Redox Signaling in Plant Heat Stress Response

Application of the composite nanoparticles of selenium and chitosan for ameliorating arsenic stress in rice seedlings

Selenium nanoparticles are well known for their antioxidant and stress-mitigating properties. In our study, composite nanoformulations of selenium and chitosan have been synthesized. The synthesized composite nanoformulations were 50 nm in diameter, spherical in shape, and had higher antioxidant activities and stability than the selenium and chitosan nanoparticles. In our study, Luit rice seedlings grown in an arsenic-treated Hoagland solution showed a reduction of growth, decreased superoxide dismutase, catalase, ascorbate peroxidase, guaiacol peroxidase, ascorbate, and glutathione content. Otherwise, superoxide anion, hydrogen peroxide, and malondialdehyde content increased in arsenic-stressed conditions. The alone application of Selenium nanoparticles, chitosan nanoparticles, and their nanoformulation improved growth, reduced stress parameters, and enhanced enzymatic and non-enzymatic activity. Additionally, the reduction of superoxide anion, hydrogen peroxide, and malondialdehyde content was higher by applying composite nanoformulations in arsenic-stressed conditions than selenium and chitosan nanoparticles. The treatment of composite nanoformulation also regulated the enzymatic and non-enzymatic antioxidant activity higher than that of other nanoparticles. It might be due to the higher stability and antioxidant activity of composite nanoformulations than that of selenium and chitosan nanoparticles. Our study suggests that the composite nanoformulation enhanced the growth of rice plants by mitigating arsenic-induced reactive oxygen species and upregulating antioxidant activity.

The thylakoid protein BCM1 sequesters antennae protein CP24 and CP29 within the grana cores thereby reducing their exposure to degradation under heat stress

Photosystem II (PSII) is one of the most thermosensitive components of photosynthetic apparatus in higher plants. Heat-inactivation of PSII may be followed by dissociation of antenna proteins, however, the fate and regulation mechanism of detached antenna proteins during this process remains unclear. Here, we investigate the regulation mechanism of two minor antenna proteins CP24 and CP29 during heat acclimation via the study on a thylakoid protein BCM1. BCM1 is distributed in both grana cores (GC) and stroma lamellae of thylakoids. However, heat stress induced its accumulation in grana cores but not stroma lamellae. Deficiency of BCM1 leads to the decline of plant resilience to heat stress, which results from the accelerated degradation of CP24 and CP29 in vivo. Heat stress induces a redistribution of CP24 and CP29 from the grana cores to the stroma lamellae, a shift that is exacerbated in bcm1 mutants, suggesting that migration of detached antennae proteins between thylakoid subcompartments may contribute to their degradation during heat acclimation. As an integral thylakoid protein, BCM1 physically interacts with CP24 and CP29. We propose that BCM1 serves as a stabilizing "anchor", effectively sequestering CP24 and CP29 within the grana cores thereby reducing their exposure to degradation in the stroma lamellae.

Transcriptome alterations related to heat stress responses of wild and cultivated barle

Heat stress, exacerbated by global warming, threatens food security by disrupting plant growth and productivity across many regions. The present study compared the transcriptome changes of heat-tolerant wild (Hordeum vulgare ssp. spontaneum L.) genotype and heat-sensitive cultivated Hordeum ('Mona' cultivar) barley subjected to control (24 ± 2 °C) and heat stress (40 ± 2 °C, 3 h) conditions via RNA sequencing with the Illumina Hiseq2500 platform. The wild barley genotype exhibited less impact from heat stress on growth and physiology than the 'Mona' cultivar. Heat stress led to 2141 differentially expressed genes (DEGs) in the heat-tolerant wild genotype and 1456 in the 'Mona' cultivar. Gene ontology enrichment analysis of the DEGs revealed that biological processes such as defense response to heat stress, proline and polyamine biosynthesis, and oxidative stress scavenging were predominantly involved in the thermo-tolerance of wild barley. Moreover, heat shock proteins, osmoprotectants, and catalytic activity were identified as the most critical molecular functions in response to high temperatures in wild barley. The significant alterations in the expression levels of candidate genes in response to heat stress highlight these genes' pivotal role in the thermo-tolerance of wild barley compared to the heat-sensitive 'Mona' cultivar. Comparing the evolved mechanisms in response to high temperatures between wild and cultivated barley helps identify the effective heat tolerance mechanisms in the thermo-tolerant wild genotype.

Genetic and phenotypic responses of temperature-independent Hessian fly-resistant durum wheat to larval attack during heat stress

BACKGROUND

Wheat production is increasingly challenged by the devastating damage caused by insect pests. The advent of global warming is further exacerbating this threat. Hessian fly (Mayetiola destructor), a dipteran gall midge, is a destructive pest of host wheat (Triticum aestivum) having severe economic consequences. Planting wheat cultivars harboring resistance genes is the most effective and economical Hessian fly management strategy. However, heat stress poses a challenge to this strategy, as elevated temperature often breaks down Hessian fly resistance in wheat. Our prior study identified temperature-independent resistant T. turgidum (durum wheat) accessions that maintained resistance to Hessian fly when challenged with an increased temperature of 30 °C. In this study, we carried out follow-up characterization of these durum lines to highlight molecular components involved during Hessian fly resistance or susceptibility in wheat following heat stress.

RESULTS

Temperature-independent resistant durum lines were greater than 70% resistant to multiple Hessian fly biotypes at the elevated temperature of 30 °C. At the molecular level, these lines showed increased transcripts of Hfr-1, a gene encoding an antinutrient lectin, unlike the heat-triggered susceptible durum wheat. The Hessian fly susceptibility-associated biomarker genes were significantly upregulated in the durum wheat with heat-triggered susceptibility at 30 °C, resembling the gene expression profile observed in susceptible wheat. None of these susceptibility-associated genes were differentially expressed in the temperature-independent resistant wheat. Genes involved in oxidative stress and jasmonic acid pathways did not reveal any specific expression pattern attributed to either heat stress or larval feeding. Neutral red staining revealed limited cell wall permeability in the temperature-independent resistant wheat, unlike the heat-triggered susceptible durum plants that were highly permeable similar to a wheat line susceptible to Hessian fly at 20 °C.

CONCLUSIONS

Temperature-independent resistant durum wheat lines provided robust resistance to multiple Hessian fly biotypes at higher temperatures. These lines offer a valuable resource for wheat producers for providing resistance following heat stress.

Unraveling the role of autophagy and antioxidants in anther and pistil responses to heat stress in rapeseed (Brassica napus L.)

KEY MESSAGE

Enhanced antioxidant enzymes activity, particularly superoxide dismutase and catalase, along with autophagy process in reproductive organs, can improve the resilience of rapeseed to heat stress, thereby securing crop yield in the face of global warming. Climate change and global warming have increasingly influenced yield and quality of rapeseed (Brassica napus) almost all across the world. The response of reproductive organs to high-temperature stress was studied in two rapeseed varieties, SAFI5 and DH13 with contrasting levels of heat stress tolerance. Pollen germination, viability, and seed set showed a significant reduction in the heat-sensitive variety (DH13). Superoxide quantification revealed higher accumulation in heat-sensitive variety, leading to decreased seed formation and floret fertility most probably due to declined pollen viability and stigma receptivity. Further microscopic analysis of the anther and pistil demonstrated a significant overlay between the damaged areas and the location of O2- accumulation. The sensitive variety showed higher O2- accumulation and a wider damage area than the tolerant one, suggesting that superoxide could incapacitate anther and pistil due to structural injury. Moreover, the activity levels and expression of superoxide dismutase and catalase antioxidant enzymes were significantly higher in the anther and pistil of the tolerant variety. Histochemical analysis also indicated markedly higher autophagosome formation in tolerant variety's anther and pistil. Consistently, the expression levels of autophagy and ubiquitin-proteasome system (UPS)-related genes including BnATG8d, BnEXO70B, BnATl1 4A, and BnNBR1, as well as ubiquitin-activating enzyme E1, were higher in both reproductive organs of the tolerant variety. Interestingly, the areas of autophagosome formation overlapped with the areas in which higher superoxide accumulation and structural changes happened, suggesting a specific role of autophagy in oxidative stress response.

Inoculation with Micromonospora sp. enhances carbohydrate and amino acid production, strengthening antioxidant metabolism to mitigate heat stress in wheat cultivars

Introduction

Heat stress caused by global warming adversely affects wheat yield through declining most nutritional quality attributes in grains, excluding grain protein content.

Methods

This research investigated the biochemical, physiological, and antioxidant responses of wheat plants under heat stress, focusing on the role of plant growth-promoting bacteria (Micromonospora sp.). Two wheat genotypes were studied: one heat-sensitive and one heat-tolerant, examining their responses to heat stress with and without bacterial inoculation.

Results

Under heat stress, the sensitive cultivar experienced significant reductions in photosynthesis rate, chlorophyll content, and RuBisCO activity (57-61%), while the tolerant cultivar had milder reductions (24-28%). Micromonospora sp. treatment notably improved these parameters in the sensitive cultivar (+48-78%), resulting in a substantial increase in biomass production (+43-53%), which was not seen in the tolerant cultivar. Additionally, oxidative stress markers (H2O2 and MDA) were elevated more in the sensitive cultivar (82% and 90% higher) compared to the tolerant one. Micromonospora sp. treatment effectively reduced these markers in the sensitive cultivar (-28% and -27%). Enhanced activity of antioxidant enzymes and ASC-GSH pathway enzymes was particularly evident in Micromonospora sp.-treated sensitive plants. Carbohydrate metabolism shifted, with increased soluble sugars and significant rises in sucrose content in Micromonospora sp.-treated plants under stress.

Discussion

The higher soluble sugar levels facilitated amino acid synthesis, contributing to biosynthesis of secondary metabolites, including flavonoids, polyphenols, and anthocyanins. This was reflected in increased activity of phenylalanine ammonia-lyase, cinnamate (CA) 4-hydroxylase, and chalcone synthase enzymes, indicating the activation of phenylpropanoid pathways. Overall, the findings suggest that Micromonospora sp. can mitigate heat stress effects by enhancing photosynthetic efficiency, antioxidant defense, and metabolic adaptations in heat-sensitive wheat cultivars.

Functional crosstalk of sucrose and G protein signaling in maize thermotolerance by modulating osmoregulation system

Sucrose (SUC) is a signaling molecule with multiple physiological functions. G protein is a kind of receptor that converts extracellular first messenger into intracellular second messenger. However, it is little known that SUC interplays with G protein signaling in maize thermotolerance. In this work, using maize seedlings as materials, the interplay between SUC and G protein signaling in maize thermotolerance was investigated. The results indicate that heat stress-decreased survival percentage and tissue viability of the seedlings was mitigated by SUC. Similarly, heat stress-increased malondialdehyde content and electrolyte leakage also was reduced by SUC. These findings show that SUC can potentially enhance thermotolerance in maize seedlings. Also, SUC-enhanced thermotolerance was abolished by suramin (G protein inhibitor) and N-ethylmaleimide (SUC transport inhibitor), but enhanced by 3-O-methyl-D-glucose (G protein activator), indicating the interplay of SUC and G protein signaling in maize thermotolerance. To investigate the possible mechanism behind SUC-G protein interaction in enhancing maize thermotolerance, osmoregulation in mesocotyls of seedlings were evaluated before and after heat stress. The results suggest that osmolytes (SUC, glucose, fructose, total soluble sugar, proline, and glycine betaine) contents in mesocotyls under non-heat and heat stress were increased by SUC in varying degrees. Likewise, the osmolyte-metabolizing enzymes (sucrose-phosphate synthase, sucrose synthase, pyrroline-5-carboxylate synthase, ornithine aminotransferase, betaine-aldehyde dehydrogenase, and trehalase) activities were enhanced by SUC. Analogously, ZmSPS1, ZmSUS6, ZmP5CS, ZmOAT, ZmBADH, and ZmTRE1 expression in mesocotyls was up-regulated by SUC to different extent. These findings illustrate that the functional crosstalk of sucrose and G protein signaling in maize thermotolerance by modulating osmoregulation system.

Impact of exogenous rhamnolipids on plant photosynthesis and biochemical parameters under prolonged heat stress

High temperatures severely affect plant growth and development leading to major yield losses. These temperatures are expected to increase further due to global warming, with longer and more frequent heat waves. Rhamnolipids (RLs) are known to protect several plants against various pathogens. To date, how RLs act under abiotic stresses is unexplored. In this study, we aimed to investigate whether RLs could modify Arabidopsis thaliana physiology during prolonged heat stress. Measurement of leaf gas exchange and chlorophyll fluorescence showed that heat stress reduces photosynthetic rate through stomatal limitation and reduction of photosystem II yield. Our study reported decreased chlorophyll content and accumulation of soluble sugars and proline in response to heat stress. RLs were shown to have no detrimental effect on photosynthesis and carbohydrate metabolism in all conditions. These results extend the knowledge of plant responses to prolonged heat stress.

Transcriptomic Analysis of the CAM Species Kalanchoë fedtschenkoi Under Low- and High-Temperature Regimes

Temperature stress is one of the major limiting environmental factors that negatively impact global crop yields. Kalanchoë fedtschenkoi is an obligate crassulacean acid metabolism (CAM) plant species, exhibiting much higher water-use efficiency and tolerance to drought and heat stresses than C3 or C4 plant species. Previous studies on gene expression responses to low- or high-temperature stress have been focused on C3 and C4 plants. There is a lack of information about the regulation of gene expression by low and high temperatures in CAM plants. To address this knowledge gap, we performed transcriptome sequencing (RNA-Seq) of leaf and root tissues of K. fedtschenkoi under cold (8 °C), normal (25 °C), and heat (37 °C) conditions at dawn (i.e., 2 h before the light period) and dusk (i.e., 2 h before the dark period). Our analysis revealed differentially expressed genes (DEGs) under cold or heat treatment in comparison to normal conditions in leaf or root tissue at each of the two time points. In particular, DEGs exhibiting either the same or opposite direction of expression change (either up-regulated or down-regulated) under cold and heat treatments were identified. In addition, we analyzed gene co-expression modules regulated by cold or heat treatment, and we performed in-depth analyses of expression regulation by temperature stresses for selected gene categories, including CAM-related genes, genes encoding heat shock factors and heat shock proteins, circadian rhythm genes, and stomatal movement genes. Our study highlights both the common and distinct molecular strategies employed by CAM and C3/C4 plants in adapting to extreme temperatures, providing new insights into the molecular mechanisms underlying temperature stress responses in CAM species.

Humboldt Review: Potassium may mitigate drought stress by increasing stem carbohydrates and their mobilization into grains

Potassium (K) deficiency occurs commonly in crop plants. Optimal K nutrition is particularly important when plants are exposed to stress conditions (especially drought and heat) because a cellular demand for K increases. Low K in plant tissues is known to aggravate the effects of drought stress by impairing the osmoregulation process and the photosynthetic carbon metabolism. However, despite numerous publications about the role of K in enhancing tolerance to drought stress in crop plants, our understanding of the major mechanisms underlying the stress-mitigating effects of K is still limited. This paper summarizes and appraises the current knowledge on the major protective effects of K under drought stress, and then proposes a new K-related drought stress-mitigating mechanism, whereby optimal K nutrition may promote partitioning of carbohydrates in stem tissues and subsequent mobilization of these carbohydrates into developing grain under drought stress. The importance of stem reserves of carbohydrates is based on limited photosynthetic capacity during the grain-filling period under drought conditions due to premature leaf senescence as well as due to impaired assimilate transport from leaves to the developing grains. Plants with a high capacity to store large amounts of soluble carbohydrates in stems before anthesis and mobilize them into grain post-anthesis have a high potential to yield well in dry and hot environments. In practice, particular attention needs to be paid to the K nutritional status of plants grown with limited water supply, especially during grain filling. Because K is the mineral nutrient deposited mainly in stem, a special consideration should be given to stems of crop plants in research dealing with the effects of K on yield formation and stress mitigation.

Understanding of Plant Salt Tolerance Mechanisms and Application to Molecular Breeding

Soil salinization is a widespread hindrance that endangers agricultural production and ecological security. High salt concentrations in saline soils are primarily caused by osmotic stress, ionic toxicity and oxidative stress, which have a negative impact on plant growth and development. In order to withstand salt stress, plants have developed a series of complicated physiological and molecular mechanisms, encompassing adaptive changes in the structure and function of various plant organs, as well as the intricate signal transduction networks enabling plants to survive in high-salinity environments. This review summarizes the recent advances in salt perception under different tissues, physiological responses and signaling regulations of plant tolerance to salt stress. We also examine the current knowledge of strategies for breeding salt-tolerant plants, including the applications of omics technologies and transgenic approaches, aiming to provide the basis for the cultivation of salt-tolerant crops through molecular breeding. Finally, future research on the application of wild germplasm resources and muti-omics technologies to discover new tolerant genes as well as investigation of crosstalk among plant hormone signaling pathways to uncover plant salt tolerance mechanisms are also discussed in this review.

Unveiling the role of epigenetic mechanisms and redox signaling in alleviating multiple abiotic stress in plants

Anthropogenic activities and subsequent global climate change instigate drastic crop productivity and yield changes. These changes comprise a rise in the number and severity of plant stress factors, which can arise simultaneously or sequentially. When abiotic stress factors are combined, their impact on plants is more substantial than that of a singleton stress factor. One such impact is the alteration of redox cellular homeostasis, which, in turn, can regulate downstream stress-responsive gene expression and resistance response. The epigenetic regulation of gene expression in response to varied stress factors is an interesting phenomenon, which, conversely, can be stable and heritable. The epigenetic control in plants in response to abiotic stress combinations and their interactions with cellular redox alteration is an emerging field to commemorate crop yield management under climate change. The article highlights the integration of the redox signaling pathways and epigenetic regulations as pivotal components in the complex network of plant responses against multi-combinatorial stresses across time and space. This review aims to lay the foundation for developing novel approaches to mitigate the impact of environmental stresses on crop productivity, bridging the gap between theoretical understanding and practical solutions in the face of a changing climate and anthropogenic disturbances.

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

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

The impact of polystyrene nanoplastics on plants in the scenario of increasing temperatures: The case of Azolla filiculoides Lam

There are great concerns for the accumulation in the environment of small dimension plastics, such as micro- and nanoplastics. Due to their small size, which facilitates their uptake by organisms, nanoplastics are of particular concern. The toxic effects of nanoplastics on plants are already reported in the literature, however nothing is known, to date, about the possible effects of climate change, in particular of increasing temperatures, on their toxicity for plants. To address this issue, plants of the water fern Azolla filiculoides were grown at optimal (25 °C) or high (35 °C) temperature, with or without polystyrene nanoplastics, and the effects of these stressors were assessed using a multidisciplinary approach. Green fluorescent polystyrene nanoplastics were used to track their possible uptake by A. filiculoides. The development and physiology of our model plant was adversely affected by both nanoplastics and high temperatures. Overall, histological, morphological, and photosynthetic parameters worsened under co-treatment, in accordance with the increased uptake of nanoplastics under higher temperature, as observed by fluorescence images. Based on our findings, the concern regarding the potential for increased toxicity of pollutants, specifically nanoplastics, at high temperatures is well-founded and warrants attention as a potential negative consequence of climate change. Additionally, there is cause for concern regarding the increase in nanoplastic uptake at high temperatures, particularly if this phenomenon extends to food and feed crops, which could lead to greater entry into the food chain.

Biological Nano-Agrochemicals for Crop Production as an Emerging Way to Address Heat and Associated Stresses

Climate change is a global problem facing all aspects of the agricultural sector. Heat stress due to increasing atmospheric temperature is one of the most common climate change impacts on agriculture. Heat stress has direct effects on crop production, along with indirect effects through associated problems such as drought, salinity, and pathogenic stresses. Approaches reported to be effective to mitigate heat stress include nano-management. Nano-agrochemicals such as nanofertilizers and nanopesticides are emerging approaches that have shown promise against heat stress, particularly biogenic nano-sources. Nanomaterials are favorable for crop production due to their low toxicity and eco-friendly action. This review focuses on the different stresses associated with heat stress and their impacts on crop production. Nano-management of crops under heat stress, including the application of biogenic nanofertilizers and nanopesticides, are discussed. The potential and limitations of these biogenic nano-agrochemicals are reviewed. Potential nanotoxicity problems need more investigation at the local, national, and global levels, as well as additional studies into biogenic nano-agrochemicals and their effects on soil, plant, and microbial properties and processes.

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

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

Biochemical properties and pigment contents of Satureja genotypes affected by plant growth regulators and temperature stress

There is little data, to our knowledge, on the biochemical properties of different Satureja sp. genotypes affected by plant growth regulators (PGR) under temperature stress. A split plot research on the basis of a complete randomized block design with three replicates examining temperature stress (planting dates, 8th of April, May and June) (main factor), and the factorial combination of plant growth regulators (PGR, control (CO), gibberellic acid (GA), fertilization (MI), and amino acid (A)), and genotypes (Khuzestani, Mutika, and Bakhtiari) on plant biochemical properties, was conducted. Plant pigment contents (chlorophyll a, and b and carotenoids (car)), antioxidant activity (catalase (CAT), ascorbate peroxidase (APX) and guaiacol peroxidase (GP)), and leaf protein were determined. Treatments significantly and differently affected the genotypes performance. PD3 and PD1resulted in significantly higher activity of APX (0.059 U. mg-1) and GP (0.190 U. mg-1), respectively (P ≤ 0.05). Temperature stress significantly affected plant CAT activity (U. mg-1) at PD1 (0.084) and PD3 (0.820). Higher temperature significantly enhanced leaf Pro, MI increased plant APX (0.054) and CAT activities (0.111 U. mg-1) significantly, and GA resulted in the highest and significantly different GP activity (0.186 U. mL-1). Treatments T1 and T3 significantly enhanced Chla and Car content, and MI resulted in significantly higher Chlb content (0.085 mg g-1 leaf fresh weight). Car and CAT are the two most sensitive biochemical traits under temperature stress and can more effectively regulate Satureja growth and activity. It is possible to alleviate temperature stress on Satureja biochemical properties by the tested PGR.

Deleterious Effects of Heat Stress on the Tomato, Its Innate Responses, and Potential Preventive Strategies in the Realm of Emerging Technologies

The tomato is a fruit vegetable rich in nutritional and medicinal value grown in greenhouses and fields worldwide. It is severely sensitive to heat stress, which frequently occurs with rising global warming. Predictions indicate a 0.2 °C increase in average surface temperatures per decade for the next three decades, which underlines the threat of austere heat stress in the future. Previous studies have reported that heat stress adversely affects tomato growth, limits nutrient availability, hammers photosynthesis, disrupts reproduction, denatures proteins, upsets signaling pathways, and damages cell membranes. The overproduction of reactive oxygen species in response to heat stress is toxic to tomato plants. The negative consequences of heat stress on the tomato have been the focus of much investigation, resulting in the emergence of several therapeutic interventions. However, a considerable distance remains to be covered to develop tomato varieties that are tolerant to current heat stress and durable in the perspective of increasing global warming. This current review provides a critical analysis of the heat stress consequences on the tomato in the context of global warming, its innate response to heat stress, and the elucidation of domains characterized by a scarcity of knowledge, along with potential avenues for enhancing sustainable tolerance against heat stress through the involvement of diverse advanced technologies. The particular mechanism underlying thermotolerance remains indeterminate and requires further elucidatory investigation. The precise roles and interplay of signaling pathways in response to heat stress remain unresolved. The etiology of tomato plants' physiological and molecular responses against heat stress remains unexplained. Utilizing modern functional genomics techniques, including transcriptomics, proteomics, and metabolomics, can assist in identifying potential candidate proteins, metabolites, genes, gene networks, and signaling pathways contributing to tomato stress tolerance. Improving tomato tolerance against heat stress urges a comprehensive and combined strategy including modern techniques, the latest apparatuses, speedy breeding, physiology, and molecular markers to regulate their physiological, molecular, and biochemical reactions.

Loss-of-function of PGL10 impairs photosynthesis and tolerance to high-temperature stress in rice

High temperature (HT) affects the production of chlorophyll (Chl) pigment and inhibits cellular processes that impair photosynthesis, and growth and development in plants. However, the molecular mechanisms underlying heat stress in rice are not fully understood yet. In this study, we identified two mutants varying in leaf color from the ethylmethanesulfonate mutant library of indica rice cv. Zhongjiazao-17, which showed pale-green leaf color and variegated leaf phenotype under HT conditions. Mut-map revealed that both mutants were allelic, and their phenotype was controlled by a single recessive gene PALE GREEN LEAF 10 (PGL10) that encodes NADPH:protochlorophyllide oxidoreductase B, which is required for the reduction of protochlorophyllide into chlorophyllide in light-dependent tetrapyrrole biosynthetic pathway-based Chl synthesis. Overexpression-based complementation and CRISPR/Cas9-based knockout analyses confirmed the results of Mut-map. Moreover, qRT-PCR-based expression analysis of PGL10 showed that it expresses in almost all plant parts with the lowest expression in root, followed by seed, third leaf, and then other green tissues in both mutants, pgl10a and pgl10b. Its protein localizes in chloroplasts, and the first 17 amino acids from N-terminus are responsible for signals in chloroplasts. Moreover, transcriptome analysis performed under HT conditions revealed that the genes involved in the Chl biosynthesis and degradation, photosynthesis, and reactive oxygen species detoxification were differentially expressed in mutants compared to WT. Thus, these results indicate that PGL10 is required for maintaining chloroplast function and plays an important role in rice adaptation to HT stress conditions by controlling photosynthetic activity.

Transcription factor CaHDZ15 promotes pepper basal thermotolerance by activating HEAT SHOCK FACTORA6a

High temperature stress (HTS) is a serious threat to plant growth and development and to crop production in the context of global warming, and plant response to HTS is largely regulated at the transcriptional level by the actions of various transcription factors (TFs). However, whether and how homeodomain-leucine zipper (HD-Zip) TFs are involved in thermotolerance are unclear. Herein, we functionally characterized a pepper (Capsicum annuum) HD-Zip I TF CaHDZ15. CaHDZ15 expression was upregulated by HTS and abscisic acid in basal thermotolerance via loss- and gain-of-function assays by virus-induced gene silencing in pepper and overexpression in Nicotiana benthamiana plants. CaHDZ15 acted positively in pepper basal thermotolerance by directly targeting and activating HEAT SHOCK FACTORA6a (HSFA6a), which further activated CaHSFA2. In addition, CaHDZ15 interacted with HEAT SHOCK PROTEIN 70-2 (CaHsp70-2) and glyceraldehyde-3-phosphate dehydrogenase1 (CaGAPC1), both of which positively affected pepper thermotolerance. CaHsp70-2 and CaGAPC1 promoted CaHDZ15 binding to the promoter of CaHSFA6a, thus enhancing its transcription. Furthermore, CaHDZ15 and CaGAPC1 were protected from 26S proteasome-mediated degradation by CaHsp70-2 via physical interaction. These results collectively indicate that CaHDZ15, modulated by the interacting partners CaGAPC1 and CaHsp70-2, promotes basal thermotolerance by directly activating the transcript of CaHSFA6a. Thus, a molecular linkage is established among CaHsp70-2, CaGAPC1, and CaHDZ15 to transcriptionally modulate CaHSFA6a in pepper thermotolerance.

Salicylic Acid and Gemma-Aminobutyric Acid Mediated Regulation of Growth, Metabolites, Antioxidant Defense System and Nutrient Uptake in Sunflower (Helianthus annuus L.) Under Arsenic Stress

Background

Arsenic (As) is a highly toxic and carcinogenic pollutant commonly found in soil and water, posing significant risks to human health and plant growth.

Objective

The objectives of this study to evaluate morphological, biochemical, and physiological markers, as well as ion homeostasis, to alleviate the toxic effects of As in sunflowers through the exogenous application of salicylic acid (SA), γ-aminobutyric acid (GABA), and their combination.

Methods

A pot experiment was conducted using two sunflower genotypes, FH-779 and FH-773, subjected to As stress (60 mg kg-1) to evaluate the effects of SA at 100 mg L-1, GABA at 200 mg L-1, and their combination on growth and related physiological and biochemical attributes under As stress.

Results

The study revealed that As toxicity had a detrimental effect on various growth parameters, chlorophyll pigments, relative water content, total proteins, and nutrient uptake in sunflower plants. It also led to increased oxidative stress, as indicated by higher levels of malondialdehyde (MDA) and hydrogen peroxide (H2O2), along with As accumulation in the roots and leaves. However, the application of SA and GABA protected against As-induced damage by enhancing the enzymatic antioxidant defense system. This was achieved through the activation of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) activities, as well as an increase in osmolytes. They also improved nutrient acquisition and plant growth under As toxicity.

Conclusions

We investigated the regulatory roles of SA and GABA in mitigating arsenic-induced phytotoxic effects on sunflower. Our results revealed a significant interaction between SA and GABA in regulating growth, photosynthesis, metabolites, antioxidant defense systems, and nutrient uptake in sunflower under As stress. These findings provide valuable insights into plant defense mechanisms and strategies to enhance stress tolerance in contaminated environments. In the future, SA and GABA could be valuable tools for managing stress in other important crops facing abiotic stress conditions.

Beyond heat waves: Unlocking epigenetic heat stress memory in Arabidopsis

Plants remember their exposure to environmental changes and respond more effectively the next time they encounter a similar change by flexibly altering gene expression. Epigenetic mechanisms play a crucial role in establishing such memory of environmental changes and fine-tuning gene expression. With the recent advancements in biochemistry and sequencing technologies, it has become possible to characterize the dynamics of epigenetic changes on scales ranging from short term (minutes) to long term (generations). Here, our main focus is on describing the current understanding of the temporal regulation of histone modifications and chromatin changes during exposure to short-term recurring high temperatures and reevaluating them in the context of natural environments. Investigations of the dynamics of histone modifications and chromatin structural changes in Arabidopsis after repeated exposure to heat at short intervals have revealed the detailed molecular mechanisms of short-term heat stress memory, which include histone modification enzymes, chromatin remodelers, and key transcription factors. In addition, we summarize the spatial regulation of heat responses. Based on the natural temperature patterns during summer, we discuss how plants cope with recurring heat stress occurring at various time intervals by utilizing 2 distinct types of heat stress memory mechanisms. We also explore future research directions to provide a more precise understanding of the epigenetic regulation of heat stress memory.

Salinity Mitigates the Negative Effect of Elevated Temperatures on Photosynthesis in the C3-C4 Intermediate Species Sedobassia sedoides

The adaptation of plants to combined stresses requires unique responses capable of overcoming both the negative effects of each individual stress and their combination. Here, we studied the C3-C4 (C2) halophyte Sedobassia sedoides in response to elevated temperature (35 °C) and salinity (300 mM NaCl) as well as their combined effect. The responses we studied included changes in water-salt balance, light and dark photosynthetic reactions, the expression of photosynthetic genes, the activity of malate dehydrogenase complex enzymes, and the antioxidant system. Salt treatment led to altered water-salt balance, improved water use efficiency, and an increase in the abundance of key enzymes involved in intermediate C3-C4 photosynthesis (i.e., Rubisco and glycine decarboxylase). We also observed a possible increase in the activity of the C2 carbon-concentrating mechanism (CCM), which allowed plants to maintain high photosynthesis intensity and biomass accumulation. Elevated temperatures caused an imbalance in the dark and light reactions of photosynthesis, leading to stromal overreduction and the excessive generation of reactive oxygen species (ROS). In response, S. sedoides significantly activated a metabolic pathway for removing excess NADPH, the malate valve, which is catalyzed by NADP-MDH, without observable activation of the antioxidant system. The combined action of these two factors caused the activation of antioxidant defenses (i.e., increased activity of SOD and POX and upregulation of FDI), which led to a decrease in oxidative stress and helped restore the photosynthetic energy balance. Overall, improved PSII functioning and increased activity of PSI cyclic electron transport (CET) and C2 CCM led to an increase in the photosynthesis intensity of S. sedoides under the combined effect of salinity and elevated temperature relative to high temperature alone.

A general concept of quantitative abiotic stress sensing

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

Application of ethanol alleviates heat damage to leaf growth and yield in tomato

Chemical priming has emerged as a promising area in agricultural research. Our previous studies have demonstrated that pretreatment with a low concentration of ethanol enhances abiotic stress tolerance in Arabidopsis and cassava. Here, we show that ethanol treatment induces heat stress tolerance in tomato (Solanum lycopersicon L.) plants. Seedlings of the tomato cultivar 'Micro-Tom' were pretreated with ethanol solution and then subjected to heat stress. The survival rates of the ethanol-pretreated plants were significantly higher than those of the water-treated control plants. Similarly, the fruit numbers of the ethanol-pretreated plants were greater than those of the water-treated ones. Transcriptome analysis identified sets of genes that were differentially expressed in shoots and roots of seedlings and in mature green fruits of ethanol-pretreated plants compared with those in water-treated plants. Gene ontology analysis using these genes showed that stress-related gene ontology terms were found in the set of ethanol-induced genes. Metabolome analysis revealed that the contents of a wide range of metabolites differed between water- and ethanol-treated samples. They included sugars such as trehalose, sucrose, glucose, and fructose. From our results, we speculate that ethanol-induced heat stress tolerance in tomato is mainly the result of increased expression of stress-related genes encoding late embryogenesis abundant (LEA) proteins, reactive oxygen species (ROS) elimination enzymes, and activated gluconeogenesis. Our results will be useful for establishing ethanol-based chemical priming technology to reduce heat stress damage in crops, especially in Solanaceae.

Heat stress memory differentially regulates the expression of nitrogen transporter genes in the filamentous red alga 'Bangia' sp. ESS1

Introduction

To withstand high temperatures that would be lethal to a plant in the naïve state, land plants must establish heat stress memory. The acquisition of heat stress tolerance via heat stress memory in algae has only been observed in the red alga 'Bangia' sp. ESS1.

Methods

In this study, we further evaluated the intrinsic ability of this alga to establish heat stress memory by monitoring hydrogen peroxide (H2O2) production and examining the relationship between heat stress memory and the expression of genes encoding nitrogen transporters, since heat stress generally reduces nitrogen absorption. Next, genes encoding nitrogen transporters were selected from our unpublished transcriptome data of 'Bangia' sp. ESS1.

Results

We observed a reduction in H2O2 content when heat stress memory was established in the alga. In addition, six ammonium transporter genes, a single-copy nitrate transporter gene and two urea transporter genes were identified. Two of these nitrogen transporter genes were induced by heat stress but not by heat stress memory, two genes showed heat stress memory-dependent expression, and one gene was induced by both treatments. Heat stress memory therefore differentially regulated the expression of the nitrogen transporter genes by reducing heat stress-inducible gene expression and inducing heat stress memory-dependent gene expression.

Discussion

These findings point to the functional diversity of nitrogen transporter genes, which play different roles under various heat stress conditions. The characteristic effects of heat stress memory on the expression of individual nitrogen transporter genes might represent an indispensable strategy for reducing the threshold of sensitivity to recurrent high-temperature conditions and for maintaining nitrogen absorption under such conditions in 'Bangia' sp. ESS1.

Prediction of biomass accumulation and tolerance of wheat seedlings to drought and elevated temperatures using hyperspectral imaging

Early prediction of important agricultural traits in wheat opens up broad prospects for the development of approaches to accelerate the selection of genotypes for further breeding trials. This study is devoted to the search for predictors of biomass accumulation and tolerance of wheat to abiotic stressors. Hyperspectral (HS) and chlorophyll fluorescence (ChlF) parameters were analyzed as predictors under laboratory conditions. The predictive ability of reflectance and normalized difference indices (NDIs), as well as their relationship with parameters of photosynthetic activity, which is a key process influencing organic matter production and crop yields, were analyzed. HS parameters calculated using the wavelengths in Red (R) band and the spectral range next to the red edge (FR-NIR) were found to be correlated with biomass accumulation. The same ranges showed potential for predicting wheat tolerance to elevated temperatures. The relationship of HS predictors with biomass accumulation and heat tolerance were of opposite sign. A number of ChlF parameters also showed statistically significant correlation with biomass accumulation and heat tolerance. A correlation between HS and ChlF parameters, that demonstrated potential for predicting biomass accumulation and tolerance, has been shown. No predictors of drought tolerance were found among the HS and ChlF parameters analyzed.

Meta-analysis of Arabidopsis thaliana microarray data in relation to heat stress response

Introduction

Increasing global warming has made heat stress a serious threat to crop productivity and global food security in recent years. One of the most promising solutions to address this issue is developing heat-stress-tolerant plants. Hence, a thorough understanding of heat stress response mechanisms, particularly molecular ones, is crucial.

Methods

Although numerous studies have used microarray expression profiling technology to explore this area, these experiments often face limitations, leading to inconsistent results. To overcome these limitations, a random effects meta-analysis was employed using advanced statistical methods. A meta-analysis of 16 microarray datasets related to heat stress response in Arabidopsis thaliana was conducted.

Results

The analysis revealed 1,972 significant differentially expressed genes between control and heat-stressed plants (826 over-expressed and 1,146 down-expressed), including 128 differentially expressed transcription factors from different families. The most significantly enriched biological processes, molecular functions, and KEGG pathways for over-expressed genes included heat response, mRNA splicing via spliceosome pathways, unfolded protein binding, and heat shock protein binding. Conversely, for down-expressed genes, the most significantly enriched categories included cell wall organization or biogenesis, protein phosphorylation, transmembrane transporter activity, ion transmembrane transporter, biosynthesis of secondary metabolites, and metabolic pathways.

Discussion

Through our comprehensive meta-analysis of heat stress transcriptomics, we have identified pivotal genes integral to the heat stress response, offering profound insights into the molecular mechanisms by which plants counteract such stressors. Our findings elucidate that heat stress influences gene expression both at the transcriptional phase and post-transcriptionally, thereby substantially augmenting our comprehension of plant adaptive strategies to heat stress.

HSF and Hsp Gene Families in sunflower: a comprehensive genome-wide determination survey and expression patterns under abiotic stress conditions

Sunflowers belong to the Asteraceae family, which comprises nutrimental and economic oilseed plants. Heat shock proteins (Hsps) are protein families vital for all organisms' growth and survival. Besides the ordinary conditions, the expression of these proteins ascends during abiotic stress factors such as high temperature, salinity, and drought. Using bioinformatics approaches, the current study identified and analyzed HSF and Hsp gene family members in the sunflower (Helianthus annuus L.) plant. HSF, sHsp, Hsp40, Hsp60, Hsp70, Hsp90, and Hsp100 domains were analyzed in the sunflower genome, and 88, 72, 192, 52, 85, 49, and 148 genes were identified, respectively. The motif structures of the proteins in the same phylogenetic tree were similar, and the α-helical form was dominant in all the protein families except for sHsp. The estimated three-dimensional structure of 28 sHsp proteins was determined as β-sheets. Considering protein-protein interactions, the Hsp60-09 protein (38 interactions) was found to be the most interacting protein. The most orthologous gene pairs (58 genes) were identified between Hsp70 genes and Arabidopsis genes. The expression analysis of selected genes was performed under high temperature, drought, and high temperature-drought combined stress conditions in two sunflower cultivars. In stress conditions, gene expressions were upregulated for almost all genes in the first half and first hours at large. The expressions of HanHSF-45 and HanHsp70-29 genes were raised in two cultivars under high temperature and high temperature-drought combined stress conditions. This study presents a blueprint for subsequent research and delivers comprehensive knowledge of this vital protein domain.

Stimulation of the Defense Mechanisms of Potatoes to a Late Blight Causative Agent When Treated with Bacillus subtilis Bacteria and Chitosan Composites with Hydroxycinnamic Acids

Phytophthora infestans is, worldwide, one of the main causal agents of epiphytotics in potato plantings. Prevention strategies demand integrated pest management, including modeling of beneficial microbiomes of agroecosystems combining microorganisms and natural products. Chitooligosaccharides and their derivatives have great potential to be used by agrotechnology due to their ability to elicit plant immune reactions. The effect of combining Bacillus subtilis 26D and 11VM and conjugates of chitin with hydroxycinnamates on late blight pathogenesis was evaluated. Mechanisms for increasing the resistance of potato plants to Phytophthora infestans were associated with the activation of the antioxidant system of plants and an increase in the level of gene transcripts that encode PR proteins: basic protective protein (PR-1), thaumatin-like protein (PR-5), protease inhibitor (PR-6), and peroxidase (PR-9). The revealed activation of the expression of marker genes of systemic acquired resistance and induced systemic resistance under the influence of the combined treatment of plants with B. subtilis and conjugates of chitin with hydroxycinnamates indicates that, in this case, the development of protective reactions in potato plants to late blight proceeds synergistically, where B. subtilis primes protective genes, and chitosan composites act as a trigger for their expression.