The language of calcium signaling

Small molecule, big impacts: Nano-nutrients for sustainable agriculture and food security

Human existence and the long-term viability of society depend on agriculture. Overuse of synthetic fertilizers results in increased contamination of the land, water, and atmosphere as well as financial constraints. In today's modern agriculture, environmentally friendly technology is becoming more and more significant as a substitute for conventional fertilizers and chemical pesticides. Using nanotechnology, agricultural output can be improved in terms of quality, biological support, financial stability, and environmental safety. There is a lot of promise for the sustainable application of nano-fertilizers in crop productivity and soil fertility, with little or no negative environmental effects. In this context, the present review provided an overview of the benefits of using nanofertilizers, its application and types. Mechanistic approach for increasing soil fertility and yield via nanofertilizers also described in detail. We concluded this article to compare the advantages of nanofertilizers over chemicals and nano-chemicals. Nonetheless, additional investigation is required to comprehend the effects and possible hazards of nanomaterials in the food production chain.

Kinase CPK10 regulates low light-induced tomato flower drop downstream of IDL6 in a calcium-dependent manner

Flower drop is a major cause for yield loss in many crops. Previously, we found that tomato (Solanum lycopersicum) INFLORESCENCE DEFICIENT IN ABSCISSION-Like (SlIDL6) contributes to flower drop induced by low light. However, the molecular mechanisms by which SlIDL6 acts as a signal to regulate low light-induced abscission remain unclear. In this study, SlIDL6 was found to elevate cytosolic Ca2+ concentrations ([Ca2+]cyt) in the abscission zone (AZ), which was required for SlIDL6-induced flower drop under low light. We further identified that one calcium-dependent protein kinase gene (SlCPK10) was highly expressed in the AZ and up-regulated by SlIDL6-triggered [Ca2+]cyt. Over-expression and knockout of SlCPK10 in tomato resulted in accelerated and delayed abscission, respectively. Genetic evidence further indicated that knockout of SlCPK10 significantly impaired the function of SlIDL6 in accelerating abscission. Furthermore, Ser-371 phosphorylation in SlCPK10 dependent on SlIDL6 was necessary and sufficient for its function in regulating flower drop, probably by stabilizing the SlCPK10 proteins. Taken together, our findings reveal that SlCPK10, as a downstream component of the IDL6 signaling pathway, regulates flower drop in tomato under low light stress.

Probing plant signal processing optogenetically by two channelrhodopsins

Early plant responses to different stress situations often encompass cytosolic Ca2+ increases, plasma membrane depolarization and the generation of reactive oxygen species1-3. However, the mechanisms by which these signalling elements are translated into defined physiological outcomes are poorly understood. Here, to study the basis for encoding of specificity in plant signal processing, we used light-gated ion channels (channelrhodopsins). We developed a genetically engineered channelrhodopsin variant called XXM 2.0 with high Ca2+ conductance that enabled triggering cytosolic Ca2+ elevations in planta. Plant responses to light-induced Ca2+ influx through XXM 2.0 were studied side by side with effects caused by an anion efflux through the light-gated anion channelrhodopsin ACR1 2.04. Although both tools triggered membrane depolarizations, their activation led to distinct plant stress responses: XXM 2.0-induced Ca2+ signals stimulated production of reactive oxygen species and defence mechanisms; ACR1 2.0-mediated anion efflux triggered drought stress responses. Our findings imply that discrete Ca2+ signals and anion efflux serve as triggers for specific metabolic and transcriptional reprogramming enabling plants to adapt to particular stress situations. Our optogenetics approach unveiled that within plant leaves, distinct physiological responses are triggered by specific ion fluxes, which are accompanied by similar electrical signals.

Response Mechanisms of Zelkova schneideriana Leaves to Varying Levels of Calcium Stress

Calcium stress can negatively impact plant growth, prompting plants to respond by mitigating this effect. However, the specific mechanisms underlying this response remain unclear. In this study, we used non-targeted metabolomics and transcriptomics to investigate the response mechanisms of Zelkova schneideriana leaves under varying degrees of calcium stress. Results revealed that calcium stress led to wilt in young leaves. When calcium stress exceeds the tolerance threshold of the leaf, it results in wilting of mature leaves, rupture of chloroplasts in palisade tissue, and extensive wrinkling and breakage of leaf cells. Transcriptomic analysis indicated that calcium stress inhibited photosynthesis by suppressing the expression of genes related to photosynthetic system II and electron transport. Leaf cells activate phenylpropanoid biosynthesis, flavonoid biosynthesis, and Vitamin B6 metabolism to resist calcium stress. When calcium accumulation gradually surpassed the tolerance threshold of the cells, this results in failure of conventional anti-calcium stress mechanisms, leading to cell death. Furthermore, excessive calcium stress inhibits the expression of CNGC and anti-pathogen genes. The results of the metabolomics study showed that five key metabolites increased in response to calcium stress, which may play an important role in countering calcium stress. This study provides insights into the response of Z. schneideriana leaves to different levels of calcium stress, which could provide a theoretical basis for cultivating Z. schneideriana in karst areas and enhance our understanding of plant responses to calcium stress.

Natural allelic diversity of the calcium signaling regulators in plants

Calcium ions act as secondary messengers in diverse signaling pathways in plants throughout their life cycle. Studies have revealed that calcium is involved in developmental events and in responses to external stimuli, such as biotic and abiotic stresses. Cellular calcium ion levels are tightly controlled by intricate molecular machinery such as calcium channels and pumps. Transient and spatial fluctuations in calcium levels are subsequently recognized by diverse calcium-decoding molecules, resulting in signal transduction. In this review, we highlight recent findings on natural variations in genes controlling calcium signaling in diverse plant biological processes. We then show how the calcium ion context is utilized by fine-tuning the natural variation in centrally important genes.

Overexpression of tonoplast Ca2+-ATPase in guard cells synergistically enhances stomatal opening and drought tolerance

Stomata play a crucial role in plants by controlling water status and responding to drought stress. However, simultaneously improving stomatal opening and drought tolerance has proven to be a significant challenge. To address this issue, we employed the OnGuard quantitative model, which accurately represents the mechanics and coordination of ion transporters in guard cells. With the guidance of OnGuard, we successfully engineered plants that overexpressed the main tonoplast Ca2+-ATPase gene, ACA11, which promotes stomatal opening and enhances plant growth. Surprisingly, these transgenic plants also exhibited improved drought tolerance due to reduced water loss through their stomata. Again, OnGuard assisted us in understanding the mechanism behind the unexpected stomatal behaviors observed in the ACA11 overexpressing plants. Our study revealed that the overexpression of ACA11 facilitated the accumulation of Ca2+ in the vacuole, thereby influencing Ca2+ storage and leading to an enhanced Ca2+ elevation in response to abscisic acid. This regulatory cascade finely tunes stomatal responses, ultimately leading to enhanced drought tolerance. Our findings underscore the importance of tonoplast Ca2+-ATPase in manipulating stomatal behavior and improving drought tolerance. Furthermore, these results highlight the diverse functions of tonoplast-localized ACA11 in response to different conditions, emphasizing its potential for future applications in plant enhancement.

Canola (Brassica napus) enhances sodium chloride and sodium ion tolerance by maintaining ion homeostasis, higher antioxidant enzyme activity and photosynthetic capacity fluorescence parameters

Under salt stress, plants are forced to take up and accumulate large amounts of sodium (Na+ ) and chloride (Cl- ). Although most studies have focused on the toxic effects of Na+ on plants, Cl- stress is also very important. This study aimed to clarify physiological mechanisms underpinning growth contrasts in canola varieties with different salt tolerance. In hydroponic experiments, 150mM Na+ , Cl- and NaCl were applied to salt-tolerant and sensitive canola varieties. Both NaCl and Na+ treatments inhibited seedling growth. NaCl caused the strongest damage to both canola varieties, and stress damage was more severe at high concentrations of Na+ than Cl- . High Cl- promoted the uptake of ions (potassium K+ , calcium Ca2+ ) and induced antioxidant defence. Salt-tolerant varieties were able to mitigate ion toxicity by maintaining lower Na+ content in the root system for a short period of time, and elevating magnesium Mg2+ content, Mg2+ /Na+ ratio, and antioxidant enzyme activity to improve photosynthetic capacity. They subsequently re-established new K+ /Na+ and Ca2+ /Na+ balances to improve their salt tolerance. High concentrations of Cl salts caused less damage to seedlings than NaCl and Na salts, and Cl- also had a positive role in inducing oxidative stress and responsive antioxidant defence in the short term.

Pectin-associated immune responses in plant-microbe interactions: A review

This review explores the role of pectin, a complex polysaccharide found in the plant cell wall, in mediating immune responses during interactions between plants and microbes. The objectives of this study were to investigate the molecular mechanisms underlying pectin-mediated immune responses and to understand how these interactions shape plant-microbe communication. Pectin acts as a signaling molecule, triggering immune responses such as the production of antimicrobial compounds, reinforcement of the cell wall, and activation of defense-related genes. Pectin functions as a target for pathogen-derived enzymes, enabling successful colonization by certain microbial species. The document discusses the complexity of pectin-based immune signaling networks and their modulation by various factors, including pathogen effectors and host proteins. It also emphasizes the importance of understanding the crosstalk between pectin-mediated immunity and other defense pathways to develop strategies for enhancing plant resistance against diseases. The insights gained from this study have implications for the development of innovative approaches to enhance crop protection and disease management in agriculture. Further investigations into the components and mechanisms involved in pectin-mediated immunity will pave the way for future advancements in plant-microbe interaction research.

Functional validation of AaCaM3 response to high temperature stress in Amorphophallus albus

Amorphophallus is a perennial monocotyledonous herbaceous plant native to the southwestern region of China, widely used in various fields such as food processing, biomedicine and chemical agriculture. However, Amorphophallus is a typical thermolabile plant, and the continuous high temperature in summer have seriously affected the growth, development and economic yield of Amorphophallus in recent years. Calmodulin (CaM), a Ca2+ sensor ubiquitous in eukaryotes, is the most important multifunctional receptor protein in plant cells, which affects plant stress resistance by participating in the activities of a variety of signaling molecules. In this study, the key gene AaCaM3 for the Ca2+-CaM regulatory pathway was obtained from A. albus, the sequence analysis confirmed that it is a typical calmodulin. The qRT-PCR results demonstrated that with the passage of heat treatment time, the expression of AaCaM3 was significantly upregulated in A. albus leaves. Subcellular localization analysis revealed that AaCaM3 localized on the cytoplasm and nucleus. Meanwhile, heterologous transformation experiments have shown that AaCaM3 can significantly improve the heat tolerance of Arabidopsis under heat stress. The promoter region of AaCaM3 was sequenced 1,338 bp by FPNI-PCR and GUS staining assay showed that the promoter of AaCaM3 was a high-temperature inducible promoter. Yeast one-hybrid analysis and Luciferase activity reporting system analysis showed that the AaCaM3 promoter may interact with AaHSFA1, AaHSFA2c, AaHSP70, AaDREB2a and AaDREB2b. In conclusion, this study provides new ideas for further improving the signal transduction network of high-temperature stress in Amorphophallus.

Vitamin D, the Sunshine Molecule That Makes Us Strong: What Does Its Current Global Deficiency Imply?

Vitamin D3 deficiency and insufficiency are becoming a common global issue for us, especially in the most industrially developed countries. The only acknowledged activity of vitamin D3 in vertebrates is to promote the absorption of calcium and, therefore, allow for the mineralization of bones. Accordingly, its deficiency is associated with diseases such as rickets. Other numerous vital functions associated with vitamin D3 are yet to be considered, and the function of vitamin D2 in plants is unknown. Thus, 100 years after its discovery, the importance of vitamin D still seems to be unacknowledged (except for rickets), with little attention given to its decrease throughout the world. In this review, I suggest that vitamin D deficiency and insufficiency may be linked to the westernized lifestyle in more developed countries. Furthermore, I suggest that, rather than the calcemic activity, the main function of vitamin D is, in general, that of strengthening living organisms. I conclude with the hypothesis that vitamin D deficiency may represent a marker for a greater risk of chronic inflammatory diseases and a shorter life expectancy.

Integrated Assays of Genome-Wide Association Study, Multi-Omics Co-Localization, and Machine Learning Associated Calcium Signaling Genes with Oilseed Rape Resistance to Sclerotinia sclerotiorum

Sclerotinia sclerotiorum (Ss) is one of the most devastating fungal pathogens, causing huge yield loss in multiple economically important crops including oilseed rape. Plant resistance to Ss pertains to quantitative disease resistance (QDR) controlled by multiple minor genes. Genome-wide identification of genes involved in QDR to Ss is yet to be conducted. In this study, we integrated several assays including genome-wide association study (GWAS), multi-omics co-localization, and machine learning prediction to identify, on a genome-wide scale, genes involved in the oilseed rape QDR to Ss. Employing GWAS and multi-omics co-localization, we identified seven resistance-associated loci (RALs) associated with oilseed rape resistance to Ss. Furthermore, we developed a machine learning algorithm and named it Integrative Multi-Omics Analysis and Machine Learning for Target Gene Prediction (iMAP), which integrates multi-omics data to rapidly predict disease resistance-related genes within a broad chromosomal region. Through iMAP based on the identified RALs, we revealed multiple calcium signaling genes related to the QDR to Ss. Population-level analysis of selective sweeps and haplotypes of variants confirmed the positive selection of the predicted calcium signaling genes during evolution. Overall, this study has developed an algorithm that integrates multi-omics data and machine learning methods, providing a powerful tool for predicting target genes associated with specific traits. Furthermore, it makes a basis for further understanding the role and mechanisms of calcium signaling genes in the QDR to Ss.

Sugarcane ScCAX4 is a Negative Regulator of Resistance to Pathogen Infection

Calcium (Ca2+) is a second messenger in various physiological processes within plants. The significance of the Ca2+/H+ exchanger (CAX) has been established in facilitating Ca2+ transport in plants; however, disease resistance functions of the CAX gene remain elusive. In this study, we conducted sequence characterization and expression analysis for a sugarcane CAX gene, ScCAX4 (GenBank Accession Number: MW206380). In order to further investigate the disease resistance functions, this gene was then transiently overexpressed in Nicotiana benthamiana leaves, which were subsequently inoculated with Fusarium solani var. coeruleum. Results showed that ScCAX4 overexpression increased the susceptibility of N. benthamiana to pathogen infection by regulating the expression of genes related to salicylic acid (SA), jasmonic acid (JA), and ethylene (ET) pathways, suggesting its negative role in disease resistance. Furthermore, we genetically transformed the ScCAX4 gene into N. benthamiana and obtained three positive T2 generation lines. Interestingly, the symptomatology of transgenic plants was consistent with that of transient overexpression after pathogen inoculation. Notably, the JA content in transgenic overexpression lines was significantly higher than that in the wild-type. RNA-seq revealed that ScCAX4 could mediate multiple signaling pathways, and the JA signaling pathway played a key role in modulating disease resistance. Finally, a regulatory model was depicted for the increased susceptibility to pathogen infection conferred by the ScCAX4 gene. This study provides genetic resources for sugarcane molecular breeding and the research direction for plant CAX genes.

Impact of translational regulation on diel expression revealed by time-series ribosome profiling in Arabidopsis

Plants have developed the ability to adjust to the day/night cycle through the expression of diel genes, which allow them to effectively respond to environmental changes and optimise their growth and development. Diel oscillations also have substantial implications in many physiological processes, including photosynthesis, floral development, and environmental stress responses. The expression of diel genes is regulated by a combination of the circadian clock and responses to environmental cues, such as light and temperature. A great deal of information is available on the transcriptional regulation of diel gene expression. However, the extent to which translational regulation is involved in controlling diel changes in expression is not yet clear. To investigate the impact of translational regulation on diel expression, we conducted Ribo-seq and RNA-seq analyses on a time-series sample of Arabidopsis shoots cultivated under a 12 h light/dark cycle. Our results showed that translational regulation is involved in about 71% of the genes exhibiting diel changes in mRNA abundance or translational activity, including clock genes, many of which are subject to both translational and transcriptional control. They also revealed that the diel expression of glycosylation and ion-transporter-related genes is mainly established through translational regulation. The expression of several diel genes likely subject to translational regulation through upstream open-reading frames was also determined.

Genome-wide identification of the CNGC gene family and negative regulation of drought tolerance by HvCNGC3 and HvCNGC16 in transgenic Arabidopsis thaliana

Cyclic nucleotide-gated ion channels (CNGCs), as non-selective cation channels, play essential roles in plant growth and stress responses. However, they have not been identified in Qingke (Hordeum vulgare L.). Here, we performed a comprehensive genome-wide identification and function analysis of the HvCNGC gene family to determine its role in drought tolerance. Phylogenetic analysis showed that 27 HvCNGC genes were divided into four groups and unevenly located on seven chromosomes. Transcription analysis revealed that two closely related members of HvCNGC3 and HvCNGC16 were highly induced and the expression of both genes were distinctly different in two extremely drought-tolerant materials. Transient expression revealed that the HvCNGC3 and HvCNGC16 proteins both localized to the plasma membrane and karyotheca. Overexpression of HvCNGC3 and HvCNGC16 in Arabidopsis thaliana led to impaired seed germination and seedling drought tolerance, which was accompanied by higher hydrogen peroxide (H2O2), malondialdehyde (MDA), proline accumulation and increased cell damage. In addition, HvCNGC3 and HvCNGC16-overexpression lines reduced ABA sensitivity, as well as lower expression levels of some ABA biosynthesis and stress-related gene in transgenic lines. Furthermore, Yeast two hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) assays revealed that HvCNGC3 and HvCNGC16 interacted with calmodulin/calmodulin-like proteins (CaM/CML), which, as calcium sensors, participate in the perception and decoding of intracellular calcium signaling. Thus, this study provides information on the CNGC gene family and provides insight into the function and potential regulatory mechanism of HvCNGC3 and HvCNGC16 in drought tolerance in Qingke.

CAMTA3 repressor destabilization triggers TIR domain protein TN2-mediated autoimmunity in the Arabidopsis exo70B1 mutant

Calcium-dependent protein kinases (CPKs) can decode and translate intracellular calcium signals to induce plant immunity. Mutation of the exocyst subunit gene EXO70B1 causes autoimmunity that depends on CPK5 and the Toll/interleukin-1 receptor (TIR) domain resistance protein TIR-NBS2 (TN2), where direct interaction with TN2 stabilizes CPK5 kinase activity. However, how the CPK5-TN2 interaction initiates downstream immune responses remains unclear. Here, we show that, besides CPK5 activity, the physical interaction between CPK5 and functional TN2 triggers immune activation in exo70B1 and may represent reciprocal regulation between CPK5 and the TIR domain functions of TN2 in Arabidopsis (Arabidopsis thaliana). Moreover, we detected differential phosphorylation of the calmodulin-binding transcription activator 3 (CAMTA3) in the cpk5 background. CPK5 directly phosphorylates CAMTA3 at S964, contributing to its destabilization. The gain-of-function CAMTA3A855V variant that resists CPK5-induced degradation rescues immunity activated through CPK5 overexpression or exo70B1 mutation. Thus, CPK5-mediated immunity is executed through CAMTA3 repressor degradation via phosphorylation-induced and/or calmodulin-regulated processes. Conversely, autoimmunity in camta3 also partially requires functional CPK5. While the TIR domain activity of TN2 remains to be tested, our study uncovers a TN2-CPK5-CAMTA3 signaling module for exo70B1-mediated autoimmunity, highlighting the direct embedding of a calcium-sensing decoder element within resistance signalosomes.

The complex transcriptional regulation of heat stress response in maize

As one of the most important food and feed crops worldwide, maize suffers much more tremendous damages under heat stress compared to other plants, which seriously inhibits plant growth and reduces productivity. To mitigate the heat-induced damages and adapt to high temperature environment, plants have evolved a series of molecular mechanisms to sense, respond and adapt high temperatures and heat stress. In this review, we summarized recent advances in molecular regulations underlying high temperature sensing, heat stress response and memory in maize, especially focusing on several important pathways and signals in high temperature sensing, and the complex transcriptional regulation of ZmHSFs (Heat Shock Factors) in heat stress response. In addition, we highlighted interactions between ZmHSFs and several epigenetic regulation factors in coordinately regulating heat stress response and memory. Finally, we laid out strategies to systematically elucidate the regulatory network of maize heat stress response, and discussed approaches for breeding future heat-tolerance maize.

Channels of Evolution: Unveiling Evolutionary Patterns in Diatom Ca2+ Signalling

Diatoms are important primary producers in marine and freshwater environments, but little is known about the signalling mechanisms they use to detect changes in their environment. All eukaryotic organisms use Ca2+ signalling to perceive and respond to environmental stimuli, employing a range of Ca2+-permeable ion channels to facilitate the movement of Ca2+ across cellular membranes. We investigated the distribution of different families of Ca2+ channels in diatom genomes, with comparison to other members of the stramenopile lineage. The four-domain voltage-gated Ca2+ channels (Cav) are present in some centric diatoms but almost completely absent in pennate diatoms, whereas single-domain voltage-gated EukCatA channels were found in all diatoms. Glutamate receptors (GLRs) and pentameric ligand-gated ion channels (pLGICs) also appear to have been lost in several pennate species. Transient receptor potential (TRP) channels are present in all diatoms, but have not undergone the significant expansion seen in brown algae. All diatom species analysed lacked the mitochondrial uniporter (MCU), a highly conserved channel type found in many eukaryotes, including several stramenopile lineages. These results highlight the unique Ca2+-signalling toolkit of diatoms and indicate that evolutionary gains or losses of different Ca2+ channels may contribute to differences in cellular-signalling mechanisms between species.

Functional differentiation and genetic diversity of rice cation exchanger (CAX) genes and their potential use in rice improvement

Cation exchanger (CAX) genes play an important role in plant growth/development and response to biotic and abiotic stresses. Here, we tried to obtain important information on the functionalities and phenotypic effects of CAX gene family by systematic analyses of their expression patterns, genetic diversity (gene CDS haplotypes, structural variations, gene presence/absence variations) in 3010 rice genomes and nine parents of 496 Huanghuazhan introgression lines, the frequency shifts of the predominant gcHaps at these loci to artificial selection during modern breeding, and their association with tolerances to several abiotic stresses. Significant amounts of variation also exist in the cis-regulatory elements (CREs) of the OsCAX gene promoters in 50 high-quality rice genomes. The functional differentiation of OsCAX gene family were reflected primarily by their tissue and development specific expression patterns and in varied responses to different treatments, by unique sets of CREs in their promoters and their associations with specific agronomic traits/abiotic stress tolerances. Our results indicated that OsCAX1a and OsCAX2 as general signal transporters were in many processes of rice growth/development and responses to diverse environments, but they might be of less value in rice improvement. OsCAX1b, OsCAX1c, OsCAX3 and OsCAX4 was expected to be of potential value in rice improvement because of their associations with specific traits, responsiveness to specific abiotic stresses or phytohormones, and relatively high gcHap and CRE diversity. Our strategy was demonstrated to be highly efficient to obtain important genetic information on genes/alleles of specific gene family and can be used to systematically characterize the other rice gene families.

Integrative physiology and transcriptome reveal salt-tolerance differences between two licorice species: Ion transport, Casparian strip formation and flavonoids biosynthesis

BACKGROUND

Glycyrrhiza inflata Bat. and Glycyrrhiza uralensis Fisch. are both original plants of 'Gan Cao' in the Chinese Pharmacopoeia, and G. uralensis is currently the mainstream variety of licorice and has a long history of use in traditional Chinese medicine. Both of these species have shown some degree of tolerance to salinity, G. inflata exhibits higher salt tolerance than G. uralensis and can grow on saline meadow soils and crusty saline soils. However, the regulatory mechanism responsible for the differences in salt tolerance between different licorice species is unclear. Due to land area-related limitations, the excavation and cultivation of licorice varieties in saline-alkaline areas that both exhibit tolerance to salt and contain highly efficient active substances are needed. The systematic identification of the key genes and pathways associated with the differences in salt tolerance between these two licorice species will be beneficial for cultivating high-quality salt-tolerant licorice G. uralensis plant varieties and for the long-term development of the licorice industry. In this research, the differences in growth response indicators, ion accumulation, and transcription expression between the two licorice species were analyzed.

RESULTS

This research included a comprehensive comparison of growth response indicators, including biomass, malondialdehyde (MDA) levels, and total flavonoids content, between two distinct licorice species and an analysis of their ion content and transcriptome expression. In contrast to the result found for G. uralensis, the salt treatment of G. inflata ensured the stable accumulation of biomass and total flavonoids at 0.5 d, 15 d, and 30 d and the restriction of Na+ to the roots while allowing for more K+ and Ca2+ accumulation. Notably, despite the increase in the Na+ concentration in the roots, the MDA concentration remained low. Transcriptome analysis revealed that the regulatory effects of growth and ion transport on the two licorice species were strongly correlated with the following pathways and relevant DEGs: the TCA cycle, the pentose phosphate pathway, and the photosynthetic carbon fixation pathway involved in carbon metabolism; Casparian strip formation (lignin oxidation and translocation, suberin formation) in response to Na+; K+ and Ca2+ translocation, organic solute synthesis (arginine, polyamines, GABA) in response to osmotic stresses; and the biosynthesis of the nonenzymatic antioxidants carotenoids and flavonoids in response to antioxidant stress. Furthermore, the differential expression of the DEGs related to ABA signaling in hormone transduction and the regulation of transcription factors such as the HSF and GRAS families may be associated with the remarkable salt tolerance of G. inflata.

CONCLUSION

Compared with G. uralensis, G. inflata exhibits greater salt tolerance, which is primarily attributable to factors related to carbon metabolism, endodermal barrier formation and development, K+ and Ca2+ transport, biosynthesis of carotenoids and flavonoids, and regulation of signal transduction pathways and salt-responsive transcription factors. The formation of the Casparian strip, especially the transport and oxidation of lignin precursors, is likely the primary reason for the markedly higher amount of Na+ in the roots of G. inflata than in those of G. uralensis. The tendency of G. inflata to maintain low MDA levels in its roots under such conditions is closely related to the biosynthesis of flavonoids and carotenoids and the maintenance of the osmotic balance in roots by the absorption of more K+ and Ca2+ to meet growth needs. These findings may provide new insights for developing and cultivating G. uralensis plant species selected for cultivation in saline environments or soils managed through agronomic practices that involve the use of water with a high salt content.

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.

Arabidopsis Calmodulin-like Proteins CML13 and CML14 Interact with Calmodulin-Binding Transcriptional Activators and Function in Salinity Stress Response

Eukaryotic cells use calcium ions (Ca2+) as second messengers, particularly in response to abiotic and biotic stresses. These signals are detected by Ca2+ sensor proteins, such as calmodulin (CaM), which regulate the downstream target proteins. Plants also possess many CaM-like proteins (CMLs), most of which remain unstudied. We recently demonstrated that Arabidopsis CML13 and CML14 interact with proteins containing isoleucine/glutamine (IQ) domains, including CaM-binding transcriptional activators (CAMTAs). Here, we show that CaM, CML13 and CML14 bind all six members of the Arabidopsis CAMTA family. Using a combination of in planta and in vitro protein-interaction assays, we tested 11 members of the CaM/CML family and demonstrated that only CaM, CML13 and CML14 bind to CAMTA IQ domains. CaM, CML13 and CML14 showed Ca2+-independent binding to the IQ region of CAMTA6 and CAMTA3, and CAMTA6 in vitro exhibited some specificity toward individual IQ domains within CAMTA6 in split-luciferase in planta assays. We show that cml13 mutants exhibited enhanced salinity tolerance during germination compared to wild-type plants, a phenotype similar to camta6 mutants. In contrast, plants overexpressing CML13-GFP or CML14-GFP in the wild-type background showed increased NaCl sensitivity. Under mannitol stress, cml13 mutants were more susceptible than camta6 mutants or wild-type plants. The phenotype of cml13 mutants could be rescued with the wild-type CML13 gene. Several salinity-marker genes under CAMTA6 control were similarly misregulated in both camta6 and cml13 mutants, further supporting a role for CML13 in CAMTA6 function. Collectively, our data suggest that CML13 and CML14 participate in abiotic stress signaling as CAMTA effectors.

A conditional mutation in a wheat (Triticum aestivum L.) gene regulating root morphology

KEY MESSAGE

Characterisation and genetic mapping of a key gene defining root morphology in bread wheat. Root morphology is central to plants for the efficient uptake up of soil water and mineral nutrients. Here we describe a conditional mutant of hexaploid wheat (Triticum aestivum L.) that when grown in soil with high Ca2+ develops a larger rhizosheath accompanied with shorter roots than the wild type. In wheat, rhizosheath size is a reliable surrogate for root hair length and this was verified in the mutant which possessed longer root hairs than the wild type when grown in high Ca2+ soil. We named the mutant Stumpy and showed it to be due to a single semi-dominant mutation. The short root phenotype at high Ca2+ was due to reduced cellular elongation which might also explain the long root hair phenotype. Analysis of root cell walls showed that the polysaccharide composition of Stumpy roots is remodelled when grown at non-permissive (high) Ca2+ concentrations. The mutation mapped to chromosome 7B and sequencing of the 7B chromosomes in both wild type and Stumpy identified a candidate gene underlying the Stumpy mutation. As part of the process to determine whether the candidate gene was causative, we identified wheat lines in a Cadenza TILLING population with large rhizosheaths but accompanied with normal root length. This finding illustrates the potential of manipulating the gene to disconnect root length from root hair length as a means of developing wheat lines with improved efficiency of nutrient and water uptake. The Stumpy mutant will be valuable for understanding the mechanisms that regulate root morphology in wheat.

Genome-wide identification of CBL gene family in Salvia miltiorrhiza and the characterization of SmCBL3 under salt stress

In plants, CBL mediated calcium signaling is widely involved in the response to plant stresses of adversity. However, to date, no comprehensive studies have been conducted on CBL family members in Salvia miltiorrhiza. Herein, we identified 8 SmCBLs in S. miltiorrhiza, and phylogenetic analysis classified SmCBLs into four groups. Analysis of cis-acting elements revealed that SmCBLs mostly have light-responsive and hormone-responsive elements. Tissue expression analysis indicated that almost all of SmCBLs were expressed in roots than in leaves and flowers. SmCBL3 responded to Abscisic Acid (ABA), polyethylene glycol (PEG), and NaCl treatments. Transgenic Arabidopsis thaliana that overexpressed SmCBL3 had higher germination rates and longer roots than the wild type (WT) when exposed to salt stress. Additionally, the transgenic lines exhibited higher levels of chlorophyll, proline, superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activity and SOS1, NHX1 and P5CS1 expression than WT, and lower levels of malondialdehyde (MDA). Furthermore, SmCBL3 interacts with SmCIPK9. In conclusion, we analyzed the protein physicochemical properties, evolutionary relationships, gene structures, and expression profiles of the SmCBL gene families in S. miltiorrhiza. Overexpression of SmCBL3 improves the salt tolerance of transgenic Arabidopsis. This study demonstrated that SmCBL3 is a positive regulator of plant salt tolerance, so the use of overexpressed SmCBL3 may serve as a potential strategy to enhance plant salt tolerance.

Research progress on the physiological response and molecular mechanism of cold response in plants

Low temperature is a critical environmental stress factor that restricts crop growth and geographical distribution, significantly impacting crop quality and yield. When plants are exposed to low temperatures, a series of changes occur in their external morphology and internal physiological and biochemical metabolism. This article comprehensively reviews the alterations and regulatory mechanisms of physiological and biochemical indices, such as membrane system stability, redox system, fatty acid content, photosynthesis, and osmoregulatory substances, in response to low-temperature stress in plants. Furthermore, we summarize recent research on signal transduction and regulatory pathways, phytohormones, epigenetic modifications, and other molecular mechanisms mediating the response to low temperatures in higher plants. In addition, we outline cultivation practices to improve plant cold resistance and highlight the cold-related genes used in molecular breeding. Last, we discuss future research directions, potential application prospects of plant cold resistance breeding, and recent significant breakthroughs in the research and application of cold resistance mechanisms.

Genome-Wide Identification of the IQM Gene Family and Their Transcriptional Responses to Abiotic Stresses in Kiwifruit (Actinidia eriantha)

IQM is a plant-specific calcium-binding protein that plays a pivotal role in various aspects of plant growth response to stressors. We investigated the IQM gene family and its expression patterns under diverse abiotic stresses and conducted a comprehensive analysis and characterization of the AeIQMs, including protein structure, genomic location, phylogenetic relationships, gene expression profiles, salt tolerance, and expression patterns of this gene family under different abiotic stresses. Based on phylogenetic analysis, these 10 AeIQMs were classified into three distinct subfamilies (I-III). Analysis of the protein motifs revealed a considerable level of conservation among these AeIQM proteins within their respective subfamilies in kiwifruit. The genomic distribution of the 10 AeIQM genes spanned across eight chromosomes, where four pairs of IQM gene duplicates were associated with segmental duplication events. qRT-PCR analysis revealed diverse expression patterns of these AeIQM genes under different hormone treatments, and most AeIQMs showed inducibility by salt stress. Further investigations indicated that overexpression of AeIQMs in yeast significantly enhanced salt tolerance. These findings suggest that AeIQM genes might be involved in hormonal signal transduction and response to abiotic stress in Actinidia eriantha. In summary, this study provides valuable insights into the physiological functions of IQMs in kiwifruit.

A Ca2+ sensor BraCBL1.2 involves in BraCRa-mediated clubroot resistance in Chinese cabbage

Clubroot disease caused by Plasmodiophora brassicae (P. brassicae) severely threatens the cultivation of Cruciferous plants, especially Chinese cabbage. Recently, resistance genes in plants have been reported to encode for a Ca2+-permeable channel in the plasma membrane, which can mediate the cytosolic Ca2+ increase in plant cells upon pathogen attack. However, the downstream Ca2+ sensor and decoder are still unknown. In this study, we identified the virulent and avirulent P. brassicae isolates (Pbs) of two near isogenic lines, CR 3-2 and CS 3-2, with CR 3-2 harboring clubroot resistant gene BraCRa. The transcriptomic analysis was then conducted with CR 3-2 after inoculating with virulent isolate PbE and avirulent isolate Pb4. From the differentially expressed genes of transcriptomic data, we identified a Ca2+-sensor encoding gene, BraCBL1.2, that was highly induced in CR 3-2 during infection by Pb4 but not by PbE. Moreover, GUS histochemical staining and subcellular localization analysis revealed that BraCBL1.2 was specifically expressed in the root hair cells of Arabidopsis and encoded a putative Ca2+ sensor localized in the plasma membrane. We also developed an assay to investigate the BraCRa-mediated hypersensitive response (HR) in tobacco leaves. The results suggest that BraCBL1.2 is involved in the BraCRa-mediated plant ETI immune response against P. brassicae. In addition, we verified that overexpression of BraCBL1.2 enhanced clubroot resistance in Arabidopsis. Collectively, our data identified the involvement of a Ca2+ sensor in BraCRa-mediated clubroot resistance in Chinese cabbage, providing a theoretical basis for further research on the resistance of Chinese cabbage to P. brassicae.

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.

Can nutrients act as signals under abiotic stress?

Plant cells are in constant communication to coordinate development processes and environmental reactions. Under stressful conditions, such communication allows the plant cells to adjust their activities and development. This is due to intercellular signaling events which involve several components. In plant development, cell-to-cell signaling is ensured by mobile signals hormones, hydrogen peroxide (H2O2), nitric oxide (NO), or hydrogen sulfide (H2S), as well as several transcription factors and small RNAs. Mineral nutrients, including macro and microelements, are determinant factors for plant growth and development and are, currently, recognized as potential signal molecules. This review aims to highlight the role of nutrients, particularly calcium, potassium, magnesium, nitrogen, phosphorus, and iron as signaling components with special attention to the mechanism of response against stress conditions.

Genome-wide analyses of calmodulin and calmodulin-like proteins in the halophyte Nitraria sibirica reveal their involvement in response to salinity, drought and cold stress

The calmodulin (CaM) and calmodulin-like (CML) proteins are major calcium sensors that play a critical role in environmental stimulus response in plants. Nevertheless, the CaM/CML proteins from the specific plants with extreme tolerance to abiotic stresses remained so far uncharacterized. In this study, 66 candidate proteins (three NsCaMs and sixty-three NsCMLs) were identified from the halophyte Nitraria sibirica, which can withstand an extreme salinity. Bioinformatic analysis of upstream cis-acting elements predicted the potential involvement of NsCaM/CMLs in abiotic stress responses and various hormone responses. Additionally, the Nitraria sibirica transcriptome revealed that 17 and 7 NsCMLs were significantly upregulated under 100 mM or 400 mM NaCl treatment. Transcription of most salt-responsive genes was similarly upregulated under cold stress, yet downregulated under drought treatment. Moreover, predictive subcellular localization analysis suggested that the stress-responsive NsCML proteins mainly localize at the cellular membrane and within the nucleus. Furthermore, transgenic overexpression of two NsCMLs (NISI03G1136 and NISI01G1645) was found to mitigate H2O2 accumulation caused by salt stress. These results provide insights into the potential function of Nitraria sibirica CaM/CML proteins, which could aid the investigation of molecular mechanisms of extreme tolerance to abiotic stresses in halophytes.

An Arabidopsis mutant line lacking the mitochondrial calcium transport regulator MICU shows an altered metabolite profile

Plant metabolism is constantly changing and requires input signals for efficient regulation. The mitochondrial calcium uniporter (MCU) couples organellar and cytoplasmic calcium oscillations leading to oxidative metabolism regulation in a vast array of species. In Arabidopsis thaliana, genetic deletion of AtMICU leads to altered mitochondrial calcium handling and ultrastructure. Here we aimed to further assess the consequences upon genetic deletion of AtMICU. Our results confirm that AtMICU safeguards intracellular calcium transport associated with carbohydrate, amino acid, and phytol metabolism modifications. The implications of such alterations are discussed.

Survival of Nutrient-Starved Diatoms Under Ocean Acidification: Perspective from Nutrient Sensing, Cadmium Detection, and Nitrogen Assimilation

Increased anthropogenic emissions of carbon dioxide (CO2) have resulted in ocean acidification (OA) that is intertwined with enhanced ocean stratification. Diatoms are assumed to suffer from a more nutrient-limited condition in the future ocean. This study aimed to explore how OA affects the diatom dynamics under nutrient-poor conditions and the ability of diatoms to perceive nutrients (nitrogen, phosphorus, silicon, and trace metals) and cadmium (Cd) stimuli and assimilate nitrogen when receiving nutrients or Cd supplementation. Our study observed that diatom population grown under OA condition declined faster than those grown under ambient condition. Ocean acidification greatly lower intracellular Ca2+ concentration in diatom cells. Intracellular Ca2+ burst was involved in phosphorus accumulation but not in nitrogen, silicon, essential metals, and cadmium uptake. Our data demonstrate slower NO3- assimilation rates of diatoms grown in acidified seawater. Our study also indicates that diatoms have a poor perception of phosphorus availability under OA condition.

Calcium Signaling and the Response to Heat Shock in Crop Plants

Climate change and the increasing frequency of high temperature (HT) events are significant threats to global crop yields. To address this, a comprehensive understanding of how plants respond to heat shock (HS) is essential. Signaling pathways involving calcium (Ca2+), a versatile second messenger in plants, encode information through temporal and spatial variations in ion concentration. Ca2+ is detected by Ca2+-sensing effectors, including channels and binding proteins, which trigger specific cellular responses. At elevated temperatures, the cytosolic concentration of Ca2+ in plant cells increases rapidly, making Ca2+ signals the earliest response to HS. In this review, we discuss the crucial role of Ca2+ signaling in raising plant thermotolerance, and we explore its multifaceted contributions to various aspects of the plant HS response (HSR).

Transcriptome analysis of tomato plants following salicylic acid-induced immunity against Clavibacter michiganensis ssp. michiganensis

Salicylic acid (SA) is known to be involved in the immunity against Clavibacter michiganensis ssp. michiganensis (Cmm) that causes bacterial canker in tomato. To identify the candidate genes associated with SA-inducible Cmm resistance, transcriptome analysis was conducted via RNA sequencing in tomato plants treated with SA. SA treatment upregulated various defense-associated genes, such as PR and GST genes, in tomato cotyledons. A comparison of SA- and Cmm-responsive genes revealed that both SA treatment and Cmm infection commonly upregulated a large number of genes. Gene Ontology (GO) analysis indicated that the GO terms associated with plant immunity were over-represented in both SA- and Cmm-induced genes. The genes commonly downregulated by both SA treatment and Cmm infection were associated with the cell cycle and may be involved in growth and immunity trade-off through cell division. After SA treatment, several proteins that were predicted to play a role in immune signaling, such as resistance gene analogs, Ca2+ sensors, and WRKY transcription factors, were transcriptionally upregulated. The W-box element, which was targeted by WRKYs, was over-represented in the promoter regions of genes upregulated by both SA treatment and Cmm infection, supporting the speculation that WRKYs are important for the SA-mediated immunity against Cmm. Prediction of protein-protein interactions suggested that genes encoding receptor-like kinases and EF-hand proteins play an important role in immune signaling. Thus, various candidate genes involved in SA-inducible Cmm resistance were identified.

Ion Changes and Signaling under Salt Stress in Wheat and Other Important Crops

High concentrations of sodium (Na+), chloride (Cl-), calcium (Ca2+), and sulphate (SO42-) are frequently found in saline soils. Crop plants cannot successfully develop and produce because salt stress impairs the uptake of Ca2+, potassium (K+), and water into plant cells. Different intracellular and extracellular ionic concentrations change with salinity, including those of Ca2+, K+, and protons. These cations serve as stress signaling molecules in addition to being essential for ionic homeostasis and nutrition. Maintaining an appropriate K+:Na+ ratio is one crucial plant mechanism for salt tolerance, which is a complicated trait. Another important mechanism is the ability for fast extrusion of Na+ from the cytosol. Ca2+ is established as a ubiquitous secondary messenger, which transmits various stress signals into metabolic alterations that cause adaptive responses. When plants are under stress, the cytosolic-free Ca2+ concentration can rise to 10 times or more from its resting level of 50-100 nanomolar. Reactive oxygen species (ROS) are linked to the Ca2+ alterations and are produced by stress. Depending on the type, frequency, and intensity of the stress, the cytosolic Ca2+ signals oscillate, are transient, or persist for a longer period and exhibit specific "signatures". Both the influx and efflux of Ca2+ affect the length and amplitude of the signal. According to several reports, under stress Ca2+ alterations can occur not only in the cytoplasm of the cell but also in the cell walls, nucleus, and other cell organelles and the Ca2+ waves propagate through the whole plant. Here, we will focus on how wheat and other important crops absorb Na+, K+, and Cl- when plants are under salt stress, as well as how Ca2+, K+, and pH cause intracellular signaling and homeostasis. Similar mechanisms in the model plant Arabidopsis will also be considered. Knowledge of these processes is important for understanding how plants react to salinity stress and for the development of tolerant crops.

Rice OsANN9 Enhances Drought Tolerance through Modulating ROS Scavenging Systems

Drought is a critical abiotic stress which leads to crop yield and a decrease in quality. Annexins belong to a multi-gene family of calcium- and lipid-binding proteins and play diverse roles in plant growth and development. Herein, we report a rice annexin protein, OsANN9, which in addition to regular annexin repeats and type-II Ca2+ binding sites, also consists of a C2H2-type zinc-finger domain. We found that the expression of OsANN9 was upregulated by polyethylene glycol (PEG) or water-deficient treatment. Moreover, plants that overexpressed OsANN9 had increased survival rates under drought stress, while both OsANN9-RNAi and osann9 mutants showed sensitivity to drought. In addition, the overexpression of OsANN9 increased superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activities, which regulate reactive oxygen species homeostasis. Collectively, these findings indicate that OsANN9 may function as a positive regulator in response to drought stress by modulating antioxidant accumulation. Interestingly, the setting rates of osann9 mutant rice plants significantly decreased in comparison to wild-type plants, suggesting that OsANN9 might be involved in other molecular mechanisms in the rice seed development stage.

Transcriptome profiling of Bergenia purpurascens under cold stress

Bergenia purpurascens is an important medicinal, edible and ornamental plant. It generally grows in high-altitude areas with complex climates. There have been no reports about how B. purpurascens survives under cold stress. Here, the B. purpurascens under low temperature were subjected to transcriptomics analysis to explore the candidate genes and pathways that involved in the cold tolerance of B. purpurascens. Compared with the control treatment, we found 9,600 up-regulated differentially expressed genes (DEGs) and 7,055 down-regulated DEGs. A significant number of DEGs were involved in the Ca2+ signaling pathway, mitogen-activated protein kinase (MAPK) cascade, plant hormone signaling pathway, and lipid metabolism. A total of 400 transcription factors were found to respond to cold stress, most of which belonged to the MYB and AP2/ERF families. Five novel genes were found to be potential candidate genes involved in the cold tolerance of B. purpurascens. The study provide insights into further investigation of the molecular mechanism of how B. purpurascens survives under cold stress.

The vacuolar Ca2+ transporter CATION EXCHANGER 2 regulates cytosolic calcium homeostasis, hypoxic signaling, and response to flooding in Arabidopsis thaliana

Flooding represents a major threat to global agricultural productivity and food security, but plants are capable of deploying a suite of adaptive responses that can lead to short- or longer-term survival to this stress. One cellular pathway thought to help coordinate these responses is via flooding-triggered Ca2+ signaling. We have mined publicly available transcriptomic data from Arabidopsis subjected to flooding or low oxygen stress to identify rapidly upregulated, Ca2+ -related transcripts. We then focused on transporters likely to modulate Ca2+ signals. Candidates emerging from this analysis included AUTOINHIBITED Ca2+ ATPASE 1 and CATION EXCHANGER 2. We therefore assayed mutants in these genes for flooding sensitivity at levels from growth to patterns of gene expression and the kinetics of flooding-related Ca2+ changes. Knockout mutants in CAX2 especially showed enhanced survival to soil waterlogging coupled with suppressed induction of many marker genes for hypoxic response and constitutive activation of others. CAX2 mutants also generated larger and more sustained Ca2+ signals in response to both flooding and hypoxic challenges. CAX2 is a Ca2+ transporter located on the tonoplast, and so these results are consistent with an important role for vacuolar Ca2+ transport in the signaling systems that trigger flooding response.

AtFH5-labeled secretory vesicles-dependent calcium oscillation drives exocytosis and stepwise bulge during pollen germination

Pollen germination is an essential step for delivering sperm cells to the embryo sac for double fertilization in flowering plants. The cytosolic Ca2+ concentration ([Ca2+]cyt) and vesicle dynamics are critical for pollen germination, but their potential correlation in pollen grains is not fully understood. Here, we report that [Ca2+]cyt oscillates periodically at the prospective germination sites during pollen germination. The [Ca2+]cyt is mainly from extracellular Ca2+ ([Ca2+]ext) influx, which implicates the Ca2+-permeable ion channel cyclic nucleotide-gated channel 18 (CNGC18). The [Ca2+]cyt oscillations spatiotemporally correlate with the accumulation of secretory vesicles labeled by a formin protein AtFH5, and disruption of vesicle accumulation inhibits the [Ca2+]cyt oscillations. In turn, the [Ca2+]cyt oscillations promote exocytosis, which leads to stepwise cell extension during pollen germination. Together, these data provide a timeline of vesicle dynamics, calcium oscillation, and exocytosis during pollen germination and highlight the importance of the correlation of these events for pollen germination.

Genome-Wide Identification and Characterization of CDPK Gene Family in Cultivated Peanut (Arachis hypogaea L.) Reveal Their Potential Roles in Response to Ca Deficiency

This study identified 45 calcium-dependent protein kinase (CDPK) genes in cultivated peanut (Arachis hypogaea L.), which are integral in plant growth, development, and stress responses. These genes, classified into four subgroups based on phylogenetic relationships, are unevenly distributed across all twenty peanut chromosomes. The analysis of the genetic structure of AhCDPKs revealed significant similarity within subgroups, with their expansion primarily driven by whole-genome duplications. The upstream promoter sequences of AhCDPK genes contained 46 cis-acting regulatory elements, associated with various plant responses. Additionally, 13 microRNAs were identified that target 21 AhCDPK genes, suggesting potential post-transcriptional regulation. AhCDPK proteins interacted with respiratory burst oxidase homologs, suggesting their involvement in redox signaling. Gene ontology and KEGG enrichment analyses affirmed AhCDPK genes' roles in calcium ion binding, protein kinase activity, and environmental adaptation. RNA-seq data revealed diverse expression patterns under different stress conditions. Importantly, 26 AhCDPK genes were significantly induced when exposed to Ca deficiency during the pod stage. During the seedling stage, four AhCDPKs (AhCDPK2/-25/-28/-45) in roots peaked after three hours, suggesting early signaling roles in pod Ca nutrition. These findings provide insights into the roles of CDPK genes in plant development and stress responses, offering potential candidates for predicting calcium levels in peanut seeds.

Calcium-Dependent Protein Kinase 5 (OsCPK5) Overexpression in Upland Rice (Oryza sativa L.) under Water Deficit

Water deficit significantly affects global crop growth and productivity, particularly in water-limited environments, such as upland rice cultivation, reducing grain yield. Plants activate various defense mechanisms during water deficit, involving numerous genes and complex metabolic pathways. Exploring homologous genes that are linked to enhanced drought tolerance through the use of genomic data from model organisms can aid in the functional validation of target species. We evaluated the upland rice OsCPK5 gene, an A. thaliana AtCPK6 homolog, by overexpressing it in the BRSMG Curinga cultivar. Transformants were assessed using a semi-automated phenotyping platform under two irrigation conditions: regular watering, and water deficit applied 79 days after seeding, lasting 14 days, followed by irrigation at 80% field capacity. The physiological data and leaf samples were collected at reproductive stages R3, R6, and R8. The genetically modified (GM) plants consistently exhibited higher OsCPK5 gene expression levels across stages, peaking during grain filling, and displayed reduced stomatal conductance and photosynthetic rate and increased water-use efficiency compared to non-GM (NGM) plants under drought. The GM plants also exhibited a higher filled grain percentage under both irrigation conditions. Their drought susceptibility index was 0.9 times lower than that of NGM plants, and they maintained a higher chlorophyll a/b index, indicating sustained photosynthesis. The NGM plants under water deficit exhibited more leaf senescence, while the OsCPK5-overexpressing plants retained their green leaves. Overall, OsCPK5 overexpression induced diverse drought tolerance mechanisms, indicating the potential for future development of more drought-tolerant rice cultivars.

A chitosan-coated lentinan-loaded calcium alginate hydrogel induces broad-spectrum resistance to plant viruses by activating Nicotiana benthamiana calmodulin-like (CML) protein 3

Control of plant virus diseases largely depends on the induced plant defence achieved by the external application of synthetic chemical inducers with the ability to modify defence-signalling pathways. However, most of the molecular mechanisms underlying these chemical inducers remain unknown. Here, we developed a chitosan-coated lentinan-loaded hydrogel and discovered how it protects plants from different virus infections. The hydrogel was synthesized by coating chitosan on the surface of the calcium alginate-lentinan (LNT) hydrogel (SL-gel) to form a CSL-gel. CSL-gels exhibit the capacity to prolong the stable release of lentinan and promote Ca2+ release. Application of CSL-gels on the root of plants induces broad-spectrum resistance against plant viruses (TMV, TRV, PVX and TuMV). RNA-seq analysis identified that Nicotiana benthamiana calmodulin-like protein gene 3 (NbCML3) is upregulated by the sustained release of Ca2+ from the CSL-gel, and silencing and overexpression of NbCML alter the susceptibility and resistance of tobacco to TMV. Our findings provide evidence that this novel and synthetic CSL-gel strongly inhibits the infection of plant viruses by the sustainable release of LNT and Ca2+ . This study uncovers a novel mode of action by which CSL-gels trigger NbCML3 expression through the stable and sustained release of Ca2+ .

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.

How do plants maintain pH and ion homeostasis under saline-alkali stress?

Salt and alkaline stresses often occur together, severely threatening plant growth and crop yields. Salt stress induces osmotic stress, ionic stress, and secondary stresses, such as oxidative stress. Plants under saline-alkali stress must develop suitable mechanisms for adapting to the combined stress. Sustained plant growth requires maintenance of ion and pH homeostasis. In this review, we focus on the mechanisms of ion and pH homeostasis in plant cells under saline-alkali stress, including regulation of ion sensing, ion uptake, ion exclusion, ion sequestration, and ion redistribution among organs by long-distance transport. We also discuss outstanding questions in this field.

Phenotypic and microarray analysis reveals salinity stress-induced oxidative tolerance in transgenic rice expressing a DEAD-box RNA helicase, OsDB10

Helicases are the motor proteins not only involved in the process of mRNA metabolism but also played a significant role in providing abiotic stresses tolerance. In this study, a DEAD-box RNA helicase OsDB10 was cloned and functionally characterized. The transcript levels of OsDB10 were increased both in shoot and root upon salt, heat, cold, and ABA application and was more prominent in shoot compared to root. Genomic integration of OsDB10 in transgenic rice was confirmed by PCR, Southern blot and qRT-PCR analysis. The transgenic plants showed quicker seed germination, reduced necrosis, higher chlorophyll, more survival rate, better seedling growth, and produced more grain yield under salinity stress. Furthermore, transgenic lines also accumulated less Na+ and high K+ ions and salinity tolerance of the transgenic were also assayed by measuring different bio-physiological indices. Moreover, the OsDB10 transgenic plants showed enhanced tolerance to salinity-induced oxidative stress by scavenging ROS and increased activity of antioxidants enzymes. Microarray analysis showed upregulation of transcriptional regulations and metabolic reprogramming as OsDB10 overexpression modulates the expression of many other genes. Altogether, our results confirmed that OsDB10 is a functional DEAD-box RNA helicase and played vital roles in plant defence response against salinity stress.

Plant Ca2+-ATPases: From biochemistry to signalling

Calcium (Ca2+)-ATPases are ATP-dependent enzymes that transport Ca2+ ions against their electrochemical gradient playing the fundamental biological function of keeping the free cytosolic Ca2+ concentration in the submicromolar range to prevent cytotoxic effects. In plants, type IIB autoinhibited Ca2+-ATPases (ACAs) are localised both at the plasma membrane and at the endomembranes including endoplasmic reticulum (ER) and tonoplast and their activity is primarily regulated by Ca2+-dependent mechanisms. Instead, type IIA ER-type Ca2+-ATPases (ECAs) are present mainly at the ER and Golgi Apparatus membranes and are active at resting Ca2+. Whereas research in plants has historically focused on the biochemical characterization of these pumps, more recently the attention has been also addressed on the physiological roles played by the different isoforms. This review aims to highlight the main biochemical properties of both type IIB and type IIA Ca2+ pumps and their involvement in the shaping of cellular Ca2+ dynamics induced by different stimuli.

Compartment-specific Ca2+ imaging in the green alga Chlamydomonas reinhardtii reveals high light-induced chloroplast Ca2+ signatures

To investigate the role of intracellular Ca2+ signaling in the perception and response mechanisms to light in unicellular microalgae, the genetically encoded ratiometric Ca2+ indicator Yellow Cameleon (YC3.6) was expressed in the model organism for green algae Chlamydomonas reinhardtii, targeted to cytosol, chloroplast, and mitochondria. Through in vivo single-cell confocal microscopy imaging, light-induced Ca2+ signaling was investigated in different conditions and different genotypes, including the photoreceptors mutants phot and acry. A genetically encoded H2 O2 sensor was also adopted to investigate the possible role of H2 O2 formation in light-dependent Ca2+ signaling. Light-dependent Ca2+ response was observed in Chlamydomonas reinhardtii cells only in the chloroplast as an organelle-autonomous response, influenced by light intensity and photosynthetic electron transport. The absence of blue and red-light photoreceptor aCRY strongly reduced the light-dependent chloroplast Ca2+ response, while the absence of the blue photoreceptor PHOT had no significant effects. A correlation between high light-induced chloroplast H2 O2 gradients and Ca2+ transients was drawn, supported by H2 O2 -induced chloroplast Ca2+ transients in the dark. In conclusion, different triggers are involved in the light-induced chloroplast Ca2+ signaling as saturation of the photosynthetic electron transport, H2 O2 formation, and aCRY-dependent light perception.

Advances in understanding the mechanism of resistance to anthracnose and induced defence response in tea plants

The tea plant (Camellia sinensis) is susceptible to anthracnose disease that causes considerable crop loss and affects the yield and quality of tea. Multiple Colletotrichum spp. are the causative agents of this disease, which spreads quickly in warm and humid climates. During plant-pathogen interactions, resistant cultivars defend themselves against the hemibiotrophic pathogen by activating defence signalling pathways, whereas the pathogen suppresses plant defences in susceptible varieties. Various fungicides have been used to control this disease on susceptible plants, but these fungicide residues are dangerous to human health and cause fungicide resistance in pathogens. The problem-solving approaches to date are the development of resistant cultivars and ecofriendly biocontrol strategies to achieve sustainable tea cultivation and production. Understanding the infection stages of Colletotrichum, tea plant resistance mechanisms, and induced plant defence against Colletotrichum is essential to support sustainable disease management practices in the field. This review therefore summarizes the current knowledge of the identified causative agent of tea plant anthracnose, the infection strategies and pathogenicity of C. gloeosporioides, anthracnose disease resistance mechanisms, and the caffeine-induced defence response against Colletotrichum infection. The information reported in this review will advance our understanding of host-pathogen interactions and eventually help us to develop new disease control strategies.

The CALCINEURIN B-LIKE 4/CBL-INTERACTING PROTEIN 3 module degrades repressor JAZ5 during rose petal senescence

Flower senescence is genetically regulated and developmentally controlled. The phytohormone ethylene induces flower senescence in rose (Rosa hybrida), but the underlying signaling network is not well understood. Given that calcium regulates senescence in animals and plants, we explored the role of calcium in petal senescence. Here, we report that the expression of calcineurin B-like protein 4 (RhCBL4), which encodes a calcium receptor, is induced by senescence and ethylene signaling in rose petals. RhCBL4 interacts with CBL-interacting protein kinase 3 (RhCIPK3), and both positively regulate petal senescence. Furthermore, we determined that RhCIPK3 interacts with the jasmonic acid response repressor jasmonate ZIM-domain 5 (RhJAZ5). RhCIPK3 phosphorylates RhJAZ5 and promotes its degradation in the presence of ethylene. Our results reveal that the RhCBL4-RhCIPK3-RhJAZ5 module mediates ethylene-regulated petal senescence. These findings provide insights into flower senescence, which may facilitate innovations in postharvest technology for extending rose flower longevity.

Global transcriptome profiling reveals root- and leaf-specific responses of barley (Hordeum vulgare L.) to H2O2

In cereal crops, such as barley (Hordeum vulgare L.), the ability to appropriately respond to environmental cues is an important factor for yield stability and thus for agricultural production. Reactive oxygen species (ROS), such as hydrogen peroxide (H2O2), are key components of signal transduction cascades involved in plant adaptation to changing environmental conditions. H2O2-mediated stress responses include the modulation of expression of stress-responsive genes required to cope with different abiotic and biotic stresses. Despite its importance, knowledge of the effects of H2O2 on the barley transcriptome is still scarce. In this study, we identified global transcriptomic changes induced after application of 10 mM H2O2 to five-day-old barley plants. In total, 1883 and 1001 differentially expressed genes (DEGs) were identified in roots and leaves, respectively. Most of these DEGs were organ-specific, with only 209 DEGs commonly regulated and 37 counter-regulated between both plant parts. A GO term analysis further confirmed that different processes were affected in roots and leaves. It revealed that DEGs in leaves mostly comprised genes associated with hormone signaling, response to H2O2 and abiotic stresses. This includes many transcriptions factors and small heat shock proteins. DEGs in roots mostly comprised genes linked to crucial aspects of H2O2 catabolism and oxidant detoxification, glutathione metabolism, as well as cell wall modulation. These categories include many peroxidases and glutathione transferases. As with leaves, the H2O2 response category in roots contains small heat shock proteins, however, mostly different members of this family were affected and they were all regulated in the opposite direction in the two plant parts. Validation of the expression of the selected commonly regulated DEGs by qRT-PCR was consistent with the RNA-seq data. The data obtained in this study provide an insight into the molecular mechanisms of oxidative stress responses in barley, which might also play a role upon other stresses that induce oxidative bursts.

Apple metabolism under oxidative stress affects plant cell wall structure and mechanical properties

Several studies have shown beneficial effects of short exposure to oxidative stress on stored fruit, such as better preservation, increased firmness, preservation of polyphenolic compounds, and reduced risk of postharvest disorders such as bitter pit and superficial scald in apples. In this study the effect of short-term oxidative stress conditions on the physiology of apple fruit was investigated. Apple fruit of three cultivars were exposed to hypoxic storage conditions of various lengths to induce anaerobiosis. The response of apple fruit to short-term oxidative stress was evaluated by means of cell wall immunolabeling and atomic force microscopy. In addition, the antioxidant capacity and antioxidative activity of apple peels was assessed. Through various techniques, it was shown that short-term oxidative stress conditions promote specific enzymatic activity that induces changes in the cell wall of apple fruit cells. Exposure to short-term stress resulted in the remodeling of cell wall pectic polysaccharides, observed as an increase in the size and complexity of extracted oxalate pectin. Structural changes in the cell wall were followed by an increase in Young's modulus (compressive stiffness of a solid material, expressed as the relationship between stress and axial strain) of the cell wall material. The data presented in this paper show in a novel way how storage under short-term oxidative stress modifies the cell wall of apple fruit at the molecular level.