Molecular cloning and expression analysis of a cytosolic Hsp70 gene from Laminaria japonica (Laminariaceae, Phaeophyta)

The characteristics of PtHSP40 gene family in Phaeodactylum tricornutum and its response to environmental stresses

Diatom has evolved response mechanisms to cope with multiple environmental stresses. Heat shock protein 40 (HSP40) plays a key role in these response mechanisms. HSP40 gene family in higher plants has been well-studied. However, the HSP40 gene family has not been systematically investigated in marine diatom. In this study, the bioinformatic characteristics, phylogenetic relationship, conserved motifs, gene structure, chromosome distribution and the transcriptional response of PtHSP40 to different environmental stresses were analyzed in the diatom Phaeodactylum tricornutum, and quantitative real-time PCR was conducted. Totally, 55 putative PtHSP40 genes are distributed to 21 chromosomes. All PtHSP40 proteins can be divided into four groups based on their evolutionary relationship, and 54 of them contain a conserved HPD (histidine-proline-aspartic acid tripeptide) motif. Additionally, six, eleven, ten and four PtHSP40 genes were significantly upregulated under the treatments of nitrogen starvation, phosphorus deprivation, 2,2',4,4'-tetrabrominated biphenyl ether (BDE-47) and ocean acidification, respectively. More interestingly, the expression level of 9 PtHSP40 genes was obviously upregulated in response to nickel stress, suggesting the sensitive to metal stress. The different expression models of PtHSP40 genes to environmental stresses imply the specificity of PtHSP40 proteins under different stresses. This study provides a systematic understanding of the PtHSP40 gene family in P. tricornutum and a comprehensive cognition in its functions and response mechanisms to environmental stresses.

Genome-wide analysis of HSP70 gene superfamily in Pyropia yezoensis (Bangiales, Rhodophyta): identification, characterization and expression profiles in response to dehydration stress

BACKGROUND

Heat shock proteins (HSPs) perform a fundamental role in protecting plants against abiotic stresses. Individual family members have been analyzed in previous studies, but there has not yet been a comprehensive analysis of the HSP70 gene family in Pyropia yezoensis.

RESULTS

We investigated 15 putative HSP70 genes in Py. yezoensis. These genes were classified into two sub-families, denoted as DnaK and Hsp110. In each sub-family, there was relative conservation of the gene structure and motif. Synteny-based analysis indicated that seven and three PyyHSP70 genes were orthologous to HSP70 genes in Pyropia haitanensis and Porphyra umbilicalis, respectively. Most PyyHSP70s showed up-regulated expression under different degrees of dehydration stress. PyyHSP70-1 and PyyHSP70-3 were expressed in higher degrees compared with other PyyHSP70s in dehydration treatments, and then expression degrees somewhat decreased in rehydration treatment. Subcellular localization showed PyyHSP70-1-GFP and PyyHSP70-3-GFP were in the cytoplasm and nucleus/cytoplasm, respectively. Similar expression patterns of paired orthologs in Py. yezoensis and Py. haitanensis suggest important roles for HSP70s in intertidal environmental adaptation during evolution.

CONCLUSIONS

These findings provide insight into the evolution and modification of the PyyHSP70 gene family and will help to determine the functions of the HSP70 genes in Py. yezoensis growth and development.

Differentiation in fitness-related traits in response to elevated temperatures between leading and trailing edge populations of marine macrophytes

The nature of species distribution boundaries is a key subject in ecology and evolution. Edge populations are potentially more exposed to climate-related environmental pressures. Despite research efforts, little is known about variability in fitness-related traits in leading (i.e., colder, high latitude) versus trailing (i.e., warmer, low latitude) edge populations. We tested whether the resilience, i.e. the resistance and recovery, of key traits differs between a distributional cold (Greenland) and warm (Portugal) range edge population of two foundation marine macrophytes, the intertidal macroalga Fucus vesiculosus and the subtidal seagrass Zostera marina. The resistance and recovery of edge populations to elevated seawater temperatures was compared under common experimental conditions using photosynthetic efficiency and expression of heat shock proteins (HSP). Cold and warm edge populations differed in their response, but this was species specific. The warm edge population of F. vesiculosus showed higher thermal resistance and recovery whereas the cold leading edge was less tolerant. The opposite was observed in Z. marina, with reduced recovery at the warm edge, while the cold edge was not markedly affected by warming. Our results confirm that differentiation of thermal stress responses can occur between leading and trailing edges, but such responses depend on local population traits and are thus not predictable just based on thermal pressures.

Identification of HSP70 gene in Corythucha ciliata and its expression profiles under laboratory and field thermal conditions

Previous laboratory studies have demonstrated that insects can tolerate high temperatures by expressing inducible heat shock proteins (HSPs). This HSP-based tolerance, however, has seldom been studied under field conditions. Here, we cloned the HSP70 gene of Corythucha ciliata (Cchsp70), an invasive insect species with substantial thermal tolerance in subtropical China. We also compared the relative mRNA expression levels of Cchsp70 in response to controlled temperature treatments (2 h at 33-43 °C at 2 °C intervals in the laboratory) and to natural increases in temperature (08:00-14:00 at 2-h intervals, 29.7-37.2 °C) on a hot summer day in the field. The complete cDNA of Cchsp70 is 2256 bp long and has a 1917 bp open reading frame that encodes a protein (CcHSP70) with 639 amino acids. The expression levels of Cchsp70 significantly increased in response to high temperatures in both laboratory and field. At similar temperatures, however, the expression levels were much higher in the field than in the laboratory. These results suggest that CcHSP70 contributes to the thermal tolerance of C. ciliata and that factors in addition to thermal stress may induce Cchsp70 expression in the field.

Molecular cloning and functional analysis of the drought tolerance gene MsHSP70 from alfalfa (Medicago sativa L.)

Heat shock proteins (HSPs) are a ubiquitously expressed class of protective proteins that play a key role in plant response to stressful conditions. This study aimed to characterize and investigate the function of an HSP gene in alfalfa (Medicago sativa). MsHSP70, which contains a 2028-bp open reading frame, was identified through homology cloning. MsHSP70 shares high sequence identity (94.47%) with HSP70 from Medicago truncatula. Expression analysis of MsHSP70 in alfalfa organs revealed a relatively higher expression level in aerial organs such as flowers, stems and leaves than in roots. MsHSP70 was induced by heat shock, abscisic acid (ABA) and hydrogen peroxide. Transgenic Arabidopsis seedlings overexpressing MsHSP70 were hyposensitive to polyethylene glycol (PEG) and ABA treatments, suggesting that exogenous expression of MsHSP70 enhanced Arabidopsis tolerance to these stresses. Examination of physiological indexes related to drought and ABA stress demonstrated that in comparison with non-transgenic plants, T3 transgenic Arabidopsis plants had an increased proline content, higher superoxide dismutase (SOD) activity, and decreased malondialdehyde (MDA) content. Furthermore, higher relative water content (RWC) was detected in transgenic plants compared with non-transgenic plants under drought stress. These findings clearly indicate that molecular manipulation of MsHSP70 in plants can have substantial effects on stress tolerance.

Differences in structure and changes in gene regulation of murrel molecular chaperone HSP family during epizootic ulcerative syndrome (EUS) infection

Heat shock proteins (HSPs) are immunogenic, ubiquitous class of molecular chaperones, which are induced in response to various environmental and microbial stressful conditions. It plays a vital role in maintaining cellular protein homeostasis in eukaryotic cells. In this study, we described a comprehensive comparative data by bioinformatics approach on three different full length cDNA sequences of HSP family at molecular level. The cDNA sequences of three HSPs were identified from constructed cDNA library of Channa striatus and named as CsCPN60, CsHSP60 and CsHSP70. We have conducted various physicochemical study, which showed that CsHSP70 (666 amino acid) possessed a larger polypeptides followed by CsCPN60 (575) and CsCPN60 (542). Three dimensional structural analysis of these HSPs showed maximum residues in α-helices and least in β-sheets; also CsHSP60 lacks β-sheet and formed helix-turn-helix structure. Further analysis indicated that each HSP carried distinct domains and gene specific signature motif, which showed that each HSP are structurally diverse. Homology and phylogenetic study showed that the sequences taken for analysis shared maximum identity with fish HSP family. Tissue specific mRNA expression analysis revealed that all the HSPs showed maximum expression in one of the major immune organ such as CsCPN60 in kidney, CsHSP60 in spleen and CsHSP70 in head kidney. To understand the function of HSPs in murrel immune system, the elevation in mRNA expression level was analyzed against microbial oxidative stressors such as fungal (Aphanomyces invadans) and bacterial (Aeromonas hydrophila). It is interesting to note that all the HSP showed a different expression pattern and reached maximum up-regulation at 48 h post-infection (p.i) during fungal stress, whereas in bacterial stress only CsCPN60 showed maximum up-regulation at 48 h p.i, but CsHSP60 and CsHSP70 showed maximum up-regulation at 24 h p.i. The differential expression pattern showed that each HSP is diverse in function. Overall, the elevation in expression levels showed that HSPs might have potential involvement in murrel immune protection thus, protecting the organism against various external stimuli including environmental and microbial stress.

Molecular cloning and characterization of the MsHSP17.7 gene from Medicago sativa L

Heat shock proteins (HSPs) are ubiquitous protective proteins that play crucial roles in plant development and adaptation to stress, and the aim of this study is to characterize the HSP gene in alfalfa. Here we isolated a small heat shock protein gene (MsHSP17.7) from alfalfa by homology-based cloning. MsHSP17.7 contains a 477-bp open reading frame and encodes a protein of 17.70-kDa. The amino acid sequence shares high identity with MtHSP (93.98 %), PsHSP17.1 (83.13 %), GmHSP17.9 (74.10 %) and SlHSP17.6 (79.25 %). Phylogenetic analysis revealed that MsHSP17.7 belongs to the group of cytosolic class II small heat shock proteins (sHSP), and likely localizes to the cytoplasm. Quantitative RT-PCR indicated that MsHSP17.7 was induced by heat shock, high salinity, peroxide and drought stress. Prokaryotic expression indicated that the salt and peroxide tolerance of Escherichia coli was remarkably enhanced. Transgenic Arabidopsis plants overexpressing MsHSP17.7 exhibited increased root length of transgenic Arabidopsis lines under salt stress compared to the wild-type line. The malondialdehyde (MDA) levels in the transgenic lines were significantly lower than in wild-type, although proline levels were similar between transgenic and wild-type lines. MsHSP17.7 was induced by heat shock, high salinity, oxidative stress and drought stress. Overexpression analysis suggests that MsHSP17.7 might play a key role in response to high salinity stress.

Conserved and novel heat stress-responsive microRNAs were identified by deep sequencing in Saccharina japonica (Laminariales, Phaeophyta)

As a temperate-cold species, Saccharina japonica often suffers heat stress when it is transplanted to temperate and subtropical zones. Study the heat stress response and resistance mechanism of Saccharina is of great significance for understanding the acclimation to heat stress under domestication as well as for breeding new cultivars with heat stress resistance. In this study, we identified a set of heat stress-responsive miRNAs and analysed their regulation during the heat stress response. CO (control) and heat stress (HS) sRNA libraries were constructed and sequenced. Forty-nine known miRNAs and 75 novel miRNAs were identified, of which seven known and 25 novel miRNAs were expressed differentially under heat stress. Quantitative PCR of six selected miRNAs confirmed that these loci were responsive to heat stress. Thirty-nine and 712 genes were predicted to be targeted by the seven known miRNAs and 25 novel miRNAs, respectively. Gene function and pathway analyses showed that these genes probably play important roles in S. japonica heat stress tolerance. The miRNAs identified represent the first set of heat-responsive miRNAs identified from S. japonica, and their identification can help elucidate the heat stress response and resistance mechanisms in S. japonica.

Cloning and expression of a cytosolic HSP90 gene in Chlorella vulgaris

Heat shock protein 90 (HSP90), a highly conserved molecular chaperone, plays essential roles in folding, keeping structural integrity, and regulating the subset of cytosolic proteins. We cloned the cDNA of Chlorella vulgaris HSP90 (named CvHSP90) by combining homology cloning with rapid amplification of cDNA ends (RACE). Sequence analysis indicated that CvHSP90 is a cytosolic member of the HSP90 family. Quantitative RT-PCR was applied to determine the expression level of messenger RNA (mRNA) in CvHSP90 under different stress conditions. C. vulgaris was kept in different temperatures (5–45°C) for 1 h. The mRNA expression level of CvHSP90 increased with temperature from 5 to 10°C, went further from 35 to 40°C, and reached the maximum at 40°C. On the other hand, for C. vulgaris kept at 35°C for different durations, the mRNA expression level of CvHSP90 increased gradually and reached the peak at 7 h and then declined progressively. In addition, the expression level of CvHSP90 at 40 or 45 in salinity (‰) was almost fourfold of that at 25 in salinity (‰) for 2 h. Therefore, CvHSP90 may be a potential biomarker to monitor environment changes.

Transcriptomic analysis of acclimation to temperature and light stress in Saccharina latissima (Phaeophyceae)

Kelps, brown algae of the order Laminariales, dominate rocky shores and form huge kelp beds which provide habitat and nurseries for various marine organisms. Whereas the basic physiological and ecophysiological characteristics of kelps are well studied, the molecular processes underlying acclimation to different light and temperature conditions are still poorly understood. Therefore we investigated the molecular mechanisms underlying the physiological acclimation to light and temperature stress. Sporophytes of S. latissima were exposed to combinations of light intensities and temperatures, and microarray hybridizations were performed to determine changes in gene expression patterns. This first large-scale transcriptomic study of a kelp species shows that S. latissima responds to temperature and light stress with a multitude of transcriptional changes: up to 32% of genes showed an altered expression after the exposure experiments. High temperature had stronger effects on gene expression in S. latissima than low temperature, reflected by the higher number of temperature-responsive genes. We gained insights into underlying molecular processes of acclimation, which includes adjustment of the primary metabolism as well as induction of several ROS scavengers and a sophisticated regulation of Hsps. We show that S. latissima, as a cold adapted species, must make stronger efforts for acclimating to high than to low temperatures. The strongest response was caused by the combination of high temperatures with high light intensities, which proved most harmful for the alga.

Heat shock protein gene family of the Porphyra seriata and enhancement of heat stress tolerance by PsHSP70 in Chlamydomonas

Heat shock proteins and molecular chaperones are key components contributing to survival in the abiotic stress response. Porphyra seriata grows on intertidal rocks exposed to dynamic environmental changes associated with the turning tides, including desiccation and heat stress. Analysis of the ESTs of P. seriata allows us to identify the nine HSP cDNAs, which are predicted to be PsHSP90, three PsHSP70, PsHSP40 and PsHSP20, and three 5'-truncated HSP cDNAs. RT-PCR results show that most of the PsHSP transcripts were detected under normal cell growth conditions as well as heat stress, with the exception of two cDNAs. In particular, PsHSP70b and PsHSP20 transcripts were upregulated by heat stress. When the putative mitochondrial PsHSP70b was introduced and overexpressed in Chlamydomonas, transformed Chlamydomonas evidenced higher rates of survival and growth than those of the wild type under heat stress conditions. Constitutive overexpression of the PsHSP70b gene increases the transcription of the HSF1 as well as the CrHSP20 and CrHSP70 gene. These results indicate that PsHSP70b is involved in tolerance to heat stress and the effects on transcription of the CrHSP20 and CrHSP70 genes.

Isolation and characterization of a cDNA encoding a heat shock protein 70 from a sterile mutant of Ulva pertusa (Ulvales, Chlorophyta)

Synthesis and accumulation of molecular chaperones are universal responses found in all cellular organisms when exposed to a variety of unfavorable conditions. Heat shock protein 70 (Hsp70), which is one of the major classes of molecular chaperones, plays a particularly important role in cellular stress responses, and the Hsp70 system is the most intensely studied in higher plants and algae. Therefore, we isolated and characterized a cDNA clone encoding Hsp70 from a sterile strain of Ulva pertusa (Ulvales, Chlorophyta). The sterile U. pertusa Hsp70 (UpHsp70) cDNA consisted of 2,272 nucleotides and had an open reading frame encoding a polypeptide of 663 amino acid (AA) residues with a molecular mass of 71.7 kDa. Amino acid alignment and phylogenetic analysis of Hsp70s from other organisms showed that UpHsp70 was more similar to cytoplasmic Hsp70s from green algae and higher plants (> or =75%) than to those from other algae and microorganisms. Southern blot analysis indicated that the sterile U. pertusa genome had at least four cytoplasmic Hsp70-encoding genes. UpHsp70 mRNA levels were significantly affected by diurnal changes, rapidly increased by high-temperature stress, and gradually increased by exposure to copper, cadmium, and lead. These results suggest that UpHsp70 plays particularly important roles in adaptation to high-temperature conditions and diurnal changes, and is potentially involved in tolerance to heavy metal toxicity.