Enhanced Heat Stress Tolerance Research Articles

CRISPR/Cas knockout of the NADPH oxidase gene OsRbohB reduces ROS overaccumulation and enhances heat stress tolerance in rice.

Heat stress (HS) has become a major factor limiting crop yields worldwide. HS inhibits plant growth by ROS accumulation, and NADPH oxidases (Rbohs) are major ROS producers in plants. Here, we show that CRISPR/Cas knockout of the OsRbohB (OsRbohB-KO) significantly increased rice tolerance to HS imposed at various different growth stages. We produced OsRbohB-KO and OsRbohB-overexpression (OsRbohB-OE) lines in a japonica cultivar, Nipponbare. Compared with nontransgenic wild-type (WT) plants, the OsRbohB-KO lines showed a significant increase in chlorophyll contents (5.2%-58.0%), plant growth (48.2%-65.6%) and grain yield (8.9%-20.5%), while reducing HS-induced ROS accumulation in seeds (21.3%-33.0%), seedlings (13.0%-30.4%), anthers (13.1%-20.3%) and grains (9.7%-22.1%), under HS conditions. Analysis of yield components revealed that the increased yield of OsRbohB-KO plants was due to increased starch synthetase activity, spikelets per panicle (2.0%-9.3%), filled spikelets (4.8%-15.5%), percentage of filled spikelets (2.4%-6.8%) and 1000-grain weight (2.9%-7.4%) under HS conditions during the reproductive stage. Grain milling and appearance quality, and starch content were also significantly increased in OsRbohB-KO plants under HS conditions during the mature stage. Furthermore, OsRbohB-KO significantly upregulated the expression levels of heat shock-related genes, OsHSP23.7, OsHSP17.7, OsHSF7 and OsHsfA2a, in rice seedlings and grains under long-term HS conditions. Conversely, OsRbohB-OE resulted in phenotypes that were opposite to OsRbohB-KO in most cases. Our results suggest that suppression of OsRbohB provides an effective approach for alleviating heat damage and improving grain yield and quality of rice under long-term HS conditions.

The role of SlCHRC in carotenoid biosynthesis and plastid development in tomato fruit

Chromoplasts are specialized plastids in plants involved in carotenoid synthesis, accumulation, and stress resistance. In tomatoes (Solanum lycopersicum), the Chromoplast-associated carotenoid binding protein (CHRC) regulates chromoplast development and carotenoid accumulation, although its precise mechanisms are not yet fully understood. To investigate the role of SlCHRC in carotenoid biosynthesis, we generated transgenic tomatoes using overexpression (oe-SlCHRC) and CRISPR/Cas9-mediated gene editing (cr-SlCHRC) techniques. The results demonstrated inhibited fruit ripening and delayed onset of color break in both transgenic lines. The oe-SlCHRC lines exhibited increased carotenoid accumulation, particularly (E/Z)-phytoene, lycopene, and γ-carotene, with abundant plastoglobules and carotenoid crystals observed via TEM. In contrast, cr-SlCHRC mutants showed a greener phenotype, reduced carotenoid content, and fewer plastoglobules at the BK + 10 stage. Transcriptome analysis indicated that SlCHRC influences key genes in carotenoid biosynthesis, such as SlNCED2, as well as genes related to chloroplast development, photosynthesis, and plastoglobule formation. Additionally, SlCHRC enhances heat stress tolerance in tomato fruits by upregulating heat shock proteins (HSPs), antioxidants, and proline accumulation. These findings indicate that SlCHRC plays a crucial role in improving tomato fruit quality under heat stress conditions.

Commercial perspectives: Genome editing as a breeding tool for health and well-being in dairy cattle

Genome editing is the latest breeding tool capable of accelerating the rate of genetic improvement for health and well-being traits in food animals. It enables the introduction of beneficial alleles within a single generation, including those of low frequency or absent in the population, while effectively bypassing linkage drag. For the dairy industry, genome editing can be used to make rapid genetic improvements that are precise, efficient, and transgene-free for functional traits that are not practically addressed without disrupting conventional breeding goals for overall economic merit based on genomic selection. Herein, various case studies for dairy cattle breeding are presented that demonstrate applications of genome editing for enhancing heat stress tolerance, reduced disease susceptibility, and/or other qualitative traits absent in some breeds. One case highlights the success of simultaneous editing of multiple loci through recent advancements in embryonic stem cell biology. Multiplexed editing is crucial for addressing the polygenic nature inherent to many economically important traits in livestock. However, maximizing the benefits of genome editing depends on the continued discovery of targets for editing that are commercially important. Commercialization also depends on rapidly evolving regulatory statutes for risk assessment, where some countries already permit the commercialization of cattle with non-GMO genome alterations through existing regulations. New breeding technologies like genome editing are now poised to have significant impact in equipping elite performance cattle to be more resilient to infectious disease and climate change without the loss of production gains obtained from decades of selection.

Putrescine enhances heat stress tolerance in Brassica juncea L. Seedlings by modulating growth and physiological responses

Putrescine enhances heat stress tolerance in Brassica juncea L. Seedlings by modulating growth and physiological responses

Molecular cloning and characterization of heat-responsive LcOPR1, a gene encoding oxophytodienoic acid reductase in lentil.

Improving crop plants using biotechnological implications is a promising and modern approach compared to traditional methods. High-temperature exposure to the reproductive stage induces flower abortion and declines grain filling performance, leading to smaller grain production and low yield in lentil and other legumes. Thus, cloning effective candidate genes and their implication in temperature stress tolerance in lentil (Lens culinaris Medik.) using biotechnological tools is highly demandable. The 12-oxophytodienoic acid reductases (OPRs) are flavin mononucleotide-dependent oxidoreductases with vital roles in plants. They are members of the old yellow enzyme (OYE) family. These enzymes are involved in the octadecanoid pathway, which contributes to jasmonic acid biosynthesis and is essential in plant stress responses. Lentil is one of the vital legume crops affected by the temperature fluctuations caused by global warming. Therefore, in this study, the LcOPR1 gene was successfully cloned and isolated from lentils using RT-PCR to evaluate its functional responses in lentil under heat stress. The bioinformatics analysis revealed that the full-length cDNA of LcOPR1 was 1303 bp, containing an 1134 bp open reading frames (ORFs), encoding 377 amino acids with a predicted molecular weight of 41.63 and a theoretical isoelectric point of 5.61. Bioinformatics analyses revealed that the deduced LcOPR1 possesses considerable homology with other plant 12-oxophytodienoic acid reductases (OPRs). Phylogenetic tree analysis showed that LcOPR1 has an evolutionary relationship with other OPRs in different plant species of subgroup I, containing enzymes that are not required for jasmonic acid biosynthesis. The expression analysis of LcOPR1 indicated that this gene is upregulated in response to the heat-stress condition and during recovery in lentil. This study finding might be helpful to plant breeders and biotechnologists in LcOPR1 engineering and/or plant breeding programs in revealing the biological functions of LcOPR1 in lentils and the possibility of enhancing heat stress tolerance by overexpressing LcOPR1 in lentil and other legume plants under high temperature.

Enhancing Cowpea Tolerance to Elevated Temperature: Achievements, Challenges and Future Directions

Despite its ability to thrive in high-temperature environments, cowpea productivity can be hampered by heat stress, particularly when night air temperatures exceed 17 °C. The crop’s germplasm pool potentially possesses significant genetic variability that can be harnessed to breed for heat-tolerant varieties. Progress in improving the crop for heat tolerance has been limited, especially under the hot, short-day environments typical of sub-Saharan Africa. Only a few heat-tolerant varieties have been released, partly due to the limited understanding of heat stress tolerance mechanisms and environmental interaction effects on genotypes, as well as imprecise phenotyping. This review contributes to the literature on cowpea heat stress by highlighting key achievements, challenges, and future directions in breeding heat-tolerant cowpea genotypes and by providing additional information from the recent literature. We opine that the genetic variability for heat tolerance-related traits in cowpea has not been sufficiently exploited in developing varieties adapted to the target production environments. Therefore, attention should be given to assessing the crop’s genetic repository by targeting adaptive, morphological, and physiological traits that enhance heat stress tolerance. We propose that breeding programs integrate phenotyping of whole-plant physiological traits and molecular breeding to identify breeder-friendly markers for routine selection. This should be followed by introgression of the heat-tolerant favourable alleles to adapted susceptible varieties using rapid and precise approaches that take advantage of modern genetic and genomic resources such as innovative genetic resources, genomic selection, speed breeding, and genome editing technologies. These tools hold great promise in fast-tracking the development of improved heat-tolerant varieties and incorporating the must-have traits preferred by cowpea farmers and consumers. In view of the likely increase in atmospheric temperature to be occasioned by climate change, there is an urgent need to develop heat-tolerant cowpea varieties to ensure the sustainability of current and future cropping and agri-food systems.

Dendrobium Nobile Alcohol Extract Extends the Lifespan of Caenorhabditis elegans via hsf-1 and daf-16.

Dendrobium nobile is a traditional Chinese herb with anti-inflammatory, antioxidant, and neuroprotective properties. However, its antiaging effects are unclear. Herein, we studied the aging-related functions and the mechanism of action of the alcohol extract of Dendrobium nobile (DnAE) in the model organism Caenorhabditis elegans. The results indicated that 1 mg/mL DnAE slowed lipofuscin accumulation, decreased the levels of reactive oxygen species, elevated superoxide dismutase activity, enhanced oxidative and heat stress resistance, extended the lifespan of nematodes, protected their dopamine neurons from 6-hydroxydopamine-induced neurodegeneration, and reduced Aβ-induced neurotoxicity. DnAE upregulated the mRNA expression of the transcription factors DAF-16 and HSF-1, promoted the nuclear localization of DAF-16, and enhanced the fluorescence intensity of HSP-16.2. However, it had no effect on the lifespan of DAF-16 mutants. Thus, DnAE can significantly extend lifespan, enhance heat stress tolerance, and delay age-related diseases through a DAF-16-dependent pathway.

Populus trichocarpa PtHSFA4a Enhances Heat Tolerance by Regulating Expression of APX1 and HSPs

Heat stress can severely inhibit plant growth and reproduction, resulting in heavy financial and crop yield losses. Heat shock transcription factors (HSFs) play an important role in regulating plant responses to abiotic stress. However, compared with the in-depth study of HSF gene function in herbaceous species, reports on the regulatory mechanism of the response of HSFs to heat stress in trees are scarce. Here, we demonstrated that PtHSFA4a is induced by high temperatures in Populus trichocarpa leaves. Intense GUS activity was detected in the leaves of PtHSFA4a promoter-GUS reporter transgenic line under heat stress. Ectopic expression of PtHSFA4a in Arabidopsis thaliana enhanced heat stress tolerance, which reduced malondialdehyde and reactive oxygen species levels. RT-qPCR revealed that the expression of key heat stress-related genes (that is, AtMBF1c, AtZAT12, AtAPX1, AtHSA32, and AtHSPs) was upregulated in PtHSFA4a transgenic plants. Additionally, PtHSFA4a directly bind to the promoters of AtAPX1 and AtHSPs under heat stress to enhance heat tolerance by upregulating the antioxidant defense system and maintaining protein folding homeostasis in A. thaliana leaves. These findings provide novel insights into the molecular mechanisms underlying PtHSFA4a-mediated regulation of plant responses to heat stress.

Heat Stress in Vegetables: Impacts and Management Strategies – A Review

Global climate change has not only caused a significant rise in the average temperature around the world but has also threatened crop productivity and food security. Heat stress disrupts various plant physiological and biochemical processes, such as inhibition of growth and development, reduction of photosynthesis rate and nutrient uptake, consequently causing yield losses. The destructive effects of heat stress are expected to worsen in the coming years. Thus, it has become imperative to understand how vegetables respond and adapt to heat stress in order to improve their heat tolerance ability. Various approaches have been adopted to enhance heat stress tolerance in vegetables, including modifying cultural practices and crop improvements through several breeding methods. This review gives comprehensive and up-to-date information on the effects of heat stress on vegetables; and existing as well as emerging methods adopted to enhance heat tolerance in vegetables. It also provides a brief overview of a new method called speed breeding, which can be leveraged to fast-track the breeding process for developing heat stress-tolerant vegetables.

NtHSP70-8b positively regulates heat tolerance and seed size in Nicotiana tabacum

Heat stress considerably restricts the geographical distribution of crops and affects their growth, development, and productivity. HSP70 plays a critical regulatory role in plant growth response to heat stress. However, the mechanisms of this regulatory remain poorly understood. Here, an HSP70 gene, NtHSP70-8b, which is involved in the heat stress response of tobacco, was cloned and identified. The expression of NtHSP70-8b was induced by exogenous abscisic acid (ABA) treatment and abiotic stress, including heat, drought, and salt. Notably, high NtHSP70-8b expression occurred under heat stress conditions, which was consistent with the β-glucuronidase histochemical analysis. Moreover, NtHSP70-8b overexpression markedly enhanced heat stress tolerance by changing the stomatal conductance and antioxidant capacity in tobacco leaves. qRT-PCR showed that the expression levels of ABA synthesis and response genes (NtNCED3 and NtAREB), stress defence genes (NtERD10C and NtLEA5), and other HSP genes (NtHSP90 and NtHSP26a) in NtHSP70-8b-overexpressing tobacco were high under heat stress. The interaction of NtHSP70-8b with NtHSP26a was further confirmed by a luciferase complementation imaging assay. In contrast, NtHSP70-8b knockout mutants showed significantly reduced antioxidant capacity compared to the wild type (WT) under heat stress conditions, suggesting that NtHSP70-8b acts as a positive regulator of heat stress in tobacco. Moreover, NtHSP70-8b overexpression increased the 1000-seed weight. Taken together, NtHSP70-8b is involved in the heat stress response, and NtHSP70-8b overexpression contributed to enhanced tolerance to heat stress, which is thus an essential gene with potential application value for developing heat stress-tolerant crops.

Thermopriming mitigates the effects of heat stress by modulating the expression of Heat shock factors in Brassica juncea (Indian mustard)

Brassica juncea (also known as Indian mustard) is an important vegetable oil seed crop whose growth and productivity is severely affected by heat stress. Interestingly, pre-exposure to sublethal heat stress, referred as thermopriming can remarkably enhance the plant heat stress tolerance. However, little is known about the impact of thermopriming on heat stress response of the important oil seed crop, B. juncea. In this study, we investigated the basal and thermopriming-induced heat stress response of 16 different cultivated, agronomically important varieties of Brassica juncea. Based on their basal heat stress response, we classify the varieties as heat sensitive, moderately tolerant or tolerant. Notably, almost all the varieties displayed enhanced heat stress tolerance upon thermopriming (acquired thermotolerance), albeit to varying magnitudes. Strikingly, the high oil-yielding, drought tolerant, heat sensitive variety Pusa Bold showed remarkable acquired thermotolerance upon thermopriming. Investigations in Pusa Bold indicate that the thermopriming-induced acquired thermotolerance predominantly correlates with the rapid activation of ROS scavenging mechanisms and differential expression of Heat Shock Family of transcription factors (BjHSFs). Taken together, our study reveals the positive impact of thermopriming in alleviating the harmful effects of heat stress on Brassica juncea seedlings and paves the path to enhance heat stress tolerance for improved productivity in the important oilseed crop Indian mustard.

The miR165/166-PHABULOSA module promotes thermotolerance by transcriptionally and posttranslationally regulating HSFA1.

Heat stress (HS) adversely affects plant growth and productivity. The Class A1 HS transcription factors (HSFA1s) act as master regulators in the plant response to HS. However, how HSFA1-mediated transcriptional reprogramming is modulated during HS remains to be elucidated. Here, we report that a module formed by the microRNAs miR165 and miR166 and their target transcript, PHABULOSA (PHB), regulates HSFA1 at the transcriptional and translational levels to control plant HS responses. HS-triggered induction of MIR165/166 in Arabidopsis thaliana led to decreased expression of target genes including PHB. MIR165/166 overexpression lines and mutations in miR165/166 target genes enhanced HS tolerance, whereas miR165/166 knockdown lines and plants expressing a miR165/166-resistant form of PHB were sensitive to HS. PHB directly repressed the transcription of HSFA1s and globally modulated the expression of HS-responsive genes. PHB and HSFA1s share a common target gene, HSFA2, which is essential for activation of plant responses to HS. PHB physically interacted with HSFA1s and exerted an antagonistic effect on HSFA1 transcriptional activity. PHB and HSFA1s co-regulated transcriptome reprogramming upon HS. Together, these findings indicate that heat-triggered regulation of the miR165/166-PHB module controls HSFA1-mediated transcriptional reprogramming and plays a critical role during HS in Arabidopsis.

Expression of ZmNAGK in tobacco enhances heat stress tolerance via activation of antioxidant-associated defense

Heat stress severely inhibits plant growth and limits crop yields. Thus, it is crucial to identify genes that are associated with plant heat stress responses. Here, we report a maize (Zea mays L.) gene, N-acetylglutamate kinase (ZmNAGK), that positively enhances plant heat stress tolerance. The ZmNAGK expression level was significantly up-regulated by heat stress in maize plants, and ZmNAGK was found to be localized in maize chloroplasts. Phenotypic analysis showed that overexpressing of ZmNAGK enhanced the tolerance of tobacco to heat stress both in the seed germination and seedling growth stages. Further physiological analysis showed that ZmNAGK overexpression in tobacco could alleviate oxidative damages that occurred during heat stress via activation of antioxidant defense signaling. Transcriptome analysis revealed that ZmNAGK could modulate the expression of antioxidant-enzyme encoding genes, such as ascorbate peroxidase 2 (APX2) and superoxide dismutase C (SODC), and heat shock network genes. Taken together, we have identified a maize gene that can provide plants with heat tolerance through the induction of antioxidant-associated defense signaling.

Meta-Analysis of Microarray Data and Their Utility in Dissecting the Mapped QTLs for Heat Acclimation in Rice.

In the current global warming scenario, it is imperative to develop crops with improved heat tolerance or acclimation, for which knowledge of major heat stress-tolerant genes or genomic regions is a prerequisite. Though several quantitative trait loci (QTLs) for heat tolerance have been mapped in rice, candidate genes from these QTLs have not been reported yet. The meta-analysis of microarray datasets for heat stress in rice can give us a better genomic resource for the dissection of QTLs and the identification of major candidate genes for heat stress tolerance. In the present study, a database, RiceMetaSys-H, comprising 4227 heat stress-responsive genes (HRGs), was created using seven publicly available microarray datasets. This included in-house-generated microarray datasets of Nagina 22 (N22) and IR64 subjected to 8 days of heat stress. The database has provisions for searching the HRGs through genotypes, growth stages, tissues, and physical intervals in the genome, as well as Locus IDs, which provide complete information on the HRGs with their annotations and fold changes, along with the experimental material used for the analysis. The up-regulation of genes involved in hormone biosynthesis and signalling, sugar metabolism, carbon fixation, and the ROS pathway were found to be the key mechanisms of enhanced heat tolerance. Integrating variant and expression analysis, the database was used for the dissection of the major effect of QTLs on chromosomes 4, 5, and 9 from the IR64/N22 mapping population. Out of the 18, 54, and 62 genes in these three QTLs, 5, 15, and 12 genes harboured non-synonymous substitutions. Fifty-seven interacting genes of the selected QTLs were identified by a network analysis of the HRGs in the QTL regions. Variant analysis revealed that the proportion of unique amino acid substitutions (between N22/IR64) in the QTL-specific genes was much higher than the common substitutions, i.e., 2.58:0.88 (2.93-fold), compared to the network genes at a 0.88:0.67 (1.313-fold) ratio. An expression analysis of these 89 genes showed 43 DEGs between IR64/N22. By integrating the expression profiles, allelic variations, and the database, four robust candidates (LOC_Os05g43870, LOC_Os09g27830, LOC_Os09g27650, andLOC_Os09g28000) for enhanced heat stress tolerance were identified. The database thus developed in rice can be used in breeding to combat high-temperature stress.

Foxtail millet SiCDPK7 gene enhances tolerance to extreme temperature stress in transgenic plants

Global climate change has resulted in increasingly harsh environments that have become the restriction factors for plants growth and development. Calcium-dependent protein kinases (CDPKs) in plants play critical roles in resisting various abiotic stresses, such as heat and cold stresses. Using the expression pattern analysis of foxtail millet CDPK family members under heat- and cold-treatments, respectively, and the SiCDPK7 was found to respond to extreme temperature stress and was selected for further study. The results suggested that overexpression of SiCDPK7 in Arabidopsis conferred tolerance to heat stress by increasing seedling survival rates and hypocotyl elongation compared with wild type (WT) plants, and also can enhance heat stress tolerance in foxtail millet. Analysis of physiological and biochemical indexes showed that SiCDPK7 transgenic plant lines had the markedly higher catalase (CAT) activity and the significantly lower malonaldehyde (MDA) content than WT plants. In addition, qRT-PCR analysis showed that the transcription levels of heat and cold stress-responsive genes were significantly increased in SiCDPK7 transgenic Arabidopsis and foxtail millet under stress conditions. This supporting evidence suggests that SiCDPK7 facilitated the extreme temperature tolerance capabilities in plants

ZmNAC074, a maize stress-responsive NAC transcription factor, confers heat stress tolerance in transgenic Arabidopsis.

The harsh environment such as high temperature greatly limits the growth, development and production of crops worldwide. NAC (NAM, ATAF1/2, and CUC2) transcription factors (TFs) play key regulatory roles in abiotic stress responses of plants. However, the functional roles of NAC TFs in heat stress response of maize remain elusive. In our present study, we identified and isolated a stress-responsive NAC transcription factor gene in maize, designated as ZmNAC074 and orthologous with rice OsNTL3. Further studies revealed that ZmNAC074 may encode a membrane-bound transcription factor (MTF) of NAC family in maize, which is comprised of 517 amino acid residues with a transmembrane domain at the C-terminus. Moreover, ZmNAC074 was highly expressed and induced by various abiotic stresses in maize seedlings, especially in leaf tissues under heat stress. Through generating ZmNAC074 transgenic plants, phenotypic and physiological analyses further displayed that overexpression of ZmNAC074 in transgenic Arabidopsis confers enhanced heat stress tolerance significantly through modulating the accumulation of a variety of stress metabolites, including reactive oxygen species (ROS), antioxidants, malondialdehyde (MDA), proline, soluble protein, chlorophyll and carotenoid. Further, quantitative real-time PCR analysis showed that the expression levels of most ROS scavenging and HSR- and UPR-associated genes in transgenic Arabidopsis were significantly up-regulated under heat stress treatments, suggesting that ZmNAC074 may encode a positive regulator that activates the expression of ROS-scavenging genes and HSR- and UPR-associated genes to enhance plant thermotolerance under heat stress conditions. Overall, our present study suggests that ZmNAC074 may play a crucial role in conferring heat stress tolerance in plants, providing a key candidate regulatory gene for heat stress tolerance regulation and genetic improvement in maize as well as in other crops.

An invasive weed-associated bacteria confers enhanced heat stress tolerance in wheat

Global temperatures are expected to increase due to climate change, and heat stress is one of the major limiting factors affecting future agriculture. To identify plant-associated microorganisms which can promote heat stress tolerance in wheat, we have screened several bacteria isolated from etiolated seedlings of the invasive noxious weed Parthenium hysterophorus. One isolate designated as Ph-04 was found to confer enhanced heat stress tolerance in wheat. The 16S rRNA gene sequence analysis showed that Ph-04 isolate shared highest sequence identity with Bacillus paramycoides species of the Bacillus cereus group. Ph-04 treated wheat seeds exhibited enhanced germination, longer coleoptile, radicle and seminal root length than control seedlings when grown in the dark at optimum and high temperatures. Similarly, under autotrophic conditions, Ph-04 treated plants also exhibited enhanced heat stress tolerance with a significant increase in membrane integrity and significantly reduced levels of H2O2 under heat stress compared to control plants. This observed heat stress tolerance is associated with constitutively higher basal levels of proline, and activity of antioxidant enzymes, catalase (CAT) and ascorbate peroxidase (APX) in Ph-04 treated plants grown under unstressed conditions with further increase under heat stress conditions compared to controls. Plant recovery after heat stress also showed that the Ph-04 treated plants exhibited significantly less damage in terms of survival percentage and exhibited better morphological and physiological characteristics compared to control plants. The study proves that invasive weeds can harbour potentially beneficial microorganisms, which can be transferred to non-native crop (host) plants to improve climate resilience characteristics.

Ethanol induces heat tolerance in plants by stimulating unfolded protein response.

Ethanol priming induces heat stress tolerance by the stimulation of unfolded protein response. Global warming increases the risk of heat stress-related yield losses in agricultural crops. Chemical priming, using safe agents, that can flexibly activate adaptive regulatory responses to adverse conditions, is a complementary approach to genetic improvement for stress adaptation. In the present study, we demonstrated that pretreatment of Arabidopsis with a low concentration of ethanol enhances heat tolerance without suppressing plant growth. We also demonstrated that ethanol pretreatment improved leaf growth in lettuce (Lactuca sativa L.) plants grown in the field conditions under high temperatures. Transcriptome analysis revealed a set of genes that were up-regulated in ethanol-pretreated plants, relative to water-pretreated controls. Binding Protein 3 (BIP3), an endoplasmic reticulum (ER)-stress marker chaperone gene, was among the identified up-regulated genes. The expression levels of BIP3 were confirmed by RT-qPCR. Root-uptake of ethanol was metabolized to organic acids, nucleic acids, amines and other molecules, followed by an increase in putrescine content, which substantially promoted unfolded protein response (UPR) signaling and high-temperature acclimation. We also showed that inhibition of polyamine production and UPR signaling negated the heat stress tolerance induced by ethanol pretreatment. These findings collectively indicate that ethanol priming activates UPR signaling via putrescine accumulation, leading to enhanced heat stress tolerance. The information gained from this study will be useful for establishing ethanol-mediated chemical priming strategies that can be used to help maintain crop production under heat stress conditions.

Priming effect of exogenous ABA on heat stress tolerance in rice seedlings is associated with the upregulation of antioxidative defense capability and heat shock-related genes

Heat stress is a major restrictive factor that suppresses rice production. In this study, we investigated the potential priming effect of exogenous abscisic acid (ABA) on heat tolerance in rice seedlings. Seedlings were pretreated with 10 µM ABA by root-drenched for 24 h and then subjected to heat stress conditions of 40 °C day/35 °C night. ABA pretreatment significantly decreased leaf withering by 2.5–28.5% and chlorophyll loss by 12.8–35.1% induced by heat stress in rice seedlings. ABA pretreatment also mitigated cell injury, as shown by lower malondialdehyde content, relative electrolytic conductivity, and expression of cell death-related genes OsKOD1, OsCP1, and OsNAC4, while expression of OsBI1, a cell death-suppressor gene, was upregulated by ABA pretreatment. Moreover, ABA pretreatment improved antioxidant defense capacity, as shown by an obvious upregulation of ROS-scavenging genes and a decrease in ROS content (O2− and H2O2), and downregulation of the OsRbohs genes. Application of fluridone, an ABA biosynthesis inhibitor, increased membrane injury and the accumulation of ROS under heat stress. Exogenous antioxidants (proanthocyanidins) significantly alleviated leaf withering by decreasing ROS overaccumulation and membrane injury induced by heat stress. In addition, ABA pretreatment significantly superinduced the expression of ABA-responsive genes SalT and OsWsi18, the ABA biosynthesis genes OsNCED3 and OsNCED4, and the heat shock-related genes OsHSP23.7, OsHSP17.7, OsHSF7, and OsHsfA2a. Taken together, these results suggest that exogenous ABA has a potential priming effect for enhancing heat stress tolerance of rice seedlings mainly by improving antioxidant defense capacity and heat shock-related genes.

FOLIAR APPLICATION OF SALICYLIC ACID AND CALCIUM CHLORIDE ENHANCE HEAT STRESS TOLERANCE IN TOMATO

The aim of this research was to enhance heat stress tolerance potential in local tomato germplasm through exogenous application of salicylic acid (SA) and calcium chloride (CaCl2). Various concentrations of salicylic acid (e.g., control, 2.5 mM, 3.5 mM and 4.5 mM) and calcium chloride (e.g., control, 0.3 mM, 0.4 mM and 0.5 mM) were applied for the duration of forty days. Physiological parameters include (stomatal conductance, photosynthetic rate, transpiration rate and water use efficiency) as well as biochemical attributes (chlorophyll content, enzyme activities of catalase, peroxidase and superoxidase dismutase) of selected tomato genotypes estimated under heat stress conditions. The results revealed that SA and CaCl2 application enhanced vegetative growth of tomato genotypes as compared with control plants. An increased concentration of SA and CaCl2 showed the improved photosynthetic rate, chlorophyll content and induced transpiration rate and stomatal conductance and antioxidant enzyme activity. The study proved that foliar spray of SA and CaCl2 involved in stabilizing the cell as well as cellular integrity under heat stress environment.