regulated by CBL-CIPK calcium signaling complexes and facilitates K+ allocation in cotton

Efficient allocation of the essential nutrient potassium (K⁺ ) is a central determinant of plant ion homeostasis and involves AKT2 K⁺ channels. Here, we characterize four AKT2 K⁺ channels from cotton and report that xylem and phloem expressed GhAKT2bD facilitates K⁺ allocation and that AKT2-silencing impairs plant growth and development. We uncover kinase activity-dependent activation of GhAKT2bD-mediated K⁺ uptake by AtCBL4-GhCIPK1 calcium signaling complexes in HEK293T cells. Moreover, AtCBL4-AtCIPK6 complexes known to convey activation of AtAKT2 in Arabidopsis also activate cotton GhAKT2bD in HEK293T cells. Collectively, these findings reveal an essential role for AKT2 in the source-sink allocation of K⁺ in cotton and identify GhAKT2bD as subject to complex regulation by CBL-CIPK Ca²⁺ sensor-kinase complexes.

Stomata in a state of emergency: H2O2 is the target locked

Stomatal movements are essential for plants to regulate photosynthesis rate, water status, and immunity. Upon stress stimulation, the production of hydrogen peroxide (H₂O₂) in the apoplasts and its accumulation within the guard cells are among key determinatives for stomatal closure. The regulatory mechanisms of H₂O₂ production and transport under plant-pathogen interaction and drought stress response in stomata are important fields of research. Specifically, the regulation of NADPH oxidases and aquaporins appears to be crucial in H₂O₂-controlled stomatal closure. In this review, we summarize how the calcium-dependent and calcium-independent mechanisms activate RESPIRATORY BURST OXIDASE HOMOLOG (RBOH)D/F NADPH oxidases and the aquaporin PIP2;1 to induce stomatal closure, and highlight how the H₂O₂ production is targeted by pathogen toxins and effectors to counteract plant immunity.

New functions of CIPK gene family are continue to emerging

CIPK protein family is a key protein family in Ca²⁺ mediated plant signaling pathway, which plays an indispensable role in plant response to stress and development. Every gene in this family encodes specific proteins. They interact with calcium ion signals, make plants to deal with various stress or stimuli. This article mainly reviews the mechanism, positioning and physiological functions of the CIPK family in different species in recent years. According to our team's research, CIPK8 interacts with CBL5 to improve salt tolerance, and CIPK23 interacts with TGA1 to regulate nitrate uptake negatively in chrysanthemum. In addition, we discussed current limitations and future research directions. The article will enhance the understanding of the functional characteristics of the CIPK gene family under different stresses, provide insights for future breeding and the development of new crop varieties with enhanced stress tolerance.