Transient Heat Stress Research Articles

LlbHLH87 interacts with LlSPT to modulate thermotolerance via activation of LlHSFA2 and LlEIN3 in lily.

Basic helix-loop-helix (bHLH) proteins comprise one of the largest families of transcription factors in plants, which play roles in plant development, secondary metabolism, and the response to biotic/abiotic stresses. However, the roles of bHLH proteins in thermotolerance are largely unknown. Herein, we identified a heat-inducible member of the bHLH family in lily (Lilium longiflorum), named LlbHLH87, which plays a role in thermotolerance. LlbHLH87 was rapidly induced by transient heat stress, and its encoded protein was localized to the nucleus, exhibiting transactivation activity in both yeast and plant cells. Overexpression of LlbHLH87 in Arabidopsis enhanced basal thermotolerance, while silencing of LlbHLH87 in lily reduced basal thermotolerance. Further analysis showed that LlbHLH87 bound to the promoters of HEAT STRESS TRANSCRIPTION FACTOR A2 (LlHSFA2) and ETHYLENE-INSENSITIVE 3 (LlEIN3) to directly activate their expression. In addition, LlbHLH87 interacted with itself and with SPATULA (LlSPT) protein. LlSPT was activated by extended heat stress and its protein competed for the homologous interaction of LlbHLH87, which reduced the transactivation ability of LlbHLH87 for target genes. Compared with that observed under LlbHLH87 overexpression alone, co-overexpression of LlbHLH87 and LlSPT reduced the basal thermotolerance of lily to sudden heat shock, but improved its thermosensitivity to prolonged heat stress treatment. Overall, our data demonstrated that LlbHLH87 regulates thermotolerance via activation of LlEIN3 and LlHSFA2, along with an antagonistic interaction with LlSPT.

Transient heat stress during gametophyte development in Brassica napus reduces subsequent floret fecundity

Oilseed rape (Brassica napus L.), also known as canola, is particularly sensitive to high temperatures during flowering. However, the impacts of heat stress during male and female gametophyte development, several days before anthesis and fertilisation, remain unclear. In this study we selected two cultivars, AV-Ruby and YM11, which exhibited different responses to heat stress in a previous study. Precise transient heat stress (maximum 32 ℃ day /22 ℃ night) or control (maximum 25 ℃ day /15 ℃ night) treatments were applied to evaluate the impact of heat stress during male and female gametophyte development on subsequent floret fecundity after pollination. We measured floret fecundity by pod set, number of seeds per pod and average seed size. Heat stress during male gametophyte development reduced pollen viability and germination rate, and resulted in fewer pods and seeds per pod on the main stem. However, despite these negative impacts, pollen tubes successfully traversed the style and were visible at a high percentage of ovules in both heat stress and control treatments. When heat stress was applied to the female gametophyte in the first five buds on the main stem, subsequent floret fecundity was reduced in the lower main stem, while florets in the upper main stem exhibited higher fecundity than in the control treatment. Heat stress during sporogenesis and/or gametogenesis in male and female organs across two cultivars had a lasting negative impact on subsequent floret fecundity, observed as a reduction in the number of pods and seeds per pod, but had no impact on average seed size.

Transient heat stress protects from severe endothelial damage and dysfunction during prolonged experimental ex-vivo lung perfusion.

The pulmonary endothelium is the primary target of lung ischemia-reperfusion injury leading to primary graft dysfunction after lung transplantation. We hypothesized that treating damaged rat lungs by a transient heat stress during ex-vivo lung perfusion (EVLP) to elicit a pulmonary heat shock response could protect the endothelium from severe reperfusion injury. Rat lungs damaged by 1h warm ischemia were reperfused on an EVLP platform for up to 6h at a constant temperature (T°) of 37°C (EVLP37°C group), or following a transient heat stress (HS) at 41.5°C from 1 to 1.5h of EVLP (EVLPHS group). A group of lungs exposed to 1h EVLP only (pre-heating conditions) was added as control (Baseline group). In a first protocol, we measured lung heat sock protein expression (HSP70, HSP27 and Hsc70) at selected time-points (n=5/group at each time). In a second protocol, we determined (n=5/group) lung weight gain (edema), pulmonary compliance, oxygenation capacity, pulmonary artery pressure (PAP) and vascular resistance (PVR), the expression of PECAM-1 (CD31) and phosphorylation status of Src-kinase and VE-cadherin in lung tissue, as well as the release in perfusate of cytokines (TNFα, IL-1β) and endothelial biomarkers (sPECAM, von Willebrand Factor -vWF-, sE-selectin and sICAM-1). Histological and immunofluorescent studies assessed perivascular edema and formation of 3-nitrotyrosine (a marker of peroxinitrite) in CD31 lung endothelium. HS induced an early (3h) and persisting expression of HSP70 and HSP27, without influencing Hsc70. Lungs from the EVLP37°C group developed massive edema, low compliance and oxygenation, elevated PAP and PVR, substantial release of TNFα, IL-1β, s-PECAM, vWF, E-selectin and s-ICAM, as well as significant Src-kinase activation, VE-cadherin phosphorylation, endothelial 3-NT formation and reduced CD31 expression. In marked contrast, all these alterations were either abrogated or significantly attenuated by HS treatment. The therapeutic application of a transient heat stress during EVLP of damaged rat lungs reduces endothelial permeability, attenuates pulmonary vasoconstriction, prevents src-kinase activation and VE-cadherin phosphorylation, while reducing endothelial peroxinitrite generation and the release of cytokines and endothelial biomarkers. Collectively, these data demonstrate that therapeutic heat stress may represent a promising strategy to protect the lung endothelium from severe reperfusion injury.

(672) - Transient Heat Stress Protects from Endothelial Injury During Prolonged Ex-Vivo Perfusion of Warm Ischemic Rat Lungs

(672) - Transient Heat Stress Protects from Endothelial Injury During Prolonged Ex-Vivo Perfusion of Warm Ischemic Rat Lungs

Decreased Photosynthetic Efficiency in Nicotiana tabacum L. under Transient Heat Stress

Heat stress is an abiotic factor that affects the photosynthetic parameters of plants. In this study, we examined the photosynthetic mechanisms underlying the rapid response of tobacco plants to heat stress in a controlled environment. To evaluate transient heat stress conditions, changes in photochemical, carboxylative, and fluorescence efficiencies were measured using an infrared gas analyser (IRGA Licor 6800) coupled with chlorophyll a fluorescence measurements. Our findings indicated that significant disruptions in the photosynthetic machinery occurred at 45 °C for 6 h following transient heat treatment, as explained by 76.2% in the principal component analysis. The photosynthetic mechanism analysis revealed that the dark respiration rate (Rd and Rd*CO2) increased, indicating a reduced potential for carbon fixation during plant growth and development. When the light compensation point (LCP) increased as the light saturation point (LSP) decreased, this indicated potential damage to the photosystem membrane of the thylakoids. Other photosynthetic parameters, such as AMAX, VCMAX, JMAX, and ΦCO2, also decreased, compromising both photochemical and carboxylative efficiencies in the Calvin–Benson cycle. The energy dissipation mechanism, as indicated by the NPQ, qN, and thermal values, suggested that a photoprotective strategy may have been employed. However, the observed transitory damage was a result of disruption of the electron transport rate (ETR) between the PSII and PSI photosystems, which was initially caused by high temperatures. Our study highlights the impact of rapid temperature changes on plant physiology and the potential acclimatisation mechanisms under rapid heat stress. Future research should focus on exploring the adaptive mechanisms involved in distinguishing mutants to improve crop resilience against environmental stressors.

Early-life stress triggers long-lasting organismal resilience and longevity via tetraspanin.

Early-life stress experiences can produce lasting impacts on organismal adaptation and fitness. How transient stress elicits memory-like physiological effects is largely unknown. Here, we show that early-life thermal stress strongly up-regulates tsp-1, a gene encoding the conserved transmembrane tetraspanin in C. elegans. TSP-1 forms prominent multimers and stable web-like structures critical for membrane barrier functions in adults and during aging. Increased TSP-1 abundance persists even after transient early-life heat stress. Such regulation requires CBP-1, a histone acetyltransferase that facilitates initial tsp-1 transcription. Tetraspanin webs form regular membrane structures and mediate resilience-promoting effects of early-life thermal stress. Gain-of-function TSP-1 confers marked C. elegans longevity extension and thermal resilience in human cells. Together, our results reveal a cellular mechanism by which early-life thermal stress produces long-lasting memory-like impact on organismal resilience and longevity.

Phenotypic and transcriptomic responses of diverse rice accessions to transient heat stress during early grain development.

Heat stress (HS) occurring during the grain-filling period has a detrimental effect on grain yield and quality in rice (Oryza sativa). The development of heat-resilient cultivars could partly solve this issue if tolerant alleles can be identified and incorporated into the germplasm. In this study, we posit that some of the phenotypic variations for heat resilience during grain development could be due to variations in gene expression among accessions. To test this, we characterized the HS response of 10 diverse rice accessions from three major sub-populations using physiological and transcriptome analyses. At a single-grain level, grain width and grain thickness emerged as the most heat-sensitive traits. During a transient HS, IND-3 was categorized as highly sensitive, while five accessions exhibited moderate heat sensitivity, and four accessions were tolerant. Only a core set of 29.4% of the differentially expressed genes was common to the three rice sub-populations. Heat-tolerant accession TEJ-5 uniquely triggered an unfolded protein response (UPR) under HS, as evident from the induction of OsbZIP50 and downstream UPR genes. OsbZIP58, a gene that positively regulates grain filling, was more highly induced by HS in IND-2 despite its moderate heat sensitivity. Collectively, our analysis suggests that both unique gene expression responses and variation in the level of responses for a given pathway distinguish diverse accessions. Only some of these responses are associated with single-grain phenotypes in a manner consistent with the known roles of these genes and pathways.

Filtration and respiration responses of mussels (Mytilus edulis) to trematode parasite infections (Renicola roscovita) and transient heat exposure.

The mussel Mytilus edulis, a host to various trematode species, experiences performance decrements due to these infections. Yet, the impact magnitude and potential interactions with environmental stressors remain largely unexplored. This study scrutinizes the effect of Renicola roscovita infections on mussel filtration and respiration. We first assessed performance in both uninfected and lab-infected mussels at a mild temperature (16°C), following an acute heat ramp to 30.5°C and subsequent cooling. The experiment revealed neither a significant direct impact of the infection on the mussels' performance, nor any significant interplay between the infection and temperature variations. To account for possible infection effects obscured by low sample sizes or mussel size disparities, we conducted a reassessment at 16°C using both small and large mussels. Infection notably hampered filtration in large mussels, with a marginal impact on smaller ones. A positive correlation was found between infection intensity and mussel filtration capacity, though the infection had no discernible impact on respiration. Our consistent finding of an 11-12 % infection effect size across all experiments indicates a slight reduction in mussel filtration due to trematode infections. While the exacerbating effect of transient heat stress on the infection's impact on filtration was not statistically significant, future investigations should explore potential interactions with prolonged heat stress. Our findings underscore the nuanced ways in which parasitic infections can influence marine bivalve physiology, emphasizing the need for more comprehensive studies that incorporate environmental stressors, such as heat stress, to fully elucidate the impact of parasitism on marine ecosystem health and resilience.

Reprogramming of the transcriptome after heat stress mediates heat hormesis in Caenorhabditis elegans

Transient stress experiences not only trigger acute stress responses, but can also have long-lasting effects on cellular functions. In Caenorhabditis elegans, a brief exposure to heat shock during early adulthood extends lifespan and improves stress resistance, a phenomenon known as heat hormesis. Here, we investigated the prolonged effect of hormetic heat stress on the transcriptome of worms and found that the canonical heat shock response is followed by a profound transcriptional reprogramming in the post-stress period. This reprogramming relies on the endoribonuclease ENDU-2 but not the heat shock factor 1. ENDU-2 co-localizes with chromatin and interacts with RNA polymerase II, enabling specific regulation of transcription after the stress period. Failure to activate the post-stress response does not affect the resistance of animals to heat shock but eliminates the beneficial effects of hormetic heat stress. In summary, our work discovers that the RNA-binding protein ENDU-2 mediates the long-term impacts of transient heat stress via reprogramming transcriptome after stress exposure.

Therapeutic reconditioning of damaged lungs by transient heat stress during ex vivo lung perfusion

Ex vivo lung perfusion (EVLP) may serve as a platform for the pharmacologic repair of lung grafts before transplantation (LTx). We hypothesized that EVLP could also permit nonpharmacologic repair through the induction of a heat shock response, which confers stress adaptation via the expression of heat shock proteins (HSPs). Therefore, we evaluated whether transient heat application during EVLP (thermal preconditioning [TP]) might recondition damaged lungs before LTx. TP was performed during EVLP (3 hours) of rat lungs damaged by warm ischemia by transiently heating (30 minutes, 41.5 °C) the EVLP perfusate, followed by LTx (2 hours) reperfusion. We also assessed the TP (30 minutes, 42 °C) during EVLP (4 hours) of swine lungs damaged by prolonged cold ischemia. In rat lungs, TP induced HSP expression, reduced nuclear factor κB and inflammasome activity, oxidative stress, epithelial injury, inflammatory cytokines, necroptotic death signaling, and the expression of genes involved in innate immune and cell death pathways. After LTx, heated lungs displayed reduced inflammation, edema, histologic damage, improved compliance, and unchanged oxygenation. In pig lungs, TP induced HSP expression, reduced oxidative stress, inflammation, epithelial damage, vascular resistance, and ameliorated compliance. Collectively, these data indicate that transient heat application during EVLP promotes significant reconditioning of damaged lungs and improves their outcomes after transplantation.

Metabolomic signatures of corals thriving across extreme reef habitats reveal strategies of heat stress tolerance.

Anthropogenic stressors continue to escalate worldwide, driving unprecedented declines in reef environmental conditions and coral health. One approach to better understand how corals can function in the future is to examine coral populations that thrive within present day naturally extreme habitats. We applied untargeted metabolomics (gas chromatography-mass spectrometry (GC-MS)) to contrast metabolite profiles of Pocillopora acuta colonies from hot, acidic and deoxygenated mangrove environments versus those from adjacent reefs. Under ambient temperatures, P. acuta predominantly associated with endosymbionts of the genera Cladocopium (reef) or Durusdinium (mangrove), exhibiting elevated metabolism in mangrove through energy-generating and biosynthesis pathways compared to reef populations. Under transient heat stress, P. acuta endosymbiont associations were unchanged. Reef corals bleached and exhibited extensive shifts in symbiont metabolic profiles (whereas host metabolite profiles were unchanged). By contrast, mangrove populations did not bleach and solely the host metabolite profiles were altered, including cellular responses in inter-partner signalling, antioxidant capacity and energy storage. Thus mangrove P. acuta populations resist periodically high-temperature exposure via association with thermally tolerant endosymbionts coupled with host metabolic plasticity. Our findings highlight specific metabolites that may be biomarkers of heat tolerance, providing novel insight into adaptive coral resilience to elevated temperatures.

Heat Stress during Meiosis Has Lasting Impacts on Plant Growth and Reproduction in Wheat (Triticum aestivum L.)

Meiosis is the least explored stage for thermotolerance in wheat. We evaluated the impact of 5 d of moderate transient daily heat stress during meiosis in the main stem spike on physiological and grain yield traits in 30 diverse wheat cultivars which vary widely in heat tolerance and sensitivity. We found that a moderate heat stress event during meiosis in the main stem spike had lasting impacts on plant growth and reproduction in heat-sensitive, but not heat-tolerant, wheat cultivars. Heat-tolerant cultivars maintained grain yield, grain number and individual grain weight in the main stem spike and also total plant grain yield and biomass in the heat stress treatment relative to the control. Heat-sensitive cultivars responded to heat stress by producing fewer and smaller grains per spikelet on the main stem, fewer tillers, lower biomass and lower total plant grain yield in the high temperature treatment relative to the control. Heat-sensitive cultivars produced higher flag leaf chlorophyll content in the high temperature treatment relative to the control than heat-tolerant cultivars during the first 3 d of heat treatment. There was small reduction in pollen viability from 98% to 96% following heat stress during meiosis which was unrelated to heat tolerance or sensitivity. Moderate transient heat stress during meiosis did not greatly reduce the production of viable male gametes, but had long-lasting negative impacts on fertilization and subsequent seed production in heat-sensitive cultivars.

Transient Heat Stress During Ex-Vivo Lung Perfusion Induces the Heat Shock Response and Preserves Lung Function in Pig Model

<h3>Purpose</h3> The heat shock response (HSR) is a highly conserved adaptative response to thermic stress, related to the induced expression of heat shock proteins (HSPs) which promote significant cytoprotection. We hypothesized that thermal preconditioning (TP) with a well-calibrated heat stress (HS) applied during EVLP elicits a HSR and improves lung graft function by interfering with immune inflammation and oxidative stress pathways. <h3>Methods</h3> Donor lungs (n=12) underwent extended hypothermic preservation of 16h. Lungs were assigned into two groups: 1) Control (n=6): 4h EVLP at 37°C; and 2) TP, (n=6): normothermic EVLP (37°C, 2h), followed by hyperthermic EVLP (42°, 30min), and normothermic EVLP (37°C, 1.5h). Ex-vivo lung function was assessed by measuring airway pressure, lung compliance and pulmonary vascular resistance. We determined expression of HSPs in tissue, and lung damage and oxidative stress biomarkers in tissue, BAL and perfusate at multiple time points. <h3>Results</h3> Lungs undergoing thermal preconditioning (TP group) showed significantly lower pulmonary arterial pressure and vascular resistance, increased dynamic and static pulmonary compliance and reduced airway pressure with no changes in oxygenation capacity as compared to lungs in the control group. At the end of EVLP, lungs in TP group had significant increase of lung mRNA of Hspa1a, Hsc70 and Hmox-1, reduction of nitrotyrosine (3-NT) in lung tissue, and reduction of LDH, CK18-M30 and proteins in BAL fluid. TP during ELVP decreased the expression of TNFα, IL6/IL10, MPO and IL-8 in BAL consistent with inflammasome inhibition. <h3>Conclusion</h3> Transient heat stress during EVLP induces HSR and reduces nitroxidative stress, cellular injury and edema, and prevents functional deterioration of pig lungs after extended cold ischemia. These data indicate the therapeutic potential of thermal preconditioning as a way to recondition damaged lungs and to improve current preservation strategies.

Predicting plant growth response under fluctuating temperature by carbon balance modelling

Quantification of system dynamics is a central aim of mathematical modelling in biology. Defining experimentally supported functional relationships between molecular entities by mathematical terms enables the application of computational routines to simulate and analyse the underlying molecular system. In many fields of natural sciences and engineering, trigonometric functions are applied to describe oscillatory processes. As biochemical oscillations occur in many aspects of biochemistry and biophysics, Fourier analysis of metabolic functions promises to quantify, describe and analyse metabolism and its reaction towards environmental fluctuations. Here, Fourier polynomials were developed from experimental time-series data and combined with block diagram simulation of plant metabolism to study heat shock response of photosynthetic CO2 assimilation and carbohydrate metabolism in Arabidopsis thaliana. Simulations predicted a stabilising effect of reduced sucrose biosynthesis capacity and increased capacity of starch biosynthesis on carbon assimilation under transient heat stress. Model predictions were experimentally validated by quantifying plant growth under such stress conditions. In conclusion, this suggests that Fourier polynomials represent a predictive mathematical approach to study dynamic plant-environment interactions.

Quantitative Trait Loci for Heat Stress Tolerance in Brassica rapa L. Are Distributed across the Genome and Occur in Diverse Genetic Groups, Flowering Phenologies and Morphotypes.

Heat stress events during flowering in Brassica crops reduce grain yield and are expected to increase in frequency due to global climate change. We evaluated heat stress tolerance and molecular genetic diversity in a global collection of Brassica rapa accessions, including leafy, rooty and oilseed morphotypes with spring, winter and semi-winter flowering phenology. Tolerance to transient daily heat stress during the early reproductive stage was assessed on 142 lines in a controlled environment. Well-watered plants of each genotype were exposed to the control (25/15 °C day/night temperatures) or heat stress (35/25 °C) treatments for 7 d from the first open flower on the main stem. Bud and leaf temperature depression, leaf conductance and chlorophyll content index were recorded during the temperature treatments. A large genetic variation for heat tolerance and sensitivity was found for above-ground biomass, whole plant seed yield and harvest index and seed yield of five pods on the main stem at maturity. Genetic diversity was assessed on 212 lines with 1602 polymorphic SNP markers with a known location in the B. rapa physical map. Phylogenetic analyses confirmed two major genetic populations: one from East and South Asia and one from Europe. Heat stress-tolerant lines were distributed across diverse geographic origins, morphotypes (leafy, rooty and oilseed) and flowering phenologies (spring, winter and semi-winter types). A genome-wide association analysis of heat stress-related yield traits revealed 57 SNPs distributed across all 10 B. rapa chromosomes, some of which were associated with potential candidate genes for heat stress tolerance.

Endoplasmic reticulum stress pathway mediates the early heat stress response of developing rice seeds.

A transient heat stress occurring during early seed development in rice (Oryza sativa) reduces seed size by altering endosperm development. However, the relationship between the timing of the stress and specific developmental stage on heat sensitivity is not well-understood. To address this, we imposed a series of non-overlapping heat stress treatments and found that young seeds are most sensitive during the first two days after flowering. Temporal transcriptome analysis of developing, heat stressed (35°C) seeds during this window shows that Inositol-requiring enzyme 1 (IRE1)-mediated endoplasmic reticulum (ER) stress response and jasmonic acid (JA) pathways are the early (1-3 h) drivers of heat stress response. We propose that increased JA levels under heat stress may precede ER stress response as JA application promotes the spliced form of OsbZIP50, an ER response marker gene linked to IRE1-specific pathway. This study presents temporal and mechanistic insights into the role of JA and ER stress signalling during early heat stress response of rice seeds that impact both grain size and quality. Modulating the heat sensitivity of the early sensing pathways and downstream endosperm development genes can enhance rice resilience to transient heat stress events.

Female reproductive organs of Brassica napus are more sensitive than male to transient heat stress

Oilseed rape (Brassica napus L.) is sensitive to heat stress during the reproductive stage, but it is not clear whether the male and female reproductive organs differ in their sensitivity to heat stress. In this study, full diallel crossing experiments were conducted among four genotypes of B. napus under control, moderate and high heat stress conditions for five days immediately before and two days after crossing. General combining ability (GCA), specific combining ability (SCA) and reciprocal effects were analyzed to evaluate the genetic basis of heat stress tolerance in male and female reproductive organs. High female temperature (Tf) and high male temperature (Tm) reduced the number of fertile pods and seeds set per floret, and the significant Tf × Tm interaction indicated that female reproductive organs were more sensitive to heat stress than male reproductive organs. There were no overall GCA, SCA or reciprocal effects across all combinations of Tf and Tm. However, a significant reciprocal × Tf effect was found, suggesting that genotypes differed in their ability to set fertile pods and seeds as Tf increased. The relative heat tolerance of G1 as a female increased as Tf increased, and the relative heat tolerance of G2 as a male decreased as Tf increased. In summary, reciprocal diallel crossing has demonstrated that female reproductive organs of B. napus are more sensitive than male to transient heat stress at the early flowering stage, and genotypes differ in relative heat tolerance in the male and female reproductive organs as Tf increases.

Gut Microbiota of Drosophila subobscura Contributes to Its Heat Tolerance and Is Sensitive to Transient Thermal Stress.

The gut microbiota can contribute to host physiology leading to an increase of resistance to abiotic stress conditions. For instance, temperature has profound effects on ectotherms, and the role of the gut microbiota on the thermal tolerance of ectotherms is a matter of recent research. However, most of these studies have been focused on single static temperatures instead of evaluating thermal tolerance in a wide range of stressful temperatures. Additionally, there is evidence supporting that the gut microbiota is sensitive to environmental temperature, which induces changes in its composition and diversity. These studies have evaluated the effects of thermal acclimation (>2 weeks) on the gut microbiota, but we know little about the impact of transient thermal stress on the composition and diversity of the gut microbiota. Thus, we investigated the role of the gut microbiota on the heat tolerance of Drosophila subobscura by measuring the heat tolerance of conventional and axenic flies exposed to different heat stressful temperatures (35, 36, 37, and 38°C) and estimating the heat tolerance landscape for both microbiota treatments. Conventional flies exposed to mild heat conditions exhibited higher thermal tolerance than axenic flies, whereas at higher stressful temperatures there were no differences between axenic and conventional flies. We also assessed the impact of transient heat stress on the taxonomical abundance, diversity, and community structure of the gut microbiota, comparing non-stressed flies (exposed to 21°C) and heat-stressed flies (exposed to 34°C) from both sexes. Bacterial diversity indices, bacterial abundances, and community structure changed between non-stressed and heat-stressed flies, and this response was sex-dependent. In general, our findings provide evidence that the gut microbiota influences heat tolerance and that heat stress modifies the gut microbiota at the taxonomical and structural levels. These results demonstrate that the gut microbiota contributes to heat tolerance and is also highly sensitive to transient heat stress, which could have important consequences on host fitness, population risk extinction, and the vulnerability of ectotherms to current and future climatic conditions.

Age‐specific sensitivity of sperm length and testes size to developmental temperature in the bruchid beetle

AbstractIn an era of global warming, the negative effects of temperature stress on fertility could intensify predicted losses of biodiversity. Male fertility is particularly sensitive to temperature stress, yet we have an incomplete understanding of when, during reproductive ontogeny, spermatogenesis is most affected. Here, we used a temperature‐switch protocol to identify when during development temperature affects the expression of sperm length and testes size in the bruchid beetle Callosobruchus maculatus. Egg‐to‐adult development took place at 17°C, 27°C or 33°C for either the full duration of pre‐imago development or it was switched at different stages during development. Full development at 17°C or 33°C resulted in significantly shorter sperm than at 27°C. However, when developing larvae were switched to higher or lower temperatures, we observed switch‐specific phenotypic expression of sperm length and testes size. Our key finding was that sperm length was sensitive to high‐temperature stress during the early stages of ontogeny and to low‐temperature stress during the latter stages of ontogeny. Such age‐specific developmental sensitivity suggests that infertility resulting from transient heat stress (i.e. heatwaves) could be mitigated by age‐related developmental heterogeneity within populations. Those individuals able to avoid severe effects of heat stress on fertility, through serendipitously being at less‐sensitive stages of development, could potentially compensate for the loss of fertility experienced by those individuals at more sensitive stages of development.

Ethylene involvement in the regulation of heat stress tolerance in plants.

Because of the rise in global temperature, heat stress has become a major concern for crop production. Heat stress deteriorates plant productivity and alters phenological and physiological responses that aid in precise monitoring and sensing of mild-to-severe transient heat stress. Plants have evolved several sophisticated mechanisms including hormone-signaling pathways to sense heat stimuli and acquire heat stress tolerance. In response to heat stress, ethylene, a gaseous hormone, is produced which is indispensable for plant growth and development and tolerance to various abiotic stresses including heat stress. The manipulation of ethylene in developing heat stress tolerance targeting ethylene biosynthesis and signaling pathways has brought promising out comes. Conversely increased ethylene biosynthesis and signaling seem to exhibit inhibitory effects in plant growth responses from primitive to maturity stages. This review mainly focuses on the recent studies of ethylene involvement in plant responses to heat stress and its functional regulation, and molecular mechanism underlying the plant responses in the mitigation of heat-induced damages. Furthermore, this review also describes the crosstalk between ethylene and other signaling molecules under heat stress and approaches to improve heat stress tolerance in plants.