Mechanism Of Thermotolerance Research Articles

Transcriptomic Analysis Reveals Important Roles of Lignin and Flavonoid Biosynthetic Pathways in Rice Thermotolerance During Reproductive Stage.

Rice is one of the major staple cereals in the world, but heat stress is increasingly threatening its yield. Analyzing the thermotolerance mechanism from new thermotolerant germplasms is very important for rice improvement. Here, physiological and transcriptome analyses were used to characterize the difference between two germplasms, heat-sensitive MH101 and heat-tolerant SDWG005. Two genotypes exhibited diverse heat responses in pollen viability, pollination characteristics, and antioxidant enzymatic activity in leaves and spikelets. Through cluster analysis, the global transcriptomic changes indicated that the ability of SDWG005 to maintain a steady-state balance of metabolic processes played an important role in thermotolerance. After analyses of gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment, we found that the thermotolerance mechanism in SDWG00 was associated with reprogramming the cellular activities, such as response to abiotic stress and metabolic reorganization. In contrast, the down-regulated genes in MH101 that appeared to be involved in DNA replication and DNA repair proofreading, could cause serious injury to reproductive development when exposed to high temperature during meiosis. Furthermore, we identified 77 and 11 differentially expressed genes (DEGs) involved in lignin and flavonoids biosynthetic pathways, respectively. Moreover, we found that more lignin deposition and flavonoids accumulation happened in SDWG005 than in MH101 under heat stress. The results indicated that lignin and flavonoid biosynthetic pathways might play important roles in rice heat resistance during meiosis.

Differential proteomic analysis of soybean anthers by iTRAQ under high-temperature stress

High-temperature has severe impacts on the functionality and development of soybean male reproductive organs. However, the molecular mechanism of thermo-tolerance in soybean remains unclear. In this study, a differential proteomic analysis was conducted between the anthers of heat-tolerant (JD21) and heat-sensitive (HD14) cultivars using an iTRAQ based approach. In total, 371, 479, and 417 differentially abundant proteins were identified between HD14 anthers treated with high-temperature stress vs HD14 anthers in the natural field conditions, JD21 anthers treated with high-temperature stress vs JD21 anthers in the natural field conditions, and HD14 vs JD21 anthers treated with high-temperature stress, respectively. The differentially abundant proteins associated with thermo-tolerance were predominantly involved in carbohydrate and energy metabolism, protein synthesis and degradation, nitrogen assimilation, and ROS detoxification. Sixteen common differentially abundant proteins were involved in known protein-protein interaction networks in three comparisons associated with heat, which may strongly influence anther growth and development. The qRT-PCR analysis validated the reliability of the iTRAQ results. In conclusion, the heat-tolerant cultivar performed better under stress than heat-sensitive cultivar through modulation of HSP family proteins, pectinesterase, profilin, S-adenosylmethionine synthase, peroxidase, GST, peptidylprolyl isomerase, and disulfide-isomerase. The results provide novel insight into the mechanism of high-temperature stress response of soybean. SignificanceIn recent years, with the high temperature (HT) stress brought by climate change frequently occurs at anthesis and negatively affects soybean productivity. The molecular mechanism underlying the response of soybean anthers to HT is a relatively complex process and thus difficult to elucidate; however, it is possible to identify differentially expressed genes or proteins between heat-sensitive and heat-tolerant cultivars under HT stress. The potential candidate genes or proteins may then be utilized in elucidating the molecular mechanism underlying the response of soybean to HT stress, as well as provide genetic resource for the improvement of heat-tolerant characteristics in soybean. In present study, quantitative and qualitative proteomic changes occurring in anthers were compared between the heat-tolerant (JD21) and heat-sensitive (HD14) cultivars under HT stress using iTRAQ-based proteomics strategy. Our results provide new insight into translational alterations in HT-resistant and HT-sensitive soybean cultivars under HT stress, which helps to address the underlying molecular mechanism of soybean in response to HT stress.

Integrated proteome and transcriptome analyses revealed key factors involved in tomato (Solanum lycopersicum) under high temperature stress

AbstractHigh temperature (HT) is an important environmental factor affecting crops growth, development, and yield. Transcriptome and proteome technologies developed in recent years can provide deeper and more reliable data to decipher the mechanisms of HT response. In the present study, the transcriptome analysis with RNA sequencing (RNA‐Seq) and integrative analysis on obtained proteomic data were performed in tomato (Solanum lycopersicum) leaves under HT stress (42°C for 4 hr). In total, 3,531 differentially expressed genes (DEGs) and 268 differentially expressed proteins (DEPs) were explored. The quantitative data were validated by qRT‐PCR and parallel reaction monitoring (PRM). Upon mapping of the DEGs/DEPs to the KEGG pathway database, “protein processing in the endoplasmic reticulum” was found to be the most significant enrichment pathway both at the transcriptional and protein levels, suggesting that endoplasmic reticulum stress may play a central role in HT tolerance. Furthermore, transcriptome‐proteome integrative analysis revealed 91 genes shared both in DEGs and DEPs, of which 79 correlations with the same changing trends were most associated with stress response and protein folding. Among these, a HT response gene designated SlBAG5 of unknown function received attention. The full‐length of SlBAG5 was cloned and ectopically overexpressed in Arabidopsis, which displayed thermosensitive phenotype. Taken together, this work provides deep insight into the molecular mechanisms of plant thermotolerance and also facilitates the identification of the key potential genes/proteins for HT response.

Terpinene and β-pinene acting as signaling molecules to improve Cinnamomum camphora thermotolerance

Cinnamomum camphora has great economic value and produces abundant of monoterpenes to improve the thermotolerance. To uncover the thermotolerance mechanisms of main functional monoterpenes for developing anti-high temperature agents, the reactive oxygen species (ROS) metabolism, photosynthetic abilities and gene expression were investigated in the plant leaves fumigated with 2 main monoterpenes (terpinene and β-pinene) under high temperature (38 °C) with fosmidomycin (Fos) inhibiting monoterpene synthesis (Fos+38 °C + terpinene and Fos+38 °C+β-pinene). High temperature (38 °C) increased the ROS and thiobarbituric acid reactive substance (TBARS) content as well as antioxidant enzyme activities, but declined the photosynthetic abilities. These variations were further aggravated under 38 °C with Fos pretreatment (Fos+38 °C), but were gradually recovered with increasing the monoterpene concentration in Fos+38 °C + terpinene and Fos+38 °C+β-pinene treatments. The expression of 73 genes involving in non-enzymatic antioxidant metabolism, photosynthesis and other pathways was changed in Fos+38 °C treatment. Interestingly, the occurrence of 10 μM terpinene and/ or β-pinene showed recovery effects on the expression of these altered genes. Therefore, terpinene and β-pinene were 2 main functional monoterpenes to improve C. camphora thermotolerance by adjusting gene expression.

Phosphoproteomic analysis of mammalian infective Trypanosoma brucei subjected to heat shock suggests atypical mechanisms for thermotolerance

The symptoms of African sleeping sickness, caused by the parasite Trypanosoma brucei, can include periods of fever as high as 41 °C which triggers a heat shock response in the parasite. To capture events involved in sensing and responding to heat shock in the mammalian infective form we have conducted a SILAC-based quantitative proteomic and phosphoproteomic analysis of T. brucei cells treated at 41 °C for 1h. Our analysis identified 193 heat shock responsive phosphorylation sites with an average of 5-fold change in abundance, but only 20 heat shock responsive proteins with average of 1.5-fold change. These data indicate that protein abundance does not rapidly respond (≤1 h) to heat shock, and that the changes observed in phosphorylation site abundance are larger and more widespread. The heat shock responsive phosphorylation sites showed enrichment of RNA binding proteins with putative roles in heat shock response included P-body / stress granules and the eukaryotic translation initiation 4F complex. The ZC3H11-MKT1 complex, which stabilises mRNAs of thermotolerance proteins, appears to represent a key signal integration node in the heat shock response. SignificanceWe report the first quantitative study of changes in protein and phosphorylation site abundance in response to heat shock in the clinically relevant form of the human parasite Trypanosoma brucei. The identification of heat shock responsive phosphorylation sites on proteins with putative roles in thermotolerance including the ZC3H11-MKT1 complex provides evidence of the role dynamic phosphorylation of RNA binding proteins in co-ordinating heat shock. Temperature changes in the host are a major physiological challenge to parasites and factors conferring tolerance to heat shock constitute overlooked virulence factors. A better understanding of these virulence factors will pave the way for the development of novel drug therapies which selectively target T. brucei.

Transcriptome analysis of Liriomyza trifolii (Diptera: Agromyzidae) in response to temperature stress

The leafminer Liriomyza trifolii is an important insect pest of ornamental and vegetable crops worldwide. Temperature is a critical environmental factor that impacts both the distribution and interspecific competition of Liriomyza spp. In this study, we compared the transcriptomes of L. trifolii exposed to ambient (25 °C), hot (43 °C), and cold (-7 °C) temperatures. RNA-seq revealed 100,041 assembled unigenes, and 50,546 of these were annotated in L. trifolii transcriptome libraries. A total of 207 and 2904 differentially expressed genes (DEGs) were identified in response to hot and cold stress, respectively. Functional classification indicated that “cellular process”, “single organism processes” and “metabolic processes” pathways were significantly enriched, along with “binding activity” and “catalytic activity”. With respect to clusters of orthologous genes (COG) classification, DEGs were assigned to “post-translational modification, protein turnover, chaperones”, “carbohydrate transport and metabolism” and “lipid transport and metabolism” categories. Subsequent annotation and enrichment analyses indicated that genes encoding heat shock proteins (HSPs) and cuticular proteins were significantly up-regulated during heat and cold stress, respectively. This study expands our knowledge of gene expression in L. trifolii during temperature stress and provides a basis for further studies aimed at understanding the mechanism of thermotolerance in this important invasive leafminer fly.

Dynamic Transcriptome Analysis of Anther Response to Heat Stress during Anthesis in Thermotolerant Rice (Oryza sativa L.).

High temperature at anthesis is one of the most serious stress factors for rice (Oryza sativa L.) production, causing irreversible yield losses and reduces grain quality. Illustration of thermotolerance mechanism is of great importance to accelerate rice breeding aimed at thermotolerance improvement. Here, we identified a new thermotolerant germplasm, SDWG005. Microscopical analysis found that stable anther structure of SDWG005 under stress may contribute to its thermotolerance. Dynamic transcriptomic analysis totally identified 3559 differentially expressed genes (DEGs) in SDWG005 anthers at anthesis under heat treatments, including 477, 869, 2335, and 2210 for 1, 2, 6, and 12 h, respectively; however, only 131 were regulated across all four-time-points. The DEGs were divided into nine clusters according to their expressions in these heat treatments. Further analysis indicated that some main gene categories involved in heat-response of SDWG005 anthers, such as transcription factors, nucleic acid and protein metabolisms related genes, etc. Comparison with previous studies indicates that a core gene-set may exist for thermotolerance mechanism. Expression and polymorphic analysis of agmatine-coumarin-acyltransferase gene OsACT in different accessions suggested that it may involve in SDWG005 thermotolerance. This study improves our understanding of thermotolerance mechanisms in rice anthers during anthesis, and also lays foundation for breeding thermotolerant varieties via molecular breeding.

Induced Thermotolerance and Expression of Three Key Hsp Genes (Hsp70, Hsp21, and sHsp21) and Their Roles in the High Temperature Tolerance of Agasicles hygrophila.

Thermal adaptation plays a fundamental role in the expansion and distribution of insects, and heat shock proteins (Hsps) play important roles in the temperature adaptation of various organisms. To determine the roles of Hsp genes (Hsp70, Hsp21, and sHsp21) on the high temperature tolerance of Agasicles hygrophila, we obtained complete cDNA (complementary DNA) sequences for Hsp70, Hsp21, and sHsp21 by rapid amplification of cDNA ends (RACE), analyzed their expression profiles under different high temperature treatments by quantitative reverse transcription polymerase chain reaction (RT-qPCR), and performed functional verification by RNA interference (RNAi). The open reading frames of Hsp70, Hsp21, and sHsp21 were 1940, 543, and 567 bp, encoding 650, 180, and 188 amino acids, respectively. Their molecular weights (MWs) were 71.757, 20.879, and 21.510 kDa, and the isoelectric points were 5.63, 6.45, and 6.24, respectively. Phylogenetic tree analysis showed that the Hsp70, Hsp21, and sHsp21 genes of A. hygrophila were relatively conserved in evolution. The Hsp70 and Hsp21 genes in A. hygrophila were homologous to those in Leptinotarsa decemlineata (87 and 79% similarity, respectively), and the sHsp21 gene in A. hygrophila was homologous to that in Lissorhoptrus oryzophilus (74% similarity). The amino acid polypeptide chain had highly conserved sequences of DLGGGTFD, VLVGGSTR, and GPTIEEVD. The sequence of EEVD was the characteristic motif of cytoplasmic Hsp70, and the highly conserved sequences of MALFR and MSLLP were characteristic sequences of Hsp2 and sHsp21, respectively. Relative quantitative real time PCR showed that the three Hsps could be induced by 4-h treatment at high temperatures. Significant upregulation of these Hsps was observed when the temperature was further increased. The RNAi results showed that the injection of the three Hsps’ dsRNA could suppress the expression at the gene level significantly. Compared with the control group, high temperature heat shock reduced the fecundity of A. hygrophila significantly, and the fecundity decreased with the increase in temperature. Our results suggest that Hsp70, Hsp21, and sHsp21 might play key roles in high temperature adaptation of A. hygrophila and help improve our understanding of their mechanism of thermotolerance.

Elevated temperatures do not trigger a conserved metabolic network response among thermotolerant yeasts

BackgroundThermotolerance is a highly desirable trait of microbial cell factories and has been the focus of extensive research. Yeast usually tolerate only a narrow temperature range and just two species, Kluyveromyces marxianus and Ogataea polymorpha have been described to grow at reasonable rates above 40 °C. However, the complex mechanisms of thermotolerance in yeast impede its full comprehension and the rare physiological data at elevated temperatures has so far not been matched with corresponding metabolic analyses.ResultsTo elaborate on the metabolic network response to increased fermentation temperatures of up to 49 °C, comprehensive physiological datasets of several Kluyveromyces and Ogataea strains were generated and used for 13C-metabolic flux analyses. While the maximum growth temperature was very similar in all investigated strains, the metabolic network response to elevated temperatures was not conserved among the different species. In fact, metabolic flux distributions were remarkably irresponsive to increasing temperatures in O. polymorpha, while the K. marxianus strains exhibited extensive flux rerouting at elevated temperatures.ConclusionsWhile a clear mechanism of thermotolerance is not deducible from the fluxome level alone, the generated data can be valued as a knowledge repository for using temperature to modulate the metabolic activity towards engineering goals.

High temperature-induced proteomic and metabolomic profiles of a thermophilic Bacillus manusensis isolated from the deep-sea hydrothermal field of Manus Basin

Thermophiles are organisms that grow optimally at 50 °C–80 °C and studies on the survival mechanisms of thermophiles have drawn great attention. Bacillus manusensis S50-6 is the type strain of a new thermophilic species isolated from hydrothermal vent in Manus Basin. In this study, we examined the growth and global responses of S50-6 to high temperature on molecular level using multi-omics method (genomics, proteomics, and metabolomics). S50-6 grew optimally at 50 °C (Favorable, F) and poorly at 65 °C (Non-Favorable, NF); it formed spores at F but not at NF condition. At NF condition, S50-6 formed long filaments containing undivided cells. A total of 1621 proteins were identified at F and NF conditions, and 613 proteins were differentially expressed between F and NF. At NF condition, proteins of glycolysis, rRNA mature and modification, and DNA/protein repair were up-regulated, whereas proteins of sporulation and amino acid/nucleotide metabolism were down-regulated. Consistently, many metabolites associated with amino acid and nucleotide metabolic processes were down-regulated at NF condition. Our results revealed molecular strategies of deep-sea B. manusensis to survive at unfavorable high temperature and provided new insights into the thermotolerant mechanisms of thermophiles. SignificanceIn this study, we systematically characterized the genomic, proteomic and metabolomic profiles of a thermophilic deep-sea Bacillus manusensis under different temperatures. Based on these analysis, we propose a model delineating the global responses of B. manusensis to unfavorable high temperature. Under unfavorable high temperature, glycolysis is a more important energy supply pathway; protein synthesis is subjected to more stringent regulation by increased tRNA modification; protein and DNA repair associated proteins are enhanced in production to promote heat survival. In contrast, energy-costing pathways, such as sporulation, are repressed, and basic metabolic pathways, such as amino acid and nucleotide metabolisms, are slowed down. Our results provide new insights into the thermotolerant mechanisms of thermophilic Bacillus.

The difference in the formation of thermotolerance of two cotton cultivars with different heat tolerance

ABSTRACTIn order to study the mechanism of thermotolerance of cotton cultivars with different heat tolerance, the response of yield component and photosynthesis to short-term heat stress (HT; average temperature 34°C) was studied. Pot experiments were carried out in 2015 and 2016 by using cotton cultivar PHY370WR (heat tolerant cultivar) and Sumian15 (heat susceptible cultivar). Results showed that heat (34°C) treatment resulted in a significant (p < 0.05) reduction in cotton yield. Path analysis showed that the direct path coefficient (0.89) of boll weight was higher, compared with the boll number (0.46). With high-temperature stress, it was the difference of boll weight reduction contributed the majority to the difference of yield reduction between cultivars, not the difference of boll number reduction. Different decrease in photosynthesis between cultivars leads to the different decline in boll weight. Different thermotolerance between the two cultivars were as follows: the heat tolerant cultivar could maintain higher photosynthesis rate under HT, and it could recover more quickly and highly in photosynthesis than the heat susceptible cultivar. More importantly, the leaf functional period of heat tolerant cultivar was less shortened by HT than that of heat susceptible cultivar.

Thermoprotective adaptations are critical for arthropods feeding on warm-blooded hosts.

Blood feeding in arthropods has evolved in multiple lineages. This feeding preference provides a source of ample proteins and lipids for egg production and survival, but ingestion of a large warm blood-meal can boost the arthropod's body temperature 15°-20°C within seconds to minutes. This represents one of, if not the most, rapid thermal change documented under a natural setting. Here, we describe mechanisms of thermoregulation and thermotolerance in arthropods during blood feeding. The ability to prevent blood-induced thermal damage is a fundamental physiological adaptation linked to the use of warm-blooded vertebrates as food sources. Specific functional and comparative studies have identified unique and divergent mechanisms that suppress or repair thermal stress during blood feeding. These mechanisms include countercurrent heat exchange, evaporative cooling, and upregulation of stress associated proteins.

Comparative study of basal thermo tolerant attributes in tolerant and susceptible wheat cultivars

Two wheat cultivars, viz. C306 and HT41, have been evaluated for their responses to heat stress in terms of some biochemical and physiological attributes. During the exposure to high temperature (40°C for 6 and 12 h), a significant reduction in RWC and FW was recorded in HT41 which was also associated with heat susceptibility. The detrimental effects of high temperature were also apparent in terms of lipid peroxidation, chlorophyll content, H2O2 generation and electrolyte leakage and these were more pronounced in HT 41. Accumulation of osmolytes like proline, total sugar increased due to heat injury and also varied between the two cultivars. In this present study evaluation and analysis of these biochemical and physiological characters under heat stress could unravel the mechanism of basal thermotolerance and thus might be useful as genetic stock to develop wheat tolerant varieties.

Induced expression of small heat shock proteins is associated with thermotolerance in female Laodelphax striatellus planthoppers.

Insects are often exposed to high temperature stress in natural environments, but the mechanisms involved in thermotolerance in many insect groups like Hemiptera are not well known. To explore possible mechanisms of thermotolerance in the hemipteran pest Laodelphax striatellus, which damages rice through direct feeding and viral transmission, small heat shock proteins (sHsps) implicated in thermotolerance in other insect groups were identified. The seven sHsps identified have a conserved alpha crystallin domain, a variable N-terminal region, and shared relative low identities to each other. Three of the sHsp genes (LsHsp20.5, LsHsp21.5, and LsHsp21.6) exhibited higher basal expression than the other four genes but showed weak or no heat-induced expression. The other four genes (LsHsp20.1, LsHsp21.2, LsHsp21.4, and LsHsp22.0) were induced up to 3306-fold by heat. Injection of dsRNA indicated that expression of these sHsps was associated with thermotolerance, and Escherichia coli transformed with LsHsp21.2 and LsHsp20.1 showed relatively higher thermotolerance. These results point to an important functional role of these sHsps for thermotolerance in L. striatellus.

Proteomics of Heat-Stress and Ethylene-Mediated Thermotolerance Mechanisms in Tomato Pollen Grains.

Heat stress is a major cause for yield loss in many crops, including vegetable crops. Even short waves of high temperature, becoming more frequent during recent years, can be detrimental. Pollen development is most heat-sensitive, being the main cause for reduced productivity under heat-stress across a wide range of crops. The molecular mechanisms involved in pollen heat-stress response and thermotolerance are however, not fully understood. Recently, we have demonstrated that ethylene, a gaseous plant hormone, plays a role in tomato (Solanum lycopersicum) pollen thermotolerance. These results were substantiated in the current work showing that increasing ethylene levels by using an ethylene-releasing substance, ethephon, prior to heat-stress exposure, increased pollen quality. A proteomic approach was undertaken, to unravel the mechanisms underlying pollen heat-stress response and ethylene-mediated pollen thermotolerance in developing pollen grains. Proteins were extracted and analyzed by means of a gel LC-MS fractionation protocol, and a total of 1,355 proteins were identified. A dataset of 721 proteins, detected in three biological replicates of at least one of the applied treatments, was used for all analyses. Quantitative analysis was performed based on peptide count. The analysis revealed that heat-stress affected the developmental program of pollen, including protein homeostasis (components of the translational and degradation machinery), carbohydrate, and energy metabolism. Ethephon-pre-treatment shifted the heat-stressed pollen proteome closer to the proteome under non-stressful conditions, namely, by showing higher abundance of proteins involved in protein synthesis, degradation, tricarboxylic acid cycle, and RNA regulation. Furthermore, up-regulation of protective mechanisms against oxidative stress was observed following ethephon-treatment (including higher abundance of glutathione-disulfide reductase, glutaredoxin, and protein disulfide isomerase). Taken together, the findings identified systemic and fundamental components of pollen thermotolerance, and serve as a valuable quantitative protein database for further research.

ITRAQ-Based Quantitative Proteomic Analysis Reveals Proteomic Changes in Mycelium of Pleurotus ostreatus in Response to Heat Stress and Subsequent Recovery.

High temperature is a key limiting factor for mycelium growth and development in Pleurotus ostreatus. Thermotolerance includes the direct response to heat stress and the ability to recover from heat stress. To better understand the mechanism of thermotolerance in P. ostreatus, we used morphological and physiological analysis combined with an iTRAQ-based proteomics analysis of P. ostreatus subjected to 40°C for 48 h followed by recovery at 25°C for 3 days. High temperature increased the concentrations of thiobarbituric acid reactive substances (TBARS) indicating that the mycelium of P. ostreatus were damaged by heat stress. However, these physiological changes rapidly returned to control levels during the subsequent recovery phase from heat stress. In comparison to unstressed controls, a total of 204 proteins were changed during heat stress and/or the recovery phase. Wherein, there were 47 proteins that responded to both stress and recovery conditions, whereas 84 and 73 proteins were responsive to only heat stress or recovery conditions, respectively. Furthermore, quantitative real-time PCR (qRT-PCR) confirmed differential expression of nine candidate genes revealed that some of the proteins, such as a mitogen-activated protein kinase (MAPK), phenylalanine ammonia-lyase (PAL), and heat shock protein (HSP), were also regulated by heat stress at the level of transcription. These differentially expressed proteins (DEPs) in mycelium of P. ostreatus under heat stress were from 13 biological processes. Moreover, protein–protein interaction analysis revealed that proteins involved in carbohydrate and energy metabolism, signal transduction, and proteins metabolism could be assigned to three heat stress response networks. On the basis of these findings, we proposed that effective regulatory protein expression related to MAPK-pathway, antioxidant enzymes, HSPs, and other stress response proteins, and glycolysis play important roles in enhancing P. ostreatus adaptation to and recovery from heat stress. Of note, this study provides useful information for understanding the thermotolerance mechanism for basidiomycetes.

Nitric oxide-mediated cross-talk of proline and heat shock proteins induce thermotolerance in Vicia faba L.

Due to the global warming, rising temperature became a serious threat to the world agriculture. Faba bean plant is very susceptible to heat stress and performs poorly under high temperature condition. Therefore, the performance of faba bean (Vicia faba L.), genotype ‘C5’ was tested to explore (i) the biosynthesis of proline (Pro) in response to heat stress (HS) and the involvement of nitric oxide (NO) and Pro in thermotolerance mechanism and (ii) the role of heat shock proteins (HSPs) and Pro in defense, and their correlation with the tolerance of faba bean plant to HS. Exposure of plants to HS for 48 h resulted in increased levels of reactive oxygen species [hydrogen peroxide (H2O2) and superoxide ions (O2•−)], nitric oxide (NO), accumulation of Pro and malondialdehyde, electrolyte leakage, DNA damage, chlorophyll (Chl) degradation and in decreased leaf relative water content (RWC) and Chl content in faba bean plants. However, at the same time increasing levels of HS (32, 37 and 42 °C) increased the accumulation of NO, Pro, activities of Pro metabolizing enzymes (Δ1-pyrroline-5-carboxylate synthetase, ornithine-δ-aminotransferase and proline dehydrogenase) and expression of HSPs (Hsp17.6, Hsp70, Hsp90-1, and Hsp101). Induced biosynthesis of NO and Pro under HS activated defense system of plants by enhancing the activities of antioxidant enzymes [superoxide dismutase, catalase, glutathione reductase and ascorbate peroxidase] and also by increasing the content of reduced glutathione (GSH), ascorbate (AsA) and oxidized glutathione (GSSG). While, an increase in GSSG content was found lesser than an increase in GSH under HS stress. Application of 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO; an NO scavenger) decreased the accumulation of leaf RWC and Pro and NO. Therefore, it can be proposed that NO acts as both signal molecule and promotor of Pro biosynthesis. The present investigation reveals that above studied parameters could be used in identifying a HS-tolerant plant that can be utilized in future breeding programs.

Characterization of two novel heat shock protein 70s and their transcriptional expression patterns in response to thermal stress in adult of Frankliniella occidentalis (Thysanoptera: Thripidae)

Heat shock protein 70 (HSP70) is one of the most important members in the heat shock protein family, and plays important roles in the thermotolerance of insect. To explore the molecular mechanism of thermotolerance of Frankliniella occidentalis adults, the difference in the expression of HSP70s in F. occidentalis male or female adults under the thermal stress was studied under the laboratory conditions. Two full length cDNAs of HSP70s gene (Fohsc704 and Fohsc705) were cloned from F. occidentalis by using RT-PCR and RACE. The genomic sequence was demonstrated by genomic validation, and the position and size of the intron were analyzed by sequence analysis of cDNA. Real-time PCR was used to analyze the HSP70 expression patterns. The cDNA of Fohsc704 and Fohsc705 possessed 2 073 and 1 476 bp which encoded 690 and 491 amino acids (aa) with a calculated molecular weight of 75 and 54 kDa, respectively. Four introns in Fohsc704 and six introns in Fohsc705 protein were found. However, the HSP70 protein sequences in our study were ended with EKKN and GIFL, which were different from the reported FoHSP70s. Various expression patterns of Fohsc704 and Fohsc705 were found in both genders of F. occidentalis under thermal stress. The expression of Fohsc704 and Fohsc705 reached to the highest level at –12 and –8°C in male adults, respectively, and Fohsc705 expressed the highest level at 33°C in female adults. In conclusion, HSP70s of F. occidentalis in our study are novel heat shock proteins. There were difference in expression patterns of the two hsc70s in genders of F. occidentalis, and the two HSP70s play important roles in the thermotolerance of F. occidentalis.

RNA-Seq-mediated transcriptomic analysis of heat stress response in a polar Chlorella sp. (Trebouxiophyceae, Chlorophyta)

The current outlook on mitigation of global warming does not appear promising, with figures in the reduction of anthropogenic greenhouse gas emissions lagging far behind climate goals. A recent environmental report even postulated a high possibility of temperature increase of at least 3 °C by 2100. Despite the low number of human inhabitants in Antarctica, the Antarctic Peninsula was reported as one of the most rapidly warming locations on earth. Many studies have shown that heat stress modulates physiological performance in many species of microalgae; however, studies to elucidate the molecular mechanisms of high-temperature thermotolerance are generally focused on the model species, i.e. Chlamydomonas reinhardtii. Furthermore, previous transcriptomic work in this aspect generally employed the microarray technique and/or involved the tropical or temperate strains, and few were conducted on the polar strains. In this study, RNA-Seq-mediated transcriptomic analysis was undertaken to compare the whole transcriptome profile of an Antarctic Chlorella sp. grown at ambient (4 °C) versus stress-inducing high (33 °C) temperatures and harvested at the 120-h time point. The findings of this study indicated a coordinated response to fine tune balance between energy production and utilisation for biosynthesis by redirecting carbon provision, and the arrest of cell division as a coping mechanism for an intense and relatively long period of stress. The strategies undertaken by this alga in acclimation to heat stress are somewhat similar to the heat stress response of the model species.

Melatonin Alleviates High Temperature-Induced Pollen Abortion in Solanum lycopersicum.

Melatonin is a pleiotropic signal molecule that plays critical roles in regulating plant growth and development, as well as providing physiological protections against various environmental stresses. Nonetheless, the mechanisms for melatonin-mediated pollen thermotolerance remain largely unknown. In this study, we report that irrigation treatment with melatonin (20 µM) effectively ameliorated high temperature-induced inactivation of pollen and inhibition of pollen germination in tomato (Solanum lycopersicum) plants. Melatonin alleviated reactive oxygen species production in tomato anthers under high temperature by the up-regulation of the transcription and activities of several antioxidant enzymes. Transmission electron micrograph results showed that high temperature-induced pollen abortion is associated with a premature degeneration of the tapetum cells and the formation of defective pollen grains with degenerated nuclei at the early uninuclear microspore stage, whilst melatonin protected degradation of organelles by enhancing the expression of heat shock protein genes to refold unfolded proteins and the expression of autophagy-related genes and formation of autophagosomes to degrade denatured proteins. These findings suggest a novel function of melatonin to protect pollen activity under high temperature and support the potential effects of melatonin on reproductive development of plants.