Heat and Drought Stresses in Crops and Approaches for Their Mitigation

Heterogeneous Expression of Arabidopsis Subclass II of SNF1-Related Kinase 2 Improves Drought Tolerance via Stomatal Regulation in Poplar

Abscisic acid (ABA) is the most important phytohormone involved in the response to drought stress. Subclass II of SNF1-related kinase 2 (SnRK2) is an important signaling kinase related to ABA signal transduction. It regulates the phosphorylation of the target transcription factors controlling the transcription of a wide range of ABA-responsive genes in Arabidopsis thaliana. The transgenic poplars (Populus tremula × P. tremuloides, clone T89) ectopically overexpressing AtSnRK2.8, encoding a subclass II SnRK2 kinase of A. thaliana, have been engineered but almost no change in its transcriptome was observed. In this study, we evaluated osmotic stress tolerance and stomatal behavior of the transgenic poplars maintained in the netted greenhouse. The transgenic poplars, line S22, showed a significantly higher tolerance to 20% PEG treatment than non-transgenic controls. The stomatal conductance of the transgenic poplars tended to be lower than the non-transgenic control. Microscopic observations of leaf imprints revealed that the transgenic poplars had significantly higher stomatal closures under the stress treatment than the non-transgenic control. In addition, the stomatal index was lower in the transgenic poplars than in the non-transgenic controls regardless of the stress treatment. These results suggested that AtSnRK2.8 is involved in the regulation of stomatal behavior. Furthermore, the transgenic poplars overexpressing AtSnRK2.8 might have improved abiotic stress tolerance through this stomatal regulation.

Root responses to abiotic stress: a comparative look at root system architecture in maize and sorghum

Under all environments, roots are important for plant anchorage and acquiring water and nutrients. However, there is a knowledge gap regarding how root architecture contributes to stress tolerance in a changing climate. Two closely related plant species, maize and sorghum, have distinct root system architectures and different levels of stress tolerance, making comparative analysis between these two species an ideal approach to resolve this knowledge gap. However, current research has focused on shared aspects of the root system that are advantageous under abiotic stress conditions rather than on differences. Here we summarize the current state of knowledge comparing the root system architecture relative to plant performance under water deficit, salt stress, and low phosphorus in maize and sorghum. Under water deficit, steeper root angles and deeper root systems are proposed to be advantageous for both species. In saline soils, a reduction in root length and root number has been described as advantageous, but this work is limited. Under low phosphorus, root systems that are shallow and wider are beneficial for topsoil foraging. Future work investigating the differences between these species will be critical for understanding the role of root system architecture in optimizing plant production for a changing global climate.

Uncovering the wide protective responses in Coffea spp. leaves to single and superimposed exposure of warming and severe water deficit

Climate changes boosted the frequency and severity of drought and heat events, with aggravated when these stresses occur simultaneously, turning crucial to unveil the plant response mechanisms to such harsh conditions. Therefore, plant responses/resilience to single and combined exposure to severe water deficit (SWD) and heat were assessed in two cultivars of the main coffee-producing species: Coffea arabica cv. Icatu and C. canephora cv. Conilon Clone 153 (CL153). Well-watered plants (WW) were exposed to SWD under an adequate temperature of 25/20°C (day/night), and thereafter submitted to a gradual increase up to 42/30°C, and a 14-d recovery period (Rec14). Greater protective response was found to single SWD than to single 37/28°C and/or 42/30°C (except for HSP70) in both cultivars, but CL153-SWD plants showed the larger variations of leaf thermal imaging crop water stress index (CWSI, 85% rise at 37/28°C) and stomatal conductance index (IG, 66% decline at 25/20°C). Both cultivars revealed great resilience to SWD and/or 37/28°C, but a tolerance limit was surpassed at 42/30°C. Under stress combination, Icatu usually displayed lower impacts on membrane permeability, and PSII function, likely associated with various responses, usually mostly driven by drought (but often kept or even strengthened under SWD and 42/30°C). These included the photoprotective zeaxanthin and lutein, antioxidant enzymes (superoxide dismutase, Cu,Zn-SOD; ascorbate peroxidase, APX), HSP70, arabinose and mannitol (involving de novo sugar synthesis), contributing to constrain lipoperoxidation. Also, only Icatu showed a strong reinforcement of glutathione reductase activity under stress combination. In general, the activities of antioxidative enzymes declined at 42/30°C (except Cu,Zn-SOD in Icatu and CAT in CL153), but HSP70 and raffinose were maintained higher in Icatu, whereas mannitol and arabinose markedly increased in CL153. Overall, a great leaf plasticity was found, especially in Icatu that revealed greater responsiveness of coordinated protection under all experimental conditions, justifying low PIChr and absence of lipoperoxidation increase at 42/30°C. Despite a clear recovery by Rec14, some aftereffects persisted especially in SWD plants (e.g., membranes), relevant in terms of repeated stress exposure and full plant recovery to stresses.

Comparative transcriptome analysis of two contrasting genotypes provides new insights into the drought response mechanism in pigeon pea (Cajanus cajan L. Millsp.)

BACKGROUND

Despite plant's ability to adapt and withstand challenging environments, drought poses a severe threat to their growth and development. Although pigeon pea is already quite resistant to drought, the prolonged dehydration induced by the aberrant climate poses a serious threat to their survival and productivity.

OBJECTIVE

Comparative physiological and transcriptome analyses of drought-tolerant (CO5) and drought-sensitive (CO1) pigeon pea genotypes subjected to drought stress were carried out in order to understand the molecular basis of drought tolerance in pigeon pea.

METHODS

The transcriptomic analysis allowed us to examine how drought affects the gene expression of C. cajan. Using bioinformatics tools, the unigenes were de novo assembled, annotated, and functionally evaluated. Additionally, a homology-based sequence search against the droughtDB database was performed to identify the orthologs of the DEGs.

RESULTS

1102 potential drought-responsive genes were found to be differentially expressed genes (DEGs) between drought-tolerant and drought-sensitive genotypes. These included Abscisic acid insensitive 5 (ABI5), Nuclear transcription factor Y subunit A-7 (NF-YA7), WD40 repeat-containing protein 55 (WDR55), Anthocyanidin reductase (ANR) and Zinc-finger homeodomain protein 6 (ZF-HD6) and were highly expressed in the tolerant genotype. Further, GO analysis revealed that the most enriched classes belonged to biosynthetic and metabolic processes in the biological process category, binding and catalytic activity in the molecular function category and nucleus and protein-containing complex in the cellular component category. Results of KEGG pathway analysis revealed that the DEGs were significantly abundant in signalling pathways such as plant hormone signal transduction and MAPK signalling pathways. Consequently, in our investigation, we have identified and validated by qPCR a group of genes involved in signal reception and propagation, stress-specific TFs, and basal regulatory genes associated with drought response.

CONCLUSION

In conclusion, our comprehensive transcriptome dataset enabled the discovery of candidate genes connected to pathways involved in pigeon pea drought response. Our research uncovered a number of unidentified genes and transcription factors that could be used to understand and improve susceptibility to drought.

Long non-coding RNA-mediated epigenetic response for abiotic stress tolerance in plants

Plants perceive environmental fluctuations as stress and confront several stresses throughout their life cycle individually or in combination. Plants have evolved their sensing and signaling mechanisms to perceive and respond to a variety of stresses. Epigenetic regulation plays a critical role in the regulation of genes, spatiotemporal expression of genes under stress conditions and imparts a stress memory to encounter future stress responses. It is quintessential to integrate our understanding of genetics and epigenetics to maintain plant fitness, achieve desired genetic gains with no trade-offs, and durable long-term stress tolerance. The long non-coding RNA >200 nts having no coding potential (or very low) play several roles in epigenetic memory, contributing to the regulation of gene expression and the maintenance of cellular identity which include chromatin remodeling, imprinting (dosage compensation), stable silencing, facilitating nuclear organization, regulation of enhancer-promoter interactions, response to environmental signals and epigenetic switching. The lncRNAs are involved in a myriad of stress responses by activation or repression of target genes and hence are potential candidates for deploying in climate-resilient breeding programs. This review puts forward the significant roles of long non-coding RNA as an epigenetic response during abiotic stresses in plants and the prospects of deploying lncRNAs for designing climate-resilient plants.

Jasmonic acid priming augments antioxidant defense and photosynthesis in soybean to alleviate combined heat and drought stress effects

In the aftermaths of global warming, plants are more frequently exposed to the combination of heat stress and drought in natural conditions. Jasmonic acid (JA) has been known to modulate numerous plant adaptive responses to diverse environmental stresses. However, the function of JA in regulating plant responses to the combined effects of heat and drought remains underexplored. In this study, we elucidated the functions of JA in enhancing the combined heat and drought tolerance of soybean (Glycine max). Our results showed that priming with JA improved plant biomass, photosynthetic efficiency and leaf relative water content, which all together contributed to the improved performance of soybean plants under single and combined heat and drought conditions. Exposure to single and combined heat and drought conditions caused oxidative damage in soybean leaves. Priming soybean plants, which were exposed to single and combined heat and drought conditions, with JA, on the other hand, substantially quenched the reactive oxygen species-induced oxidative burden possibly by bolstering their antioxidant defense system. Together, our findings provide direct evidence of the JA-mediated protective mechanisms in maintaining the optimal photosynthetic rate and plant performance under combined heat and drought conditions.

Study of the genetic variability of durum wheat (Triticum durum Desf.) in the face of combined stress: water and heat

The devastating effects and extent of abiotic stress on cereal production continue to increase globally, affecting food security in several countries, including Tunisia. Heat waves and the scarcity of rainfall strongly affect durum wheat yields. The present study aims to screen for tolerance to combined water and heat stresses in durum wheat at the juvenile stage. Three combined treatments were tested, namely: T0 (100% field capacity (FC) at 24 °C), T1 (50% FC at 30 °C), and T2 (25% FC at 35 °C). The screening was carried out based on morphological, physiological, and biochemical criteria. The results showed that the combined stress significantly affected all the measured parameters. The relative water content (RWC) decreased by 37.6% under T1 compared to T0. Quantum yield (Fv/m) and photosynthetic efficiency (Fv/0) decreased under severe combined stress (T2) by 37.15% and 37.22%, respectively. Under T2 stress, LT increased by 63.7%. A significant increase in osmoprotective solutes was also observed, including proline, which increased by 154.6% under T2. Correlation analyses of the combination of water and heat stress confirm that the traits RWC, chlorophyll b content, Fv/m, proline content, Fv/0 and leaf temperature can be used as reliable screening criteria for the two stresses combined. The principal component analysis highlighted that Aouija tolerates the two levels of stresses studied, while the genotypes Karim and Hmira are the most sensitive. The results show that the tolerance of durum wheat to combined water and heat stress involves several adaptation mechanisms proportional to the stress intensity.

Enhancing climate change resilience in agricultural crops

Climate change threatens global food and nutritional security through negative effects on crop growth and agricultural productivity. Many countries have adopted ambitious climate change mitigation and adaptation targets that will exacerbate the problem, as they require significant changes in current agri-food systems. In this review, we provide a roadmap for improved crop production that encompasses the effective transfer of current knowledge into plant breeding and crop management strategies that will underpin sustainable agriculture intensification and climate resilience. We identify the main problem areas and highlight outstanding questions and potential solutions that can be applied to mitigate the impacts of climate change on crop growth and productivity. Although translation of scientific advances into crop production lags far behind current scientific knowledge and technology, we consider that a holistic approach, combining disciplines in collaborative efforts, can drive better connections between research, policy, and the needs of society.

Acclimation response and management strategies to combat heat stress in wheat for sustainable agriculture: A state-of-the-art review

Unpredicted variability in climate change on the planet is associated with frequent extreme high-temperature events impacting crop yield globally. Wheat is an economically and nutritionally important crop that fulfils global food requirements and each degree rise in temperature results in ∼6% of its yield reduction. Thus, understanding the impact of climate change, especially the terminal heat stress on global wheat production, becomes critically important for policymakers, crop breeders, researchers and scientists to ensure global food security. This review describes how wheat perceives heat stress and induces stress adaptation events by its morpho-physiological, phenological, molecular, and biochemical makeup. Temperature above a threshold level in crop vicinity leads to irreversible injuries, viz. destruction of cellular membranes and enzymes, generation of active oxygen species, redox imbalance, etc. To cope with these changes, wheat activates its heat tolerance mechanisms characterized by hoarding up soluble carbohydrates, signalling molecules, and heat tolerance gene expressions. Being vulnerable to heat stress, increasing wheat production without delay seeks strategies to mitigate the detrimental effects and provoke the methods for its sustainable development. Thus, to ensure the crop's resilience to stress and increasing food demand, this article circumscribes the integrated management approaches to enhance wheat's performance and adaptive capacity besides its alleviating risks of increasing temperature anticipated with climate change. Implementing these integrated strategies in the face of risks from rising temperatures will assist us in producing sustainable wheat with improved yield.

Effects of Heat Stress on Plant-Nutrient Relations: An Update on Nutrient Uptake, Transport, and Assimilation

As a consequence of global climate change, the frequency, severity, and duration of heat stress are increasing, impacting plant growth, development, and reproduction. While several studies have focused on the physiological and molecular aspects of heat stress, there is growing concern that crop quality, particularly nutritional content and phytochemicals important for human health, is also negatively impacted. This comprehensive review aims to provide profound insights into the multifaceted effects of heat stress on plant-nutrient relationships, with a particular emphasis on tissue nutrient concentration, the pivotal nutrient-uptake proteins unique to both macro- and micronutrients, and the effects on dietary phytochemicals. Finally, we propose a new approach to investigate the response of plants to heat stress by exploring the possible role of plant peroxisomes in the context of heat stress and nutrient mobilization. Understanding these complex mechanisms is crucial for developing strategies to improve plant nutrition and resilience during heat stress.

Current Scenario and Future Prospects of Endophytic Microbes: Promising Candidates for Abiotic and Biotic Stress Management for Agricultural and Environmental Sustainability

Globally, substantial research into endophytic microbes is being conducted to increase agricultural and environmental sustainability. Endophytic microbes such as bacteria, actinomycetes, and fungi inhabit ubiquitously within the tissues of all plant species without causing any harm or disease. Endophytes form symbiotic relationships with diverse plant species and can regulate numerous host functions, including resistance to abiotic and biotic stresses, growth and development, and stimulating immune systems. Moreover, plant endophytes play a dominant role in nutrient cycling, biodegradation, and bioremediation, and are widely used in many industries. Endophytes have a stronger predisposition for enhancing mineral and metal solubility by cells through the secretion of organic acids with low molecular weight and metal-specific ligands (such as siderophores) that alter soil pH and boost binding activity. Finally, endophytes synthesize various bioactive compounds with high competence that are promising candidates for new drugs, antibiotics, and medicines. Bioprospecting of endophytic novel secondary metabolites has given momentum to sustainable agriculture for combating environmental stresses. Biotechnological interventions with the aid of endophytes played a pivotal role in crop improvement to mitigate biotic and abiotic stress conditions like drought, salinity, xenobiotic compounds, and heavy metals. Identification of putative genes from endophytes conferring resistance and tolerance to crop diseases, apart from those involved in the accumulation and degradation of contaminants, could open new avenues in agricultural research and development. Furthermore, a detailed molecular and biochemical understanding of endophyte entry and colonization strategy in the host would better help in manipulating crop productivity under changing climatic conditions. Therefore, the present review highlights current research trends based on the SCOPUS database, potential biotechnological interventions of endophytic microorganisms in combating environmental stresses influencing crop productivity, future opportunities of endophytes in improving plant stress tolerance, and their contribution to sustainable remediation of hazardous environmental contaminants.

Gene Co-Expression Analysis Reveals the Transcriptome Changes and Hub Genes of Fructan Metabolism in Garlic under Drought Stress

Drought has become a serious environmental factor that affects the growth and yield of plants. Fructan, as an important storage compound in garlic, plays an important role in drought tolerance. Genomic changes in plants under drought stress clarify the molecular mechanism of plants' responses to stress. Therefore, we used RNA-seq to determine the transcriptomic changes in garlic under drought stress and identified the key module related to fructan metabolism by weighted gene co-expression network analysis. We conducted a comprehensive analysis of the garlic transcriptome under drought stress over a time course (0, 3, 6, 9, 12, 15 d). Drought significantly induces changes in gene expression. The number of specifically expressed genes were 1430 (3 d), 399 (6 d), 313 (9 d), 351 (12 d), and 1882 (15 d), and only 114 genes responded at each time point. The number of upregulated DEGs was higher than the number of downregulated DEGs. Gene ontology and a Kyoto Encyclopedia of Genes and Genomes analysis showed that garlic was more likely to cause changes in carbohydrate metabolism pathways under drought stress. Fructan content measurements showed that drought stress significantly induced fructan accumulation in garlic. To determine whether there were modules involved in the transcriptional regulation of fructan content in garlic, we further analyzed the genes related to fructan metabolism using WGCNA. They were enriched in two modules, with F-box protein and GADPH as hub genes, which are involved in garlic fructan metabolism in response to drought stress. These results provide important insights for the future research and cultivation of drought-tolerant garlic varieties.

Metabolic pathways engineering for drought or/and heat tolerance in cereals

Drought (D) and heat (H) are the two major abiotic stresses hindering cereal crop growth and productivity, either singly or in combination (D/+H), by imposing various negative impacts on plant physiological and biochemical processes. Consequently, this decreases overall cereal crop production and impacts global food availability and human nutrition. To achieve global food and nutrition security vis-a-vis global climate change, deployment of new strategies for enhancing crop D/+H stress tolerance and higher nutritive value in cereals is imperative. This depends on first gaining a mechanistic understanding of the mechanisms underlying D/+H stress response. Meanwhile, functional genomics has revealed several stress-related genes that have been successfully used in target-gene approach to generate stress-tolerant cultivars and sustain crop productivity over the past decades. However, the fast-changing climate, coupled with the complexity and multigenic nature of D/+H tolerance suggest that single-gene/trait targeting may not suffice in improving such traits. Hence, in this review-cum-perspective, we advance that targeted multiple-gene or metabolic pathway manipulation could represent the most effective approach for improving D/+H stress tolerance. First, we highlight the impact of D/+H stress on cereal crops, and the elaborate plant physiological and molecular responses. We then discuss how key primary metabolism- and secondary metabolism-related metabolic pathways, including carbon metabolism, starch metabolism, phenylpropanoid biosynthesis, γ-aminobutyric acid (GABA) biosynthesis, and phytohormone biosynthesis and signaling can be modified using modern molecular biotechnology approaches such as CRISPR-Cas9 system and synthetic biology (Synbio) to enhance D/+H tolerance in cereal crops. Understandably, several bottlenecks hinder metabolic pathway modification, including those related to feedback regulation, gene functional annotation, complex crosstalk between pathways, and metabolomics data and spatiotemporal gene expressions analyses. Nonetheless, recent advances in molecular biotechnology, genome-editing, single-cell metabolomics, and data annotation and analysis approaches, when integrated, offer unprecedented opportunities for pathway engineering for enhancing crop D/+H stress tolerance and improved yield. Especially, Synbio-based strategies will accelerate the development of climate resilient and nutrient-dense cereals, critical for achieving global food security and combating malnutrition.

Influence of High-Temperature and Intense Light on the Enzymatic Antioxidant System in Ginger (Zingiber officinale Roscoe) Plantlets

Environmental stressors such as high temperature and intense light have been shown to have negative effects on plant growth and productivity. To survive in such conditions, plants activate several stress response mechanisms. The synergistic effect of high-temperature and intense light stress has a significant impact on ginger, leading to reduced ginger production. Nevertheless, how ginger responds to this type of stress is not yet fully understood. In this study, we examined the phenotypic changes, malonaldehyde (MDA) content, and the response of four vital enzymes (superoxide dismutase (SOD), catalase (CAT), lipoxygenase (LOX), and nitrate reductase (NR)) in ginger plants subjected to high-temperature and intense light stress. The findings of this study indicate that ginger is vulnerable to high temperature and intense light stress. This is evident from the noticeable curling, yellowing, and wilting of ginger leaves, as well as a decrease in chlorophyll index and an increase in MDA content. Our investigation confirms that ginger plants activate multiple stress response pathways, including the SOD and CAT antioxidant defenses, and adjust their response over time by switching to different pathways. Additionally, we observe that the expression levels of genes involved in different stress response pathways, such as SOD, CAT, LOX, and NR, are differently regulated under stress conditions. These findings offer avenues to explore the stress mechanisms of ginger in response to high temperature and intense light. They also provide interesting information for the choice of genetic material to use in breeding programs for obtaining ginger genotypes capable of withstanding high temperatures and intense light stress.

Exogenous Allantoin Confers Rapeseed (Brassica campestris) Tolerance to Simulated Drought by Improving Antioxidant Metabolism and Physiology

Allantoin is an emerging plant metabolite, but its role in conferring drought-induced oxidative stress is still elusive. Therefore, an experiment was devised to explore the role of allantoin (0.5 and 1.0 mM; foliar spray) in rapeseed (Brassica campestris cv. BARI Sarisha-17) under drought. Seedlings at fifteen days of age were subjected to drought, maintaining soil moisture levels at 50% and 25% field capacities, while well-irrigated plants served as the control group. Drought-stressed plants exhibited increased levels of lipid peroxidation and hydrogen peroxide, electrolyte leakage, and impaired glyoxalase systems. Thus, the growth, biomass, and yield attributes of rapeseed were significantly impaired under drought. However, the allantoin-supplemented plants showed a notable increase in their contents of ascorbate and glutathione and decreased dehydroascorbate and glutathione disulfide contents under drought. Moreover, the activity of antioxidant enzymes such as ascorbate peroxidase, dehydroascorbate reductase, glutathione reductase, glutathione peroxidase, and catalase were accelerated with the allantoin spray and the glyoxalase system was also enhanced under drought. Moreover, the improvement in water balance with reduction in proline and potassium ion contents was also observed when allantoin was applied to the plants. Overall, the beneficial effects of allantoin supplementation resulted in the improved plant growth, biomass, and yield of rapeseed under drought conditions. These findings suggest that allantoin acts as an efficient metabolite in mitigating the oxidative stress caused by reactive oxygen species by enhancing antioxidant defense mechanisms and the glyoxalase system.

Integrating Full-Length Transcriptome and RNA Sequencing of Siberian Wildrye (Elymus sibiricus) to Reveal Molecular Mechanisms in Response to Drought Stress

Drought is one of the most significant limiting factors affecting plant growth and development on the Qinghai-Tibet Plateau (QTP). Mining the drought-tolerant genes of the endemic perennial grass of the QTP, Siberian wildrye (Elymus sibiricus), is of great significance to creating new drought-resistant varieties which can be used in the development of grassland livestock and restoring natural grassland projects in the QTP. To investigate the transcriptomic responsiveness of E. sibiricus to drought stress, PEG-induced short- and long-term drought stress was applied to two Siberian wildrye genotypes (drought-tolerant and drought-sensitive accessions), followed by third- and second-generation transcriptome sequencing analysis. A total of 40,708 isoforms were detected, of which 10,659 differentially expressed genes (DEGs) were common to both genotypes. There were 2107 and 2498 unique DEGs in the drought-tolerant and drought-sensitive genotypes, respectively. Additionally, 2798 and 1850 DEGs were identified in the drought-tolerant genotype only under short- and long-term conditions, respectively. DEGs numbering 1641 and 1330 were identified in the drought-sensitive genotype only under short- and long-term conditions, respectively. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis revealed that all the DEGs responding to drought stress in E. sibiricus were mainly associated with the mitogen-activated protein kinase (MAKP) signaling pathway, plant hormone signal transduction, the linoleic acid metabolism pathway, the ribosome pathway, and plant circadian rhythms. In addition, Nitrate transporter 1/Peptide transporter family protein 3.1 (NPF3.1) and Auxin/Indole-3-Acetic Acid (Aux/IAA) family protein 31(IAA31) also played an important role in helping E. sibiricus resist drought. This study used transcriptomics to investigate how E. sibiricus responds to drought stress, and may provide genetic resources and references for research into the molecular mechanisms of drought resistance in native perennial grasses and for breeding drought-tolerant varieties.

Cosuppression of AtGELP22 and AtGELP23, two ubiquitinated target proteins of RING E3 ligase AtAIRP5, increases tolerance to drought stress in Arabidopsis

AtAIRP5 RING E3 ubiquitin ligase was recently identified as a positive regulator of the abscisic acid (ABA)-mediated drought stress response by stimulating the degradation of serine carboxypeptidase-like 1. Here, we identified GDSL-type esterase/lipase 22 (AtGELP22) and AtGELP23 as additional interacting partners of AtAIRP5. Yeast two-hybrid, pull-down, co-immunoprecipitation, and ubiquitination analyses verified that AtGELP22 and AtGELP23 are ubiquitinated target proteins of AtAIRP5. AtGELP22 and AtGELP23 were colocalized with AtAIRP5 to punctate-like structures in the cytosolic fraction, in which PYK10 and NAI2, two ER body marker proteins, are localized. T-DNA insertion atgelp22 and atgelp23 single knockout mutant plants showed phenotypes indistinguishable from those of wild-type plants under ABA treatment. In contrast, RNAi-mediated cosuppression of AtGELP22 and AtGELP23 resulted in hypersensitive ABA-mediated stomatal movements and higher tolerance to drought stress than that of the single mutant and wild-type plants. Taken together, our results suggest that the putative GDSL-type esterases/lipases AtGELP22 and AtGELP23 act as redundant negative regulators of the ABA-mediated drought stress response in Arabidopsis.

Heat, drought, and combined stress effect on transgenic potato plants overexpressing the StERF94 transcription factor

Despite their economic importance worldwide, potato plants are sensitive to various abiotic constraints, such as drought and high temperatures, which cause significant losses in yields and tuber quality. Moreover, because of the climate change phenomenon, plants are frequently subjected to combined stresses, mainly high temperatures and drought. In this context, breeding for tolerant varieties should consider not only plant response to drought or high temperature but also to combined stresses. In the current study, we studied transgenic potato plants overexpressing an ethylene response transcription factor (TF; StERF94) involved in abiotic stress response signaling pathways. Our previous results showed that these transgenic plants display tolerance to salt stress more than wildtype (WT). In this work, we aimed to investigate the effects of drought, heat, and combined stresses on transgenic potato plants overexpressing StERF94 TF under in vitro culture conditions. The obtained results revealed that StERF94 overexpression improved the tolerance of the transgenic plants to drought, heat, and combined stresses through better control of the leaf water and chlorophyll contents, activation of antioxidant enzymes, and an accumulation of proline, especially in the leaves. Indeed, the expression level of antioxidant enzyme-encoding genes (CuZnSOD, FeSOD, CAT1, and CAT2) was significantly induced by the different stress conditions in the transgenic potato plants compared with the WT plants. This study further confirms that StERF94 TF may be implicated in regulating the expression of target genes encoding antioxidant enzymes.

Global Proteome Profiling Revealed the Adaptive Reprogramming of Barley Flag Leaf to Drought and Elevated Temperature

Plants, as sessile organisms, have developed sophisticated mechanisms to survive in changing environments. Recent advances in omics approaches have facilitated the exploration of plant genomes; however, the molecular mechanisms underlying the responses of barley and other cereals to multiple abiotic stresses remain largely unclear. Exposure to stress stimuli affects many proteins with regulatory and protective functions. In the present study, we employed liquid chromatography coupled with high-resolution mass spectrometry to identify stress-responsive proteins on the genome-wide scale of barley flag leaves exposed to drought, heat, or both. Profound alterations in the proteome of genotypes with different flag leaf sizes were found. The role of stress-inducible proteins was discussed and candidates underlying the universal stress response were proposed, including dehydrins. Moreover, the putative functions of several unknown proteins that can mediate responses to stress stimuli were explored using Pfam annotation, including calmodulin-like proteins. Finally, the confrontation of protein and mRNA abundances was performed. A correlation network between transcripts and proteins performance revealed several components of the stress-adaptive pathways in barley flag leaf. Taking the findings together, promising candidates for improving the tolerance of barley and other cereals to multivariate stresses were uncovered. The presented proteomic landscape and its relationship to transcriptomic remodeling provide novel insights for understanding the molecular responses of plants to environmental cues.

The plant protection preparation GZM improves crop immunity, yield, and quality

Lauryl alcohol, a natural compound found in plants and other organisms, is widely used to make surfactants, food, and pharmaceuticals. GZM, a plant protection preparation with lauryl alcohol as its major component is thought to establish a physical barrier on the plant surface, but its physiological functions are unknown. Here, we show that GZM improves the performance of peanut (Arachis hypogaea) plants in both the laboratory and the field. We demonstrate that the treatment with GZM or lauryl alcohol raises the contents of several specific lysophospholipids and induces the biosynthesis of phenylpropanoids, flavonoids, and wax in various plant species. In the field, GZM improves crop immunity, yield, and quality. In addition, GZM and lauryl alcohol can inhibit the growth of some pathogenic fungi. Our findings provide insights into the physiological and biological effects of GZM treatment on plants and show that GZM and lauryl alcohol are promising preparations in agricultural production.

A holistic and sustainable approach linked to drought tolerance of Mediterranean crops

The rapid increase in average temperatures and the progressive reduction in rainfalls caused by climate change is reducing crop yields worldwide, particularly in regions with hot and semi-arid climates such as the Mediterranean area. In natural conditions, plants respond to environmental drought stress with diverse morphological, physiological, and biochemical adaptations in an attempt to escape, avoid, or tolerate drought stress. Among these adaptations to stress, the accumulation of abscisic acid (ABA) is of pivotal importance. Many biotechnological approaches to improve stress tolerance by increasing the exogenous or endogenous content of ABA have proved to be effective. In most cases the resultant drought tolerance is associated with low productivity incompatible with the requirements of modern agriculture. The on-going climate crisis has provoked the search for strategies to increase crop yield under warmer conditions. Several biotechnological strategies, such as the genetic improvement of crops or the generation of transgenic plants for genes involved in drought tolerance, have been attempted with unsatisfactory results suggesting the need for new approaches. Among these, the genetic modification of transcription factors or regulators of signaling cascades provide a promising alternative. To reconcile drought tolerance with crop yield, we propose mutagenesis of genes controlling key signaling components downstream of ABA accumulation in local landraces to modulate responses. We also discuss the advantages of tackling this challenge with a holistic approach involving different knowledge and perspectives, and the problem of distributing the selected lines at subsidized prices to guarantee their use by small family farms.

Drought-free future climate conditions enhance cadmium phytoremediation capacity by Brassica napus through improved physiological status

This study aimed to assess Cd phytoextraction efficiency in well-watered and drought-stressed B. napus plants under current climate (CC, 21/14 °C, 400 ppm CO₂) and future climate (FC, 25/18 °C, 800 ppm CO₂) conditions. The underlying physiological mechanisms underpinning the obtained results were investigated by studying Cd (1, 10, 50, and 100 mg kg^-1) effect on B. napus photosynthetic performance and nutritional status. Only the Cd-50 and Cd-100 treatments caused visible leaf lesions, growth retardation, reductions in both gas exchange and chlorophyll fluorescence-related parameters, and disturbed mineral nutrient balance. Under CC conditions, well-watered plants were affected more than under FC conditions. The most important pathway by which Cd affected B. napus photosynthetic efficiency in well-watered plants was the damage to both photosystems, lowering photosynthetic electron transport. Meanwhile, non-stomatal and stomatal limitations were responsible for the higher reduction in the photosynthetic rate (P_r) of drought-stressed compared to well-watered plants. The significantly higher shoot dry weight, which had a strong positive relationship with P_r, was the main factor determining significantly higher shoot Cd accumulation in high Cd treatments in well-watered plants under FC conditions, resulting in a 65% (p < 0.05) higher soil Cd removal rate in the Cd-50 treatment.

Morphogenetic peculiarities of reproductive biology in sugar beet (Beta vulgaris L.) breeding

This review considers the processes of morphogenesis used in the development of propagation methods and the creation of a new starting material for sugar beet. It has been demonstrated that methods of particulation, in vitro microcloning and cell breeding that reflect non-sexual forms of plant reproduction increase the effectiveness of breeding experiments. The review describes the in vitro culture methods maintaing a tendency in plants for vegetative propagation and stimulating increase in genetic variability of properties when mutagens such as ethyl methanesulfonate, alien genetic structures with mf2 and mf3 bacterial genes in Agrobacterium tumefaciens strains, and selective agents (Сd++ ions and abscisic acid) are incorporated into plant cells. It presents the results of using fluorescent microscopy, cytophotometry, biochemical analysis and determining the level of phytohormones and content of nucleic acids in nuclei for forecasting the seed setting ability. It has demonstrated that long self-pollination of plants causes decrease in fertility of pollen grains, resulting in the sterilization of male gametes and the appearance of pistillody flowers. Self-fertile plants isolated from these lines serve as sterility fixers, while the apomixis elements increased the ovule number, additional embryo sacs and embryos. A role of apomixis in contributing to variability in the onto- and phylogenetic development of plants have been substantiated. The review reflects the morphological features of the in vitro development of sexual and somatic cells in embryos during the formation of seedlings based on floral and vegetative embryoidogeny. Use of the SNP and SSR (Unigenes) molecular-genetic markers having a high polymorphism level has appeared effective to characterize the developed breeding material and hybrid components when carrying out crossings. The study of sugar beet starting materials for the presence of TRs mini-satellite loci making it possible to reveal O-type plants-pollinators (sterility fixing agent) and MS-form plants are of interest for breeding as well. The selected material can be widely used in breeding to produce hybrids, allowing for a 2-3- fold reduction of the development period. The review also discusses the prospects for the development and implementation of new methods and original schemes in sugar beet genetics, biotechnology and breeding.

Abscisic acid increases hydrogen peroxide in mitochondria to facilitate stomatal closure

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

Detrimental effects of Cd and temperature on rice and functions of microbial community in paddy soils

Heavy metal (HM) contamination and high environmental temperature (HT) are caused by anthropogenic activities that negatively impact soil microbial communities and agricultural productivity. Although HM contaminations have deleterious effects on microbes and plants; there are hardly any reports on the combined effects of HM and HT. Here, we reported that HT coupled with cadmium (Cd) accumulation in soil and irrigated water could seriously affect crop growth and productivity, alternatively influencing the microbial community and nutrient cycles of paddy soils in rice fields. We analyzed different mechanisms of plants and microflora in the rhizospheric region, such as plant rhizospheric nitrification, endophytes colonization, nutrient uptake, and physiology of temperature-sensitive (IR64) and temperature-resistant Huanghuazhan (HZ) rice cultivars against different Cd levels (2, 5 and 10 mg kg^-1) with rice plants grown under 25 °C and 40 °C temperatures. Consequently, an increment in Cd accumulation was observed with rising temperature leading to enhanced expression of OsNTRs. In contrast, a greater decline in the microbial community was detected in IR64 cultivar than HZ. Similarly, ammonium oxidation, root-IAA, shoot-ABA production, and 16S rRNA gene abundance in the rhizosphere and endosphere were significantly influenced by HT and Cd levels, resulting in a significant decrease in the colonization of endophytes and the surface area of roots, leading to a decreased N uptake from the soil. Overall, the outcomes of this study unveiled the novel effects of Cd, temperature, and their combined effect on rice growth and functions of the microbial community. These results provide effective strategies to overcome Cd-phytotoxicity on the health of endophytes and rhizospheric bacteria in Cd-contaminated soil by using temperature-tolerant rice cultivars.

Sensitivity of the Photosynthetic Apparatus in Maize and Sorghum under Different Drought Levels

Drought is one of the main environmental stress factors affecting plant growth and yield. The impact of different PEG concentrations on the photosynthetic performance of maize (Zea mays L. Mayflower) and sorghum (Sorghum bicolor L. Foehn) was investigated. The activity of the photosynthetic apparatus was assessed using chlorophyll fluorescence (PAM and JIP test) and photooxidation of P₇₀₀. The data revealed that water deficiency decreased the photochemical quenching (qP), the ratio of photochemical to nonphotochemical processes (Fv/Fo), the effective quantum yield of the photochemical energy conversion in PSII (Φ_PSII), the rate of the electron transport (ETR), and the performance indexes PI_total and PI_ABS, as the impact was stronger in sorghum than in maize and depended on drought level. The PSI photochemistry (P₇₀₀ photooxidation) in sorghum was inhibited after the application of all studied drought levels, while in maize, it was registered only after treatment with higher PEG concentrations (30% and 40%). Enhanced regulated energy losses (Φ_NPQ) and activation of the state transition under drought were also observed in maize, while in sorghum, an increase mainly in nonregulated energy losses (Φ_NO). A decrease in pigment content and relative water content and an increase in membrane damage were also registered after PEG treatment. The experimental results showed better drought tolerance of maize than sorghum. This study provides new information about the role of regulated energy losses and state transition for the protection of the photosynthetic apparatus under drought and might be a practical approach to the determination of the drought tolerance of plants.

Garlic Ecotypes Utilise Different Morphological, Physiological and Biochemical Mechanisms to Cope with Drought Stress

Drought negatively affects plants by altering morphological, physiological and metabolic processes and ultimately reducing yields. Garlic (Allium sativum L.), an important member of the Alliaceae family, is also sensitive to drought and maximizing the yield of garlic bulbs is largely dependent on water availability. The objective of this study was to determine the effects of drought stress on morphological and physiological characteristics, as well as on phenolic, sugar, inulin and free amino acid content and antioxidant activity in two Croatian garlic ecotypes, 'Istarski crveni' (IC) and Istarski bijeli (IB). Drought was induced by using polyethylene glycol 8000 (PEG) solution (-0.6 MPa) starting 21 days after clove planting and lasted for 20 days. Drought reduced plant height, number of leaves and plant weight, but increased root length in both ecotypes compared to the control treatment. Among the physiological parameters, significant differences were observed between the two ecotypes studied in the spectral characteristics of the leaves, namely reflection in red, green and blue, VAL, values of the vegetation indices related to the chlorophyll content (CHI, GI), and the anthocyanin content (ARI). Ecotype IC showed higher antioxidant activity in the control treatment due to higher total phenolic content (TPC), but under drought conditions higher DPPH radical scavenging activity was determined in ecotype IB and higher values of FRAP in IC. Sucrose and glucose generally decreased under drought, while inulin increased in IB but decreased in IC. Total free amino acid content increased under drought in both ecotypes. In conclusion, drought tolerance of IB might be associated with increased accumulation of inulin and higher levels of amino acids, especially those shown to contribute to drought resistance. In IC, drought tolerance is associated with an increase in some amino acid compounds and better root growth in depth, probably due to a more efficient translocation of sucrose to the underground part of the plant.

Effect of selenium nanoparticles on biological and morphofunctional parameters of barley seeds (Hordéum vulgáre L.)

The purpose of this work was to study the effect of selenium nanoparticles (Se NPs) on the biological and morphofunctional parameters of barley seeds (Hordéum vulgáre L.) We used seeds of Hordéum vulgáre L. with reduced morphofunctional characteristics. For the experiment, Se NPs were synthesized and stabilized with didecyldimethylammonium chloride. It was found that Se NPs have a spherical shape and a diameter of about 50 nm. According to dynamic light scattering data, the average hydrodynamic radius of the particles was 28 ± 8 nm. It is observed that the nanoparticles have a positive ζ-potential (+ 27.3 mV). For the experiment, we treated Hordéum vulgáre L. seeds with Se NPs (1, 5, 10 and 20 mg/L). The experiment showed that treatment of Hordéum vulgáre L. seeds with Se NPs has the best effect on the length of roots and sprout at concentration of 5 mg/L and on the number and thickness of roots at 10 mg/L. Germinability and germination energy of Hordéum vulgáre L. seeds were higher in group treated with 5 mg/L Se NPs. Analysis of macrophotographs of samples, histological sections of roots and 3D visualization of seeds by microcomputing tomography confirmed the best effect at 5 mg/L Se NPs. Moreover, no local destructions were detected at concentrations > 5 mg/L, which is most likely due to the inhibition of regulatory and catalytic processes in the germinating seeds. the treatment of Hordéum vulgáre L. seeds with > 5 mg/L Se NPs caused significant stress, coupled with intensive formation of reactive oxygen species, leading to a reorientation of root system growth towards thickening. Based on the results obtained, it was concluded that Se NPs at concentrations > 5 mg/L had a toxic effect. The treatment of barley seeds with 5% Se NPs showed maximum efficiency in the experiment, which allows us to further consider Se NPs as a stimulator for the growth and development of crop seeds under stress and reduced morphofunctional characteristics.

Ca2+-dependent oxidation of exogenous NADH and NADPH by the mitochondria of spring wheat and its relation with AOX capacity and ROS content at high temperatures

Mitochondria are sources of reactive oxygen species (ROS) in a plant cell under high temperature. Mitochondrial alternative NAD(P)H dehydrogenases (type II NAD(P)H DHs) and cyanide-resistant oxidase (AOX) can regulate ROS production, but their role at high temperatures is unknown. This study investigates the influence heat acclimation (37 °C) and heat shock (50 °C) temperatures on ROS content, activity and protein abundance of external Ca²⁺-dependent NAD(P)H DHs (NDB) and AOX in mitochondria of 4- and 8-day-old seedlings of spring wheat (Triticum aestivum L., var. Novosibirskya 29). The shoots of 4-day-old seedlings contained more carbohydrates, had a higher rate of total respiration and a high rate of oxidation of exogenous NADH, a greater AOX capacity and a lower of ROS content, as compared to leaves of 8-day-old seedlings, and were more resistant to heat shock. The activity of external NADH DH was higher than the one of NADPH DH in mitochondria of both shoots and leaves. At 37 °C, high NADH oxidation was associated with increased AOX capacity in mitochondria of both shoots and leaves, whereas NADPH oxidation with COX capacity. At 50 °C, the NADPH oxidation by shoots' mitochondria increased and the NADH oxidation stayed high. The content of NDB and AOX proteins depends on heat treatments and differs between mitochondria of shoots and leaves. Our data indicate that Ca²⁺-dependent type II NAD(P)H DHs can regulate the ROS content and together with AOX are involved in heat tolerance, depending on the development phase of spring wheat and is, probably, tissue-specific.

Brassinosteroids mediate moderate soil-drying to alleviate spikelet degeneration under high temperature during meiosis of rice

This study tested the hypothesis that brassinosteroids (BRs) mediate moderate soil-drying (MD) to alleviate spikelet degeneration under high temperature (HT) stress during meiosis of rice (Oryza sativa L.). A rice cultivar was pot-grown and subjected to normal temperature (NT) and HT treatments during meiosis, and two irrigation regimes including well-watered (WW) and MD were imposed to the plants simultaneously. The MD effectively alleviated the spikelet degeneration and yield loss under HT stress mainly via improving root activity and canopy and panicle traits including higher photosynthetic capacity, tricarboxylic acid cycle activity, and antioxidant capacity than WW. These parameters were regulated by BRs levels in plants. The decrease in BRs levels at HT was due mainly to the enhanced BRs decomposition, and the MD could rescue the BRs deficiency at HT via enhancing BRs biosynthesis and impeding decomposition. The connection between BRs and HT was verified by using rice BRs-deficient mutants, transgenic rice lines, and chemical regulators. Similar results were obtained in the open-air field experiment. The results suggest that BRs can mediate the MD to alleviate spikelet degeneration under HT stress during meiosis mainly via enhancing root activity, canopy traits, and young panicle traits of rice.

Overexpression of the Brassica rapa bZIP Transcription Factor, BrbZIP-S, Increases the Stress Tolerance in Nicotiana benthamiana

In higher plants, S1-basic region-leucine zipper (S1-bZIP) transcription factors fulfill crucial roles in the physiological homeostasis of carbon and amino acid metabolisms and stress responses. However, very little is known about the physiological role of S1-bZIP in cruciferous vegetables. Here, we analyzed the physiological function of S1-bZIP from Brassica rapa (BrbZIP-S) in modulating proline and sugar metabolism. Overexpression of BrbZIP-S in Nicotiana benthamiana resulted in delayed chlorophyll degradation during the response to dark conditions. Under heat stress or recovery conditions, the transgenic lines exhibited a lower accumulation of H2O2, malondialdehyde, and protein carbonyls compared to the levels in transgenic control plants. These results strongly indicate that BrbZIP-S regulates plant tolerance against dark and heat stress. We propose that BrbZIP-S is a modulator of proline and sugar metabolism, which are required for energy homeostasis in response to environmental stress conditions.

Synergism: biocontrol agents and biostimulants in reducing abiotic and biotic stresses in crop

In today's fast-shifting climate change scenario, crops are exposed to environmental pressures, abiotic and biotic stress. Hence, these will affect the production of agricultural products and give rise to a worldwide economic crisis. The increase in world population has exacerbated the situation with increasing food demand. The use of chemical agents is no longer recommended due to adverse effects towards the environment and health. Biocontrol agents (BCAs) and biostimulants, are feasible options for dealing with yield losses induced by plant stresses, which are becoming more intense due to climate change. BCAs and biostimulants have been recommended due to their dual action in reducing both stresses simultaneously. Although protection against biotic stresses falls outside the generally accepted definition of biostimulant, some microbial and non-microbial biostimulants possess the biocontrol function, which helps reduce biotic pressure on crops. The application of synergisms using BCAs and biostimulants to control crop stresses is rarely explored. Currently, a combined application using both agents offer a great alternative to increase the yield and growth of crops while managing stresses. This article provides an overview of crop stresses and plant stress responses, a general knowledge on synergism, mathematical modelling used for synergy evaluation and type of in vitro and in vivo synergy testing, as well as the application of synergism using BCAs and biostimulants in reducing crop stresses. This review will facilitate an understanding of the combined effect of both agents on improving crop yield and growth and reducing stress while also providing an eco-friendly alternative to agroecosystems.

Dual Inoculation with Rhizophagus irregularis and Bacillus megaterium Improves Maize Tolerance to Combined Drought and High Temperature Stress by Enhancing Root Hydraulics, Photosynthesis and Hormonal Responses

Climate change is leading to combined drought and high temperature stress in many areas, drastically reducing crop production, especially for high-water-consuming crops such as maize. This study aimed to determine how the co-inoculation of an arbuscular mycorrhizal (AM) fungus (Rhizophagus irregularis) and the PGPR Bacillus megaterium (Bm) alters the radial water movement and physiology in maize plants in order to cope with combined drought and high temperature stress. Thus, maize plants were kept uninoculated or inoculated with R. irregularis (AM), with B. megaterium (Bm) or with both microorganisms (AM + Bm) and subjected or not to combined drought and high temperature stress (D + T). We measured plant physiological responses, root hydraulic parameters, aquaporin gene expression and protein abundances and sap hormonal content. The results showed that dual AM + Bm inoculation was more effective against combined D + T stress than single inoculation. This was related to a synergistic enhancement of efficiency of the phytosystem II, stomatal conductance and photosynthetic activity. Moreover, dually inoculated plants maintained higher root hydraulic conductivity, which was related to regulation of the aquaporins ZmPIP1;3, ZmTIP1.1, ZmPIP2;2 and GintAQPF1 and levels of plant sap hormones. This study demonstrates the usefulness of combining beneficial soil microorganisms to improve crop productivity under the current climate-change scenario.

Exogenous Melatonin Alters Stomatal Regulation in Tomato Seedlings Subjected to Combined Heat and Drought Stress through Mechanisms Distinct from ABA Signaling

The understanding of stomatal regulation in climate stress is essential for ensuring resilient crops. The investigation of the stomatal regulation in combined heat and drought stress aimed to link effects of exogenous melatonin on stomatal conductance (g_s) and its mechanistic interactions with ABA or ROS signaling. Melatonin-treated and non-treated tomato seedlings were subjected to moderate and severe levels of heat (38°C for one or three days) and drought stress (soil relative water content of 50% or 20%) applied individually and in combination. We measured g_s, stomatal anatomy, ABA metabolites and enzymatic ROS scavengers. The stomata in combined stress responded predominantly to heat at soil relative water content (SRWC) = 50% and to drought stress at SRWC = 20%. Drought stress increased ABA levels at severe stress, whereas heat stress caused an accumulation of the conjugated form, ABA glucose ester, at both moderate and severe stress. The melatonin treatment affected g_s and the activity of ROS scavenging enzymes but had no effect on ABA levels. The ABA metabolism and conjugation of ABA might play a role in stomatal opening toward high temperatures. We provide evidence that melatonin increases g_s in combined heat and drought stress, but the effect is not mediated through ABA signaling.

The Potyviral Protein 6K2 from Turnip Mosaic Virus Increases Plant Resilience to Drought

Virus infection can increase drought tolerance of infected plants compared with noninfected plants; however, the mechanisms mediating virus-induced drought tolerance remain unclear. In this study, we demonstrate turnip mosaic virus (TuMV) infection increases Arabidopsis thaliana survival under drought compared with uninfected plants. To determine if specific TuMV proteins mediate drought tolerance, we cloned the coding sequence for each of the major viral proteins and generated transgenic A. thaliana that constitutively express each protein. Three TuMV proteins, 6K1, 6K2, and NIa-Pro, enhanced drought tolerance of A. thaliana when expressed constitutively in plants compared with controls. While in the control plant, transcripts related to abscisic acid (ABA) biosynthesis and ABA levels were induced under drought, there were no changes in ABA or related transcripts in plants expressing 6K2 under drought compared with well-watered conditions. Expression of 6K2 also conveyed drought tolerance in another host plant, Nicotiana benthamiana, when expressed using a virus overexpression construct. In contrast to ABA, 6K2 expression enhanced salicylic acid (SA) accumulation in both Arabidopsis and N. benthamiana. These results suggest 6K2-induced drought tolerance is mediated through increased SA levels and SA-dependent induction of plant secondary metabolites, osmolytes, and antioxidants that convey drought tolerance. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Identification and Characterization of Phytocyanin Family Genes in Cotton Genomes

Phytocyanins (PCs) are a class of plant-specific blue copper proteins that have been demonstrated to play a role in electron transport and plant development. Through analysis of the copper ligand residues, spectroscopic properties, and domain architecture of the protein, PCs have been grouped into four subfamilies: uclacyanins (UCs), stellacyanins (SCs), plantacyanins (PLCs), and early nodulin-like proteins (ENODLs). The present study aimed to identify and characterise the PCs present in three distinct cotton species (Gossypium hirsutum, Gossyium arboreum, and Gossypium raimondii) through the identification of 98, 63, and 69 genes respectively. We grouped PCs into four clades by using bioinformatics analysis and sequence alignment, which exhibit variations in gene structure and motif distribution. PCs are distributed across all chromosomes in each of the three species, with varying numbers of exons per gene and multiple conserved motifs, and with a minimum of 1 and maximum of 11 exons found on one gene. Transcriptomic data and qRT-PCR analysis revealed that two highly differentiated PC genes were expressed at the fibre initiation stage, while three highly differentiated PCs were expressed at the fibre elongation stage. These findings serve as a foundation for further investigations aimed at understanding the contribution of this gene family in cotton fibre production.

Growth and Molecular Responses of Tomato to Prolonged and Short-Term Heat Exposure

Tomatoes are one of the most important vegetables for human consumption. In the Mediterranean's semi-arid and arid regions, where tomatoes are grown in the field, global average surface temperatures are predicted to increase. We investigated tomato seed germination at elevated temperatures and the impact of two different heat regimes on seedlings and adult plants. Selected exposures to 37 °C and heat waves at 45 °C mirrored frequent summer conditions in areas with a continental climate. Exposure to 37 °C or 45 °C differently affected seedlings' root development. Both heat stresses inhibited primary root length, while lateral root number was significantly suppressed only after exposure to 37 °C. Heat stress treatments induced significant accumulation of indole-3-acetic acid (IAA) and reduced abscisic acid (ABA) levels in seedlings. As opposed to the heat wave treatment, exposure to 37 °C increased the accumulation of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC), which may have been involved in the root architecture modification of seedlings. Generally, more drastic phenotypic changes (chlorosis and wilting of leaves and bending of stems) were found in both seedlings and adult plants after the heat wave-like treatment. This was also reflected by proline, malondialdehyde and heat shock protein HSP90 accumulation. The gene expression of heat stress-related transcription factors was perturbed and DREB1 was shown to be the most consistent heat stress marker.

Impact of climate perturbations on seeds and seed quality for global agriculture

In agriculture, seeds are the most basic and vital input on which croplands productivity depends. These implies a good starting material, good production lines and good storage options. High-quality seed lots must be free of pests and pathogens and contain a required degree of genetic purity. Seeds need also to be stored in good condition between harvest and later sowing, to insure later on the field a good plant density and higher crop yield. In general, these parameters are already widely accepted and considered in many countries where advanced technologies evaluate them. However, the more and more frequently devastating climate changes observed around the world has put seed quality under threat, and current seeds may not be adapted to hazardous and unpredictable conditions. Climate-related factors such as temperature and water availability directly affect seed development and later germination. For these reasons, investigating seed quality in response to climate changes is a step to propose new crop varieties and practices that will bring solutions for our future.

Transcriptomic and weighted gene co-expression network analysis of tropic and temperate maize inbred lines recovering from heat stress

Heat stress (HS) causes imbalance of cellular homeostasis, growth impairment and extensively yield loss in crop production. In the present study, the tropic maize inbred CIMBL55 showed more thermotolerance than the maize temperate inbred B73, with less leaf damage rate and ROS accumulation. Transcriptome profiling of CIMBL55 and B73 upon (exposing at 45 ℃ for 0, 1, and 6 h) and post (recovering at 28 ℃ for 1 and 6 h) HS were further assessed and a total of 20204 DEGs were identified. Functional annotation revealed that HS activated unfolded protein response in endoplasmic reticulum in both two inbreds. Moreover, in CIMBL55, far more primary and secondary metabolism pathways were transcriptional altered. Afterwards, weighted gene co-expression analysis grouped all expressed genes into eighteen co-expressed modules. Four HS responsive and four CIMBL55 recovery-related modules were subsequently identified. Highly connected genes (hub genes) in these modules were characterized as transcription factors, heat shock proteins, Ca²⁺ signaling related genes and various enzymes. Moreover, one hub gene, ZmHsftf13 was verified to positively regulate thermotolerance by heterologous expressing in Arabidopsis and its Mu insertion mutant. The present research provides promising genes related to HS response in maize and is of great significance for breeding.

Photosynthetic, antioxidant activities, and osmoregulatory responses in winter wheat differ during the stress and recovery periods under heat, drought, and combined stress

There will be longer and more intense periods of heat and drought stress in the future for terrestrial ecosystems. Although the responses of wheat plants to heat and drought stress alone have been extensively investigated, little is known about the extent to which their recovery can be assured after stress relief. In this study, a winter wheat pot experiment was conducted to investigate the changes in photosynthetic performance, antioxidant activity, osmoregulation, and membrane lipid peroxidation under heat stress (36 °C), drought (45-55% of soil water holding capacity), and combined stress conditions. The results showed that heat and drought stress significantly reduced the photosynthetic rate and the contents of chlorophyll and carotenoid. Superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and glutathione reductase (GR) activities were greatly activated by heat and drought stress to scavenge overproduced superoxide anion (O₂^-). Plants exhibited positive osmoregulation through the synthesis of soluble protein (SP), soluble sugar (SS), and proline (Pro) to improve membrane stability. Within a range of stress, combined heat and drought stress exhibited significant interactive effects in the above mentioned indicators. After stress relief, the majority of physiological processes were reversible, as indicated by the effective recovery of pigment contents, photosynthetic rate, antioxidant enzyme activities, osmoregulatory substance contents, and O₂^- production. Antioxidant enzyme activities tended to increase after recovering from 12 days of combined stress, whereas they were still not effective in mitigating oxidative damage. High levels of O₂^- and malondialdehyde (MDA) and a low relative growth rate during the recovery confirmed the irreversible damage caused by combined heat and drought stress. ROC (receiver operating characteristic) analysis indicated that GR and SS could accurately detect individual heat and drought stress that wheat plants were suffering or had suffered (AUC = 0.812-0.965), while POD and Pro had greater potential for diagnosing combined heat and drought stress (AUC = 0.871-0.958). Physiological indicators of stress tolerance were closely related to the photosynthetic rate during the stress, particularly Pro and GR. Collectively, the physiological processes of plants are reversible within a certain range of stress. POD, GR, Pro, and SS play vital roles in identifying and resisting heat, drought, and combined stress, and the recovery of these indicators contributed to improving photosynthesis and thereby increasing wheat growth. Our research contributes to the understanding of the underlying physiological mechanisms of plants in response to combined heat and drought stress and after stress relief.

Effects of high air temperature, drought, and both combinations on maize: A case study

High air temperature (HAT) and natural soil drought (NSD) have seriously affected crop yield and frequently take place in a HAT-NSD combination. Maize (Zea mays) is an important crop, thermophilic but not heat tolerant. In this study, HAT, NSD, and HAT-NSD effects on maize inbred line Huangzao4 -were characterized. Main findings were as follows: H₂O₂ and O^- accumulated much more in immature young leaves than in mature old leaves under the stresses. Lateral roots were highly distributed near the upper pot mix layers under HAT and near root tips under HAT-NSD. Saccharide accumulated mainly in stressed root caps (RC) and formed a highly accumulated saccharide band at the boundary between RC and meristematic zone. Lignin deposition was in stressed roots under NSD and HAT-NSD. Chloroplasts increased in number and formed a high-density ring around leaf vascular bundles (VB) under HAT and HAT-NSD, and sparsely scattered in the peripheral area of VBs under NSD. The RC cells containing starch granules were most under NAD-HAT but least under HAT. Under NSD and HAT-NSD followed by re-watering, anther number per tassel spikelet reduced to 3. These results provide multiple clues for further distinguishing molecular mechanisms for maize to tolerate these stresses.

Resilience of soybean cultivars to drought stress during flowering and early-seed setting stages

Drought stress during the reproductive stage and declining soybean yield potential raise concerns about yield loss and economic return. In this study, ten cultivars were characterized for 20 traits to identify reproductive stage (R1-R6) drought-tolerant soybean. Drought stress resulted in a marked reduction (17%) in pollen germination. The reduced stomatal conductance coupled with high canopy temperature resulted in reduced seed number (45%) and seed weight (35%). Drought stress followed by rehydration increased the hundred seed weight at the compensation of seed number. Further, soybean oil decreased, protein increased, and cultivars responded differently under drought compared to control. In general, cultivars with high tolerance scores for yield displayed lower tolerance scores for quality content and vice versa. Among ten cultivars, LS5009XS and G4620RX showed maximum stress tolerance scores for seed number and seed weight. The observed variability in leaf reflectance properties and their relationship with physiological or yield components suggested that leaf-level sensing information can be used for differentiating drought-sensitive soybean cultivars from tolerant ones. The study led to the identification of drought-resilient cultivars/promising traits which can be exploited in breeding to develop multi-stress tolerant cultivars.

Growth, Physiological, and Biochemical Responses of Ethiopian Red Pepper (Capsicum annum L.) Cultivars to Drought Stress

Red pepper (Capsicum annum L.) is an increasingly important economic crop in the world. Thus, this study aimed to investigate the growth, physiological, and biochemical responses of red pepper cultivars under drought stress conditions. A pot culture experiment was conducted in a completely randomized design with three replications, four treatments, and three cultivars. Totally, 36 pots and six seeds per pot were used to grow the seeds. After five weeks, the cultivars were exposed to different drought stress conditions (100% FC or control, 80% FC or low stress, 60% FC or moderate stress, and 40% FC or severe stress). All the collected data were subjected to an analysis of variance (ANOVA). Shoot length was reduced significantly (p < 0.05) in the Hagerew cultivar under severe drought stress. The photosynthesis rate was reduced by 21.11% (p < 0.05) in the Mitmita cultivar under severe drought stress. The highest percentage reduction of chlorophyll content (77.28%) was recorded in the Hagerew cultivar. Both Markofana and Mitmita responded to drought stress by increasing the accumulation of proline and phenolic compounds. The root-to-shoot ratio was increased significantly in both Markofana and Mitmita cultivars (27.91% and 50.92%), respectively, under drought-stress conditions. This study depicted that the cultivar Mitmita was the most drought-tolerant cultivar among the three cultivars.

Differential tolerance of the woody invasive Hakea sericea to drought and terminal heat stress

Drought and extreme temperatures are likely to be more common and intense in the Mediterranean region as a consequence of climate change. Both stresses usually arise together in the field, but our understanding of their joint influence on the performance of invasive alien species (IAS) is limited. Thus, the main objective of the present study is to fill this gap by analyzing the individual and combined effects of drought and terminal heat stress on the leaf physiology, biochemistry and growth of Hakea sericea Schrader, one of the most problematic IAS in the Mediterranean-type ecosystems. In this study, 1-year-old plants of H. sericea were exposed to four treatments under controlled conditions: control (CT), drought (DS), terminal heat stress (Ht), and combined Ht and DS (DHt). The DS treatment alone caused a marked reduction in shoot biomass, net photosynthetic (A) rate and stomatal conductance, while increasing the proline content, as compared with CT plants. In turn, the Ht treatment promoted the accumulation of malondialdehyde but hastened the decline in all gas exchange parameters, and also decreased leaf photosynthetic pigments, carotenoids, proline and relative water contents Exposure of H. sericea plants to the combined DHt exacerbated the impacts of Ht, which was accompanied by significant decreases in net photosynthetic and transpiration rates, and intrinsic water-use efficiency. Principal component analysis clearly separated the DHt from the other treatments and revealed similarities between DS and CT treatment. These findings suggest that xerothermic weather conditions might modify the fitness, competitive ability, resilience and spread of this IAS, thereby providing opportunities for its control.

Physiomorphic and molecular-based evaluation of wheat germplasm under drought and heat stress

Drought and heat stress are potential problems that can reduce wheat yield, particularly during the terminal growth stages in arid and semiarid regions of the world. The current study intended to examine the impact of individual and combined drought and heat stress on the biochemical contents (antioxidant enzymes, proline, soluble proteins, and soluble sugars), physiological parameters (chlorophyll content, cell membrane stability, photosynthesis, stomatal conductance, and transpiration), plant-water relations (relative water content, water potential, osmotic potential, and pressure potential), agronomic traits (flag leaf area, plant height, number of tillers per plant, spike length, grains per spike, and thousand-grain weight), and gene expression (TaHSF1a, TaWRKY-33, TaNAC2L, and TaGASR1) in four different thermostable and drought-tolerant wheat genotypes (i.e., Gold-16, HS-240, Suntop, and Hemai-13) collected from different countries. The tri-replicate experiment was conducted using two factorial arrangements in a randomized complete block design (RCBD). All measured traits, except total soluble sugars, proline, and cell membrane stability index, showed significant reduction under both combined and individual treatments. Furthermore, correlation analysis revealed a significant association between biochemical and physiological characteristics and crop agronomic productivity. Furthermore, principal component analysis (PCA) and heatmap analysis demonstrated significant levels of variation in traits according to the type of stress and nature of wheat genotype. The spectrographs and micrographs generated by scanning electron microscopy for the selected high- and low- tolerance samples revealed clear differences in mineral distribution and starch granulation. All studied genes showed comparatively high levels of relative expression under combined treatments of drought and heat stress in all wheat genotypes, but this expression was the highest in 'Gold-16' followed by 'HS-240', 'Suntop', and 'Hemai-13'. Overall, this study concluded that plants are proactive entities and they respond to stresses at all levels; however, the tolerant plants tend to retain the integrity of their biochemical, physiological, and molecular equilibrium.

Physio-biochemical characterization of wheat genotypes under temperature stress

Thermal stress is a major abiotic stress in wheat and is highly complex in mechanism. A large area in northwestern plain zones (NWPZ), which is the wheat bowl of India is affected by heat stress. Climate change also causes an abrupt increase in temperature at different growth stages of wheat. Thus, wiser selection of stress tolerant varieties is an important strategy to combat the climate change effect. The present study aims for physiological and biochemical screening of timely sown NWPZ wheat varieties (WB2, HD3086, DBW88, DPW621-50, DBW17, HD2967 and PBW550) of India for their thermal stress tolerance along with heat tolerant (RAJ3765) and susceptible checks (RAJ4014) at seedling stage. The experiment was conducted in completely randomized design under controlled laboratory condition and heat stress was induced at 37 °C at seedling stage. Later different physio-biochemical traits were studied in both control and stress seedlings. All traits exhibited significant variations among genotypes under heat stress condition. Root and shoot weight, relative water content, chlorophyll content index and chlorophyll fluorescence reduced significantly, whereas membrane leakage, osmotic potential, catalase, ascorbate peroxidase, guaiacol peroxidase, malondialdehyde content and proline content were increased in stress plants. A tolerance matrix was prepared based on stress response of the genotypes for each trait and a final tolerance score was given to each genotype. Based on this tolerance matrix, DBW88 and PBW550 were identified as tolerant, DPW621-50, DBW17 and HD2967 as moderately susceptible and HD3086 and WB2 as susceptible to heat stress. Earlier studies parade that seedling level stress tolerance has high correlation with adult level stress tolerance under field condition in wheat. Hence, this study helps in wiser selection of varieties for sowing in NWPZ based on weather forecast of the location for creating varietal mosaic in context of climate change.

Drought-induced recruitment of specific root-associated bacteria enhances adaptation of alfalfa to drought stress

Drought is a major abiotic stress that threatens crop production. Soil microbiomes are thought to play a role in enhancing plant adaptation to various stresses. However, it remains unclear whether soil microbiomes play a key role when plants are challenged by drought and whether different varieties are enriched with specific bacteria at the rhizosphere. In this study, we measured changes in growth phenotypes, physiological and biochemical characteristics of drought-tolerant alfalfa (AH) and drought-sensitive (QS) under sterilized and unsterilized soil conditions with adequate watering and with drought stress, and analyzed the rhizosphere bacterial community composition and changes using 16S rRNA high-throughput sequencing. We observed that the unsterilized treatment significantly improved the growth, and physiological and biochemical characteristics of alfalfa seedlings under drought stress compared to the sterilized treatment. Under drought stress, the fresh and dry weight of seedlings increased by 35.24, 29.04, and 11.64%, 2.74% for unsterilized AH and QS, respectively, compared to sterilized treatments. The improvement was greater for AH than for QS. AH and QS recruited different rhizosphere bacteria when challenged by drought. Interestingly, under well-watered conditions, the AH rhizosphere was already rich in drought-tolerant bacterial communities, mainly Proteobacteria and Bacteroidetes, whereas these bacteria started to increase only when QS was subjected to drought. When drought stress was applied, AH was enriched with more drought-tolerant bacteria, mainly Acidobacteria, while the enrichment was weaker in QS rhizosphere. Therefore, the increase in drought tolerance of the drought-tolerant variety AH was greater than that of the drought-sensitive variety QS. Overall, this study confirmed the key role of drought-induced rhizosphere bacteria in improving the adaptation of alfalfa to drought stress, and clarified that this process is significantly related to the variety (genotype). The results of this study provide a basis for improving drought tolerance in alfalfa by regulating the rhizosphere microbiome.

Enhancement of Heat and Drought Stress Tolerance in Rice by Genetic Manipulation: A Systematic Review

As a result of global warming, plants are subjected to ever-increasing abiotic stresses including heat and drought. Drought stress frequently co-occurs with heat stress as a result of water evaporation. These stressors have adverse effects on crop production, which in turn affects human food security. Rice is a major food resource grown widely in crop-producing regions throughout the world. However, increasingly common heat and drought stresses in growth regions can have negative impacts on seedling morphogenesis, reproductive organ establishment, overall yield, and quality. This review centers on responses to heat and drought stress in rice. Current knowledge of molecular regulation mechanisms is summarized. We focus on approaches to cope with heat and drought stress, both at the genetic level and from an agricultural practice perspective. This review establishes a basis for improving rice stress tolerance, grain quality, and yield for human benefit.

Melatonin and nitric oxide: Dual players inhibiting hazardous metal toxicity in soybean plants via molecular and antioxidant signaling cascades

Melatonin (MT), a ubiquitous signaling molecule, is known to improve plant growth. Its regulatory function alongside nitric oxide (NO) is known to induce heavy metal (Cd and Pb) stress tolerance, although the underlying mechanisms remain unknown. Here, we observed that the combined application of MT and NO remarkably enhanced plant biomass by reducing oxidative stress. Both MT and NO minimized metal toxicity by significantly lowering the levels of endogenous abscisic acid and jasmonic acid via downregulating NCED3 and upregulating catabolic genes (CYP707A1 and CYP707A2). MT/NO-induced mitigation of Cd and Pb stress was associated with increased endo-melatonin and variable endo-S-nitrosothiol levels caused by enhanced expression of gmNR and gmGSNOR mRNAs. Remarkably, the combined application of MT/NO reduced soil Cd and Pb mobilization by increasing the uptake of Ca²⁺ and K⁺ and increasing the exudation of organic acids into the rhizosphere. These results correlated with the upregulation of MTF-1 and WARKY27 during metal translocation. MT/NO regulates the MAPK and CDPK cascades to promote plant cell survival and Ca²⁺ signaling, thereby imparting resistance to heavy metal toxicity. In conclusion, MT/NO modulates the stress-resistance machinery to mitigate Cd and Pb toxicity by regulating the activation of antioxidant and molecular transcription factors.