Tolerance To High Temperature Stress Research Articles

Melatonin imparts tolerance to combined drought and high-temperature stresses in tomato through osmotic adjustment and ABA accumulation.

In recent years, environmental stresses viz., drought and high-temperature negatively impacts the tomato growth, yield and quality. The effects of combined drought and high-temperature (HT) stresses during the flowering stage were investigated. The main objective was to assess the effects of foliar spray of melatonin under both individual and combined drought and HT stresses at the flowering stage. Drought stress was imposed by withholding irrigation, whereas HT stress was imposed by exposing the plants to an ambient temperature (AT)+5°C temperature. The drought+HT stress was imposed by exposing the plants to drought first, followed by exposure to AT+5°C temperature. The duration of individual and combined drought or HT stress was 10 days. The results showed that drought+HT stress had a significant negative effect compared with individual drought or HT stress alone. However, spraying 100 µM melatonin on the plants challenged with individual or combined drought and HT stress showed a significant increase in total chlorophyll content [drought: 16%, HT: 14%, and drought+HT: 11%], Fv/Fm [drought: 16%, HT: 15%, and drought+HT: 13%], relative water content [drought: 10%, HT: 2%, and drought+HT: 8%], and proline [drought: 26%, HT: 17%, and drought+HT: 14%] compared with their respective stress control. Additionally, melatonin positively influenced the stomatal and trichome characteristics compared with stress control plants. Also, the osmotic adjustment was found to be significantly increased in the melatonin-sprayed plants, which, in turn, resulted in an increased number of fruits, fruit set percentage, and fruit yield. Moreover, melatonin spray also enhanced the quality of fruits through increased lycopene content, carotenoid content, titratable acidity, and ascorbic acid content, compared with the stress control. Overall, this study highlights the usefulness of melatonin in effectively mitigating the negative effects of drought, HT, and drought+HT stress, thus leading to an increased drought and HT stress tolerance in tomato.

The Promising B-Type Response Regulator hst1 Gene Provides Multiple High Temperature and Drought Stress Tolerance in Rice.

High temperatures, drought, and salt stresses severely inhibit plant growth and production due to the effects of climate change. The Arabidopsis ARR1, ARR10, and ARR12 genes were identified as negative salt and drought stress regulators. However, in rice, the tolerance capacity of the hst1 gene, which is orthologous to the ARR1, ARR10, and ARR12 genes, to drought and multiple high temperature and drought stresses remains unknown. At the seedling and reproductive stages, we investigated the drought (DS) high temperature (HT) and multiple high temperature and drought stress (HT+DS) tolerance capacity of the YNU31-2-4 (YNU) genotype, which carries the hst1 gene, and its nearest genomic relative Sister Line (SL), which has a 99% identical genome without the hst1 gene. At the seedling stage, YNU demonstrated greater growth, photosynthesis, antioxidant enzyme activity, and decreased ROS accumulation under multiple HT+DS conditions. The YNU genotype also demonstrated improved yield potential and grain quality due to higher antioxidant enzyme activity and lower ROS generation throughout the reproductive stage under multiple HT+DS settings. Furthermore, for the first time, we discovered that the B-type response regulator hst1 gene controls ROS generation and antioxidant enzyme activities by regulating upstream and downstream genes to overcome yield reduction under multiple high temperatures and drought stress. This insight will help us to better understand the mechanisms of high temperature and drought stress tolerance in rice, as well as the evolution of tolerant crops that can survive increased salinity to provide food security during climate change.

Determination of the tolerance of physiological, morphological, and yield parameters of landrace durum wheat (Triticum durum Desf.) to high-temperature stress

In the South-eastern Anatolia Region, where the climate is favorable to cultivation for durum wheat, there have been notable reductions in both yield and quality due to biotic and abiotic stress factors in the region. Primary one of these stresses is high-temperature stress. High-temperature stress, specifically during the late flowering stage and early grain filling stage, results in substantial reductions in both crop yield and quality. In this study, several practical, easily and rapidly quantifiable physiological, morphological, and yield-related parameters that may be used in durum wheat improvement programs in the region for high-temperature stress tolerance were investigated. Ninety landrace durum genotypes and 4 standard cultivars were used. The study was carried out at GAP (South-eastern Anatolia Project) International Agricultural Research and Training Centre in an air conditioning room according to an augmented design under optimum conditions and stressful conditions where high-temperature stress was created. Compared to optimum conditions, there were reductions in flag leaf greening time by 20%, days to maturity by 7%, spike length by 10%, peduncle length by 18%, grain filling time by 23%, number of spikelets on the spike by 12%, number of grains on the spike by 39%, and thousand-kernel weight by 33%, while grain filling rate increased under high-temperature stress conditions. The genotypes 82, 83, 87, 88, 99, and 103 and the standard varieties Artuklu and Sümerli prevailed in both optimum and stress conditions. The fact that leaf erectness, flag leaf greening time, grain filling time, and leaf chlorophyll content among morphological and physiological characteristics had a significant correlation with yield components under both conditions indicates that these characteristics can be used as selection criteria for tolerance to stressful conditions in the region.

Genome-wide identification of the heat shock transcription factor gene family in two kiwifruit species.

High temperatures have a significant impact on plant growth and metabolism. In recent years, the fruit industry has faced a serious threat due to high-temperature stress on fruit plants caused by global warming. In the present study, we explored the molecular regulatory mechanisms that contribute to high-temperature tolerance in kiwifruit. A total of 36 Hsf genes were identified in the A. chinensis (Ac) genome, while 41 Hsf genes were found in the A. eriantha (Ae) genome. Phylogenetic analysis revealed the clustering of kiwifruit Hsfs into three distinct groups (groups A, B, and C). Synteny analysis indicated that the expansion of the Hsf gene family in the Ac and Ae genomes was primarily driven by whole genome duplication (WGD). Analysis of the gene expression profiles revealed a close relationship between the expression levels of Hsf genes and various plant tissues and stress treatments throughout fruit ripening. Subcellular localization analysis demonstrated that GFP-AcHsfA2a/AcHsfA7b and AcHsfA2a/AcHsfA7b -GFP were localized in the nucleus, while GFP-AcHsfA2a was also observed in the cytoplasm of Arabidopsis protoplasts. The results of real-time quantitative polymerase chain reaction (RT-qPCR) and dual-luciferase reporter assay revealed that the majority of Hsf genes, especially AcHsfA2a, were expressed under high-temperature conditions. In conclusion, our findings establish a theoretical foundation for analyzing the potential role of Hsfs in high-temperature stress tolerance in kiwifruit. This study also offers valuable information to aid plant breeders in the development of heat-stress-resistant plant materials.

Transcriptome analysis and identification of leaf, tuberous root and fibrous root tissue-specific high temperature stress-responsive genes in sweet potato

Sweet Potato is an important food crop, and its production is affected by environmental stresses, including high temperature. The gene expression patterns and molecular responses in different tissues of sweet potato under high temperature stress were studied using microarray data sets. Analysis revealed that modulation in the expression of key genes and pathways associated with various proteins including enzymes under high temperature stress in leaf, fibrous root and storage root tissues. Tissue-specific responses, with both common and unique cellular responses were observed among the tissues. Pathway analysis revealed the differential regulation of genes involved in DNA replication, metabolism, transport, signaling, and stress response during high temperature stress. Six genes viz., DnaJ-domain protein (IpDnaJ), nuclear protein (IpELF5), heat shock protein 90.1 (IpHsp90.1), ABC   transporter   (IpABC)   hydrolase (IpNUDX1)   and alternative oxidase 1a (IpAO1a), were up-regulated in the leaf, fibrous root and tuberous root tissues. These six genes might play an important role in imparting high temperature stress tolerance in the leaf, fibrous root and tuberous root tissues of sweet potato. The information generated provides valuable insights on leaf, tuberous root and fibrous root tissue-specific high temperature stress-responsive genes in sweet potato. These datasets will be helpful in selecting candidate genes and pathways for further functional and genomic analyses, facilitating the genetic improvement of sweet potato with enhanced stress tolerance.

Effect of nitrogen application on enhancing high-temperature stress tolerance of tomato plants during the flowering and fruiting stage.

This study was conducted to investigate the effects of nitrogen application on growth, photosynthetic performance, nitrogen metabolism activities, and fruit quality of tomato plants under high-temperature (HT) stress. Three levels of daily minimum/daily maximum temperature were adopted during the flowering and fruiting stage, namely control (CK; 18°C/28°C), sub-high temperature (SHT; 25°C/35°C), and high-temperature (HT; 30°C/40°C) stress. The levels of nitrogen (urea, 46% N) were set as 0 (N1), 125 (N2), 187.5 (N3), 250 (N4), and 312.5 (N5) kg hm2, respectively, and the duration lasted for 5 days (short-term). HT stress inhibited the growth, yield, and fruit quality of tomato plants. Interestingly, short-term SHT stress improved growth and yield via higher photosynthetic efficiency and nitrogen metabolism whereas fruit quality was reduced. Appropriate nitrogen application can enhance the high-temperature stress tolerance of tomato plants. The maximum net photosynthetic rate (P Nmax), stomatal conductance (g s), stomatal limit value (LS), water-use efficiency (WUE), nitrate reductase (NR), glutamine synthetase (GS), soluble protein, and free amino acids were the highest in N3, N3, and N2, respectively, for CK, SHT, and HT stress, whereas carbon dioxide concentration (C i), was the lowest. In addition, maximum SPAD value, plant morphology, yield, Vitamin C, soluble sugar, lycopene, and soluble solids occurred at N3-N4, N3-N4, and N2-N3, respectively, for CK, SHT, and HT stress. Based on the principal component analysis and comprehensive evaluation, we found that the optimum nitrogen application for tomato growth, yield, and fruit quality was 230.23kg hm2 (N3-N4), 230.02kg hm2 (N3-N4), and 115.32kg hm2 (N2), respectively, at CK, SHT, and HT stress. Results revealed that the high yield and good fruit quality of tomato plants at high temperatures can be maintained by higher photosynthesis, nitrogen efficiency, and nutrients with moderate nitrogen.

Genetic variability predicting breeding potential of upland cotton (Gossypium hirsutum L.) for high temperature tolerance

BackgroundHigh temperature stress at peak flowering stage of cotton is a major hindrance for crop potential. This study aimed to increase genetic divergence regarding heat tolerance in newly developed cultivars and hybrids. Fifty cotton genotypes and 40 F1 (hybrids) were tested under field conditions following the treatments, viz., high temperature stress and control at peak flowering stage in August and October under April and June sowing, respectively.ResultsThe mean squares revealed significant differences among genotypes, treatments, genotype × treatment for relative cell injury, chlorophyll contents, canopy temperature, boll retention and seed cotton yield per plant. The genetic diversity among 50 genotypes was analyzed through cluster analysis and heat susceptibility index (HSI). The heat tolerant genotypes including FH-Noor, NIAB-545, FH-466, FH-Lalazar, FH-458, NIAB-878, IR-NIBGE-8, Weal-AG-Shahkar, and heat sensitive, i.e., CIM-602, Silky-3, FH-326, SLH-12 and FH-442 were hybridized in line × tester fashion to produce F1 populations. The breeding materials’ populations (40 F1) revealed higher specific combining ability variances along with dominance variances, decided the non-additive type gene action for all the traits. The best general combining ability effects for most of the traits were displayed by the lines, i.e., FH-Lalazar, NIAB-878 along with testers FH-326 and Silky-3. Specific combining ability effects and better-parent heterosis were showed by the crosses, viz., FH-Lalazar × Silky-3, FH-Lalazar × FH-326, NIAB-878 × Silky-3, and NIAB-878 × FH-326 for seed cotton yield and yield contributing traits under high temperature stress.ConclusionHeterosis breeding should be carried out in the presence of non-additive type gene action for all the studied traits. The best combiner parents with better-parent heterosis may be used in crossing program to develop high yielding cultivars, and hybrids for high temperature stress tolerance.

Oat AsDA1-2D enhances heat stress tolerance and negatively regulates seed-storage globulin

The importance of oats has increased because of their high nutritional value and health benefits in the human diet. High-temperature stress during the reproductive growth period has a detrimental effect on grain morphology by changing the structure and concentration of several seed-storage proteins. DA1, a conserved ubiquitin-proteasome pathway component, plays an important role in regulating grain size by controlling cell proliferation in maternal integuments during the grain-filling stage. However, there have been no reports or studies on oat DA1 genes. In this study, we identified three DA1-like genes (AsDA1-2D, AsDA1-5A, and AsDA1-1D) using genome-wide analysis. Among these, AsDA1-2D was found to be responsible for high-temperature stress tolerance via a yeast thermotolerance assay. The physical interaction of AsDA1-2D with oat-storage-globulin (AsGL-4D) and a protease inhibitor (AsPI-4D) was observed using yeast two-hybrid screening. A subcellular localization assay revealed that AsDA1-2D and its interacting proteins are localized in the cytosol and plasma membrane. An in vitro pull-down assay showed that AsDA1-2D forms a complex with both AsPI-4D and AsGL-4D. An in vitro cell-free degradation assay showed that AsGL-4D was degraded by AsDA1-2D under high-temperature conditions and that AsPI-4D inhibited the function of AsDA1-2D. These results suggest that AsDA1-2D acts as a cysteine protease and negatively regulates oat-grain-storage-globulin under heat stress.

Bioinformatics Analysis, Expression Profiling, and Functional Characterization of Heat Shock Proteins in Wolfi-poria cocos

Heat shock proteins (HSPs) play critical roles in regulating different mechanisms under high-temperature conditions. HSPs have been identified and well-studied in different plants. However, there is a lack of information about their genomic organization and roles in medicinal plants and fungi, especially in Wolfi-poria cocos (W. cocos). We identified sixteen heat shock proteins (HSPs) in W. cocos and analyzed in terms of phylogenetic analysis, gene structure, motif distribution patterns, physiochemical properties, and expression comparison in different strains. Based on phylogenetic analysis, HSPs were divided into five subgroups (WcHSP100, WcHSP90, WcHSP70, WcHSP60, and WcsHSP). Subgroups WcHSP100s, WcHSP90s, WcHSP70s, WcHSP60, and WcsHSPs were further divided into 3, 2, 3, 1, and 6 subfamilies, respectively. Moreover, the expression profiling of all HSP genes in five strains of W. cocos under different temperature extremes revealed that expression of most HSPs were induced by high temperature. However, every subfamily showed different expression suggesting distinctive role in heat stress tolerance. WcHSP70-4, WcHSP90-1, and WcHSP100-1 showed the highest response to high temperature stress. Heterologous expression of WcHSP70-4, WcHSP90-1, and WcHSP100-1 genes in Escherichia coli enhanced survival rate of E. coli during heat stress. These findings suggest the role of W. cocos heat shock genes in the high temperature stress tolerance.

Nitric Oxide and Proline Modulate Redox Homeostasis and Photosynthetic Metabolism in Wheat Plants under High Temperature Stress Acclimation

The effects of exogenously-sourced NO (nitric oxide, as 100 µM SNP) and proline (50 mM) in the protection of the photosynthetic performance of wheat (Triticum aestivum L.) plants against heat stress were investigated. The study focused on the mechanisms of proline accumulation, activity, gene expression of antioxidant enzymes, and NO generation. Plants were exposed to a temperature of 40 °C for 6 h per day over 15 days, then allowed to recover at 28 °C. Heat-stressed plants showed increased oxidative stress, with higher levels of H2O2 and TBARS (thiobarbituric acid reactive substances) and increased proline accumulation, ACS activity, ethylene evolution, and NO generation, which in turn leads to increased accumulation of antioxidant enzymes and reduced photosynthetic attributes. In the tested wheat cultivar, the exogenous application of SNP and proline under heat stress improved the photosynthesis and reduced oxidative stress by enhancing the enzymatic antioxidant defense system. Potentially, the promoter AOX (alternative oxidase) played a role in maintaining redox homeostasis by lowering H2O2 and TBARS levels. The genes for GR antioxidant and photosystem II core protein encoding psbA and psbB were highly up-regulated in nitric oxide and proline treated heat-stressed plants, indicating that ethylene positively impacted photosynthesis under high temperature stress. Moreover, nitric oxide supplementation under high temperature stress optimized ethylene levels to regulate the assimilation and metabolism of proline and the antioxidant system, lowering the adverse effects. The study showed that nitric oxide and proline increased high temperature stress tolerance in wheat by increasing the osmolytes accumulation and the antioxidant system, resulting in enhanced photosynthesis.

Abscisic-Acid-Modulated Stomatal Conductance Governs High-Temperature Stress Tolerance in Rice Accessions

Rising air temperature is a major constraint for crop productivity under the current climate change scenario. Rice crops are known to be sensitive to high-temperature (HT) stress at anthesis and post-anthesis stages. Photosynthesis is an important metabolic process and is affected by HT stress. A pot study was planned to screen a set of seventy-three Indian rice accessions based upon changes in the rate of photosynthesis (Pn) and related gas exchange traits under HT, and to characterize the contrasting rice accessions for component traits of HT stress tolerance. All accessions were raised under ambient temperature (AT) until the booting stage and exposed to HT using controlled chambers at anthesis and post-anthesis. HT exposure led to a large reduction (up to 50%) in Pn, but stomatal conductance (gs) and the rate of transpiration (E) increased significantly across the rice accessions. Based on the photosynthetic response under HT, two contrasting rice accessions (IRGC 135883, tolerant, and IRGC 127222, sensitive) were selected and characterized for HT tolerance, along with an NL-44 check. Among them, Pn decreased marginally but gs and E showed significant increases under HT in the tolerant accession, while sensitive accession showed an up to 50% reduction in Pn and marginal increase in gs and E. No significant changes were recorded for chlorophyll fluorescence (Fv/Fm) in both the genotypes, but tissue temperature depression (TTD) was higher in IRGC 135883 accession under HT. Endogenous abscisic acid (ABA) content increased under HT in the flag leaf of both the accessions, and the highest increase was observed in the sensitive accession. Similarly, spikelet fertility and grain yield showed large reductions in sensitive rice accession under HT. A large increase in ABA concentration in the leaves of the sensitive rice accession might be affecting its gs and cooling capacity under an HT environment. Finally, the study concludes that tolerant rice accessions can be recommended as donors and exploited in future rice breeding programs for developing climate-resilient rice genotypes.

Elucidating the role of key physio-biochemical traits and molecular network conferring heat stress tolerance in cucumber.

Cucumber is an important vegetable crop grown worldwide and highly sensitive to prevailing temperature condition. The physiological, biochemical and molecular basis of high temperature stress tolerance is poorly understood in this model vegetable crop. In the present study, a set of genotypes with contrasting response under two different temperature stress (35/30°C and 40/35°C) were evaluated for important physiological and biochemical traits. Besides, expression of the important heat shock proteins (HSPs), aquaporins (AQPs), photosynthesis related genes was conducted in two selected contrasting genotypes at different stress conditions. It was established that tolerant genotypes were able to maintain high chlorophyll retention, stable membrane stability index, higher retention of water content, stability in net photosynthesis, high stomatal conductance and transpiration in combination with less canopy temperatures under high temperature stress conditions compared to susceptible genotypes and were considered as the key physiological traits associated with heat tolerance in cucumber. Accumulation of biochemicals like proline, protein and antioxidants like SOD, catalase and peroxidase was the underlying biochemical mechanisms for high temperature tolerance. Upregulation of photosynthesis related genes, signal transduction genes and heat responsive genes (HSPs) in tolerant genotypes indicate the molecular network associated with heat tolerance in cucumber. Among the HSPs, higher accumulation of HSP70 and HSP90 were recorded in the tolerant genotype, WBC-13 under heat stress condition indicating their critical role. Besides, Rubisco S, Rubisco L and CsTIP1b were upregulated in the tolerant genotypes under heat stress condition. Therefore, the HSPs in combination with photosynthetic and aquaporin genes were the underlying important molecular network associated with heat stress tolerance in cucumber. The findings of the present study also indicated negative feedback of G-protein alpha unit and oxygen evolving complex in relation to heat stress tolerance in cucumber. These results indicate that the thermotolerant cucumber genotypes enhanced physio-biochemical and molecular adaptation under high-temperature stress condition. This study provides foundation to design climate smart genotypes in cucumber through integration of favorable physio-biochemical traits and understanding the detailed molecular network associated with heat stress tolerance in cucumber.

Screening of Rice (Oryza sativa L.) Genotypes for High Temperature Stress under Temperature Induction Response

Plants are exposed to multifarious external environmental conditions that affect plant growth, development and productivity. Heat stress is one of the abiotic stress that occurs due to high ambient temperature. Also, it is a serious threat to crop production worldwide. Rice is a major food crop cultivated all over the globe. In the present study, temperature induction response (TIR) was carried out for screening the rice genotypes. Initially, three rice genotypes namely Swarnamukhi, Kasalth and N22 (tolerant check) were used to standardize the optimum induction temperature and lethal temperature. Optimum induction temperature was 46-54o C and the lethal temperature 56oC were standardized for rice. At this temperature, a total of 58 diverse genotypes were screened for high-temperature stress tolerance. Among the genotypes tried, sivapu chithiraikar (94.33%), kavya (93.67%), kasalath(94.23), samleshwari (93.56), poongar (87.34), vedhividangan (75.10), Naveen (89.56), surakuruvai (84.90), swarnamukhi (92.10), vellaikatrai (80.50) and kavuni (92.60) expressed higher seedling survival percentage of tolerance (93.5%) to high temperature and remaining were identified as temperature susceptible as compared to control (100% survival). There was a considerable variation among the genotypes screened for acquired thermotolerance. Results suggested that TIR is a simple and powerful technique and can be used to screen a large population at the seedling stage to identify thermotolerant lines.

Lipidomics-Assisted GWAS (lGWAS) Approach for Improving High-Temperature Stress Tolerance of Crops.

High-temperature stress (HT) over crop productivity is an important environmental factor demanding more attention as recent global warming trends are alarming and pose a potential threat to crop production. According to the Sixth IPCC report, future years will have longer warm seasons and frequent heat waves. Thus, the need arises to develop HT-tolerant genotypes that can be used to breed high-yielding crops. Several physiological, biochemical, and molecular alterations are orchestrated in providing HT tolerance to a genotype. One mechanism to counter HT is overcoming high-temperature-induced membrane superfluidity and structural disorganizations. Several HT lipidomic studies on different genotypes have indicated the potential involvement of membrane lipid remodelling in providing HT tolerance. Advances in high-throughput analytical techniques such as tandem mass spectrometry have paved the way for large-scale identification and quantification of the enormously diverse lipid molecules in a single run. Physiological trait-based breeding has been employed so far to identify and select HT tolerant genotypes but has several disadvantages, such as the genotype-phenotype gap affecting the efficiency of identifying the underlying genetic association. Tolerant genotypes maintain a high photosynthetic rate, stable membranes, and membrane-associated mechanisms. In this context, studying the HT-induced membrane lipid remodelling, resultant of several up-/down-regulations of genes and post-translational modifications, will aid in identifying potential lipid biomarkers for HT tolerance/susceptibility. The identified lipid biomarkers (LIPIDOTYPE) can thus be considered an intermediate phenotype, bridging the gap between genotype–phenotype (genotype–LIPIDOTYPE–phenotype). Recent works integrating metabolomics with quantitative genetic studies such as GWAS (mGWAS) have provided close associations between genotype, metabolites, and stress-tolerant phenotypes. This review has been sculpted to provide a potential workflow that combines MS-based lipidomics and the robust GWAS (lipidomics assisted GWAS-lGWAS) to identify membrane lipid remodelling related genes and associations which can be used to develop HS tolerant genotypes with enhanced membrane thermostability (MTS) and heat stable photosynthesis (HP).

Hydrogen Sulfide, Ethylene, and Nitric Oxide Regulate Redox Homeostasis and Protect Photosynthetic Metabolism under High Temperature Stress in Rice Plants.

Rising temperatures worldwide due to global climate change are a major scientific issue at present. The present study reports the effects of gaseous signaling molecules, ethylene (200 µL L−1; 2-chloroethylphosphonic acid; ethephon, Eth), nitric oxide (NO; 100 µM sodium nitroprusside; SNP), and hydrogen sulfide (H2S; 200 µM sodium hydrosulfide, NaHS) in high temperature stress (HS) tolerance, and whether or not H2S contributes to ethylene or NO-induced thermo-tolerance and photosynthetic protection in rice (Oryza sativa L.) cultivars, i.e., Taipei-309, and Rasi. Plants exposed to an HS of 40 °C for six h per day for 15 days caused a reduction in rice biomass, associated with decreased photosynthesis and leaf water status. High temperature stress increased oxidative stress by increasing the content of hydrogen peroxide (H2O2) and thiobarbituric acid reactive substance (TBARS) in rice leaves. These signaling molecules increased biomass, leaf water status, osmolytes, antioxidants, and photosynthesis of plants under non-stress and high temperature stress. However, the effect was more conspicuous with ethylene than NO and H2S. The application of H2S scavenger hypotaurine (HT) reversed the effect of ethylene or NO on photosynthesis under HS. This supports the findings that the ameliorating effects of Eth or SNP involved H2S. Thus, the presence of H2S with ethylene or NO can enhance thermo-tolerance while also protecting plant photosynthesis.

Intriguing Role of Proline in Redox Potential Conferring High Temperature Stress Tolerance.

Proline is a proteinogenic amino acid synthesized from glutamate and ornithine. Pyrroline-5-carboxylate synthetase and pyrroline-5-carboxylate reductase are the two key enzymes involved in proline synthesis from glutamate. On the other hand, ornithine-δ-aminotransferase converts ornithine to pyrroline 5-carboxylate (P5C), an intermediate in the synthesis of proline as well as glutamate. Both proline dehydrogenase and P5C dehydrogenase convert proline back to glutamate. Proline accumulation is widespread in response to environmental challenges such as high temperatures, and it is known to defend plants against unpropitious situations promoting plant growth and flowering. While proline accumulation is positively correlated with heat stress tolerance in some crops, it has detrimental consequences in others. Although it has been established that proline is a key osmolyte, its exact physiological function during heat stress and plant ontogeny remains unknown. Emerging evidence pointed out its role as an overriding molecule in alleviating high temperature stress (HTS) by quenching singlet oxygen and superoxide radicals. Proline cycle acts as a shuttle and the redox couple (NAD+/NADH, NADP+/NADPH) appears to be highly crucial for energy transfer among different cellular compartments during plant development, exposure to HTS conditions and also during the recovery of stress. In this review, the progress made in recent years regarding its involvement in heat stress tolerance is highlighted.

Canopy cooling traits associated with yield performance in heat-stressed oat

In the upper U.S. Midwest, oat is a promising crop for diversifying local cropping systems and providing local consumers with a healthy food option. However, as a result of climate change, the crop is facing increasingly severe episodes of high temperature (HT) stress during reproductive development, which limit its yield potential. The goal of this 3-year field study was to identify locally-adapted HT stress-tolerant oat breeding lines, propose a parsimonious mechanistic basis for HT stress tolerance and leverage it to develop a screening method with the potential to support a breeding program. Because water supply is rarely limiting in the region, we tested the hypothesis that canopy latent cooling would be a desirable trait. To this end, we deployed “heat tents” on a core panel of 30 oat lines between booting and heading, where we measured i) grain yield and quality traits (protein, oil and beta-glucan), ii) pollen viability, percentage of filled florets, and grain number, iii) gas exchange and canopy cooling parameters (e.g., photosynthesis, transpiration rate, stomatal conductance, canopy temperature depression). Additionally, we developed a thermal imaging approach to remotely quantify canopy temperature on contrasted lines. Significant genotypic variability was detected in yield and quality trait responses to the HT stress and a physiological path model identified canopy cooling as a main process explaining superior yield performance of HT stress tolerant lines. Interestingly, pollen viability was not found to be the main driver of yield declines, suggesting a role played by other reproductive processes, including those underlying female tissue/organs sensitivity to HT stress. Finally, canopy cooling parameters correlated with geographic locations of breeding programs from which the tested germplasm originated, indicating that they are under selection. Overall, this study opens the way for a breeding program targeting the development of more climate-resilient oats adapted to northern climates.

Herbaceous peony AP2/ERF transcription factor binds the promoter of the tryptophan decarboxylase gene to enhance high-temperature stress tolerance.

Global warming has multifarious adverse effects on plant growth and productivity. Nonetheless, the effects of endogenous phytomelatonin on the high-temperature resistance of plants and the underlying genetic mechanisms remain unclear. Here, herbaceous peony (Paeonia lactiflora Pall.) tryptophan decarboxylase (TDC) gene involved in phytomelatonin biosynthesis was shown to respond to high-temperature stress at the transcriptional level, and its transcript level was positively correlated with phytomelatonin production. Moreover, overexpression of PlTDC enhanced phytomelatonin production and high-temperature stress tolerance in transgenic tobacco, while silencing PlTDC expression decreased these parameters in P. lactiflora. In addition, a 2402 bp promoter fragment of PlTDC was isolated, and DNA pull-down assay revealed that one APETALA2/ethylene-responsive element-binding factor (AP2/ERF) transcription factor, PlTOE3, could specifically activate the PlTDC promoter, which was further verified by yeast one-hybrid assay and luciferase reporter assay. PlTOE3 was a nucleus-localized protein, and its transcript level responded to high-temperature stress. Additionally, transgenic tobacco overexpressing PlTOE3 showed enhanced phytomelatonin production and high-temperature stress tolerance, while silencing PlTDC expression obtained the opposite results. These results illustrated that PlTOE3 bound the PlTDC promoter to enhance high-temperature stress tolerance by increasing phytomelatonin production in P. lactiflora.

CsbZIP2-miR9748-CsNPF4.4 Module Mediates High Temperature Tolerance of Cucumber Through Jasmonic Acid Pathway.

High temperature stress seriously affects the growth of cucumber seedlings, and even leads to a decline in yield and quality. miRNAs have been shown to be involved in regulating the response to stress in plants, but little is known about its effects on cucumber high temperature stress tolerance. Here, we found that high temperature stress induced the expression of miR9748 in cucumber. Overexpression of cucumber miR9748 in Arabidopsis improved high temperature tolerance. Transcriptome analysis revealed that miR9748 might mediate high temperature tolerance through plant hormone signal pathway. 5′ RNA ligase-mediated rapid amplification of cDNA ends (5′ RLM-RACE) and transient transformation technology demonstrated that CsNPF4.4 was the target gene of miR9748. CsNPF4.4 overexpression plants decreased high temperature tolerance accompanied by reducing the content of jasmonic acid (JA), but alleviated by foliar application of methyl jasmonate, indicating that CsNPF4.4 negatively regulated high temperature stress tolerance through inhibition JA signal pathway. Furthermore, high temperature stress also increased the expression level of CsbZIP2. Yeast one-hybrid and dual-luciferase assays showed that CsbZIP2 directly bound to the promoter of MIR9748 to induce its expression. Taken together, our results indicated that CsbZIP2 directly regulated miR9748 expression to cleave CsNPF4.4 to mediate high temperature tolerance through JA pathway.

CsRCI2D enhances high-temperature stress tolerance in Camelina sativa L. through endo-membrane trafficking from the plasma membrane

Rare Cold Inducible 2s (RCI2s) are hydrophobic proteins in cell membranes that participate in abiotic stress tolerance mechanisms. Additionally, they are used as traceable membrane trafficking markers in endocytosis studies. Plants regulate cell homeostasis through endocytosis by limiting the activity of plasma membrane transporter proteins to adapt to stressful conditions. In this study, we found high temperature (HT) stress-induced membrane trafficking of RCI2D in Camelina sativa L. The gene expression and protein synthesis were increased by HT stress at 37 °C. Moreover, rapid membrane trafficking of CsRCI2D was traced by multiple-phase membrane fractionation using sucrose density gradients and compared with CsRCI2E/F/G from the same protein family subgroup. The distribution of CsRCI2s was shown to be similar to that of the clathrin heavy chain, which is known as a major endocytosis protein. Subcellular localization of CsRCI2D was observed in the plasma membrane and endo-membranes and overlapped with membrane lipids. CsRCI2D co-localized with lipids, and its overexpression increased the intracellular lipid content compared to that of wild-type camelina. Moreover, transgenic camelina lines showed enhanced HT stress tolerance during germination and hypocotyl elongation when compared to the wild type. These results suggest that HT-induced CsRCI2D membrane trafficking enhances HT stress tolerance in camelina.