SmHSFA8 Enhances the Heat Tolerance of Eggplant by Regulating the SmEGY3-SmCSD1 Module and Promoting SmF3H-mediated Flavonoid Biosynthesis

High temperature (HT) is a major environmental factor that restrains eggplant growth and production. Heat shock factors (HSFs) play a vital role in the response of plants to high-temperature stress (HTS). However, the molecular mechanism by which HSFs regulate heat tolerance in eggplants remains unclear. Previously, we reported that SmEGY3 enhanced the heat tolerance of eggplant. Herein, SmHSFA8 activated SmEGY3 expression and interacted with SmEGY3 protein to enhance the activation function of SmEGY3 on SmCSD1. Virus-induced gene silencing (VIGS) and overexpression assays suggested that SmHSFA8 positively regulated heat tolerance in plants. SmHSFA8 enhanced the heat tolerance of tomato plants by promoting SlEGY3 expression, H2O2 production and H2O2-mediated retrograde signalling pathway. DNA affinity purification sequencing (DAP-seq) analysis revealed that SmHSPs (SmHSP70, SmHSP70B and SmHSP21) and SmF3H were candidate downstream target genes of SmHSFA8. SmHSFA8 regulated the expression of HSPs and F3H and flavonoid content in plants. The silencing of SmF3H by VIGS reduced the flavonoid content and heat tolerance of eggplant. In addition, exogenous flavonoid treatment alleviated the HTS damage to eggplants. These results indicated that SmHSFA8 enhanced the heat tolerance of eggplant by activating SmHSPs exprerssion, mediating the SmEGY3-SmCSD1 module, and promoting SmF3H-mediated flavonoid biosynthesis.

Lipidomic profiling reveals the protective mechanism of nitrogen-controlled atmosphere on brown rice quality during storage

Rice, a globally important staple, requires effective preservation methods to maintain its quality during extended storage. This study explored the efficacy of nitrogen-controlled atmosphere (NCA) storage in preserving the quality of brown rice during a one-year period using UHPLC-MS/MS based lipidomic profiling. A total of 1013 lipids were identified and categorized into five main groups. Specific lipids including triglycerides (TG), diglycerides (DG), phosphatidylethanolamines (PE), cardiolipins (CL), and ceramides (Cer), were highlighted as potential biomarkers for assessing rice rancidity. NCA storage significantly suppressed lipase and lipoxygenase activities, reducing lipid hydrolysis and oxidation to effectively delayed rice quality deterioration. Furthermore, NCA regulated glycerolipid and glycerophospholipid metabolisms, promoting lipid remodeling while reducing the degradation of TGs and phospholipids. This regulation preserved cellular membrane integrity, limited fatty acid release, and mitigate rancidity and quality loss during storage. These findings elucidate the mechanism by which NCA storage delays deterioration and extends the stored rice shelf-life.

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

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

Physical map of QTL for eleven agronomic traits across fifteen environments, identification of related candidate genes, and development of KASP markers with emphasis on terminal heat stress tolerance in common wheat

KEY MESSAGE

Key message This study identified stable QTL, promising candidate genes and developed novel KASP markers for heat tolerance, providing genomic resources to assist breeding for the development of high-yielding and heat-tolerant wheat germplasm and varieties. To understand the genetic architecture of eleven agronomic traits under heat stress, we used a doubled-haploid population (177 lines) derived from a heat-sensitive cultivar (PBW343) and a heat-tolerant genotype (KSG1203). This population was evaluated under timely, late and very late sown conditions over locations and years comprising fifteen environments. Best linear unbiased estimates and a genetic map (5,710 SNPs) developed using sequencing-based genotyping were used for QTL mapping. The identified 66 QTL (20 novel) were integrated into wheat physical map (14,263.4 Mb). These QTL explained 5.3% (QDth.ccsu-4A for days to heading and QDtm.ccsu-5B for days to maturity) to 24.9% (QGfd.ccsu-7D for grain filling duration) phenotypic variation. Thirteen stable QTL explaining high phenotypic variation were recommended for marker-assisted recurrent selection (MARS) for optimum/heat stress environments. Selected QTL were validated by their presence in high-yielding doubled-haploid lines. Some QTL for 1000-grain weight (TaERF3-3B, TaFER-5B, and TaZIM-A1), grain yield (TaCol-B5), and developmental traits (TaVRT-2) were co-localized with known genes. Specific known genes for traits like abiotic/biotic stress, grain quality and yield were co-located with 26 other QTL. Furthermore, 209 differentially expressed candidate genes for heat tolerance in plants that encode 28 different proteins were identified. KASP markers for three major/stable QTL, namely QGfd.ccsu-7A for grain filling duration on chromosome 7A (timely sown), QNgs.ccsu-3A for number of grains per spike on 3A, and QDth.ccsu-7A for days to heading on 7A (late and very late sown) environments were developed for MARS focusing on the development of heat-tolerant wheat varieties/germplasm.

Wild grass-derived alleles represent a genetic architecture for the resilience of modern common wheat to stresses

This review explores the integration of wild grass-derived alleles into modern bread wheat breeding to tackle the challenges of climate change and increasing food demand. With a focus on synthetic hexaploid wheat, this review highlights the potential of genetic variability in wheat wild relatives, particularly Aegilops tauschii, for improving resilience to multifactorial stresses like drought, heat, and salinity. The evolutionary journey of wheat (Triticum spp.) from diploid to hexaploid species is examined, revealing significant genetic contributions from wild grasses. We also emphasize the importance of understanding incomplete lineage sorting in the genomic evolution of wheat. Grasping this information is crucial as it can guide breeders in selecting the appropriate alleles from the gene pool of wild relatives to incorporate into modern wheat varieties. This approach improves the precision of phylogenetic relationships and increases the overall effectiveness of breeding strategies. This review also addresses the challenges in utilizing the wheat wild genetic resources, such as the linkage drag and cross-compatibility issues. Finally, we culminate the review with future perspectives, advocating for a combined approach of high-throughput phenotyping tools and advanced genomic techniques to comprehensively understand the genetic and regulatory architectures of wheat under stress conditions, paving the way for more precise and efficient breeding strategies.

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

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

Exogenous Methyl Jasmonate Mediated MiRNA-mRNA Network Improves Heat Tolerance of Perennial Ryegrass

Heat stress can hinder the growth of perennial ryegrass (Lolium perenne L.). Methyl jasmonate (MeJA) applied exogenously can increase heat stress tolerance in plants; however, the regulatory mechanisms involved in heat tolerance mediated by MeJA are poorly understood in perennial ryegrass. Here, the microRNA (miRNA) expression profiles of perennial ryegrass were assessed to elucidate the regulatory pathways associated with heat tolerance induced by MeJA. Plants were subjected to four treatments, namely, control (CK), MeJA pre-treatment (T), heat stress treatment (H), and MeJA pre-treatment + heat stress (TH). According to the results, 102 miRNAs were up-regulated in all treatments, with 20, 27, and 33 miRNAs being up-regulated in the T, H, and TH treatment groups, respectively. The co-expression network analysis between the deferentially expressed miRNAs and their corresponding target genes showed that 20 miRNAs modulated 51 potential target genes. Notably, the miRNAs that targeted genes related to with regards to heat tolerance were driven by MeJA, and they were involved in four pathways: novel-m0258-5p mediated signal transduction, novel-m0350-5p mediated protein homeostasis, miR397-z, miR5658-z, and novel-m0008-5p involved in cell wall component, and miR1144-z and miR5185-z dominated chlorophyll degradation. Overall, the findings of this research paved the way for more research into the heat tolerance mechanism in perennial ryegrass and provided a theoretical foundation for developing cultivars with enhanced heat tolerance.

Membrane Fluidization Governs the Coordinated Heat-Inducible Expression of Nucleus- and Plastid Genome-Encoded Heat Shock Protein 70 Genes in the Marine Red Alga Neopyropia yezoensis

Heat shock protein 70 (HSP70) is an evolutionarily conserved protein chaperone in prokaryotic and eukaryotic organisms. This family is involved in the maintenance of physiological homeostasis by ensuring the proper folding and refolding of proteins. The HSP70 family in terrestrial plants can be divided into cytoplasm, endoplasmic reticulum (ER)-, mitochondrion (MT)-, and chloroplast (CP)-localized HSP70 subfamilies. In the marine red alga Neopyropia yezoensis, the heat-inducible expression of two cytoplasmic HSP70 genes has been characterized; however, little is known about the presence of other HSP70 subfamilies and their expression profiles under heat stress conditions. Here, we identified genes encoding one MT and two ER HSP70 proteins and confirmed their heat-inducible expression at 25 °C. In addition, we determined that membrane fluidization directs gene expression for the ER-, MT-, and CP-localized HSP70 proteins as with cytoplasmic HSP70s. The gene for the CP-localized HSP70 is carried by the chloroplast genome; thus, our results indicate that membrane fluidization is a trigger for the coordinated heat-driven induction of HSP70 genes harbored by the nuclear and plastid genomes in N. yezoensis. We propose this mechanism as a unique regulatory system common in the Bangiales, in which the CP-localized HSP70 is usually encoded in the chloroplast genome.

A Trifolium repens flavodoxin-like quinone reductase 1 (TrFQR1) improves plant adaptability to high temperature associated with oxidative homeostasis and lipids remodeling

Maintenance of stable mitochondrial respiratory chains could enhance adaptability to high temperature, but the potential mechanism was not elucidated clearly in plants. In this study, we identified and isolated a TrFQR1 gene encoding the flavodoxin-like quinone reductase 1 (TrFQR1) located in mitochondria of leguminous white clover (Trifolium repens). Phylogenetic analysis indicated that amino acid sequences of FQR1 in various plant species showed a high degree of similarities. Ectopic expression of TrFQR1 protected yeast (Saccharomyces cerevisiae) from heat damage and toxic levels of benzoquinone, phenanthraquinone and hydroquinone. Transgenic Arabidopsis thaliana and white clover overexpressing TrFQR1 exhibited significantly lower oxidative damage and better photosynthetic capacity and growth than wild-type in response to high-temperature stress, whereas AtFQR1-RNAi A. thaliana showed more severe oxidative damage and growth retardation under heat stress. TrFQR1-transgenic white clover also maintained better respiratory electron transport chain than wild-type plants, as manifested by significantly higher mitochondrial complex II and III activities, alternative oxidase activity, NAD(P)H content, and coenzyme Q10 content in response to heat stress. In addition, overexpression of TrFQR1 enhanced the accumulation of lipids including phosphatidylglycerol, monogalactosyl diacylglycerol, sulfoquinovosyl diacylglycerol and cardiolipin as important compositions of bilayers involved in dynamic membrane assembly in mitochondria or chloroplasts positively associated with heat tolerance. TrFQR1-transgenic white clover also exhibited higher lipids saturation level and phosphatidylcholine:phosphatidylethanolamine ratio, which could be beneficial to membrane stability and integrity during a prolonged period of heat stress. The current study proves that TrFQR1 is essential for heat tolerance associated with mitochondrial respiratory chain, cellular reactive oxygen species homeostasis, and lipids remodeling in plants. TrFQR1 could be selected as a key candidate marker gene to screen heat-tolerant genotypes or develop heat-tolerant crops via molecular-based breeding.

The hot science in rice research: How rice plants cope with heat stress

Global climate change has great impacts on plant growth and development, reducing crop productivity worldwide. Rice (Oryza sativa L.), one of the world's most important food crops, is susceptible to high-temperature stress from seedling stage to reproductive stage. In this review, we summarize recent advances in understanding the molecular mechanisms underlying heat stress responses in rice, including heat sensing and signalling, transcriptional regulation, transcript processing, protein translation, and post-translational regulation. We also highlight the irreversible effects of high temperature on reproduction and grain quality in rice. Finally, we discuss challenges and opportunities for future research on heat stress responses in rice.

The Karrikin Receptor Karrikin Insensitive2 Positively Regulates Heat Stress Tolerance in Arabidopsis thaliana

In this study, we investigated the potential role of the karrikin receptor KARRIKIN INSENSITIVE2 (KAI2) in the response of Arabidopsis seedlings to high-temperature stress. We performed phenotypic, physiological and transcriptome analyses of Arabidopsis kai2 mutants and wild-type (WT) plants under control (kai2_C and WT_C, respectively) and 6- and 24-h heat stress conditions (kai2_H6, kai2_H24, WT_H6 and WT_H24, respectively) to understand the basis for KAI2-regulated heat stress tolerance. We discovered that the kai2 mutants exhibited hypersensitivity to high-temperature stress relative to WT plants, which might be associated with a more highly increased leaf surface temperature and cell membrane damage in kai2 mutant plants. Next, we performed comparative transcriptome analysis of kai2_C, kai2_H6, kai2_H24, WT_C, WT_H6 and WT_H24 to identify transcriptome differences between WT and kai2 mutants in response to heat stress. K-mean clustering of normalized gene expression separated the investigated genotypes into three clusters based on heat-treated and non-treated control conditions. Within each cluster, the kai2 mutants were separated from WT plants, implying that kai2 mutants exhibited distinct transcriptome profiles relative to WT plants. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analyses showed a repression in 'misfolded protein binding', 'heat shock protein binding', 'unfolded protein binding' and 'protein processing in endoplasmic reticulum' pathways, which was consistent with the downregulation of several genes encoding heat shock proteins and heat shock transcription factors in the kai2 mutant versus WT plants under control and heat stress conditions. Our findings suggest that chemical or genetic manipulation of KAI2 signaling may provide a novel way to improve heat tolerance in plants.

Physiological responses induced by phospholipase C isoform 5 upon heat stress in Arabidopsis thaliana

Plant's perception of heat stress involves several pathways and signaling molecules, such as phosphoinositide, which is derived from structural membrane lipids phosphatidylinositol. Phospholipase C (PLC) is a well-known signaling enzyme containing many isoforms in different organisms. In the present study, Phospholipase C Isoform 5 (PLC5) was investigated for its role in thermotolerance in Arabidopsis thaliana. Two over-expressing lines and one knock-down mutant of PLC5 were first treated at a moderate temperature (37 °C) and left for recovery. Then again exposed to a high temperature (45 °C) to check the seedling viability and chlorophyll contents. Root behavior and changes in ³²P_i labeled phospholipids were investigated after their exposure to high temperatures. Over-expression of PLC5 (PLC5 OE) exhibited quick and better phenotypic recovery with bigger and greener leaves followed by chlorophyll contents as compared to wild-type (Col-0) and PLC5 knock-down mutant in which seedling recovery was compromised. PLC5 knock-down mutant illustrated well-developed root architecture under controlled conditions but stunted secondary roots under heat stress as compared to over-expressing PLC5 lines. Around 2.3-fold increase in phosphatidylinositol 4,5-bisphosphate level was observed in PLC5 OE lines upon heat stress compared to wild-type and PLC5 knock-down mutant lines. A significant increase in phosphatidylglycerol was also observed in PLC5 OE lines as compared to Col-0 and PLC5 knock-down mutant lines. The results of the present study demonstrated that PLC5 over-expression contributes to heat stress tolerance while maintaining its photosynthetic activity and is also observed to be associated with primary and secondary root growth in Arabidopsis thaliana.

Type-A response regulators negatively mediate heat stress response by altering redox homeostasis in Arabidopsis

Besides the long-standing role of cytokinins (CKs) as growth regulators, their current positioning at the interface of development and stress responses is coming into recognition. The current evidence suggests the notion that CKs are involved in heat stress response (HSR), however, the role of CK signaling components is still elusive. In this study, we have identified a role of the CK signaling components type-A Arabidopsis response regulators (ARRs) in HSR in Arabidopsis. The mutants of multiple type-A ARR genes exhibit improved basal and acquired thermotolerance and, altered response to oxidative stress in our physiological analyses. Through proteomics profiling, we show that the type-A arr mutants experience a 'stress-primed' state enabling them to respond more efficiently upon exposure to real stress stimuli. A substantial number of proteins that are involved in the heat-acclimatization process such as the proteins related to cellular redox status and heat shock, are already altered in the type-A arr mutants without a prior exposure to stress conditions. The metabolomics analyses further reveal that the mutants accumulate higher amounts of α-and γ-tocopherols, which are important antioxidants for protection against oxidative damage. Collectively, our results suggest that the type-A ARRs play an important role in heat stress response by affecting the redox homeostasis in Arabidopsis.

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).

Grain Transcriptome Dynamics Induced by Heat in Commercial and Traditional Bread Wheat Genotypes

High temperature (HT) events have negative impact on wheat grains yield and quality. Transcriptome profiles of wheat developing grains of commercial genotypes (Antequera and Bancal) and landraces (Ardito and Magueija) submitted to heatwave-like treatments during grain filling were evaluated. Landraces showed significantly more differentially expressed genes (DEGs) and presented more similar responses than commercial genotypes. DEGs were more associated with transcription and RNA and protein synthesis in Antequera and with metabolism alterations in Bancal and landraces. Landraces upregulated genes encoding proteins already described as HT responsive, like heat shock proteins and cupins. Apart from the genes encoding HSP, two other genes were upregulated in all genotypes, one encoding for Adenylate kinase, essential for the cellular homeostasis, and the other for ferritin, recently related with increased tolerance to several abiotic stress in Arabidopsis. Moreover, a NAC transcription factor involved in plant development, known to be a negative regulator of starch synthesis and grain yield, was found to be upregulated in both commercial varieties and downregulated in Magueija landrace. The detected diversity of molecular processes involved in heat response of commercial and traditional genotypes contribute to understand the importance of genetic diversity and relevant pathways to cope with these extreme events.

Rosmarinic acid and hesperidin regulate gas exchange, chlorophyll fluorescence, antioxidant system and the fatty acid biosynthesis-related gene expression in Arabidopsis thaliana under heat stress

The impacts of exogenous rosmarinic acid (RA, 100 μM) and/or hesperidin (HP, 100 μM) were evaluated in improving tolerance on the gas exchange, chlorophyll fluorescence and efficiencies, phenomenological fluxes of photosystems, antioxidant system and gene expression related to the lipid biosynthesis under heat stress. For this purpose, Arabidopsis thaliana was grown under RA and HP with heat stress (S, 38 °C) for 24 h(h). As shown in gas exchange parameters, heat stress caused mesophyll efficiency and non-stomatal restrictions. Both alone and combined forms of RA and HP to stress-treated A. thaliana alleviated the disturbance of carbon assimilation, transpiration rate and internal CO2 concentrations. Stress impaired the levels of energy flow reaching reaction centers of PSII and the photon capture ability of active reaction centers. RA and/or HP enhanced photosystems' structural/functional characteristics and photosynthetic performance. Histochemical staining and biochemical analyses revealed that heat stress caused the oxidation in A. thaliana. By activating several defensive mechanisms, RA and/or HP could reverse the harm caused by radical production. Both alone and combined forms of RA and HP removed superoxide anion radical (O2•-) accumulation, inducing superoxide dismutase (SOD). The common enzyme that scavenged hydrogen peroxide (H2O2) at all three applications (S + RA, S + HP and S + RA + HP) was POX. Also, only RA could utilize the ascorbate (AsA) regeneration in response to stress, suggesting increased ascorbate peroxidase (APX), monodehydroascorbate (MDHAR) and dehydroascorbate (DHAR) activities. However, the regeneration/redox state of AsA and glutathione (GSH) did not maintain under S + HP and S + RA + HP. While RA had no positive influence on the saturated fatty acids under stress, HP increased the total saturated fatty acids (primarily palmitic acid). Besides, the combined application of RA + HP effectively created the stress response by increasing the expression of genes involved in fatty acid synthesis. The synergetic interactions of RA and HP could explain the increased levels of saturated fatty acids in combining these compounds. The data obtained from the study will contribute to the responses of phenolic compounds in plants to heat stress.

Membrane-Fluidization-Dependent and -Independent Pathways Are Involved in Heat-Stress-Inducible Gene Expression in the Marine Red Alga Neopyropia yezoensis

Heat stress responses are complex regulatory processes, including sensing, signal transduction, and gene expression. However, the exact mechanisms of these processes in seaweeds are not well known. We explored the relationship between membrane physical states and gene expression in the red alga Neopyropia yezoensis. To analyze heat-stress-induced gene expression, we identified two homologs of the heat-inducible high temperature response 2 (HTR2) gene in Neopyropia seriata, named NyHTR2 and NyHTR2L. We found conservation of HTR2 homologs only within the order Bangiales; their products contained a novel conserved cysteine repeat which we designated the Bangiales cysteine-rich motif. A quantitative mRNA analysis showed that expression of NyHTR2 and NyHTR2L was induced by heat stress. However, the membrane fluidizer benzyl alcohol (BA) did not induce expression of these genes, indicating that the effect of heat was not due to membrane fluidization. In contrast, expression of genes encoding multiprotein-bridging factor 1 (NyMBF1) and HSP70s (NyHSP70-1 and NyHSP70-2) was induced by heat stress and by BA, indicating that it involved a membrane-fluidization-dependent pathway. In addition, dark treatment under heat stress promoted expression of NyHTR2, NyHTR2L, NyMBF1, and NyHSP70-2, but not NyHSP70-1; expression of NyHTR2 and NyHTR2L was membrane-fluidization-independent, and that of other genes was membrane-fluidization-dependent. These findings indicate that the heat stress response in N. yezoensis involves membrane-fluidization-dependent and -independent pathways.

Molecular insights into sensing, regulation and improving of heat tolerance in plants

Climate-change-mediated increase in temperature extremes has become a threat to plant productivity. Heat stress-induced changes in growth pattern, sensitivity to pests, plant phonologies, flowering, shrinkage of maturity period, grain filling, and increased senescence result in significant yield losses. Heat stress triggers multitude of cellular, physiological and molecular responses in plants beginning from the early sensing followed by signal transduction, osmolyte synthesis, antioxidant defense, and heat stress-associated gene expression. Several genes and metabolites involved in heat perception and in the adaptation response have been isolated and characterized in plants. Heat stress responses are also regulated by the heat stress transcription factors (HSFs), miRNAs and transcriptional factors which together form another layer of regulatory circuit. With the availability of functionally validated candidate genes, transgenic approaches have been applied for developing heat-tolerant transgenic maize, tobacco and sweet potato. In this review, we present an account of molecular mechanisms of heat tolerance and discuss the current developments in genetic manipulation for heat tolerant crops for future sustainable agriculture.

Exogenous melatonin mitigates salinity-induced damage in olive seedlings by modulating ion homeostasis, antioxidant defense, and phytohormone balance

Melatonin (MEL) is a ubiquitous molecule with pleiotropic roles in plant adaption to stress. In this study, we investigated the effects of foliar spray of 100 and 200 μM MEL on the biochemical and physiological traits linked with the growth performance of olive seedlings exposed to moderate (45 mM NaCl) and severe (90 mM NaCl) salinity. Both salt stress conditions caused a considerable reduction in leaf relative water content and the contents of photosynthetic pigments (carotenoids, chlorophylls a and b, and total chlorophylls), K⁺ and Ca⁺² , while the contents of Na⁺ and the activities of antioxidant enzymes increased. In addition, salt-stressed olive seedlings showed high accumulations of hydrogen peroxide (H₂ O₂ ), malondialdehyde (MDA), and electrolyte leakage (EL), indicating that olive seedlings suffered from salinity-induced oxidative damage. In contrast, MEL application revived the growth of olive seedlings, including shoot height, root length and biomass under salt stress conditions. MEL protected the photosynthetic pigments and decreased the Na⁺ /K⁺ ratio under both moderate and severe salt stresses. Furthermore, MEL induced the accumulations of proline, total soluble sugars, glycine betaine, abscisic acid, and indole acetic acid in salt-stressed olive seedlings, which showed a positive correlation with improved leaf water status and biomass. MEL application also increased the activities of catalase, superoxide dismutase, ascorbate peroxidase, and peroxidase in salt-stressed seedlings, resulting in lower levels of H₂ O₂ , MDA, and EL in these plants. Taken together, MEL mitigates salinity through its roles in various biochemical and physiological processes, thereby representing a promising agent for application in crop protection.

Genomic Basis of Transcriptome Dynamics in Rice under Field Conditions

How genetic variations affect gene expression dynamics of field-grown plants remains unclear. Expression quantitative trait loci (eQTL) analysis is frequently used to find genomic regions underlying gene expression polymorphisms. This approach requires transcriptome data for the complete set of the QTL mapping population under the given conditions. Therefore, only a limited range of environmental conditions is covered by a conventional eQTL analysis. We sampled sparse time series of field-grown rice from chromosome segment substitution lines (CSSLs) and conducted RNA sequencing (RNA-Seq). Then, by using statistical analysis integrating meteorological data and the RNA-Seq data, we identified 1,675 eQTLs leading to polymorphisms in expression dynamics under field conditions. A genomic region on chromosome 11 influences the expression of several defense-related genes in a time-of-day- and scaled-age-dependent manner. This includes the eQTLs that possibly influence the time-of-day- and scaled-age-dependent differences in the innate immunity between Koshihikari and Takanari. Based on the eQTL and meteorological data, we successfully predicted gene expression under environments different from training environments and in rice cultivars with more complex genotypes than the CSSLs. Our novel approach of eQTL identification facilitated the understanding of the genetic architecture of expression dynamics under field conditions, which is difficult to assess by conventional eQTL studies. The prediction of expression based on eQTLs and environmental information could contribute to the understanding of plant traits under diverse field conditions.

Genotype- and tissue-specific physiological and biochemical changes of two chickpea (Cicer arietinum) varieties following a rapid dehydration

In nature, plants may suffer rapid dehydration (RD), which causes significant loss of the annual global chickpea production. Thus, ascertaining more knowledge concerning the RD-tolerance mechanisms in chickpea is crucial for developing high drought-tolerant varieties to assure sustainable chickpea production under sudden water deficit. Here, we focused on genotype-driven variation in leaf relative water content (RWC) and associated differences in RD-responsive physiological and biochemical attributes in roots and leaves of two chickpea varieties, FLIP00-21C and FLIP02-89C, subjected to well-watered and RD conditions. FLIP00-21C showed higher RD-tolerance than FLIP02-89C, evident by its higher leaf RWC during RD. Consistently, FLIP00-21C exhibited lower membrane injury due to lower hydrogen peroxide (H₂ O₂ ) accumulation than FLIP02-89C during RD, indicating reduced RD-induced oxidative damage. Under RD conditions, total phenolics in roots and flavonoids in roots and leaves increased more in FLIP02-89C compared to FLIP00-21C; however, the increased activities of superoxide dismutase and H₂ O₂ -scavenging enzymes were more properly coordinated in FLIP00-21C than in FLIP02-89C, which might contribute to more efficient antioxidant defense in FLIP00-21C than in FLIP02-89C. The higher leaf RWC of FLIP00-21C versus FLIP02-89C under RD might be associated with greater increases in the levels of the osmo-regulators proline and total free amino acids (TFAAs) in FLIP00-21C than in FLIP02-89C. Collectively, the higher RD-tolerance of FLIP00-21C is mainly associated with the maintenance of higher RWC, stronger antioxidant defense, and greater accumulation of proline and TFAAs. These traits could be useful for evaluating the drought-tolerance of chickpea varieties and further marker-assisted breeding approaches for improvement of chickpea productivity.

The Heat is On: How Crop Growth, Development and Yield Respond to High Temperature

Plants are exposed to a wide range of temperatures during their life cycle and need to continuously adapt. These adaptations need to deal with temperature changes on a daily and seasonal level and with temperatures affected by climate change. Increasing global temperatures negatively impact crop performance, and several physiological, biochemical, morphological and developmental responses to increased temperature have been described that allow plants to mitigate this. In this review, we assess various growth, development, and yield-related responses of crops to extreme and moderate high temperature, focusing on knowledge gained from both monocot (e.g. wheat, barley, maize, rice) and dicot crops (e.g. soybean and tomato) and incorporating information from model plants (e.g. Arabidopsis and Brachypodium). This revealed common and different responses between dicot and monocot crops, and defined different temperature thresholds depending on the species, growth stage and organ.

A comparative UHPLC-Q/TOF-MS-based eco-metabolomics approach reveals temperature adaptation of four Nepenthes species

Nepenthes, as the largest family of carnivorous plants, is found with an extensive geographical distribution throughout the Malay Archipelago, specifically in Borneo, Philippines, and Sumatra. Highland species are able to tolerate cold stress and lowland species heat stress. Our current understanding on the adaptation or survival mechanisms acquired by the different Nepenthes species to their climatic conditions at the phytochemical level is, however, limited. In this study, we applied an eco-metabolomics approach to identify temperature stressed individual metabolic fingerprints of four Nepenthes species: the lowlanders N. ampullaria, N. rafflesiana and N. northiana, and the highlander N. minima. We hypothesized that distinct metabolite regulation patterns exist between the Nepenthes species due to their adaptation towards different geographical and altitudinal distribution. Our results revealed not only distinct temperature stress induced metabolite fingerprints for each Nepenthes species, but also shared metabolic response and adaptation strategies. The interspecific responses and adaptation of N. rafflesiana and N. northiana likely reflected their natural habitat niches. Moreover, our study also indicates the potential of lowlanders, especially N. ampullaria and N. rafflesiana, to produce metabolites needed to deal with increased temperatures, offering hope for the plant genus and future adaption in times of changing climate.