Chemical Induction of Stress Proteins Does Not Induce Splicing Thermotolerance under Conditions Producing Survival Thermotolerance

Cell survival during a severe heat stress can be enhanced when heat shock proteins are induced prior to the severe heat treatment. Induction can be accomplished either by heat or chemical treatments. The increase in survival at these severe elevated temperatures after pretreatment has been referred to as thermotolerance, which we now refer to as survival thermotolerance. It has also been shown previously that mild heat treatment allows splicing in cells subjected to a severe heat treatment, now referred to as splicing thermotolerance. The experiments shown here demonstrate that even though chemical induction of the heat shock proteins leads to survival thermotolerance, this same treatment does not induce splicing thermotolerance. These are the first results that demonstrate at least two distinct aspects of thermotolerance.     

作物花粉高温应答机制研究进展

随着全球气候变暖加剧, 农作物面临更加严峻的高温威胁。高温胁迫影响作物生长发育各个阶段, 其中花粉发育过程对高温胁迫最为敏感, 因此花粉高温应答机制成为当前植物学研究热点。研究表明, 花粉可以通过质膜上的钙离子通道、内质网中的未折叠蛋白反应、活性氧积累以及H2A.Z等机制感知高温胁迫, 并通过调控热激蛋白表达、糖代谢、激素水平及活性氧清除能力适应高温胁迫。该文从高温对花粉发育的影响、花粉高温胁迫应答机制以及花粉高温胁迫研究的实验设计等方面进行综述, 旨在为相关研究提供借鉴。     

植物耐热性及热激信号转导机制研究进展

随着温室效应的加剧,全球气候变暖已经成为现代农业生产体系所面临的严峻挑战．高温灾害性气候是影响作物产量的一种主要的非生物胁迫．因此,对于农作物生产而言,研究植物耐热信号转导机制不仅有重要的科学意义,而且有现实的紧迫性．最近几年,在阐明植物耐热信号转导机制的研究方面取得了很多重要的进展,这些进展涵盖植物高温胁迫的感受机制、热激转录因子和热激蛋白的表达调控、热激转录因子结合蛋白参与耐热性调控的分子机制等几个主要的方面．热胁迫影响细胞膜系统、RNA、蛋白质的稳定性,同时改变酶的活性和细胞骨架系统．当热胁迫来临时,植物的转录组会发生显著变化,所涉及的基因大约占基因组的2％．这些高温胁迫响应基因构成了热激响应网络,是植物抵御热胁迫的第一道防线．植物的耐热性分为基础耐热性和获得性耐热性．基础耐热性是植物固有的耐热性．获得性耐热性是温和的热驯化诱导的耐热性．获得性耐热性状的形成反映了植物在自然生长环境下适应高温胁迫的生理机制．     

Heat‐stress Memory is Responsible for Acquired Thermotolerance in Bangia fuscopurpurea

The environmental stresses that sessile organisms experience usually fluctuate dramatically and are often recurrent. Terrestrial plants can acquire memory of exposure to sublethal heat stress to acquire thermotolerance and survive subsequent lethal high‐temperature stress; however, little is known concerning whether seaweeds acquire thermotolerance via heat‐stress memory. We have demonstrated that the red seaweed Bangia fuscopurpurea can indeed acquire memory of sublethal high‐temperature stress, resulting in the acquisition of thermotolerance that protects against subsequent lethal high‐temperature stress. Moreover, the maintenance of heat‐stress memory was associated with a slight increase in the saturation level of membrane fatty acids. This suggests that the modification of membrane fluidity via changes in membrane fatty acid composition is involved in the establishment and maintenance of heat‐stress memory in B. fuscopurpurea. These findings provide insights into the physiological survival and growth strategies of sessile red seaweeds to cope with recurrent changes in environmental conditions.     

Acquisition of thermotolerance in bay scallops, Argopecten irradians irradians, via differential induction of heat shock proteins

Many cells and organisms are rendered transiently resistant to lethal heat shock by short exposure to sublethal temperatures. This induced thermotolerance is thought to be related to increased amounts of heat shock proteins (HSPs) which, as molecular chaperones, protect cells from stress-induced damage. As part of a study on bivalve stress and thermotolerance, work was undertaken to examine the effects of sublethal heat shock on stress tolerance of juveniles of the northern bay scallop, Argopecten irradians irradians, in association with changes in the levels of cytoplasmic HSP70 and 40. Juvenile bay scallops heat-shocked at a sublethal temperature of 32 °C survived an otherwise lethal heat treatment at 35 °C for at least 7 days. As determined by ELISA, acquisition of induced thermotolerance closely paralleled HSP70 accumulation, whereas HSP40 accrual appeared less closely associated with thermotolerance. Quantification of scallop HSPs following lethal heat treatment, with or without conditioning, suggested a causal role for HSP70 in stress tolerance, with HSP40 contributing to a lesser, but significant extent. Overall, this study demonstrated that sublethal heat shock promotes survival of A. irradians irradians juveniles upon thermal stress and the results support the hypothesis that HSPs have a role in this induced thermotolerance. Exploitation of the induced thermotolerance response shows promise as a means to improve survival of bay scallops in commercial culture.     

Beat the heat: correlates,compounds, and mechanisms involved in fungal thermotolerance

Understanding the how behind the polyphyletic trait of fungal thermotolerance has important implications to both medical and industrial pursuits. In this review, our goal is to synthesize research on fungal thermotolerance from industry, biology, and health science to provide an overview of where the field stands. We first consider correlative traits, which may not directly cause thermotolerance but have demonstrated strong associations with it. We then look into the biomolecules involved in sensing and responding to heat shock and/or stress. Lastly, we examine an overview of physiological mechanisms, both natural and man-made, which fungi can use to withstand heat stress both in the moment and among their progeny. Each section makes attempts to list relevant applications of various traits, in addition to potential knowledge gaps that will need to be addressed in future research. This review highlights that, although thermotolerance is a complex concept with diverse manifestations throughout the fungal kingdom, there are multiple patterns in the heat-shock response worthy of further study.     

Yeast thermotolerance does not require protein synthesis.

Heat shock at 37 degrees C induces synthesis of stress (heat shock) proteins in Saccharomyces cerevisiae and also induces thermotolerance. Amino acid analogs that are powerful inducers of stress protein synthesis failed to induce thermotolerance, suggesting that the stress proteins do not play a causal role in acquired thermotolerance at 37 degrees C. This suggestion was confirmed by the observation that protein synthesis was not required for the induction of thermotolerance at 37 degrees C.     

Interleukin-6 induces thermotolerance in cultured Caco-2 cells independent of the heat shock response

In recent studies, induction of the heat shock response increased IL-6 production in gut mucosa in vivo and in cultured Caco-2 cells in vitro. The heat shock response is associated with increased survival of cells exposed to otherwise lethal hyperthermia, so called thermotolerance, but the role of IL-6 in the induction of thermotolerance is not known. We tested the hypothesis that treatment of cultured Caco-2 cells with IL-6 results in the development of thermotolerance. Cells were treated with human recombinant IL-6 for 1h followed by 3 h recovery in cytokine-free medium whereafter cells were exposed to heat stress (48 degrees C for 2 h). In untreated cells, the heat stress resulted in an approximately 80% cell death. In cells treated with IL-6, cell viability after heat stress was significantly improved and was doubled at an IL-6 concentration of 20 ng/ml. Treatment of the cells with other cytokines (IL-4, IL-10, IL-1beta, or TNFalpha) did not induce thermotolerance, suggesting that the effect of IL-6 may be specific for this cytokine. The induction of thermotolerance by IL-6 was blocked by an IL-6 receptor antibody, suggesting that the development of thermotolerance was receptor-mediated. Treatment of cells with IL-6 did not induce an heat shock response as suggested by unaltered heat shock protein 70 and 90 levels and unaffected heat shock factor DNA binding activity. In addition, the IL-6-induced thermotolerance was not inhibited by quercetin. The present study provides the first evidence of IL-6-induced thermotolerance and suggests that this effect of IL-6 is independent of the heat shock response.     

Molecular events associated with acquisition of heat tolerance by the yeast Saccharomyces cerevisiae

Abstract: The heat shock response is an inducible protective system of all living cells. It simultaneously induces both heat shock proteins and an increased capacity for the cell to wisthstand potentially lethal temperatures (an increased thermotolerance). This has lead to the suspicion that these two phenomena must be inexorably linked. However, analysis of heat shock protein function in Saccharomyces cerevisiae by molecular genetic techniques has revealed only a minority of the heat shock proteins of this organism having appreciable influences on thermotolerance. Instead, physiological perturbations and the accumulation of trehalose with heat stress may be more important in the development of thermotolerance during a preconditioning heat shock. Vegetative S. cerevisiae also acquires thermotolerance through osmotic dehydration, through treatment with certain chemical agents and when, due to nutrient limitation, it arrests growth in the GI phase of the cell cycle. There is evidence for the activities of the cAMP-dependent protein kinase and plasma membrane ATPase being very important in thermotolerance determination. Also, intracellular water activity and trehalose probably exert a strong influence over thermotolerance through their effects on stabilisation of membranes and intracellular assemblies. Future investigations should address the unresolved issue of whether the different routes to thermotolerance induction cause a common change to the physical state of the intracellular environment, a change that may result in an increased stabilisation of cellular structures through more stable hydrogen bonding and hydrophobic interactions.     

Heat shock-induced SRSF10 dephosphorylation displays thermotolerance mediated by Hsp27

Gene regulation in response to environmental stress is critical for the survival of all organisms. From Saccharomyces cerevisiae to humans, it has been observed that splicing of mRNA precursors is repressed upon heat shock. However, a mild heat pretreatment often prevents splicing inhibition in response to a subsequent and more severe heat shock, a phenomenon called splicing thermotolerance. We have shown previously that the splicing regulator SRSF10 (formerly SRp38) is specifically dephosphorylated by the phosphatase PP1 in response to heat shock and that dephosphorylated SRSF10 is responsible for splicing repression caused by heat shock. Here we report that a mild heat shock protects SRSF10 from dephosphorylation during a second and more severe heat shock. Furthermore, this "thermotolerance" of SRSF10 phosphorylation, like that of splicing, requires de novo protein synthesis, specifically the synthesis of heat shock proteins. Indeed, overexpression of one of these proteins, Hsp27, inhibits SRSF10 dephosphorylation in response to heat shock and does so by interaction with SRSF10. Our data thus provide evidence that splicing thermotolerance is acquired through maintenance of SRSF10 phosphorylation and that this is mediated at least in part by Hsp27.     

Paclobutrazol- and Hardening-Induced Thermotolerance of Wheat: Are Heat Shock Proteins Involved?

The present report describes the effects of paclobutrazol andheat hardening treatments on the protein synthesis patternsin imbibing and germinating wheat seedlings (Triticum aestivumL. cv Frederick) during heat stress. A heat hardening treatmentgiven during the imbibition period induced the transient expressionof 118, 90, 70 and 18 kDa heat shock proteins (HSPs). However,the hardening and paclobutrazol treatments did not enhance thethermotolerance of imbibed seeds or etiolated seedlings. Bycontrast, the hardening and paclobutrazol treatments enhancedthe thermotolerance of light-grown seedlings. While, both hardenedand unhardened control seedlings synthesized several HSPs duringa high temperature stress period, these proteins were not synthesizedby the paclobutrazol-treated, light-grown seedlings. Thus, HSPsynthesis during heat shock may have been a manifestation ofstress perception by the seedlings and may not have mediatedthe thermotolerance induced by the triazole treatments. Sincedifferential thermotolerance was only apparent in light-grownseedlings, it is suggested that chloroplasts may be requiredfor the expression of paclobutrazol- and hardening-induced thermoprotection.Additional evidence indicating that chloroplasts are an importantsite of injury during high temperature stress was obtained fromchlorophyll fluorescence measurements. (Received July 11, 1994; Accepted October 26, 1994)     

Molecular characterization of a heat inducible rice gene,OsHSP1, and implications for rice thermotolerance

Higher plants have acquired complex molecular mechanisms to withstand heat stress through years of natural evolutionary processes. Although physiological responses to elevated temperatures have been well studied, thermotolerance mechanisms at the molecular level are poorly understood in rice plants. In order to identify the genes involved in the thermotolerance of rice, we used a publicly available microarray dataset and identified a number of heat stress-responsive genes. Herein, we report details of the rice gene OsHSP1, which is upregulated by heat stress. In addition, OsHSP1 is highly expressed when exposed to salt and osmotic treatments but not cold treatment. Sequence analysis indicated that OsHSP1 belongs to the heat shock protein 90 family of genes. The biological function of OsHSP1 was investigated by heterologous overexpression in Arabidopsis. Transgenic Arabidopsis overexpressing the OsHSP1 gene exhibited enhanced thermotolerance but was hypersensitive under salt and osmotic stresses. Subcellular localization analysis indicated that the OsHSP1 protein is predominantly targeted to the cytosol and nucleus under heat stress. The coexpression network showed 39 interactions for the functionally interacting genes of OsHSP1. Taken together, these findings suggest that OsHSP1 is a heat-inducible gene that may play an important role in the thermotolerance of rice.     

TPK gene products mediate cAMP-independent thermotolerance in Saccharomyces cerevisiae.

Incubation of Saccharomyces cerevisiae with the plant cytokinin N6-(delta 2-isopentenyl)adenine (2iP) resulted in an induction of thermotolerance similar to that induced by sublethal temperatures. Intracellular cAMP levels did not change significantly either during incubation at a sublethal temperature or in the presence of 2iP or ethanol. This suggested that stress-induced thermotolerance is triggered by a mechanism independent of cAMP activation. However, measurement of stress-induced thermotolerance in two mutant strains (tpk1, tpk2, TPK3; tpk1, TPK2, tpk3) each deficient in two of the catalytic subunits of the cAMP-dependent protein kinase (cAPK), revealed that sublethal heat induces thermotolerance by a mechanism part-mediated by the catalytic subunits of cAPK. In contrast, 2iP and ethanol induced thermotolerance by a mechanism fully dependent on the catalytic subunits of cAPK for expression. Therefore, this implies there must be an alternative novel mechanism, other than cAMP, for activating cAPK during stress. Sublethal heating resulted in large increases in intracellular trehalose levels which correlated with the induction of thermotolerance. However, incubation in 2iP or ethanol had no significant effect. This suggests trehalose synthesis is either coincidental with heat stress or that different stress factors induce thermotolerance by alternative mechanisms. Incubation with protein synthesis inhibitors reduced the levels of trehalose synthesized during sublethal heating, suggesting that synthesis of trehalose-6-phosphate synthase during heat stress could be accounting for the increased trehalose levels.     

Loss of Hsp70 in Drosophila is pleiotropic, with effects on thermotolerance, recovery from heat shock and neurodegeneration

The heat-shock response is a programmed change in gene expression carried out by cells in response to environmental stress, such as heat. This response is universal and is characterized by the synthesis of a small group of conserved protein chaperones. In Drosophila melanogaster the Hsp70 chaperone dominates the profile of protein synthesis during the heat-shock response. We recently generated precise deletion alleles of the Hsp70 genes of D. melanogaster and have used those alleles to characterize the phenotypes of Hsp70-deficient flies. Flies with Hsp70 deletions have reduced thermotolerance. We find that Hsp70 is essential to survive a severe heat shock, but is not required to survive a milder heat shock, indicating that a significant degree of thermotolerance remains in the absence of Hsp70. However, flies without Hsp70 have a lengthened heat-shock response and an extended developmental delay after a non-lethal heat shock, indicating Hsp70 has an important role in recovery from stress, even at lower temperatures. Lack of Hsp70 also confers enhanced sensitivity to a temperature-sensitive lethal mutation and to the neurodegenerative effects produced by expression of a human polyglutamine disease protein.     

Root carbon and protein metabolism associated with heat tolerance

Extensive past efforts have been taken toward understanding heat tolerance mechanisms of the aboveground organs. Root systems play critical roles in whole-plant adaptation to heat stress, but are less studied. This review discusses recent research results revealing some critical physiological and metabolic factors underlying root thermotolerance, with a focus on temperate perennial grass species. Comparative analysis of differential root responses to supraoptimal temperatures by a heat-adapted temperate C3 species, Agrostis scabra, which can survive high soil temperatures up to 45 °C in geothermal areas in Yellow Stone National Park, and a heat-sensitive cogeneric species, Agrostis stolonifera, suggested that efficient carbon and protein metabolism is critical for root thermotolerance. Superior root thermotolerance in a perennial grass was associated with a greater capacity to control respiratory costs through respiratory acclimation, lowering carbon investment in maintenance for protein turnover, and efficiently partitioning carbon into different metabolic pools and alternative respiration pathways. Proteomic analysis demonstrated that root thermotolerance was associated with an increased maintenance of stability and less degradation of proteins, particularly those important for metabolism and energy production. In addition, thermotolerant roots are better able to maintain growth and activity during heat stress by activating stress defence proteins such as those participating in antioxidant defence (i.e. superoxide dismutase, peroxidase, glutathione S-transferase) and chaperoning protection (i.e. heat shock protein).