Advances and current challenges in calcium signaling

A bi-kinase module sensitizes and potentiates plant immune signaling

Systemic signaling is an essential hallmark of multicellular life. Pathogen encounter occurs locally but triggers organ-scale and organismic immune responses. In plants, elicitor perception provokes systemically expanding Ca2+ and H2O2 signals conferring immunity. Here, we identify a Ca2+ sensing bi-kinase module as becoming super-activated through mutual phosphorylation and as imposing synergistically enhanced NADPH oxidase activation. A combined two-layer bi-kinase/substrate phospho-code allows for sensitized signaling initiation already by near-resting elevations of Ca2+ concentration. Subsequently, it facilitates further signal wave proliferation with minimal Ca2+ amplitude requirement, triggering protective defense responses throughout the plant. Our study reveals how plants build and perpetuate trans-cellular immune signal proliferation while avoiding disturbance of ongoing cellular signaling along the path of response dissemination.

HDAC9-mediated deacetylation of CALML6 promotes excessive proliferation of glomerular mesangial cells in IgA nephropathy

PURPOSE

This study seeks to investigate the fundamental molecular processes through which histone deacetylase 9 (HDAC9) governs the proliferation of glomerular mesangial cells in the context of immunoglobulin A nephropathy (IgAN) and to identify novel targets for clinical research on IgAN.

METHODS

Data from high-throughput RNA sequencing for IgAN were procured from the Gene Expression Omnibus database to assess the expression profiles and clinical diagnostic significance of histone deacetylase family proteins (HDACs). Blood samples from 20 IgAN patients were employed in RT-qPCR analysis, and the spearman linear regression method was utilized to analyze the clinical correlation. The proliferation of glomerular mesangial cells (GMCs) under the influence of HDAC9 was examined using the 5-ethynyl-2'-deoxyuridine (EdU) assay. Proteins interacting with HDAC9 were predicted utilizing the STRING database. Immunoprecipitation and protein immunoblotting employing anti-acetylated lysine antibodies were conducted to determine the acetylation status of calmodulin-like protein 6 (CALML6).

RESULTS

Analysis of the GSE141295 dataset revealed a significant upregulation of HDAC9 expression in IgAN and the results of RT-qPCR demonstrated a substantial increase in HDAC9 expression in IgAN patients. Receiver operating characteristic (ROC) analysis indicated that the area under the curve (AUC) value for HDAC9 were 0.845 and Spearman correlation analysis showed that HDAC9 expression was positively correlated with blood levels of blood urea nitrogen (BUN) and serum creatinine (Crea). The EdU cell proliferation assay indicated that HDAC9 facilitated the excessive proliferation of GMCs. The STRING database and recovery experiments identified CALML6 as a downstream effector of HDAC9 in controlling abnormal GMC multiplication. Co-immunoprecipitation assays demonstrated that HDAC9 modulates CALML6 expression through acetylation modification.

CONCLUSION

HDAC9 is markedly upregulated in IgAN, and it mediates the excessive proliferation of GMCs by regulating the deacetylation of CALML6.

ZjMAPKK4 Interacted With ZjNAC78 Regulates Cold Tolerance Response in Jujube

Jujube (Ziziphus ujuba Mill.) holds great importance as a fruit tree in China, with strong tolerance to drought and saline stress, but its growth is limited by vulnerability to cold stress. Consequently, the role of MAPK cascades in mediating jujube cold stress response remains unclear, with the specific function of ZjMAPKK4 in this context yet to be fully elucidated. Thus, in the current study, it was found that ZjMAPKK4 was significantly upregulated compared with other ZjMAPK cascade genes after cold treatment. Heterologous transformation of ZjMAPKK4 in Arabidopsis, VIGS-induced ZjMAPKK4 transiently silencing and overexpression of ZjMAPKK4 in jujube callus assays demonstrated that ZjMAPKK4 positively regulated the cold resistance of jujube. Furthermore, to elucidate the molecular regulation mechanism behind ZjMAPKK4 under cold stress, 25 key DEGs were screened out by transcriptome analysis. Yeast screening cDNA library, yeast two-hybrid, LCA and Co-IP analysis showed ZjMAPKK4 interacted with ZjNAC78 and VIGS-induced ZjNAC78 silenced sour jujube plants showed cold sensitivity and the expression level of cold response genes were downregulated after cold stress. All the results demonstrated that ZjMAPKK4 could interact with ZjNAC78 to regulate the downstream ZjICE-ZjCBF genes to regulate the cold tolerance of jujube.

The interaction of nutrient uptake with biotic and abiotic stresses in plantsFA

Plants depend heavily on efficient nutrient uptake and utilization for optimal growth and development. However, plants are constantly subjected to a diverse array of biotic stresses, such as pathogen infections, insect pests, and herbivory, as well as abiotic stress like drought, salinity, extreme temperatures, and nutrient imbalances. These stresses significantly impact the plant's ability to take up nutrient and use it efficiency. Understanding how plants maintain nutrient uptake and use efficiency under biotic and abiotic stress conditions is crucial for improving crop resilience and sustainability. This review explores the recent advancements in elucidating the mechanisms underlying nutrient uptake and utilization efficiency in plants under such stress conditions. Our aim is to offer a comprehensive perspective that can guide the breeding of stress-tolerant and nutrition-efficient crop varieties, ultimately contributing to the advancement of sustainable agriculture.

A light-addressable potentiometric sensor-based extracellular calcium dynamic monitoring and imaging platform for cellular calcium channel drug evaluation

Disruption and dysregulation of cellular calcium channel function can lead to diseases such as ischemic stroke, heart failure, and arrhythmias. Corresponding calcium channel drugs typically require preliminary efficacy evaluations using in vitro models such as cells and simulated tissues before clinical testing. However, traditional detection and evaluation methods often encounter challenges in long-term continuous monitoring and lack calcium specificity. In this study, a dynamic monitoring system based on ion-sensitive membranes for light-addressable potentiometric sensor (LAPS) was developed to meet the demand for monitoring changes in extracellular calcium ion (Ca2+) concentration in live cells. The effects of Ca2+ channel agonists and blockers on 2D and 3D HL-1 cells were investigated, with changes in extracellular Ca2+ concentration reflecting cellular calcium metabolism, facilitating drug evaluation. Additionally, calcium imaging technology with optical addressing capability complemented the LAPS system's ability to perceive 3D cell morphology, enhancing its drug evaluation capabilities. This work provides a novel, label-free, specific, and stable technique for monitoring cellular calcium metabolism. It achieves both continuous monitoring at single points and custom sensing area calcium imaging, holding significant implications for drug screening and disease treatment related to human calcium homeostasis.

Investigation of Arabidopsis root skototropism with different distance settings

Plants can activate protective and defense mechanisms under biotic and abiotic stresses. Their roots naturally grow in the soil, but when they encounter sunlight in the top-soil layers, they may move away from the light source to seek darkness. Here we investigate the skototropic behavior of roots, which promotes their fitness and survival. Glutamate-like receptors (GLRs) of plants play roles in sensing and responding to signals, but their role in root skototropism is not yet understood. Light-induced tropisms are known to be affected by auxin distribution, mainly determined by auxin efflux proteins (PIN proteins) at the root tip. However, the role of PIN proteins in root skototropism has not been investigated yet. To better understand root skototropism and its connection to the distance between roots and light, we established five distance settings between seedlings and darkness to investigate the variations in root bending tendencies. We compared differences in root skototropic behavior across different expression lines of Arabidopsis thaliana seedlings (atglr3.7 ko, AtGLR3.7 OE, and pin2 knockout) to comprehend their functions. Our research shows that as the distance between roots and darkness increases, the root's positive skototropism noticeably weakens. Our findings highlight the involvement of GLR3.7 and PIN2 in root skototropism.

Effects of different eco-stoichiometric ratios of calcium and cadmium on the detoxification mechanisms of Capsicum annuum L. under cadmium stress

The eco-stoichiometry of Ca/Cd in soil significantly affects Cd uptake and accumulation by plants in carbonate regions. In this study, the physiological responses and detoxification mechanisms of Capsicum annuum L. (capsicum) were investigated based on the eco-stoichiometric relationship of Ca/Cd in production substrates under varying pH levels (5, 6, and 7). The results revealed that increased Ca/Cd ratio enhanced the Cd accumulation in roots at pH values of 5 and 6. The enrichment of Cd in stems and leaves gradually decreased with varying Ca/Cd ratios at different pH levels. In addition, root vigor, relative chlorophyll content, biomass, and catalase and peroxidase activities increased across various pH levels, while the concentration of protein carbonyl and malondialdehyde decreased. The ability of pectin and cellulose in the cell wall and that of soluble components within the cell to adsorb and partition Cd improved as the Ca/Cd ratio increased at different pH values. Notably, the effects of varying Ca/Cd ratios were most significant at pH 6. Overall, Ca enhanced the tolerance of capsicum to Cd stress, thereby promoting the fixation of Cd in root cells, reducing its transfer to aboveground tissues, and improving both the growth and antioxidant stress response. The effect was attributed to different Ca/Cd stoichiometric ratios, pH levels, and their interactions. These findings enhance the understanding of the mechanism of the interaction between Ca and Cd on crops in the karst agroecosystem.

Arabidopsis calcium-dependent protein kinases 4/5/6/11 negatively regulate hydrotropism via phosphorylation of MIZU-KUSSEI1

Hydrotropism facilitates the orientation of plant roots toward regions of elevated water potential, enabling them to absorb adequate water. Although calcium signaling plays a crucial role in plant response to water tracking, the exact regulatory mechanisms remain a mystery. Here, we employed the Arabidopsis (Arabidopsis thaliana) hydrotropism-specific protein MIZU-KUSSEI1 (MIZ1) as bait and found that calcium-dependent protein kinases 4/5/6/11 (CPK4/5/6/11) interacted with MIZ1 in vitro and in vivo. The cpk4/5/6/11 mutant exhibited increased sensitivity to water potential and enhanced root tip curvature. Furthermore, CPK4/5/6/11 primarily phosphorylated MIZ1 at Ser14/36 residues. Additionally, CPK-mediated phosphorylation of MIZ1 relieved its inhibitory effect on the activity of the endoplasmic reticulum-localized Ca2+ pump ECA1, altering the balance between cytoplasmic Ca2+ inflow and outflow, thereby negatively regulating the hydrotropic growth of plants. Overall, our findings unveil the molecular mechanisms by which the CPK4/5/6/11-MIZ1 module functions in regulating plant hydrotropism responses and provide a theoretical foundation for enhancing plant water use efficiency and promoting sustainable agriculture.

Characterization of the Calmodulin-Like Protein Family in Chara braunii and their Conserved Interaction with the Calmodulin-Binding Transcription Activator Family

Calcium sensor proteins play important roles by detecting changes in intracellular calcium and relaying that information onto downstream targets through protein-protein interaction. Very little is known about calcium sensors from plant species that predate land colonization and the evolution of embryophytes. Here, we examined the genome of the multicellular algae, Chara braunii, for orthologs to the evolutionarily conserved calcium sensor calmodulin (CaM) and for CaM-like (CML) proteins. We identified one CaM and eight CML isoforms that range in size from 16.4 to 21.3 kDa and are predicted to have between two to four calcium-binding (EF-hand) domains. Using recombinant protein, we tested whether CbCaM and CbCML1-CbCML7 possess biochemical properties of typical calcium sensors. CbCaM and the CbCMLs all displayed high-affinity calcium binding with estimated global KD,app values in the physiological µM range. In response to calcium binding, CbCaM and the CbCMLs exhibited varying degrees of increase in exposed hydrophobicity, suggesting that different calcium-induced conformational changes occur among isoforms. We found many examples of putative CaM targets encoded in the C. braunii genome and explored the ability of CbCaM and CbCMLs to interact in planta with a representative putative target, a C. braunii CaM-binding transcription factor (CbCAMTA1). CbCaM, CbCML2 and CbCML4 each associated with the C-terminal region of CbCAMTA1. Collectively, our data support the hypothesis that complex calcium signaling and sensing networks involving CaM and CMLs evolved early in the green lineage. Similarly, it seems likely that calcium-mediated regulation of transcription occurs in C. braunii via CAMTAs and is an ancient trait predating embryophytic emergence.

Guard cells count the number of unitary cytosolic Ca2+ signals to regulate stomatal dynamics

Transient stimulus-specific increases in the cytosolic Ca2+ concentration ("calcium signatures") of guard cells have been proposed to regulate the opening and closure of stomatal pores on plant leaves. However, the mechanism by which these Ca2+ signatures are generated and translated into stomatal movement is still largely unresolved. We used a light-gated, Ca2+-permeable variant of ChannelRhodopsin 2 (ChR2-XXM2.0) that was stimulated by tailored light pulses to investigate this phenomenon. We found that activation of the ChR2-XXM2.0 channel provoked characteristic increases in the cytosolic concentration of Ca2+. We also demonstrated that the endoplasmic reticulum (ER) was involved in the generation of these calcium signatures. Using ChR2-XXM2.0 technology, we showed that transient increases in Ca2+ activated S-type anion channels and determined the extent and speed of stomatal closure with their number and frequency. Our data reveal that guard cells are capable of counting Ca2+ transients in order to optimize stomatal aperture in the prevailing environmental conditions.

AtCIPK20 regulates microtubule stability to mediate stomatal closure under drought stress in Arabidopsis

Drought stress is a common abiotic challenge that profoundly impacts plant growth and development. As sessile organisms, plants rely on various physiological and morphological adaptations to cope with drought conditions. The CIPK (calcineurin B-like protein-interacting protein kinase) family proteins play a pivotal role in mediating plant responses to abiotic stress through modulation of cellular membrane events via the CBL-CIPK complex. However, reports documenting the CIPKs' regulation of non-membrane events are scant. In this study, we discovered a novel subcellular localisation pattern of the AtCIPK20 protein of Arabidopsis, specifically to cortical microtubules (cMT), which is distinct from previously reported localisation patterns of plant CIPKs. AtCIPK20 regulates ABA-induced loss of cMT organisation in guard cells, thereby facilitating stomatal closure, mitigating leaf water loss, and protecting plants from drought stress in Arabidopsis. The C-terminal regulatory domain of AtCIPK20 governs its cMT targeting, whereas the interaction of AtCIPK20 with its CBL partners disrupts this localisation. Notably, the cMT targeting characteristic of AtCIPK20 is not exclusive, as several other CIPK members in Arabidopsis, maize, and rice exhibit similar localisation patterns. These findings broaden our current understanding of the role of plant CIPK members in abiotic stress resistance and suggest that future exploration of CIPK molecular functions should adopt a more comprehensive perspective.

Arbuscular mycorrhizal fungi and exogenous Ca2+ application synergistically enhance salt and alkali resistance in perennial ryegrass through diverse adaptive strategies

The challenge of soil salinization and alkalization, with its significant impact on crop productivity, has raised growing concerns with global population growth and enhanced environmental degradation. Although arbuscular mycorrhizal fungi (AMF) and calcium ions (Ca2+) are known to enhance plant resistance to stress, their combined effects on perennial ryegrass' tolerance to salt and alkali stress and the underlying mechanisms remain poorly understood. This study aimed to elucidate the roles of Arbuscular mycorrhizal (AM) fungus Rhizophagus irregularis and exogenous Ca2+ application in molecular and physiological responses to salt-alkali stress. AM symbiosis and exogenous Ca2+ application enhanced antioxidant enzyme activity and non-enzymatic components, promoting reactive oxygen species (ROS) scavenging and reducing lipid peroxidation while alleviating oxidative damage induced by salt-alkali stress. Furthermore, they enhanced osmotic balance by increasing soluble sugar content (Proportion of contribution of the osmotic adjustment were 34∼38 % in shoots and 30∼37 % in roots) under salt stress and organic acid content (Proportion of contribution of the osmotic adjustment were 32∼36 % in shoots and 37∼42 % in roots) under alkali stress. Changes in organic solute and inorganic cation-anion contents contributed to ion balance, while hormonal regulation played a role in these protective mechanisms. Moreover, the protective mechanisms involved activation of Ca2+-mediated signaling pathways, regulation of salt-alkali stress-related genes (including LpNHX1 and LpSOS1), increased ATPase activity, elevated ATP levels, enhanced Na+ extrusion, improved K+ absorption capacity, and a reduced Na+/K+ ratio, all contributing to the protection of photosynthetic pigments and the enhancement of photosynthetic efficiency. Ultimately, the combined application of exogenous Ca2+ and AMF synergistically alleviated the inhibitory effects of salt-alkali stress on perennial ryegrass growth. This finding suggested that exogenous Ca2+ may participate in the colonization of perennial ryegrass plants by R. irregularis, while AM symbiosis may activate Ca2+ pathways. Consequently, the combined treatment of AM and Ca2+ is beneficial for enhancing plant regulatory mechanisms and increasing crop yield under salt-alkali stress.

Effects of dark septate endophyte on root growth, physiology and transcriptome of Ammopiptanthus mongolicus seedlings under drought stress

As the only evergreen relict species in the desert environment of western China, Ammopiptanthus mongolicus (Leguminosae) roots is colonized with dark septate endophytes (DSE), but the potential of DSE to alleviate the adverse effects of drought on seedling roots remains uncertain. This study examined the effects of DSE on root growth, physiology and transcriptome of A. mongolicus under drought stress. Drought drastically reduced root biomass by 47.7%, while all DSE strains established positive symbiosis with A.mongolicus, with G.hyphopodioides having the most pronounced promoting effect. Inoculation with G. hyphopodioides alleviated drought stress injury by increasing CAT activity, AsA content and soluble sugar content in the roots, with a significant reduction in MDA accumulation by 97.7%. G. hyphopodioides also significantly increased zeatin and brassinosteroid contents, which in turn regulated the root structure and increased root activity, resulting in a 208.6% increase in root biomass. Transcriptome analysis screened 1246 differentially expressed genes (542 up-regulated and 704 down-regulated) between G. hyphopodioides inoculation under drought treatment, mainly associated with phenylpropanoid biosynthesis, ascorbic acid and aldehyde metabolism, hormone synthesis and signalling, sucrose and starch metabolism, and vitamin B6 metabolism, and further investigated and identified key potential genes and transcription factors (DREB, ERF, NAC, MYB, C2H2). These findings reveal the physiological and molecular mechanisms by which DSE symbiosis improves the drought resistance of A. mongolicus seedlings, providing valuable guidance on the use of DSE resources to promote ecological construction and production of desert plants.

Molecular Regulation of Photosynthetic Carbon Assimilation in Oat Leaves Under Drought Stress

Common oat (Avena sativa L.) is one of the important minor grain crops in China, and drought stress severely affects its yield and quality. To investigate the drought resistance characteristics of oat seedlings, this study used Baiyan 2, an oat cultivar at the three-leaf stage, as the experimental material. Drought stress was simulated using polyethylene glycol (PEG) to treat the seedlings. The photosynthetic parameters and physicochemical indices of the treatment groups at 6 h and 12 h were measured and compared with the control group at 0 h. The results showed that drought stress did not significantly change chlorophyll content, but it significantly reduced net photosynthetic rate and other photosynthetic parameters while significantly increasing proline content. Transcriptome analysis was conducted using seedlings from both the control and treatment groups, comparing the two treatment groups with the control group using Tbtool software (v2.136). This analysis identified 344 differentially expressed genes. Enrichment analysis of these differentially expressed genes revealed significant enrichment in physiological pathways such as photosynthesis and ion transport. Ten differentially expressed genes related to the physiological process of photosynthetic carbon assimilation were identified, all of which were downregulated. Additionally, seven differentially expressed genes were related to ion transport. Through gene co-expression analysis combined with promoter region structure analysis, 11 transcription factors (from MYB, AP2/ERF, C2C2-dof) were found to regulate the expression of 10 genes related to photosynthetic carbon assimilation. Additionally, five transcription factors regulate the expression of two malate transporter protein-related genes (from LOB, zf-HD, C2C2-Dof, etc.), five transcription factors regulate the expression of two metal ion transporter protein-related genes (from MYB, zf-HD, C2C2-Dof), five transcription factors regulate the expression of two chloride channel protein-related genes (from MYB, bZIP, AP2/ERF), and two transcription factors regulate the expression of one Annexin-related gene (from NAC, MYB). This study provides a theoretical foundation for further research on the molecular regulation of guard cells and offers a molecular basis for enhancing drought resistance in oats.

Plant intelligence dux: a comprehensive rebuttal of Kingsland and Taiz

Intelligence is a fundamental property for all life enabling an increased probability of survival and reproduction under wild circumstances. Kingsland and Taiz (2024) think that plants are not intelligent but seem unaware of the extensive literature about intelligence, memory, learning and chromatin topology in plants. Their views are consequently rejected. Their claim of fake quotations is shown to result from faulty reasoning and lack of understanding of practical biology. Their use of social media as scholarly evidence is unacceptable. Darwin's views on intelligence are described, and their pertinence to the adaptive responses of plants is discussed. Justifications for comments I have made concerning McClintock and her "thoughtful" cell, von Sachs writings as indicating purpose (teleonomy) to plant behaviour, Went and Thimann's allusions to plant intelligence and Bose legacy as the father of plant electrophysiology are described. These scientists were usually first in their field of knowledge, and their understanding was consequently deeper. The article finishes with a brief critical analysis of the 36 scientists who were used to condemn plant neurobiology as of no use. It is concluded that participants signed up to a false prospectus because contrary evidence was omitted.

Regulating programmed cell death in plant cells: Intracellular acidification plays a pivotal role together with calcium signaling

Programmed cell death (PCD) occurs in different tissues in response to a number of different signals in plant cells. Drawing from work in several different contexts, including root-cap cell differentiation, plant response to biotic and abiotic stress, and some self-incompatibility (SI) systems, the data suggest that, despite differences, there are underlying commonalities in the early decision-making stages of PCD. Here, we focus on how 2 cellular events, increased [Ca2+]cyt levels and cytosolic acidification, appear to act as early signals involved in regulating both developmental and stimulus-induced PCD in plant cells.

SmJAZs-SmbHLH37/SmERF73-SmSAP4 module mediates jasmonic acid signaling to balance biosynthesis of medicinal metabolites and salt tolerance in Salvia miltiorrhiza

Salvia miltiorrhiza holds significant importance in traditional Chinese medicine. Stress-associated proteins (SAP), identified by A20/AN1 zinc finger structural domains, play crucial roles in regulating plant growth, development, resistance to biotic and abiotic stress, and hormone responses. Herein, we conducted a genome-wide identification of the SAP gene family in S. miltiorrhiza. The expression analysis revealed a significant upregulation of SmSAP4 under methyl jasmonate (MeJA) and salt stress. Overexpressing SmSAP4 in S. miltiorrhiza hairy roots increased tanshinones content while decreasing salvianolic acids content, while RNAi-silencing SmSAP4 had the opposite effect. SmSAP4 overexpression in both Arabidopsis thaliana and S. miltiorrhiza hairy roots decreased their salt stress tolerance, accompanied by increased activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), and a hindered ability to maintain the Na+ : K+ ratio. Further investigations demonstrated that MeJA alleviated the inhibitory effect of SmJAZ3 on SmSAP4 activation by SmbHLH37 and SmERF73. However, MeJA did not affect the inhibition of SmSAP4 activation by SmJAZ8 through SmbHLH37. In summary, our research reveals that SmSAP4 negatively regulates the accumulation of salvianic acid through the SmJAZs-SmbHLH37/SmERF73-SmSAP4 module and positively impacting the accumulation of tanshinones. Additionally, it functions as a negative regulator under salt stress.

Effect of fertility levels and stress mitigating chemicals on nutrient content, uptake, intercropping advantage and competition effect in cowpea-baby corn intercropping

The primary goal of this study was to analyze how various row ratios of intercrops, in conjunction with different fertilizer levels with spray of two stress mitigating chemical, affect nutrient content, land productivity, and economic viability during Summer season. Furthermore, we aimed to explore the competitive dynamics within legume/cereal intercropping systems. Hence, A field experiment at Agriculture University, Kota, during the summers of 2019 and 2020, investigated different cowpea + baby corn intercropping system's intercropping indices, nutrient dynamics, uptake, and post-harvest soil nutrient balance under varying recommended fertilizer levels and foliar spray of stress mitigating chemicals. Using a split-split plot design replicated four times, the experiment involved thirty treatment combinations, including five intercropping techniques viz. Sole cowpea, sole baby corn, cowpea + baby corn 2:1, cowpea + baby corn 3:1, cowpea + baby corn 4:1 in the main plot, three fertility levels viz. 100 %, 125 % and 150 % recommended dose of fertilizer (RDF) in subplots, and two stress mitigation chemicals; CaCl2 0.5 % and KNO3 1% in sub-subplots. The findings revealed notable trends, including nitrogen (N) and (P) content in cowpea seeds and straw, baby corn cobs and fodder, as well as enhanced land-equivalent ratio (LER) and monetary advantage index (MAI) within the cowpea + baby corn 2:1 row ratio. However, despite these advantages, total N and P uptake were markedly higher in sole crops. Notably, sole cowpea demonstrated the highest actual N and P balance and lowest was under sole baby corn. Among the fertility levels, the 150 % RDF level exhibited the most favorable outcomes across various parameters, including LER, MAI, NP content, and uptake in both crops. Additionally, higher fertility levels correlated with increased apparent and actual soil nutrient balances. While, among stress mitigation chemicals, CaCl2 0.5 % resulted in significantly heightened N and P uptake. Hence, to optimize intercropping dynamics and maintain soil nutrient balance, it is advisable to intensify cowpea cultivation along with baby corn in a 2:1 row ratio, utilizing 150 % RDF is beneficial. Additionally, alleviating higher temperature stress during the summer season can be achieved by applying a 0.5 % solution CaCl2 through spraying at the flowering and pod development stages of cowpea.

Conserved N-terminal Regulation of the ACA8 Calcium Pump with Two Calmodulin Binding Sites

The autoinhibited plasma membrane calcium ATPase ACA8 from A. thaliana has an N-terminal autoinhibitory domain. Binding of calcium-loaded calmodulin at two sites located at residues 42-62 and 74-96 relieves autoinhibition of ACA8 activity. Through activity studies and a yeast complementation assay we investigated wild-type (WT) and N-terminally truncated ACA8 constructs (Δ20, Δ30, Δ35, Δ37, Δ40, Δ74 and Δ100) to explore the role of conserved motifs in the N-terminal segment preceding the calmodulin binding sites. Furthermore, we purified WT, Δ20- and Δ100-ACA8, tested activity in vitro and performed structural studies of purified Δ20-ACA8 stabilized in a lipid nanodisc to explore the mechanism of autoinhibition. We show that an N-terminal segment between residues 20 and 35 including conserved Phe32, upstream of the calmodulin binding sites, is important for autoinhibition and the activation by calmodulin. Cryo-EM structure determination at 3.3 Å resolution of a beryllium fluoride inhibited E2 form, and at low resolution for an E1 state combined with AlphaFold prediction provide a model for autoinhibition, consistent with the mutational studies.

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

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

Integrated transcriptomic, metabolomic, and functional analyses unravel the mechanism of bagging delaying fruit cracking of pomegranate (Punica granatum L.)

The economic impact of fruit cracking in pomegranate products is substantial. In this study, we present the inaugural comprehensive analysis of transcriptome and metabolome in the outermost pericarp of pomegranate fruit in bagging conditions. Our investigation revealed a notable upregulation of differentially expressed genes (DEGs) associated with the calcium signaling pathway (76.92%) and xyloglucan endotransglucosylase/hydrolase (XTH) genes (87.50%) in the fruit peel of non-cracking fruit under bagging. Metabolomic analysis revealed that multiple phenolics, flavonoids, and tannins were identified in pomegranate. Among these, calmodulin-like 23 (PgCML23) exhibited a significant correlation with triterpenoids and demonstrated a marked upregulation under bagging treatment. The transgenic tomatoes overexpressing PgCML23 exhibited significantly higher cellulose content and xyloglucan endotransglucosylase (XET) enzyme activity in the pericarp at the red ripening stage compared to the wild type. Conversely, water-soluble pectin content, polygalacturonase (PG), and β-galactosidase (β-GAL) enzyme activities were significantly lower in the transgenic tomatoes. Importantly, the heterologous expression of PgCML23 led to a substantial reduction in the fruit cracking rate in tomatoes. Our findings highlight the reduction of fruit cracking in bagging conditions through the manipulation of PgCML23 expression.

Connecting calcium signaling with boron transport: the crucial role of CPK10 protein kinase

This article is a Commentary on Wang et al. (2024), 243: 1795–1809.

Calcium signaling regulates the accumulation of phenolic acids in response to UV-B stress in Rhododendron chrysanthum Pall

KEY MESSAGE

This study, using multi-omics combined with physiologic assays, found that calcium-ion signaling can regulate phenolic acid accumulation in R. chrysanthum leaves in response to UV-B stress. UV-B stress is a severe abiotic stress capable of destroying cellular structures and affecting plant growth. Rhododendron chrysanthum Pall. (R. chrysanthum) is a plant that has been exposed to high levels of UV-B radiation for an extended period, leading to the development of adaptive responses to mitigate UV-B stress. As such, it serves as a valuable experimental material for studying plant resilience to UV-B stress. We utilized R. chrysanthum as the experimental material and subjected it to UV-B stress. We conducted a comprehensive analysis of the changes in R. chrysanthum under both control and UV-B stress conditions using multi-omic and physiologic assays. Our aim was to investigate the molecular mechanism underlying R. chrysanthum's resistance to UV-B stress, with a focus on calcium-ion signaling. UV-B stress was found to impact the photosynthesis of R. chrysanthum by decreasing the maximum photosynthetic efficiency of photosystem II, reducing Fm, and increasing F0. In addition, the composition of numerous phenolic acid compounds was significantly altered. Genes and proteins related to calcium signaling showed significant differences, with some proteins (CML, CPK1, CRK3, ATP2C, ERG3, CAR7) being modified by acetylation. The correlation between genes and proteins involved in calcium signaling and phenolic compounds suggested that calcium signaling may play a role in regulating the accumulation of phenolic compounds under UV-B stress to help R. chrysanthum adapt. This study examines the impact of calcium-ion signaling on the accumulation of phenolic acid compounds, offering insights for future research on the molecular mechanisms underlying plant resilience to UV-B stress.

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.

Characterization of Arabidopsis aldolases AtFBA4, AtFBA5, and their inhibition by morin and interaction with calmodulin

Fructose bisphosphate aldolases (FBAs) catalyze the reversible cleavage of fructose 1,6-bisphosphate into dihydroxyacetone phosphate and glyceraldehyde 3-phosphate. We analyzed two previously uncharacterized cytosolic Arabidopsis FBAs, AtFBA4 and AtFBA5. Based on a recent report, we examined the interaction of AtFBA4 with calmodulin (CaM)-like protein 11 (AtCML11). AtFBA4 did not bind AtCML11; however, we found that CaM bound AtFBA5 in a Ca2+-dependent manner with high specificity and affinity (KD ~ 190 nm) and enhanced its stability. AtFBA4 and AtFBA5 exhibited Michaelis-Menten kinetics with Km and Vmax values of 180 μm and 4.9 U·mg-1 for AtFBA4, and 6.0 μm and 0.30 U·mg-1 for AtFBA5, respectively. The flavonoid morin inhibited both isozymes. Our study suggests that Ca2+ signaling and flavanols may influence plant glycolysis/gluconeogenesis.

The VAMP-associated protein VAP27-1 plays a crucial role in plant resistance to ER stress by modulating ER-PM contact architecture in Arabidopsis

The endoplasmic reticulum (ER) and the plasma membrane (PM) form ER-PM contact sites (EPCSs) that allow the ER and PM to exchange materials and information. Stress-induced disruption of protein folding triggers ER stress, and the cell initiates the unfolded protein response (UPR) to resist the stress. However, whether EPCSs play a role in ER stress in plants remains unclear. VESICLE-ASSOCIATED MEMBRANE PROTEIN (VAMP)-ASSOCIATED PROTEIN 27-1 (VAP27-1) functions in EPCS tethering and is encoded by a family of 10 genes (VAP27-1-10) in Arabidopsis thaliana. Here, we used CRISPR-Cas9-mediated genome editing to obtain a homozygous vap27-1 vap27-3 vap27-4 (vap27-1/3/4) triple mutant lacking three of the key VAP27 family members in Arabidopsis. The vap27-1/3/4 mutant exhibits defects in ER-PM connectivity and EPCS architecture, as well as excessive UPR signaling. We further showed that relocation of VAP27-1 to the PM mediates specific VAP27-1-related EPCS remodeling and expansion under ER stress. Moreover, the spatiotemporal dynamics of VAP27-1 at the PM increase ER-PM connectivity and enhance Arabidopsis resistance to ER stress. In addition, we revealed an important role for intracellular calcium homeostasis in the regulation of UPR signaling. Taken together, these results broaden our understanding of the molecular and cellular mechanisms of ER stress and UPR signaling in plants, providing additional clues for improving plant broad-spectrum resistance to different stresses.

MicroRNA1432 regulates rice drought stress tolerance by targeting the CALMODULIN-LIKE2 gene

Due to climate change, drought has become a major threat to rice (Oryza sativa L.) growth and yield worldwide. Understanding the genetic basis of drought tolerance in rice is therefore of great importance. Here, we identified a microRNA, miR1432, which regulates rice drought tolerance by targeting the CALMODULIN-LIKE2 (OsCaML2) gene. Mutation of MIR1432 or suppression of miR1432 expression significantly impaired seed germination and seedling growth under drought-stress conditions. Molecular analysis demonstrated that miR1432 affected rice drought tolerance by directly targeting OsCaML2, which encodes an EF-hand chiral calcium-binding protein. Overexpression of a miR1432-resistant form of OsCaML2 (OEmCaML2) phenocopied the mir1432 mutant and miR1432 suppression plants. Furthermore, the suppression of miR1432 severely affected the expression of genes involved in responses to stimulation, metabolism and signal transduction, especially the mitogen-activated protein kinase (MAPK) pathway and hormone transduction pathway in rice under drought stress. Thus, our findings show that the miR1432-OsCaML2 module plays an important role in the regulation of rice drought tolerance, suggesting its potential utilization in developing molecular breeding strategies that improve crop drought tolerance.

A dual function of the IDA peptide in regulating cell separation and modulating plant immunity at the molecular level

The abscission of floral organs and emergence of lateral roots in Arabidopsis is regulated by the peptide ligand inflorescence deficient in abscission (IDA) and the receptor protein kinases HAESA (HAE) and HAESA-like 2 (HSL2). During these cell separation processes, the plant induces defense-associated genes to protect against pathogen invasion. However, the molecular coordination between abscission and immunity has not been thoroughly explored. Here, we show that IDA induces a release of cytosolic calcium ions (Ca2+) and apoplastic production of reactive oxygen species, which are signatures of early defense responses. In addition, we find that IDA promotes late defense responses by the transcriptional upregulation of genes known to be involved in immunity. When comparing the IDA induced early immune responses to known immune responses, such as those elicited by flagellin22 treatment, we observe both similarities and differences. We propose a molecular mechanism by which IDA promotes signatures of an immune response in cells destined for separation to guard them from pathogen attack.

Positive roles of the Ca2+ sensors GbCML45 and GbCML50 in improving cotton Verticillium wilt resistance

As a universal second messenger, cytosolic calcium (Ca2+) functions in multifaceted intracellular processes, including growth, development and responses to biotic/abiotic stresses in plant. The plant-specific Ca2+ sensors, calmodulin and calmodulin-like (CML) proteins, function as members of the second-messenger system to transfer Ca2+ signal into downstream responses. However, the functions of CMLs in the responses of cotton (Gossypium spp.) after Verticillium dahliae infection, which causes the serious vascular disease Verticillium wilt, remain elusive. Here, we discovered that the expression level of GbCML45 was promoted after V. dahliae infection in roots of cotton, suggesting its potential role in Verticillium wilt resistance. We found that knockdown of GbCML45 in cotton plants decreased resistance while overexpression of GbCML45 in Arabidopsis thaliana plants enhanced resistance to V. dahliae infection. Furthermore, there was physiological interaction between GbCML45 and its close homologue GbCML50 by using yeast two-hybrid and bimolecular fluorescence assays, and both proteins enhanced cotton resistance to V. dahliae infection in a Ca2+-dependent way in a knockdown study. Detailed investigations indicated that several defence-related pathways, including salicylic acid, ethylene, reactive oxygen species and nitric oxide signalling pathways, as well as accumulations of lignin and callose, are responsible for GbCML45- and GbCML50-modulated V. dahliae resistance in cotton. These results collectively indicated that GbCML45 and GbCML50 act as positive regulators to improve cotton Verticillium wilt resistance, providing potential targets for exploitation of improved Verticillium wilt-tolerant cotton cultivars by genetic engineering and molecular breeding.

Hydrotropism mechanisms and their interplay with gravitropism

Plants partly optimize their water recruitment from the growth medium by directing root growth toward a moisture source, a phenomenon termed hydrotropism. The default mechanism of downward growth, termed gravitropism, often functions to counteract hydrotropism when the water-potential gradient deviates from the gravity vector. This review addresses the identity of the root sites in which hydrotropism-regulating factors function to attenuate gravitropism and the interplay between these various factors. In this context, the function of hormones, including auxin, abscisic acid, and cytokinins, as well as secondary messengers, calcium ions, and reactive oxygen species in the conflict between these two opposing tropisms is discussed. We have assembled the available data on the effects of various chemicals and genetic backgrounds on both gravitropism and hydrotropism, to provide an up-to-date perspective on the interactions that dictate the orientation of root tip growth. We specify the relevant open questions for future research. Broadening our understanding of root mechanisms of water recruitment holds great potential for providing advanced approaches and technologies that can improve crop plant performance under less-than-optimal conditions, in light of predicted frequent and prolonged drought periods due to global climate change.

Revisiting the Role of Sensors for Shaping Plant Research: Applications and Future Perspectives

Plant health monitoring is essential for understanding the impact of environmental stressors (biotic and abiotic) on crop production, and for tailoring plant developmental and adaptive responses accordingly. Plants are constantly exposed to different stressors like pathogens and soil pollutants (heavy metals and pesticides) which pose a serious threat to their survival and to human health. Plants have the ability to respond to environmental stressors by undergoing rapid transcriptional, translational, and metabolic reprogramming at different cellular compartments in order to balance growth and adaptive responses. However, plants' exceptional responsiveness to environmental cues is highly complex, which is driven by diverse signaling molecules such as calcium Ca2+, reactive oxygen species (ROS), hormones, small peptides and metabolites. Additionally, other factors like pH also influence these responses. The regulation and occurrence of these plant signaling molecules are often undetectable, necessitating nondestructive, live research approaches to understand their molecular complexity and functional traits during growth and stress conditions. With the advent of sensors, in vivo and in vitro understanding of some of these processes associated with plant physiology, signaling, metabolism, and development has provided a novel platform not only for decoding the biochemical complexity of signaling pathways but also for targeted engineering to improve diverse plant traits. The application of sensors in detecting pathogens and soil pollutants like heavy metal and pesticides plays a key role in protecting plant and human health. In this review, we provide an update on sensors used in plant biology for the detection of diverse signaling molecules and their functional attributes. We also discuss different types of sensors (biosensors and nanosensors) used in agriculture for detecting pesticides, pathogens and pollutants.

Rapid Propagation of Ca2+ Waves and Electrical Signals in the Liverwort Marchantia polymorpha

In response to both biotic and abiotic stresses, vascular plants transmit long-distance Ca2+ and electrical signals from localized stress sites to distant tissues through their vasculature. Various models have been proposed for the mechanisms underlying the long-distance signaling, primarily centered around the presence of vascular bundles. We here demonstrate that the non-vascular liverwort Marchantia polymorpha possesses a mechanism for propagating Ca2+ waves and electrical signals in response to wounding. The propagation velocity of these signals was approximately 1-2 mm s-1, equivalent to that observed in vascular plants. Both Ca2+ waves and electrical signals were inhibited by La3+ as well as tetraethylammonium chloride, suggesting the crucial importance of both Ca2+ channel(s) and K+ channel(s) in wound-induced membrane depolarization as well as the subsequent long-distance signal propagation. Simultaneous recordings of Ca2+ and electrical signals indicated a tight coupling between the dynamics of these two signaling modalities. Furthermore, molecular genetic studies revealed that a GLUTAMATE RECEPTOR-LIKE (GLR) channel plays a central role in the propagation of both Ca2+ waves and electrical signals. Conversely, none of the three two-pore channels were implicated in either signal propagation. These findings shed light on the evolutionary conservation of rapid long-distance Ca2+ wave and electrical signal propagation involving GLRs in land plants, even in the absence of vascular tissue.

Calmodulin-like protein MdCML15 interacts with MdBT2 to modulate iron homeostasis in apple

BTB and TAZ domain proteins (BTs) function as specialized adaptors facilitating substrate recognition of the CUL3-RING ubiquitin ligase (CRL3) complex that targets proteins for ubiquitination in reaction to diverse pressures. Nonetheless, knowledge of the molecular mechanisms by which the apple scaffold protein MdBT2 responds to external and internal signals is limited. Here we demonstrate that a putative Ca 2+ sensor, calmodulin-like 15 (MdCML15), acts as an upstream regulator of MdBT2 to negatively modulate its functions in plasma membrane H+-ATPase regulation and iron deficiency tolerance. MdCML15 was identified to be substantially linked to MdBT2, and to result in the ubiquitination and degradation of the MdBT2 target protein MdbHLH104. Consequently, MdCML15 repressed the MdbHLH104 target, MdAHA8's expression, reducing levels of a specific membrane H+-ATPase. Finally, the phenotype of transgenic apple plantlets and calli demonstrated that MdCML15 modulates membrane H+-ATPase-produced rhizosphere pH lowering alongside iron homeostasis through an MdCML15-MdBT2-MdbHLH104-MdAHA8 pathway. Our results provide new insights into the relationship between Ca2+ signaling and iron homeostasis.

The potential of proline as a key metabolite to design real-time plant water deficit and low-light stress detector in ornamental plants

Nowadays, people are interested to use plants, especially air-purifying plants, in residential and other indoor settings to purify indoor air and increase the green area in the building. In this study, we investigated the effect of water deficit and low light intensity on the physiology and biochemistry of popular ornamental plants, including Sansevieria trifasciata, Episcia cupreata and Epipremnum aureum. Plants were grown under low light intensity in the range of 10-15 μmol quantum m-2 s-1 and 3 days of water deficit. The results showed that these three ornamental plants responded to water deficit with different pathways. Metabolomic analysis indicated that water deficit affected Episcia cupreata and Epipremnum aureum by inducing a 1.5- to 3-fold increase of proline and a 1.1- to 1.6-fold increase in abscisic acid compared to well-watered conditions, which led to hydrogen peroxide accumulation. This resulted in a reduction of stomatal conductance, photosynthesis rate and transpiration. Sansevieria trifasciata responded to water deficit by significantly increasing gibberellin by around 2.8-fold compared to well-watered plants and proline contents by around 4-fold, while stomatal conductance, photosynthesis rate and transpiration were maintained. Notably, proline accumulation under water deficit stress could be attributed to both gibberellic acid and abscisic acid, depending on plant species. Therefore, the enhancement of proline accumulation in ornamental plants under water deficit could be detected early from day 3 after water deficit conditions, and this compound can be used as a key compound for real-time biosensor development in detecting plant stress under water deficit in a future study.

Early signaling enhance heat tolerance in Arabidopsis through modulating jasmonic acid synthesis mediated by HSFA2

Given the detrimental impact of global warming on crop production, it is particularly important to understand how plants respond and adapt to higher temperatures. Using the non-invasive micro-test technique and laser confocal microscopy, we found that the cascade process of early signals (K+, H2O2, H+, and Ca2+) ultimately resulted in an increase in the cytoplasmic Ca2+ concentration when Arabidopsis was exposed to heat stress. Quantitative real-time PCR demonstrated that heat stress significantly up-regulated the expression of CAM1, CAM3 and HSFA2; however, after CAM1 and CAM3 mutation, the upregulation of HSFA2 was reduced. In addition, heat stress affected the expression of LOX3 and OPR3, which was not observed when HSFA2 was mutated. Luciferase reporter gene expression assay and electrophoretic mobility shift assay showed that HSFA2 regulated the expression of both genes. Determination of jasmonic acid (JA) content showed that JA synthesis was promoted by heat stress, but was damaged when HSFA2 and OPR3 were mutated. Finally, physiological experiments showed that JA reduced the relative electrical conductivity of leaves, enhanced chlorophyll content and relative water content, and improved the survival rate of Arabidopsis under heat stress. Together, our results reveal a new pathway for Arabidopsis to sense and transmit heat signals; HSFA2 is involved in the JA synthesis, which can act as a defensive compound improving Arabidopsis heat tolerance.

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.

Osmosensor-mediated control of Ca2+ spiking in pollen germination

Higher plants survive terrestrial water deficiency and fluctuation by arresting cellular activities (dehydration) and resuscitating processes (rehydration). However, how plants monitor water availability during rehydration is unknown. Although increases in hypo-osmolarity-induced cytosolic Ca2+ concentration (HOSCA) have long been postulated to be the mechanism for sensing hypo-osmolarity in rehydration1,2, the molecular basis remains unknown. Because osmolarity triggers membrane tension and the osmosensing specificity of osmosensing channels can only be determined in vivo3-5, these channels have been classified as a subtype of mechanosensors. Here we identify bona fide cell surface hypo-osmosensors in Arabidopsis and find that pollen Ca2+ spiking is controlled directly by water through these hypo-osmosensors-that is, Ca2+ spiking is the second messenger for water status. We developed a functional expression screen in Escherichia coli for hypo-osmosensitive channels and identified OSCA2.1, a member of the hyperosmolarity-gated calcium-permeable channel (OSCA) family of proteins6. We screened single and high-order OSCA mutants, and observed that the osca2.1/osca2.2 double-knockout mutant was impaired in pollen germination and HOSCA. OSCA2.1 and OSCA2.2 function as hypo-osmosensitive Ca2+-permeable channels in planta and in HEK293 cells. Decreasing osmolarity of the medium enhanced pollen Ca2+ oscillations, which were mediated by OSCA2.1 and OSCA2.2 and required for germination. OSCA2.1 and OSCA2.2 convert extracellular water status into Ca2+ spiking in pollen and may serve as essential hypo-osmosensors for tracking rehydration in plants.

The crosstalk between mitochondrial quality control and metal-dependent cell death

Mitochondria are the centers of energy and material metabolism, and they also serve as the storage and dispatch hubs of metal ions. Damage to mitochondrial structure and function can cause abnormal levels and distribution of metal ions, leading to cell dysfunction and even death. For a long time, mitochondrial quality control pathways such as mitochondrial dynamics and mitophagy have been considered to inhibit metal-induced cell death. However, with the discovery of new metal-dependent cell death including ferroptosis and cuproptosis, increasing evidence shows that there is a complex relationship between mitochondrial quality control and metal-dependent cell death. This article reviews the latest research results and mechanisms of crosstalk between mitochondrial quality control and metal-dependent cell death in recent years, as well as their involvement in neurodegenerative diseases, tumors and other diseases, in order to provide new ideas for the research and treatment of related diseases.

Inroads into saline-alkaline stress response in plants: unravelling morphological, physiological, biochemical, and molecular mechanisms

MAIN CONCLUSION

This article discusses the complex network of ion transporters, genes, microRNAs, and transcription factors that regulate crop tolerance to saline-alkaline stress. The framework aids scientists produce stress-tolerant crops for smart agriculture. Salinity and alkalinity are frequently coexisting abiotic limitations that have emerged as archetypal mediators of low yield in many semi-arid and arid regions throughout the world. Saline-alkaline stress, which occurs in an environment with high concentrations of salts and a high pH, negatively impacts plant metabolism to a greater extent than either stress alone. Of late, saline stress has been the focus of the majority of investigations, and saline-alkaline mixed studies are largely lacking. Therefore, a thorough understanding and integration of how plants and crops rewire metabolic pathways to repair damage caused by saline-alkaline stress is of particular interest. This review discusses the multitude of resistance mechanisms that plants develop to cope with saline-alkaline stress, including morphological and physiological adaptations as well as molecular regulation. We examine the role of various ion transporters, transcription factors (TFs), differentially expressed genes (DEGs), microRNAs (miRNAs), or quantitative trait loci (QTLs) activated under saline-alkaline stress in achieving opportunistic modes of growth, development, and survival. The review provides a background for understanding the transport of micronutrients, specifically iron (Fe), in conditions of iron deficiency produced by high pH. Additionally, it discusses the role of calcium in enhancing stress tolerance. The review highlights that to encourage biomolecular architects to reconsider molecular responses as auxiliary for developing tolerant crops and raising crop production, it is essential to (a) close the major gaps in our understanding of saline-alkaline resistance genes, (b) identify and take into account crop-specific responses, and (c) target stress-tolerant genes to specific crops.

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.

Impact of biotic stresses on the Brassicaceae family and opportunities for crop improvement by exploiting genotyping traits

MAIN CONCLUSION

Utilizing RNAi, miRNA, siRNA, lncRNA and exploiting genotyping traits can help safeguard the food supply from illnesses and pest damage to Brassicas, as well as reduce yield losses caused by plant pathogens and insect pests. In the natural environment, plants face significant challenges in the form of biotic stress, due to various living organisms, leading to biological stress and a sharp decline in crop yields. To cope with these effects, plants have evolved specialized mechanisms to mitigate these challenges. Plant stress tolerance and resistance are influenced by genes associated with stress-responsive pathogens that interact with various stress-related signaling pathway components. Plants employ diverse strategies and mechanisms to combat biological stress, involving a complex network of transcription factors that interact with specific cis-elements to regulate gene expression. Understanding both plant developmental and pathogenic disease resistance mechanisms can allow us to develop stress-tolerant and -resistant crops. Brassica genus includes commercially important crops, e.g., broccoli, cabbage, cauliflower, kale, and rapeseed, cultivated worldwide, with several applications, e.g., oil production, consumption, condiments, fodder, as well as medicinal ones. Indeed, in 2020, global production of vegetable Brassica reached 96.4 million tones, a 10.6% rise from the previous decade. Taking into account their commercial importance, coupled to the impact that pathogens can have in Brassica productivity, yield losses up to 60%, this work complies the major diseases caused due to fungal, bacterial, viral, and insects in Brassica species. The review is structured into three parts. In the first part, an overview is provided of the various pathogens affecting Brassica species, including fungi, bacteria, viruses, and insects. The second part delves into the exploration of defense mechanisms that Brassica plants encounter against these pathogens including secondary metabolites, duplicated genes, RNA interference (RNAi), miRNA (micro-RNA), siRNA (small interfering RNA), and lncRNA (long non-coding RNA). The final part comprehensively outlines the current applications of CRISPR/Cas9 technology aimed at enhancing crop quality. Taken collectively, this review will contribute to our enhanced understanding of these mechanisms and their role in the development of resistance in Brassica plants, thus supporting strategies to protect this crucial crop.

Role of calcium signaling in cadmium stress mitigation by indol-3-acetic acid and gibberellin in chickpea seedlings

Given the adverse impacts of heavy metals on plant development and physiological processes, the present research investigated the protective role of indole-3-acetic acid (IAA) and gibberellic acid (GA3) against cadmium (Cd)-induced injury in chickpea seedlings. Therefore, seeds germinated for 6 days in a medium containing 200 μM Cd alone or combined with 10 μM GA3 or 10 μM IAA. Both GA3 and IAA mitigated Cd-imposed growth delays in roots and shoots (80% and 50% increase in root and shoot length, respectively). This beneficial effect was accompanied by a significant reduction in Cd2+ accumulation in both roots (74% for IAA and 38% for GA3) and shoots (68% and 35%, respectively). Furthermore, these phytohormones restored the cellular redox state by reducing the activity of NADPH oxidase and downregulating the transcription level of RbohF and RbohD genes. Likewise, hydrogen peroxide contents were reduced by GA3 and IAA supply. Additionally, GA3 and IAA countered the Cd-induced reduction in total phenols, flavonoids, and reducing sugars in both roots and shoots. The exogenous effectors enhanced the activities of catalase, ascorbate peroxidase, and thioredoxin, as well as the corresponding gene expressions. Interestingly, adding GA3 and IAA to the Cd-contaminated germination media corrected the level of calcium (Ca2+) ion within seedling tissues. This effect coincided with the upregulation of key genes associated with stress sensing and signal transduction, including auxin-binding protein (ABP19a), mitogen-activated protein kinase (MAPK2), calcium-dependent protein kinase (CDPK1), and calmodulin (CaM). Overall, the current results suggest that GA3 and IAA sustain the Ca2+ signaling pathway, resulting in metal phytotoxicity relief. Amendment of agricultural soils contaminated with heavy metals with GA3 or IAA could represent an effective practice to improve crop yield.

Molecular mechanisms of cadmium-induced cytotoxicity in human ovarian granulosa cells identified using integrated omics

Epidemiological and clinical data have demonstrated that exposure to cadmium (Cd), a toxic heavy metal, is associated with an increased risk of female infertility. Granulosa cells, the main somatic cells comprising ovarian follicles, are one of the main targets of Cd in the ovaries. However, the mechanism by which Cd induces cytotoxicity in granulosa cells has not been fully elucidated. In this study, we exposed human ovarian granulosa cells (KGN cells) to Cd and conducted in vitro cell experiments and multi-omics (metabolomics and transcriptomics) methods to elucidate these mechanisms. Cd exposure was found to not only induce the apoptosis of the KGN cells but also further reduced mitochondrial function by decreasing mitochondrial membrane potential, ATP production, and respiratory chain complex activity as well as increasing mitochondrial reactive oxygen species (ROS) production. A total of 443 differentially expressed metabolites (160 upregulated and 283 downregulated) and 5200 differentially expressed genes (4634 upregulated and 566 downregulated) were observed in the Cd exposed-cells. The multi-omics data showed that Cd interfered with citric acid cycle (TCA cycle), amino acid (including alanine, glycine, serine, threonine, arginine, and proline) metabolism, and calcium signaling. These findings help to better elucidate the potential toxicity mechanisms of Cd on granulosa cells and the ovary.

Genome-wide analysis of the peanut CaM/CML gene family reveals that the AhCML69 gene is associated with resistance to Ralstonia solanacearum

BACKGROUND

Calmodulins (CaMs)/CaM-like proteins (CMLs) are crucial Ca2+-binding sensors that can decode and transduce Ca2+ signals during plant development and in response to various stimuli. The CaM/CML gene family has been characterized in many plant species, but this family has not yet been characterized and analyzed in peanut, especially for its functions in response to Ralstonia solanacearum. In this study, we performed a genome-wide analysis to analyze the CaM/CML genes and their functions in resistance to R. solanacearum.

RESULTS

Here, 67, 72, and 214 CaM/CML genes were identified from Arachis duranensis, Arachis ipaensis, and Arachis hypogaea, respectively. The genes were divided into nine subgroups (Groups I-IX) with relatively conserved exon‒intron structures and motif compositions. Gene duplication, which included whole-genome duplication, tandem repeats, scattered repeats, and unconnected repeats, produced approximately 81 pairs of homologous genes in the AhCaM/CML gene family. Allopolyploidization was the main reason for the greater number of AhCaM/CML members. The nonsynonymous (Ka) versus synonymous (Ks) substitution rates (less than 1.0) suggested that all homologous pairs underwent intensive purifying selection pressure during evolution. AhCML69 was constitutively expressed in different tissues of peanut plants and was involved in the response to R. solanacearum infection. The AhCML69 protein was localized in the cytoplasm and nucleus. Transient overexpression of AhCML69 in tobacco leaves increased resistance to R. solanacearum infection and induced the expression of defense-related genes, suggesting that AhCML69 is a positive regulator of disease resistance.

CONCLUSIONS

This study provides the first comprehensive analysis of the AhCaM/CML gene family and potential genetic resources for the molecular design and breeding of peanut bacterial wilt resistance.

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.

Visualizing calcium-dependent signaling networks in plants

Calcium-dependent protein kinases (CDPKs) are a multigene protein kinase family that have key regulatory roles in plants. However, imaging CDPK signals in plant cells remains challenging. The recently developed genetically encoded CDPK-Förster resonance energy transfer (FRET) reporter developed by Liese et al. allows visualization of calcium (Ca2+)-dependent conformational changes during activation or inactivation of CDPKs, providing a powerful tool for real-time monitoring of calcium decoding in plants.

Imaging of plant calcium-sensor kinase conformation monitors real time calcium-dependent decoding in planta

Changes in cytosolic calcium (Ca2+) concentration are among the earliest reactions to a multitude of stress cues. While a plethora of Ca2+-permeable channels may generate distinct Ca2+ signatures and contribute to response specificities, the mechanisms by which Ca2+ signatures are decoded are poorly understood. Here, we developed a genetically encoded Förster resonance energy transfer (FRET)-based reporter that visualizes the conformational changes in Ca2+-dependent protein kinases (CDPKs/CPKs). We focused on two CDPKs with distinct Ca2+-sensitivities, highly Ca2+-sensitive Arabidopsis (Arabidopsis thaliana) AtCPK21 and rather Ca2+-insensitive AtCPK23, to report conformational changes accompanying kinase activation. In tobacco (Nicotiana tabacum) pollen tubes, which naturally display coordinated spatial and temporal Ca2+ fluctuations, CPK21-FRET, but not CPK23-FRET, reported oscillatory emission ratio changes mirroring cytosolic Ca2+ changes, pointing to the isoform-specific Ca2+-sensitivity and reversibility of the conformational change. In Arabidopsis guard cells, CPK21-FRET-monitored conformational dynamics suggest that CPK21 serves as a decoder of signal-specific Ca2+ signatures in response to abscisic acid and the flagellin peptide flg22. Based on these data, CDPK-FRET is a powerful approach for tackling real-time live-cell Ca2+ decoding in a multitude of plant developmental and stress responses.

SCAB1 coordinates sequential Ca2+ and ABA signals during osmotic stress induced stomatal closure in Arabidopsis

Hyperosmotic stress caused by drought is a detrimental threat to plant growth and agricultural productivity due to limited water availability. Stomata are gateways of transpiration and gas exchange, the swift adjustment of stomatal aperture has a strong influence on plant drought resistance. Despite intensive investigations of stomatal closure during drought stress in past decades, little is known about how sequential signals are integrated during complete processes. Here, we discovered that the rapid Ca2+ signaling and subsequent abscisic acid (ABA) signaling contribute to the kinetics of both F-actin reorganizations and stomatal closure in Arabidopsis thaliana, while STOMATAL CLOSURE-RELATED ACTIN BINDING PROTEIN1 (SCAB1) is the molecular switch for this entire process. During the early stage of osmotic shock responses, swift elevated calcium signaling promotes SCAB1 phosphorylation through calcium sensors CALCIUM DEPENDENT PROTEIN KINASE3 (CPK3) and CPK6. The phosphorylation restrained the microfilament binding affinity of SCAB1, which bring about the F-actin disassembly and stomatal closure initiation. As the osmotic stress signal continued, both the kinase activity of CPK3 and the phosphorylation level of SCAB1 attenuated significantly. We further found that ABA signaling is indispensable for these attenuations, which presumably contributed to the actin filament reassembly process as well as completion of stomatal closure. Notably, the dynamic changes of SCAB1 phosphorylation status are crucial for the kinetics of stomatal closure. Taken together, our results support a model in which SCAB1 works as a molecular switch, and directs the microfilament rearrangement through integrating the sequentially generated Ca2+ and ABA signals during osmotic stress induced stomatal closure.

Calcium oxide nanoparticles mitigate lead stress in Abelmoschus esculentus though improving the key antioxidative enzymes, nutritional content and modulation of stress markers

Lead (Pb) is thought to be one of most injurious metals on the earth. Lead stress in plants enhances synthesis of highly toxic reactive oxygen species (ROS). During present research, impact of calcium-oxide nanoparticles (CaO-NPs) was observed on antioxidative defense mechanism in Abelmoschus esculentus plants prone to Pb stress. A CRD experiment was employed with 5 replicates having four treatments (T0 = Control, T1 = Pb stress (200 ppm), T2 = CaO-NPs and T3 = Pb + CaO-NPs). Pb-stressed seedlings exhibited decreased root growth, shoot growth, chlorophyll concentration and biomass accumulation. Moreover, higher synthesis of hydrogen-peroxide (H2O2), malondialdehyde (MDA) and electrolyte leakage (EL) resulting in cellular injuries were noted in plants growing in Pb spiked conditions. Similarly, stressed plants showed higher accumulation of total soluble sugar and proline content besides elevated activity of antioxidative enzymes counting catalase (CAT), superoxide dismutase (SOD), glutathione reductase (GR) and ascorbate peroxidase (APX). On the contrary side, CaO-NPs alleviated the Pb induced phytotoxicity through improving activity of antioxidative enzymes. The elevated activity of antioxidant enzymes reduced biosynthesis of H2O2 and MDA which was revealed through the increased growth parameters. In addition, CaO-NPs persuaded enhancement in plant defence machinery by decreased chlorophyll deprivation and augmented the uptake of plant nutrients including K and Ca content. Hence, CaO-NPs can be potent regulators of the antioxidative enzymes and stress markers to ameliorate abiotic stresses.

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.