The capacity of Drosophila to heat harden associates with low rates of heat-shocked protein synthesis

The thermotolerance of a species or of an ecotype is important for determining its habitat range and vigour, and considerable research has focused on identifying underlying physiological, biochemical and genetic bases of thermotolerance traits. Rates of protein synthesis in tissues when organisms experience a sudden heat stress as occurs on rare hot days may be important to avoid heat-induced paralysis and to survive. While natural variation in Drosophila melanogaster thermotolerance has been associated with heat-shock gene expression, little attention has been given to examining the thermo-protective role of protein synthesis generally. Using two independently derived sets of single-pair mating lines, we characterised variation in rates of protein synthesis in dissected ovarian tissues, both before and after a heat shock applied at different severities in the two sets. In both sets of lines heat-shocked protein synthesis rates were negatively associated with the increase in heat knockdown tolerance after hardening. These associations occurred in a different sex in each set. Variation in rates of Hsp70 synthesis failed to associate with levels of heat tolerance or general protein synthesis. Our results suggest heritable variation in the rate of protein synthesis following heat stress, independently of Hsp70 variation, contributes to heat tolerance variation in this species.     

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.     

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.     

碳源对玫烟色虫草菌丝生长、芽生孢子产生及其耐热性的影响

提高虫生真菌孢子应对热胁迫的能力是生防菌应用研究的关键,为研究菌丝培养阶段碳源对玫烟色虫草Cordyceps fumosorosea IF-1106耐热性的影响,选择了麦芽糖、可溶性淀粉、蔗糖、葡萄糖、果糖、海藻糖为碳源的培养基对玫烟色虫草IF-1106进行液体培养,评估了不同碳源条件下菌丝的生长、产孢及所产芽生孢子的耐热性。结果表明,在菌株培养阶段,培养基中碳源的种类及浓度对菌丝产量、产孢量及所产芽生孢子的耐热性有显著影响,其中蔗糖为碳源时,所产芽生孢子的耐热性强,45 ℃热胁迫条件下LT₅₀为1.65 h;蔗糖浓度为40 g/L时,可产生大量耐热芽生孢子,液体培养3 d后产孢量可达3.43×10⁷个孢子/mL。为探索不同培养条件下所产芽生孢子耐热性不同的原因,提取了孢子内的海藻糖并采用离子色谱法对其进行了定量分析,发现耐热性高的芽生孢子胞内海藻糖含量普遍较低,可见海藻糖是与芽生孢子耐热性密切相关的内源物质。综上所述,选择适宜的培养基是调控孢子耐热性的有效途径,本研究为生产高耐热的玫烟色虫草生防制剂提供了有益的指导。     

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。     

A genetic analysis of variation for the ability to fly after exposure to thermal stress in Drosophila mojavensis

To help us understand how adaptive tolerance to heat stress has evolved, we made F₁ hybrid crosses and backcrosses amongst populations of Drosophila mojavensis, and tested their ability to fly after exposure to a debilitating, but non-lethal, heat stress. Previous work identified that these populations vary in thermotolerance as measured for a variety of traits. Hybrid superiority was observed when crossing all four pairs of strains. Patterns of inheritance in flight ability after stress varied depending on which strains were used to set up complete reciprocal backcrosses, and, for both population pairs, results supported a multigenic model. This quantitative inheritance may be an outcome of the many different physiological and biochemical systems recently shown to influence muscle activity during heat stress. Therefore, the ability to maintain flight in the presence of high temperatures has the potential to vary considerably among populations in nature. As effects occur at temperatures well below those causing mortality, variation in this trait may greatly impact organismal fitness.     

Correlated changes in thermotolerance traits and body color phenotypes in montane populations of Drosophila melanogaster: analysis of within- and between-population variations

Thermotolerance traits vary across geographical gradients but there is a lack of clinal variation in some Drosophila species. Thus, it is not clear whether thermotolerance or other correlated traits are the target of natural selection. In order to test selection responses, we investigated body melanization and thermotolerance traits in six altitudinal populations of Drosophila melanogaster . Based on rearing different geographical populations under uniform growth conditions at 21 °C (common garden experiments), clinal variations for cold resistance are in the direction opposite to heat resistance along an altitudinal gradient, that is darker flies from highland populations evidenced higher levels of cold resistance while lowland populations showed higher heat resistance. Phenotypic plastic responses for body melanization at 17–28 °C showed significant correlations with thermotolerance traits. At 17 °C, regression coefficients as a function of altitude are highly significant and positive for cold resistance but negative for heat knockdown. However, for flies reared at 28 °C, there is no elevational change in melanization as well as thermotolerance traits. Thus, both genetic and plastic changes of body melanization and thermotolerance traits suggest a correlated selection response. Further, within-population analyses of body melanization (based on dark, intermediate and light color phenotypes) showed significant associations with thermotolerance traits. Correlated variations in body melanization and thermal tolerances are associated with climatic thermal variability ( T _cv) but not with T _min. or T _max. along an altitudinal gradient.     

Overexpression of a Metarhizium robertsii HSP25 gene increases thermotolerance and survival in soil

Temperature extremes are an important adverse factor limiting the effectiveness of microbial pest control agents. They reduce virulence and persistence in the plant root-colonizing insect pathogen Metarhizium robertsii. Small heat shock proteins have been shown to confer thermotolerance in many organisms. In this study, we report on the cloning and characterization of a small heat shock protein gene hsp25 from M. robertsii. hsp25 expression was upregulated when the fungus was grown at extreme temperatures (4, 35, and 42 °C) or in the presence of oxidative or osmotic agents. Expression of hsp25 in Escherichia coli increased bacterial thermotolerance confirming that hsp25 encodes a functional heat shock protein. Overexpressing hsp25 in M. robertsii increased fungal growth under heat stress either in nutrient-rich medium or on locust wings and enhanced the tolerance of heat shock-treated conidia to osmotic stress. In addition, overexpression of hsp25 increased the persistence of M. robertsii in rhizospheric soils in outdoor microcosms, though it did not affect survival in bulk soil, indicating that M. robertsii's survival in soil is dependent on interactions with plant roots.     

Transfer and mapping of the heat tolerance component traits of <Emphasis Type="Italic">Aegilops speltoides</Emphasis> in tetraploid wheat <Emphasis Type="Italic">Triticum durum</Emphasis>

Aegilops speltoides is an important genetic resource for wheat improvement and has high levels of heat tolerance. A heat-tolerant accession of Ae. speltoides pau3809 was crossed with Triticum durum cv. PDW274, and BC₂F_4-6 backcross introgression lines (BILs) were developed, phenotyped for important physiological traits, genotyped using SSR markers and used for mapping the QTL governing heat tolerance component traits. A set of 90 BILs was selected from preliminary evaluation of a broader set of 262 BILs under heat stress. Phenotyping was conducted for physiological traits such as cell membrane thermostability, chlorophyll content, acquired thermotolerance, canopy temperature and stay green. Much variation for these traits was observed in random as well as selected sets of BILs, and comparison of the BILs with the recurrent parent showed improvement for these traits under normal as well as heat stress conditions, indicating that introgressions from Ae. speltoides might have led to the improvement in the heat tolerance potential of the BILs. Introgression profiling of the 90 BILs using SSR markers identified Ae. speltoides introgression on all the 14 chromosomes with introgressions observed on A as well as B genome chromosomes. QTL mapping identified loci for various heat tolerance component traits on chromosomes 2B, 3A, 3B, 5A, 5B and 7A at significant LOD scores and with phenotypic contributions varying from 11.1 to 28.7 % for different traits. The heat-tolerant BILs and QTL reported in the present study form a potential resource that can be used for wheat germplasm enhancement for heat stress tolerance.     

C. elegans STI-1, the Homolog of Sti1/Hop, Is Involved in Aging and Stress Response

Environmental and physiological stresses such as heat shock, oxidative stress, heavy metals, and pathogenic conditions induce cellular stress response. This response is often mediated by heat shock proteins that function as molecular chaperones. A stress-inducible cochaperone, Sti1/Hop (Hsp organizer protein), functions as an adaptor protein that simultaneously binds with Hsp70 and Hsp90 to transfer client proteins from Hsp70 to Hsp90. However, the biological role of STI-1 in vivo is poorly understood in metazoans. Here, we report the characterization of the Caenorhabditis elegans homolog of Sti1/Hop, which is approximately 56% identical with human STI-1. C. elegans STI-1 (CeSTI-1) is expressed in the pharynx, intestine, nervous system, and muscle from larvae to adults. Analysis of proteins immunoprecipitated with anti-STI-1 antibody by mass spectrometry revealed that CeSTI-1 can bind with both Hsp70 and Hsp90 homologs like its mammalian counterpart. sti-1 expression is elevated by heat stress, and an sti-1(jh125) null mutant shows decreased fertility under heat stress conditions. These mutants also show abnormally high lethality in extreme heat and may be functioning with DAF-16 in thermotolerance. In addition, sti-1(jh125) mutants have a shortened life span. Our results confirm that CeSTI-1 is a cochaperone protein that may maintain homeostatic functions during episodes of stress and can regulate longevity in nematodes.     

Cold activity of Beauveria and Metarhizium, and thermotolerance of Beauveria

Heat and cold are environmental abiotic factors that restrict the use of entomopathogenic fungi as agents for biological control of insects. The thermotolerance and cold activity of 60 entomopathogenic fungal isolates, including five species of Beauveria and one isolate of Engyodontium albus (=Beauveria alba) were examined as to tolerance of temperatures that might be encountered during field use. In addition, cold activity of eight Metarhizium spp. isolates was evaluated. The isolates were from various geographic regions, arthropod hosts or substrates. High variability in conidial thermotolerance was found among the Beauveria spp. isolates after exposure to 45 °C for 2 h, as evidenced by low (0-20%), medium (20-60%), or high germination (60-80%). The thermal death point (0% germination) for three rather thermotolerant B. bassiana isolates (CG 138, GHA and ARSEF 252) was 46 °C for 6 h. At low temperatures (5 °C), with few exceptions (e.g. CG 66, UFPE 479, CG 227, CG 02), most of the B. bassiana isolates germinated well (ca. 100%). On the other hand, only one isolate of Metarhizium sp. was cold-active (i.e. ARSEF 4343 from Macquarie Island, 54.4°S, Australia). This probably is a M. frigidum isolate. The E. albus isolate (UFPE 3138) was the most susceptible isolate to both heat and cold stress. Isolates ARSEF 252 and GHA of B. bassiana, on the other hand, presented exceptionally high thermotolerance and cold activity. Some isolates with high cold activity, however, were thermosensitive (e.g. ARSEF 1682) and others with high thermotolerance had low cold activity (e.g. CG 227). An attempt to correlate the latitude of origin with thermotolerance or cold activity indicated that B. bassiana isolates from higher latitudes were more cold-active than isolates from nearer the equator, but there was not a similar correlation for heat.     

Lactobacilli and pediococci as versatile cell factories – Evaluation of strain properties and genetic tools

This review discusses opportunities and bottlenecks for cell factory development of Lactic Acid Bacteria (LAB), with an emphasis on lactobacilli and pediococci, their metabolism and genetic tools. In order to enable economically feasible bio-based production of chemicals and fuels in a biorefinery, the choice of product, substrate and production organism is important. Currently, the most frequently used production hosts include Escherichia coli and Saccharomyces cerevisiae, but promising examples are available of alternative hosts such as LAB. Particularly lactobacilli and pediococci can offer benefits such as thermotolerance, an extended substrate range and increased tolerance to stresses such as low pH or high alcohol concentrations. This review will evaluate the properties and metabolism of these organisms, and provide an overview of their current biotechnological applications and metabolic engineering. We substantiate the review by including experimental results from screening various lactobacilli and pediococci for transformability, growth temperature range and ability to grow under biotechnologically relevant stress conditions. Since availability of efficient genetic engineering tools is a crucial prerequisite for industrial strain development, genetic tool development is extensively discussed. A range of genetic tools exist for Lactococcus lactis, but for other species of LAB like lactobacilli and pediococci such tools are less well developed. Whereas lactobacilli and pediococci have a long history of use in food and beverage fermentation, their use as platform organisms for production purposes is rather new. By harnessing their properties such as thermotolerance and stress resistance, and by using emerging high-throughput genetic tools, these organisms are very promising as versatile cell factories for biorefinery applications.     

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).     

Overexpression of GASA5 increases the sensitivity of Arabidopsis to heat stress

Basal thermotolerance is very important for plant growth and development when plants are subjected to heat stress. However, little is known about the functional mechanism of gibberellins (GAs) in the basal thermotolerance of plants. In the present work, we provide molecular evidence that a member of the gene family encoding the GA-stimulated Arabidopsis (GASA) peptides, namely GASA5, is involved in the regulation of seedling thermotolerance. The GASA5-overexpressing plants displayed a weak thermotolerance, with a faster cotyledon-yellowing rate, lower seedling-survival rate, and slower hypocotyl elongation, in comparison to the wild-type and GASA5 null-mutant (gasa5-1) plants, after heat-stress treatment. The short-hypocotyl phenotype of GASA5-overexpressing plants could be rescued by the exogenous application of salicylic acid (SA), the hormone found to protect plants from heat stress-induced damage. GASA5 expression was inhibited by heat stress but unaffected by the application of exogenous SA. However, expression of the gene encoding the noexpresser of PR genes 1 (NPR1), a key component of the SA-signaling pathway, was downregulated by GASA5 overexpression. Importantly, when different GASA5-genotype plants were treated with heat stress, several genes encoding heat-shock proteins, including HSP101, HSP70B, HSP90.1, HSP17.6-C1, and HSP60, were inhibited by GASA5 overexpression. Meanwhile, hydrogen peroxide was accumulated at high levels in heat stress-treated GASA5-overexpressing plants. These results suggest that the Arabidopsis GASA5 gene acts as a negative regulator in thermotolerance by regulating both SA signaling and heat shock-protein accumulation.     

Changes in thermotolerance and Hsp70 expression with domestication in Drosophila melanogaster

To examine how the duration of laboratory domestication may affect Drosophila stocks used in studies of thermotolerance, we measured expression of the inducible heat‐shock protein Hsp70 and survival after heat shock in D. melanogaster strains recently collected from nature and maintained in laboratory culture for up to 50 or more generations. After an initial increase in both Hsp70 expression and thermotolerance immediately after transfer to laboratory medium, both traits remained fairly constant over time and variation among strains persisted through laboratory domestication. Furthermore, variation in heat tolerance and Hsp70 expression did not correlate with the length of time populations evolved in the laboratory. Therefore, while environmental variation likely contributed most to early shifts in strain tolerance and Hsp70 expression, other population parameters, for example genetic drift, inbreeding, and selection likely affected these traits little. As long as populations are maintained with large numbers of individuals, the culture of insects in the laboratory may have little effect on the tolerance of different strains to thermal stress.