Scientific trends and discoveries on heat tolerance in pepper plants (Capsicum spp.): a bibliometric analysis.

Silicon-mediated heat tolerance in higher plants: A mechanistic outlook

The transcriptional and post-transcriptional regulation in perennial creeping bentgrass in response to γ-aminobutyric acid (GABA) and heat stress

Calcium signaling has been postulated to be critical for both heat and chilling tolerance in plants, but its molecular mechanisms are not fully understood. Here, we investigated the function of two closely related cyclic nucleotide-gated ion channel (CNGC) proteins, OsCNGC14 and OsCNGC16, in temperature-stress tolerance in rice (Oryza sativa) by examining their loss-of-function mutants generated by genome editing. Under both heat and chilling stress, both the cngc14 and cngc16 mutants displayed reduced survival rates, higher accumulation levels of hydrogen peroxide, and increased cell death. In the cngc16 mutant, the extent to which some genes were induced and repressed in response to heat stress was altered and some Heat Shock factor (HSF) and Heat Shock Protein (HSP) genes were slightly more induced compared to the wild type. Furthermore, the loss of either OsCNGC14 or OsCNGC16 reduced or abolished cytosolic calcium signals induced by either heat or chilling stress. Therefore, OsCNGC14 and OsCNGC16 are required for heat and chilling tolerance and are modulators of calcium signals in response to temperature stress. In addition, loss of their homologs AtCNGC2 and AtCNGC4 in Arabidopsis (Arabidopsis thaliana) also led to compromised tolerance of low temperature. Thus, this study indicates a critical role of CNGC genes in both chilling and heat tolerance in plants, suggesting a potential overlap in calcium signaling in response to high- and low-temperature stress.

EF-Tu proteins of plastids, mitochondria, and the cytosolic counterpart EF-1αin plants, as well as EF-Tu proteins of bacteria, are highly conserved and multifunctional. The functions of EF-Tu include transporting the aminoacyl-tRNA complex to the A site of the ribosome during protein biosynthesis; chaperone activity in protecting other proteins from aggregation caused by environmental stresses, facilitating renaturation of proteins when conditions return to normal; displaying a protein disulfide isomerase activity; participating in the degradation of N-terminally blocked proteins by the proteasome; eliciting innate immunity and triggering resistance to pathogenic bacteria in plants; participating in transcription when anE. colihost is infected with phages. EF-Tu genes are upregulated by abiotic stresses in plants, and EF-Tu plays important role in stress responses. Expression of a plant EF-Tu gene confers heat tolerance inE. coli, maize knock-out EF-Tu null mutants are heat susceptible, and over-expression of an EF-Tu gene improves heat tolerance in crop plants. This review paper summarizes the current knowledge of EF-Tu proteins in stress responses in plants and progress on application of EF-Tu for developing crop varieties tolerant to abiotic stresses, such as high temperatures.

SUMMARYTwo methods were developed for the rapid estimation of heat tolerance in plants using excised tissue pieces. The first method was a modification of the conductivity-bridge method and could yield results in less than 3 h. The second method combined plasmolysis with vital staining for the estimation of tissue injury following a regulated heat stress. This method was first developed and perfected using onion bulb epidermis tissue. It was later adapted for estimation of heat tolerance in intact tomato plants. Results from this method could be obtained within 1 h. The advantages and limitations of the two methods are compared and discussed.

Global warming is a serious challenge plant production has to face. Heat stress not only affects plant growth and development but also reduces crop yield and quality. Studying the response mechanisms of plants to heat stress will help humans use these mechanisms to improve the heat tolerance of plants, thereby reducing the harm of global warming to plant production. Research on plant heat tolerance has gradually become a hotspot in plant molecular biology research in recent years. In view of the special role of chloroplasts in the response to heat stress in plants, this review is focusing on three perspectives related to chloroplasts and their function in the response of heat stress in plants: the role of chloroplasts in sensing high temperatures, the transmission of heat signals, and the improvement of heat tolerance in plants. We also present our views on the future direction of research on chloroplast related heat tolerance in plants.

Heat shock factors (HSFs) are pivotal in regulating plant heat tolerance; however, the mechanisms HSFs employ in regulating transcription to maintain a balance of plant growth and heat tolerance are poorly understood. This study reports that two maize HSF12 knockout lines are more sensitive to heat stress. ZmHSF12 encodes two alternative spliced transcripts: ZmHSF12-1 and ZmHSF12-2; overexpression of ZmHSF12-2 enhances, whereas overexpression of ZmHSF12-1 decreases plant heat tolerance, indicating the distinct functions of these two transcripts in plant heat stress response. In addition, ZmHSF12-2 upregulates RAFFINOSE SYNTHASE (ZmRAFS) and CYTOKININ OXIDASE (ZmCKO2) gene expression, controlling raffinose and cytokinin concentration in the cell, enhancing plant heat tolerance and inhibiting plant growth. ZmHSF12-1 interacts with ZmHSF12-2 and represses the transcriptional regulation of ZmHSF12-2 on ZmCKO2 and ZmRAFS. Co-overexpression of ZmHSF12-1 and ZmHSF12-2 in Arabidopsis not only improved the heat tolerance of plants but also compensated for the growth defect phenotype of ZmHSF12-2 overexpressing Arabidopsis plants. These findings deepen our understanding of plant heat tolerance and significantly impact the scientific community. They support the potential application of co-overexpressing ZmHSF12-1 and ZmHSF12-2 to improve crop heat tolerance without causing growth retardation and yield compensation, thereby offering a promising avenue for crop improvement.

As a consequence of global warming, increasing temperature is a serious threat to crop production worldwide. Studies on plant stress tolerance and signaling are of important significance in both basic research and grain production. In recent years, major advances have been made in better understanding of heat stress signaling in higher plants, including several aspects such as sensory mechanisms of heat stress, regulatory networks involved in heat-responsive activation of <italic>Hsf</italic> and <italic>HSP</italic> genes, functional characterization of HSBP in establishment of heat tolerance in plants. As a harmful effect on cellular homeostasis, heat stress destabilizes membrane systems and structures of RNA and proteins, and leads to a dramatic alteration in enzymatic activities and cytoskeleton systems. Transcriptome analysis revealed that about 2% genes in the whole genome were activated in response to heat stress. Heat stress response represents the first line of inducible defense against imbalances in cellular homeostasis. Heat tolerance in plants is classified into basal thermotolerance and acquired thermotolerance. The acquired thermotolerance reflects the physiological adaptation of plants to heat stress when grown in the field.

High temperatures can harm the growth and development of plants. Autophagy, as a conserved degradation system in eukaryotic cells, is essential for plant response to stress. However, the role of CaATG6 under heat stress is unclear. In this research, we discovered that CaATG6 contains a conserved APG6 domain, and CaATG6 had a closer phylogenetic relationship to other Solanaceae homologues. Silencing of CaATG6 reduced pepper heat tolerance, while overexpression of CaATG6 in Arabidopsis enhanced the heat tolerance. CaATG6 can improve heat tolerance in plants by upregulating the expression of CaHsfA2 , CaHSP16.4 , CaHSP25.9 and CaHSP70.1 , as well as enhancing autophagy levels. Moreover, we discovered that CaATG6 interacts with CaSKIP34 , an F‐box protein of the E3 ubiquitin ligase SCF complex. Interestingly, both silencing and overexpression of CaSKIP34 reduced heat tolerance in plants. We also observed that the protein level of CaSKIP34 decreased after heat stress treatment, but this reduction was inhibited by autophagy and proteasome inhibitors. Therefore, we hypothesise that CaATG6 may regulate plant heat tolerance by modulating CaSKIP34 stability. This study offers fresh perspectives on the role of the autophagy core gene CaATG6 in thermotolerance in pepper.

Heat tolerance of plants related to cell membrane thermostability is commonly estimated via the measurement of ion leakage from plant segments after defined heat treatment. To compare heat tolerance of various plants, it is crucial to select suitable heating conditions. This selection is time-consuming and optimizing the conditions for all investigated plants may even be impossible. Another problem of the method is its tendency to overestimate basal heat tolerance. Here we present an improved ion leakage method, which does not suffer from these drawbacks. It is based on gradual heating of plant segments in a water bath or algal suspensions from room temperature up to 70-75°C. The electrical conductivity of the bath/suspension, which is measured continuously during heating, abruptly increases at a certain temperature TCOND (within 55-70°C). The TCOND value can be taken as a measure of cell membrane thermostability, representing the heat tolerance of plants/organisms. Higher TCOND corresponds to higher heat tolerance (basal or acquired) connected to higher thermostability of the cell membrane, as evidenced by the common ion leakage method. The new method also enables determination of the thermostability of photochemical reactions in photosynthetic samples via the simultaneous measurement of Chl fluorescence.

Abscisic acid (ABA) may play roles in mediating cross stress tolerance in plants. The objectives of this study were to investigate the priming effects of drought and ABA on heat tolerance and to determine how ABA may be involved in enhanced heat tolerance by drought. Focusing on the transcriptional level, two independent experiments were conducted, using a perennial grass species, tall fescue (Festuca arundinacea) and Arabidopsis. In experiment 1, tall fescue plants were exposed to mild drought by withholding irrigation for 8 days (drought priming) and foliar sprayed with ABA or an ABA-synthesis inhibitor (fluridone). After that they were subsequently subjected to heat stress (38/33°C day/night) for 25 days in growth chambers. In experiment 2, Arabidopsis Columbia ecotype (wild-type) and ABA-deficient mutant (aba3-1, CS157) were pre-treated with drought priming and then exposed to heat stress (45/40°C) for 3 days. The physiological analysis demonstrated that both drought priming and foliar application of ABA-enhanced heat tolerance in tall fescue, while drought priming had no significant effects on heat tolerance in ABA-deficient Arabidopsis plants. Application of fluridone to tall fescue and ABA-deficient mutants of Arabidopsis exhibited diminished or attenuated positive effects of drought priming on heat tolerance. ABA mediation of acquired heat tolerance by drought priming was associated with the upregulation of CDPK3, MPK3, DREB2A, AREB3, MYB2, MYC4, HsfA2, HSP18, and HSP70. Our study revealed the roles of ABA in drought priming-enhanced heat tolerance, which may involve transcriptional regulation for stress signaling, ABA responses and heat protection.

Although high temperature stress is a major cause of yield loss in several cereal crop plants, especially in the arid and semi-arid areas of the world, we have a limited understanding of the genetic and physiological basis of heat tolerance in these plants. Genetic variability in heat tolerance has been reported within various crop species (Blum 1985 for review), but the genes regulating heat tolerance and the nature of specific gene products responsible for observed genetic differences are yet to be identified. As a consequence, plant breeders currently lack a specific biochemical or genetic marker for direct selection and gene manipulation to improve heat tolerance in plants.

Improving drought-, salinity-, and heat-tolerance in transgenic plants by co-overexpressing Arabidopsis vacuolar pyrophosphatase gene AVP1 and Larrea Rubisco activase gene RCA

Frequent co-occurrences of high temperature and drought in tropical regions make heat and drought tolerance of landscape plants core physiological traits that determine their landscape adaptability and community stability. However, systematic elucidation of the differentiation patterns of stress resistance between specialist and generalist tropical landscape plant species, the intrinsic correlations between heat and drought tolerance traits, and the regulatory mechanisms of leaf functional traits remains lacking. In this study, eight typical tropical landscape plant species in Xishuangbanna Tropical Botanical Garden were selected as research objects. By determining leaf chlorophyll fluorescence parameters, water relation parameters and leaf functional traits, we systematically analyzed the differences in heat and drought tolerance and interspecific differentiation characteristics between specialist and generalist species, and simultaneously elucidated the correlation patterns of drought-heat tolerance traits as well as the regulatory effects of leaf functional traits on these traits. The results showed that the turgor loss point water potential (ΨTLP) of generalist tropical landscape plant species was significantly higher than that of specialist species, with superior drought tolerance; in contrast, the half-lethal temperature of photosystem II (T50) of specialist species was significantly higher than that of generalist species, with stronger heat tolerance. Among the eight tested species, Bombax ceiba exhibited the strongest drought tolerance, while Baccaurea ramiflora had the optimal heat tolerance. The study also found that the drought and heat tolerance traits of tropical landscape plants exhibited stress-specific trade-offs; leaf functional traits had limited overall explanatory power for the stress resistance of tropical landscape plants and only exerted a certain regulatory effect on drought tolerance. This study clearly reveals the differences in heat and drought tolerance between specialist and generalist species. This finding not only enhances our mechanistic understanding of stress resistance in tropical plants but also provides data support for ecological restoration and conservation practices in tropical gardens.

Hydrogen sulfide (H2S) which is involved in plant growth, development, and the acquisition of stress tolerance including heat tolerance, is considered as the third signal molecule after nitric oxide and reactive oxygen species, while betaine is an important osmolyte with multiple physiological functions, but interaction between H2S and betaine in the acquisition of heat tolerance in plants is not clear. In this study, pretreatment with H2S donor sodium hydrosulfide (NaHS), as comparison to the control seedlings without NaHS treatment, significantly improved the activity of betaine aldehyde dehydrogenase (BADH), a key enzyme in the biosynthesis of betaine, which in turn induced the accumulation of endogenous betaine, eventually enhanced the survival percentage of maize seedlings under heat stress. In contrast, these effects induced by NaHS were eliminated by application of H2S scavenger hypotaurine and inhibitor of BADH disulfiram, respectively, indicating that H2S-improved heat tolerance of maize seedlings may be closely associated with the accumulation of endogenous betaine by activating the activity of BADH. In addition, exogenous betaine treatment enhanced the content of endogenous betaine, followed by improved the survival percentage of maize seedlings compared with the control without betaine treatment. All of the above-mentioned results showed that NaHS pretreatment could induce the accumulation of endogenous betaine by increasing BADH activity, and this accumulation may be involved in the acquisition of heat tolerance of maize seedlings, bridging a gap between H2S and betaine in the acquisition of heat tolerance in plants.