Gene and Metabolite Integration Analysis through Transcriptome and Metabolome Brings New Insight into Heat Stress Tolerance in Potato (Solanum tuberosum L.)

MicroRNAs (miRNAs) are known to regulate expression of genes under stress. We report here the deep sequencing of small RNAs expressed during control, short and prolonged heat stress and recovery. Genome-wide identification of miRNAs in tolerant (Nagina 22) and susceptible (Vandana) rice cultivars was performed in 16 samples representing root and shoot of 13-day-old seedlings. The expression profile of miRNAs was analysed in 36 pairwise combinations to identify the genotype-, treatment- and tissue-dependent expression of miRNAs. Small-RNA sequencing of 16 libraries yielded ~271 million high-quality raw sequences; 162 miRNA families were identified. The highly expressed miRNAs in rice tissues were miR166, miR168, miR1425, miR529, mR162, miR1876, and miR1862. Expression of osa-miR1436, osa-miR5076, osa-miR5161, and osa-miR6253 was observed only in stressed tissue of both genotypes indicating their general role in heat stress response. Expression of osa-miR1439, osa-miR1848, osa-miR2096, osa-miR2106, osa-miR2875, osa-miR3981, osa-miR5079, osa-miR5151, osa-miR5484, osa-miR5792, and osa-miR5812 was observed only in Nagina 22 during high temperature, suggesting a specific role of these miRNAs in heat stress tolerance. This study provides details of the repertoire of miRNAs expressed in root and shoot of heat susceptible and tolerant rice genotypes under heat stress and recovery.

Polyamines involve in gene regulation by interacting with and modulating the functions of various anionic macromolecules such as DNA, RNA and proteins. In this study, we identified an important function of the polyamine transporter LHR1 (LOWER EXPRESSION OF HEAT RESPONSIVE GENE1) in heat-inducible gene expression in Arabidopsis thaliana. The lhr1 mutant was isolated through a forward genetic screening for altered expression of the luciferase reporter gene driven by the promoter from the heat-inducible gene AtHSP18.2. The lhr1 mutant showed reduced induction of the luciferase gene in response to heat stress and was more sensitive to high temperature than the wild type. Map-based cloning identified that the LHR1 gene encodes the polyamine transporter PUT3 (POLYAMINE UPTAKE TRANSPORTER 3) localized in the plasma membrane. The LHR1/PUT3 is required for the uptake of extracellular polyamines and plays an important role in stabilizing the mRNAs of several crucial heat stress responsive genes under high temperature. Genome-wide gene expression analysis using RNA-seq identified an array of differentially expressed genes, among which the transcript levels of some of the heat shock protein genes significantly reduced in response to prolonged heat stress in the lhr1 mutant. Our findings revealed an important heat stress response and tolerance mechanism involving polyamine influx which modulates mRNA stability of heat-inducible genes under heat stress conditions.

Recent studies have shown that exposure to warm water can trigger gonadal degeneration and germ cell loss in fish of both sexes, but the mechanism behind this pathology is still not understood. This study was designed to characterize this process histologically and determine whether apoptosis plays any role during high temperature-induced gonadal cell degeneration in subadult pejerrey (Odontesthes bonariensis). For this purpose, fish were reared continuously at constant temperatures of 24 degrees C (control) and 29 degrees C (prolonged heat stress) or exposed for 36 h to 31 degrees C and then returned to 24 degrees C (short heat stress). Gonads were sampled at various times (hours, days, weeks) after the start of the experiment and were analyzed by light microscopy and stereometry for histological integrity/degeneration and germ cell counts, as well as by acridine orange fluorescence microscopy, TUNEL, and caspase activity assay for histochemical and biochemical signs of apoptosis. The results clearly implicate apoptosis in heat-induced somatic and germ cell degeneration in pejerrey and revealed that the dynamics and severity of this process were proportional to the magnitude of the thermal stress. Even a 36-h exposure to 31 degrees C induced significant increases in caspase-3 activity and number of apoptotic cells in both sexes, but males were shown to be more sensitive to heat stress than females.

In vitro tuberization as a potential screening method for heat stress tolerance in potato, was assessed on nodal expiants of Desiree, LT-2, Kennebec and Russet Burbank. Two tuber inducing media protocols were evaluated at 20 C and 28 or 30 C. Independently of the media protocol, heat stress significantly reduced tuberization. A delay in the formation of tuber initials was also observed in Desiree, Kennebec and LT-2 at 28 and 30 C compared to 20 C. Russet Burbank failed to tuberize under heat stress on both media. At higher temperatures Desiree either did not tuberize, or tuberized poorly on high sucrose-agar medium and tuberized the best of all cultivars, on low sucrose-Gelrite medium. Kennebec and LT-2 tuberized on both media. Medium with Gelrite gave better tuberization and more reproducible results than with agar. A high sucrose-agar medium, on the other hand, separated the heat tolerant clone LT-2 from the other cultivars. Higher temperature reduced accumulation of patatin and 22 kDa protein in all cultivars. The reduction was greater in Kennebec and least in LT-2. The results indicate that microtuber production under heat stress conditions, combined with SDS-PAGE protein electrophoresis, can be considered as a preliminary method in screening potato germplasm for subtropical and tropical climates.

The involvement of heat-inducible genes, including the heat-shock genes, in the acute response to temperature stress is well established. However, their importance in genetic adaptation to long-term temperature stress is less clear. Here we use high-density arrays to examine changes in expression for 35 heat-inducible genes in three independent lines of Escherichia coli that evolved at high temperature (41.5 degrees C) for 2,000 generations. These lines exhibited significant changes in heat-inducible gene expression relative to their ancestor, including parallel changes in fkpA, gapA, and hslT. As a group, the heat-inducible genes were significantly more likely than noncandidate genes to have evolved changes in expression. Genes encoding molecular chaperones and ATP-dependent proteases, key components of the cytoplasmic stress response, exhibit relatively little expression change; whereas genes with periplasmic functions exhibit significant expression changes suggesting a key role for the extracytoplasmic stress response in the adaptation to high temperature. Following acclimation at 41.5 degrees C, two of the three lines exhibited significantly improved survival at 50 degrees C, indicating changes in inducible thermotolerance. Thus evolution at high temperature led to significant changes at the molecular level in heat-inducible gene expression and at the organismal level in inducible thermotolerance and fitness.

BackgroundWater spinach (Ipomoea aquatica) is an important heat-resistant leafy vegetable that can survive under long-time heat stress condition. However, the physiological characteristics and molecular changes in its response to heat stress are poorly understood.ResultsIn this study the selected water spinach cultivars with different thermo resistance and their physiological response to heat stress were examined. Under prolonged heat stress, plant growth was inhibited in all tested cultivars. This inhibition was accompanied by the reduction of photosynthetic performance. The reactive oxygen species system in terms of superoxide and hydrogen peroxide contents, as well as antioxidant polyphenols, were evaluated. The results showed that prolonged heat stress caused reduced antioxidant capacity, but the role of antioxidant capacity in a prolonged thermotolerance was not predominant. Transcriptomic analysis of the water spinach subjected to heat stress revealed that 4145 transcripts were specifically expressed with 2420 up-regulated and 1725 down-regulated in heat-sensitive and heat-tolerant cultivars treated with 42 °C for 15 days. Enrichment analysis of these differentially expressed genes showed that the main metabolic differences between heat-sensitive and heat-tolerant cultivars were the carbohydrate metabolism and phenylpropanoid biosynthesis. The results of carbohydrate profiles and RT-qPCR also suggested that heat stress altered carbohydrate metabolism and associated changes in transcriptional level of genes involved in sugar transport and metabolic transition.ConclusionsThe prolonged heat stress resulted in a reduced antioxidant capacity while the role of antioxidant capacity in a prolonged thermotolerance of water spinach was not predominant. Transcriptome analysis and the measurement of carbohydrates as well as the gene expression evaluation indicated that the response of the metabolic pathway such as carbohydrate and phenylpropanoid biosynthesis to heat stress may be a key player in thermo resistance.

to provide the morphological characteristics of experimental Hantavirus infection under heat stress conditions to identify the possibilities of its modeling in resistant laboratory animals. Experiments were carried out on outbred albino mice that were divided into 4 groups: 1) intact mice unexposed to heating; 2) those exposed to heating; 3) Hantavirus-infected animals unexposed to preheating; 4) those exposed to preheating. The animals in Groups 2-4 were long exposed to heat stress at a temperature of 30 °C for 3 hours during 3 days. Strain Aa 60343 (PM-79-95) of the Far East genovariant of Hantaan virus (the genus Hantavirus, family Bunyaviridae) from the collection of the G.P. Somov Research Institute of Epidemiology and Microbiology was used to induce infection. The animals in Groups 3 and 4 were intraperitoneally injected with 700 FFU of Hantavirus per mouse. Materials (lung, liver, kidney, and spleen) taken from Groups 2-4 animals were collected for histological examination on days 1, 3, 7 and 14 of observation. The intact albino mice in Group 1 showed no histopathological changes in the organs. After heat exposure, Group 2 animals were found to have an immunomorphological response in the interstitial tissues of the lung, liver and kidney in partial lymphoid hypoplasia of the spleen. There were no signs of inapparent infection in the presence of marked immunomorphological changes in the organs in Group 3 of hantavirus-infected animals unexposed to preheating. In Group 4, those exposed to preheating exhibited dystrophic and destructive changes in the target organs (lungs, kidneys) in the presence of immunodeficiency manifestations of manifestations that were more pronounced in dead animals. In an unresponsive model (adult albino mice), Hantavirus infection caused only obvious immunomorphological changes in the organs. Prolonged preheat stress in the hantavirus-infected animals promoted inapparent infection and morphological manifestations of induced secondary immunodeficiency that was responsible for the manifestation of an infectious process in some animals.

Gamma radiation degradation of chitosan for application in growth promotion and induction of stress tolerance in potato (Solanum tuberosum L.)

Potato stress resilience: Unraveling the role of signalling molecules and phytohormones

Identification of quantitative trait loci (QTL) responsible for stress tolerance could help to develop new tolerant potato cultivars through markers-assisted selection. The objective of the research was to identify and map loci that may play major role in the control of osmotic stress tolerance in potato under in vitro vegetative growth conditions. Mannitol-induced osmotic stress response of cv. White Lady and breeding line S440 as well as their 85F1 progeny for root number and root length under in vitro conditions was investigated. Interval mapping based on 200 informative markers produced a molecular marker map comprising 13 linkage groups for White Lady and 14 for S440. In total, 14 QTLs with LOD > 2 were identified from which 6 were confirmed as major QTLs. Of those six, three were associated with root length and three with root number. For root length, one major QTL was identified on chromosome XII (LOD = 4.8), which explained 52.3 % of the phenotypic variance. Two other major QTLs from an unidentified chromosome explained 64.9 and 51 % of the phenotypic variance with LODs of 5.34 and 4.8, respectively. For root number, one QTL with 19.2 % of the phenotypic variance (LOD of 2.9) was tentatively identified on chromosome IX, while another was putatively identified on chromosome XII (LOD of 2.4), together explaining 26.8 % of the phenotypic variance.

Effects of acute versus chronic heat stress on broiler response to dietary protein

Various physiological processes may deteriorate in response to increasing temperatures, contributing to the decline in turf quality for cool-season turfgrasses during heat stress. This study was performed to investigate metabolic changes (membrane lipid peroxidation, total protein content, amino acid content, and protease activity) associated with turf quality decline for creeping bentgrass (Agrostis stolonifera Huds.) in response to gradually increasing temperatures for a short duration and prolonged exposure to lethally high temperature. Plants were subjected to increasing temperatures of 20, 25, 30, 35, and 40 °C for 7 days at each level of temperature [gradual heat stress (GHS)] or exposed to high temperature of 40 °C for 28 days [prolonged heat stress (PHS)] in growth chambers. During the GHS treatment, significant decline in turf quality occurred when plants were exposed to 30 °C for 7 days; simultaneously, malondialdehyde (MDA) content increased and total protein content in shoots decreased significantly compared to those at 20 °C. Protease activity increased at 25 °C and then decreased as temperature was elevated from 30 to 40 °C during the GHS treatment. Amino acid content decreased under GHS, beginning at 25 °C. Under the PHS treatment, turf quality declined and MDA content increased significantly, beginning at 14 days of PHS, while total protein content decreased at 7 days of PHS. Protease activity and amino acid content increased at 7 days of PHS, and then declined with longer stress duration. Our results indicated that protease activity, and amino acid and total protein content were more responsive to GHS or PHS than that of lipid peroxidation and turf quality. Changes in metabolic parameters of protease activity, amino acid and total protein content, and lipid peroxidation may contribute to leaf senescence and poor turf performance under severe or prolonged heat stress conditions for creeping bentgrass.

Increasing temperatures associated with climate change will be the next challenge for crop improvement, especially for turfgrass species that are often grown in urban green spaces. Previous research on turfgrass heat stress tolerance has been limited to a small number of species and cultivars with different heat stress conditions between studies; therefore, we assessed heat stress tolerance of 34 turfgrasses representing 14 species. Four replicates of each entry were established for at least 12 wk and then subjected to 49 d of heat stress (35/25 °C day/night) followed by a 4 wk recovery period (25/15 °C day/night). Turfgrass entries were assessed using the normalized difference vegetative index, the percentage of green obtained with digital image analysis, and membrane stability estimated by electrolyte leakage. Buffalograss [Bouteloua dactyloides (Nutt.) J.T. Columbus], Kentucky bluegrass (Poa pratensis L.), tall fescue [Schedonorus arundinaceus (Schreb.) Dumort], and slender creeping red fescue (Festuca rubra ssp. littoralis) were more tolerant of heat stress than the other species. The Canada bluegrass (Poa compressa L.), blue grama [Bouteloua gracilis (Willd. ex Kunth.) Lag. ex Griffiths], and smooth brome (Bromus inermis Leyss.) cultivars were all tolerant of heat stress; however, only one cultivar for these three species was tested, making species‐wide generalizations difficult. In some cases, the cultivars and/or selections within a given species differed in heat stress response. Almost all entries were able to recover from the heat stress by the end of the recovery period. Altogether, we were able to identify turfgrasses that should perform adequately in high‐temperature urban environments.

Epigenetic factors determine responses to internal and external stimuli in eukaryotic organisms. Whether and how environmental conditions feed back to the epigenetic landscape is more a matter of suggestion than of substantiation. Plants are suitable organisms with which to address this question due to their sessile lifestyle and diversification of epigenetic regulators. We show that several repetitive elements of Arabidopsis thaliana that are under epigenetic regulation by transcriptional gene silencing at ambient temperatures and upon short term heat exposure become activated by prolonged heat stress. Activation can occur without loss of DNA methylation and with only minor changes to histone modifications but is accompanied by loss of nucleosomes and by heterochromatin decondensation. Whereas decondensation persists, nucleosome loading and transcriptional silencing are restored upon recovery from heat stress but are delayed in mutants with impaired chromatin assembly functions. The results provide evidence that environmental conditions can override epigenetic regulation, at least transiently, which might open a window for more permanent epigenetic changes.

Humans are occasionally exposed to extreme environmental heat for a prolonged period of time. Here, we investigated testicular responses to whole-body heat exposure by placing mice in a warm chamber. Among the examined tissues, the testis was found to be most susceptible to heat stress. Heat stress induces direct responses within germ cells, such as eukaryotic initiation factor 2αphosphorylation and stress granule (SG) formation. Prolonged heat stress (42°C for 6 hr) also disturbed tissue organization, such as through blood-testis barrier (BTB) leakage. Germ cell apoptosis was induced by heat stress for 6 hr in a cell type- and developmental stage-specific manner. We previously showed that spermatocytes in the early tubular stages (I-VI) form SGs for protection against heat stress. In the mid-tubular stages (VII-VIII), BTB leakage synergistically enhances the adverse effects of heat stress on pachytene spermatocyte apoptosis. In the late tubular stages (IX-XII), SGs are not formed and severe leakage of the BTB does not occur, resulting in mild apoptosis of late-pachytene spermatocytes near meiosis. Our results revealed that multiple stress responses are involved in germ cell damage resulting from prolonged heat stress (42°C for 6 hr).