Expression of a gene encoding a 16.9-kDa heat-shock protein, Oshsp16.9, in Escherichia coli enhances thermotolerance

Effects of small heat shock proteins from thermotolerant bacteria on the stress resistance of Escherichia coli to temperature, pH, and hyperosmolarity

Small heat shock proteins (HSPs), such as HSP20, represent cellular thermal resistance mechanisms, to avoid protein aggregation at elevated temperatures. Recombinantly expressed HSP20s serve as a molecular tool for improving the tolerance of living cells to various physical and chemical stressors. Here, we aimed to heterologously express 18 HSP20s from 12 thermotolerant bacteria in Escherichia coli and evaluate their effects on various physical and chemical cellular stresses. Seventeen HSP20s were successfully expressed as soluble proteins. Recombinant E. coli cells were subjected to heat, cold, acidic, alkaline, and hyperosmolar stress to evaluate the effects of HSP20 proteins on stress resistance. Notably, the overexpression of 15 HSP20s enhanced the stress resistance of E. coli compared to that of the control strain. In particular, HSPs from Tepidimonas sediminis and Oceanithermus profundus improved the stress tolerance of E. coli under all tested conditions. In addition, E. coli harboring HSP20 from T. sediminis retained cell viability even after heat treatment at 52 °C for 5 days. To our knowledge, this is the first report of E. coli tolerance to prolonged (> 100 h) high-temperature stress. These findings indicate the potential of thermotolerant HSPs as molecular tools for improving stress tolerance in E. coli.

Assessment of biofilm, enzyme production and antibiotic susceptibility of bacteria from milk pre- and post-pasteurization pipelines in Algeria

Bacterial biofilm is a major concern of dairy industry due to its association with milk contamination and its derived products. Algerian pasteurized milk shelf-life does not exceed one day, which may reflect the high level of contamination of this product and presence of extracellular enzymes such as lipases and proteases. This work aimed to investigate the microbial biodiversity in milk-processing surfaces of a dairy plant in Algeria. Therefore, stainless steel cylinders were placed in piping system of the dairy system before and after pasteurization of the milk, being removed after 7 days, for biofilm maturation and microorganism isolation and identification by mass spectrometry. Fifty-nine Gram-positive isolates were identified, namely Bacillus altitudinis, Bacillus cereus, Bacillus pumilus, Bacillus subtilis, Bacillus weithenstephanensis, Enterococcus casseliflavus, Enterococcus faecium, and Staphylococcus epidermidis. In addition, twenty-four Gram-negative isolates were identified, namely Acinetobacter schindleri Enterobacter cloacae, Enterobacter xiangfangensis, Leclercia adecarboxylata, and Raoultella ornithinolytica. Bacterial isolates showed ability for production of extracellular enzymes, being 49 % capable of both proteolytic and lipolytic activities. Milk isolates were tested for the ability to form biofilms on stainless steel. The cell numbers recovered on plate count agar plates from stainless steel biofilms ranged from 3.52 to 6.92 log10 CFU/cm2, being the maximum number detected for Enterococcus casseliflavus. Bacterial isolates showed intermediate and/or resistant profiles to multiple antibiotics. Resistance to amoxicillin, cefoxitin and/or erythromycin was commonly found among the bacterial isolates.

Rice OsHsp16.9A interacts with OsHsp101 to confer thermotolerance

Class I small heat shock proteins (CI sHSPs), OsHsp16.9A and OsHsp18.0, share 74% identity in amino acid sequences and accumulate in response to heat shock treatments. Individual rice transformants overexpressing OsHsp16.9A and OsHsp18.0 exhibit distinct thermoprotection/thermotolerance modes. Under high temperature stress, OsHsp16.9A-overexpressing lines showed higher seed germination rate, seedling survival, and pollen germination than wild-type controls, while OsHsp18.0 overexpression provided higher thermoprotection/thermotolerance for seedling survival. To elucidate the functional roles of OsHsp16.9A, mass spectrometry was used to identify OsHsp16.9A-interacting proteins. OsHsp101 was consistently identified in the OsHsp16.9A protein complex in several mass spectrometry analyses of seed proteins from OsHsp16.9A-overexpressing lines. Both OsHsp16.9A and OsHsp101 proteins accumulated during similar developmental stages of rice seeds and formed a heat-stable complex under high temperature treatments in in vitro assays. Co-localization of OsHsp16.9A and OsHsp101 was observed via ratiometric bimolecular fluorescence complementation analyses. Amino acid mutation studies revealed that OsHsp16.9A glutamate residue 74 and amino acid residues 23-36 were essential for OsHsp16.9A-OsHsp101 interaction. Moreover, overexpressing OsHsp16.9A in OsHsp101 knockdown mutants did not increase the seed germination rate under heat stress, which further confirmed the functional roles of OsHsp16.9A-OsHsp101 interaction in conferring thermotolerance to rice plants.

Is the lipochaperone activity of sHSP a key to the stress response encoded in its primary sequence?

Several strategies have been put in place by organisms to adapt to their environment. One of these strategies is the production of stress proteins such as sHSPs, which have been widely described over the last 30 years for their role as molecular chaperones. Some sHSPs have, in addition, the particularity to exert a lipochaperone role by interacting with membrane lipids to maintain an optimal membrane fluidity. However, the mechanisms involved in this sHSP-lipid interaction remain poorly understood and described rather sporadically in the literature. This review gathers the information concerning the structure and function of these proteins available in the literature in order to highlight the mechanism involved in this interaction. In addition, analysis of primary sequence data of sHSPs available in database shows that sHSPs can interact with lipids via certain amino acid residues present on some β sheets of these proteins. These residues could have a key role in the structure and/or oligomerization dynamics of sHPSs, which is certainly essential for interaction with membrane lipids and consequently for maintaining optimal cell membrane fluidity.

Archaeal Hsp14 drives substrate shuttling between small heat shock proteins and thermosome: insights into a novel substrate transfer pathway

Heat shock proteins maintain protein homeostasis and facilitate the survival of an organism under stress. Archaeal heat shock machinery usually consists of only sHsps, Hsp70, and Hsp60. Moreover, Hsp70 is absent in thermophilic and hyperthermophilic archaea. In the absence of Hsp70, how aggregating protein substrates are transferred to Hsp60 for refolding remains elusive. Here, we investigated the crosstalk in the heat shock response pathway of thermoacidophilic crenarchaeon Sulfolobus acidocaldarius. In the present study, we biophysically and biochemically characterized one of the small heat shock proteins, Hsp14, of S. acidocaldarius. Moreover, we investigated its ability to interact with Hsp20 and Hsp60 to facilitate the substrate proteins' folding under stress conditions. Like Hsp20, we demonstrated that the dimer is the active form of Hsp14, and it forms an oligomeric storage form at a higher temperature. More importantly, the dynamics of the Hsp14 oligomer are maintained by rapid subunit exchange between the dimeric states, and the rate of subunit exchange increases with increasing temperature. We also tested the ability of Hsp14 to form hetero-oligomers via subunit exchange with Hsp20. We observed hetero-oligomer formation only at higher temperatures (50 °C-70 °C). Furthermore, experiments were performed to investigate the interaction between small heat shock proteins and Hsp60. We demonstrated an enthalpy-driven direct physical interaction between Hsp14 and Hsp60. Our results revealed that Hsp14 could transfer sHsp-captured substrate proteins to Hsp60, which then refolds them back to their active form.

The Caenorhabditis elegans 12-kDa small heat shock proteins with little in vitro chaperone activity play crucial roles for its dauer formation, longevity, and reproduction

Small heat shock proteins (sHSPs) are known to exhibit in vitro chaperone activity by suppressing the aggregation of misfolded proteins. The 12-kDa sHSPs (Hsp12s) subfamily members from Caenorhabditis elegans, including Hsp12.2, Hsp12.3, and Hsp12.6, however, are devoid of such chaperone activity, and their in vivo functions are poorly understood. Here we verified that Hsp12.1, similar to its homologs Hsp12.2, Hsp12.3, and Hsp12.6, hardly exhibited any chaperone activity. Strikingly, we demonstrated that these Hsp12s seem to play crucial physiological roles in C. elegans, for suppressing dauer formation and promoting both longevity and reproduction. A unique sHSP gene from Filarial nematode worm Brugia malayi was identified such that it encodes two products, one as a full-length Hsp12.6 protein and the other one having an N-terminal arm of normal length but lacks the C-terminal extension. This gene may represent an intermediate form in evolution from a common sHSP to a Hsp12. Together, our study offers insights on what biological functions the chaperone-defective sHSPs may exhibit and also implicates an evolutionary scenario for the unique Hsp12s subfamily.

Network of Entamoeba histolytica HSP18.5 dimers formed by two overlapping [IV]-X-[IV] motifs

Small heat shock proteins (sHSPs) are ATP-independent molecular chaperones with low molecular weight that prevent the aggregation of proteins during stress conditions and maintain protein homeostasis in the cell. sHSPs exist in dynamic equilibrium as a mixture of oligomers of various sizes with a constant exchange of subunits between them. Many sHSPs form cage-like assemblies that may dissociate into smaller oligomers during stress conditions. We carried out the functional and structural characterization of a small heat shock protein, HSP18.5, from Entamoeba histolytica (EhHSP18.5). It showed a pH-dependent change in its oligomeric state, which varied from a tetramer to larger than 48-mer. EhHSP18.5 protected Nde I and lysozyme substrates from temperature and chemical stresses, respectively. The crystal structure of EhHSP18.5 was determined at a resolution of 3.28 Å in C2221 cell with four subunits in the asymmetric unit forming two non-metazoan sHSP-type dimers. Unlike the reported cage-like structures, EhHSP18.5 formed a network of linear chains of molecules in the crystal. Instead of a single [IV]-X-[IV] motif, EhHSP18.5 has two overlapping I/V-X-I/V sequences at the C-terminus giving rise to novel interactions between the dimers. Negative staining Electron Microscopy images of EhHSP18.5 showed the presence of multiple oligomers: closed structures of various sizes and long tube-like structures.

In Vivo, High-Throughput Selection of Thermostable Cyclohexanone Monooxygenase (CHMO)

Cyclohexanone monooxygenase (CHMO) from Acinetobacter sp. NCIMB 9871 is characterized as having wide substrate versatility for the biooxidation of (cyclic) ketones into esters and lactones with high stereospecificity. Despite industrial potential, CHMO usage is restricted by poor thermostability. Limited high-throughput screening tools and challenges in rationally engineering thermostability have impeded CHMO engineering efforts. We demonstrate the application of an aerobic, high-throughput growth selection platform in Escherichia coli (strain MX203) for the discovery of thermostability enhancing mutations for CHMO. The selection employs growth for the easy readout of CHMO activity in vivo, by requiring nicotinamide adenine dinucleotide phosphate (NADPH)-consuming enzymes to restore cellular redox balance. In the presence of the native substrate cyclohexanone, variant CHMO GV (A245G-A288V) was discovered from a random mutagenesis library screened at 42 °C. This variant retained native activity, exhibited ~4.4-fold improvement in residual activity after 30 °C incubation, and demonstrated ~5-fold higher cyclohexanone conversion at 37 °C compared to the wild type. Molecular modeling indicates that CHMO GV experiences more favorable residue packing and supports additional backbone hydrogen bonding. Further rational design resulted in CHMO A245G-A288V-T415C with improved thermostability at 45 °C. Our platform for oxygenase evolution enabled the rapid engineering of protein stability critical for industrial scalability.

A class I cytosolic HSP20 of rice enhances heat and salt tolerance in different organisms

Small heat shock proteins (sHSPs) have been thought to function as chaperones, protecting their targets from denaturation and aggregation when organisms are subjected to various biotic and abiotic stresses. We previously reported an sHSP from Oryza sativa (OsHSP20) that homodimerizes and forms granules within the cytoplasm but its function was unclear. We now show that OsHSP20 transcripts were significantly up-regulated by heat shock and high salinity but not by drought. A recombinant protein was purified and shown to inhibit the thermal aggregation of the mitochondrial malate dehydrogenase (MDH) enzyme in vitro, and this molecular chaperone activity suggested that OsHSP20 might be involved in stress resistance. Heterologous expression of OsHSP20 in Escherichia coli or Pichia pastoris cells enhanced heat and salt stress tolerance when compared with the control cultures. Transgenic rice plants constitutively overexpressing OsHSP20 and exposed to heat and salt treatments had longer roots and higher germination rates than those of control plants. A series of assays using its truncated mutants showed that its N-terminal arm plus the ACD domain was crucial for its homodimerization, molecular chaperone activity in vitro, and stress tolerance in vivo. The results supported the viewpoint that OsHSP20 could confer heat and salt tolerance by its molecular chaperone activity in different organisms and also provided a more thorough characterization of HSP20-mediated stress tolerance in O. sativa.

Silencing of class I small heat shock proteins affects seed-related attributes and thermotolerance in rice seedlings

MAIN CONCLUSION

Silencing of CI-sHsps by RNAi negatively affected the seed germination process and heat stress response of rice seedlings. Seed size of RNAiCI-sHsp was reduced as compared to wild-type plants. Small heat shock proteins (sHsps) are the ATP-independent chaperones ubiquitously expressed in response to diverse environmental and developmental cues. Cytosolic sHsps constitute the major repertoire of sHsp family. Rice cytosolic class I (CI)-sHsps consists of seven members (Hsp16.9A, Hsp16.9B, Hsp16.9C, Hsp17.4, Hsp17.7, Hsp17.9A and Hsp18). Purified OsHsp17.4 and OsHsp17.9A proteins exhibited chaperone activity by preventing formation of large aggregates with model substrate citrate synthase. OsHsp16.9A and OsHsp17.4 showed nucleo-cytoplasmic localization, while the localization of OsHsp17.9A was preferentially in the nucleus. Transgenic tobacco plants expressing OsHsp17.4 and OsHsp17.9A proteins and Arabidopsis plants ectopically expressing OsHsp17.4 protein showed improved thermotolerance to the respective trans-hosts during the post-stress recovery process. Single hairpin construct was designed to generate all CI-sHsp silenced (RNAiCI-sHsp) rice lines. The major vegetative and reproductive attributes of the RNAiCI-sHsp plants were comparable to the wild-type rice plants. Basal and acquired thermotolerance response of RNAiCI-sHsp seedlings of rice was mildly affected. The seed length of RNAiCI-sHsp rice plants was significantly reduced. The seed germination process was delayed and seed thermotolerance of RNAiCI-sHsp was negatively affected than the non-transgenic seeds. We, thus, implicate that sHsp genes are critical in seedling thermotolerance and seed physiology.

Genome-wide identification and transcriptional profiling of small heat shock protein gene family under diverse abiotic stress conditions in Sorghum bicolor (L.)

The small heat shock proteins (sHsps/Hsp20s) are the molecular chaperones that maintain proper folding, trafficking and disaggregation of proteins under diverse abiotic stress conditions. In the present investigation, a genome-wide scan revealed the presence of a total of 47 sHsps in Sorghum bicolor (SbsHsps), distributed across 10 subfamilies, the major subfamily being P (plastid) group with 17 genes. Chromosomes 1 and 3 appear as the hot spot regions for SbsHsps, and majority of them were found acidic, hydrophilic, unstable and intron less. Interestingly, promoter analysis indicated that they are associated with both biotic and abiotic stresses, as well as plant development. Sorghum sHsps exhibited 15 paralogous and 20 orthologous duplications. Expression analysis of 15 genes selected from different subfamilies showed high transcript levels in roots and leaves implying that they are likely to participate in the developmental processes. SbsHsp genes were highly induced by diverse abiotic stresses inferring their critical role in mediating the environmental stress responses. Gene expression data revealed that SbsHsp-02 is a candidate gene expressed in all the tissues under varied stress conditions tested. Our results contribute to the understanding of the complexity of SbsHsp genes and help to analyse them further for functional validation.

AgsA response to cadmium and copper effects at different temperatures in Escherichia coli

Small heat shock proteins (sHsps), present from prokaryotes to eukaryotes, are a highly conserved molecular chaperone family. They play a crucial role in protecting organisms against cellular insults from single or multiple environmental stressors including heavy metal exposure, heat or cold shock, oxidative stress, desiccation, etc. Here, the toxicity of cadmium and copper, and their ability to modify the cellular growth rate at different temperatures in Escherichia coli cells were tested. Also, the response mechanism of the sHSP aggregation-suppressing protein (AgsA) in such multiple stress conditions was investigated. The results showed that the half effect concentration (EC₅₀ ) of cadmium in AgsA-transformed E. coli cells at 37°C, 42°C, and 50°C were 11.106, 29.50, and 4.35 mg/L, respectively, and that of the control cells lacking AgsA were 5.05, 0.93, and 0.18 mg/L, respectively, while the half effect concentration (EC₅₀ ) of copper in AgsA-transformed E. coli cells at 37°C, 42°C, and 50°C were 27.3, 3.40, and 1.28 mg/L, respectively, and that of the control cells lacking AgsA were 27.7, 5.93, and 0.134 mg/L, respectively. The toxicities of cadmium and copper at different temperatures as observed by their modification of the cellular growth rate and inhibitory effects were in a dose-dependent manner. Additionally, biochemical characterization of AgsA protein in cells subjected to cadmium and copper stresses at different temperatures implicated suppressed aggregation of cellular proteins in AgsA-transformed E. coli cells. Altogether, our data implicate the AgsA protein as a sensitive protein-based biomarker for metal-induced toxicity monitoring.

The oligomeric plasticity of Hsp20 of Sulfolobus acidocaldarius protects environment-induced protein aggregation and membrane destabilization

Small heat shock proteins (sHsps) are a ubiquitous family of molecular chaperones that rescue misfolded proteins from irreversible aggregation during cellular stress. Many such sHsps exist as large polydisperse species in solution, and a rapid dynamic subunit exchange between oligomeric and dissociated forms modulates their function under a variety of stress conditions. Here, we investigated the structural and functional properties of Hsp20 from thermoacidophilic crenarchaeon Sulfolobus acidocaldarius. To provide a framework for investigating the structure-function relationship of Hsp20 and understanding its dynamic nature, we employed several biophysical and biochemical techniques. Our data suggested the existence of a ~24-mer of Hsp20 at room temperature (25 °C) and a higher oligomeric form at higher temperature (50 °C-70 °C) and lower pH (3.0-5.0). To our surprise, we identified a dimeric form of protein as the functional conformation in the presence of aggregating substrate proteins. The hydrophobic microenvironment mainly regulates the oligomeric plasticity of Hsp20, and it plays a key role in the protection of stress-induced protein aggregation. In Sulfolobus sp., Hsp20, despite being a non-secreted protein, has been reported to be present in secretory vesicles and it is still unclear whether it stabilizes substrate proteins or membrane lipids within the secreted vesicles. To address such an issue, we tested the ability of Hsp20 to interact with membrane lipids along with its ability to modulate membrane fluidity. Our data revealed that Hsp20 interacts with membrane lipids via a hydrophobic interaction and it lowers the propensity of in vitro phase transition of bacterial and archaeal lipids.

In a quest for engineering acidophiles for biomining applications: challenges and opportunities

Biomining with acidophilic microorganisms has been used at commercial scale for the extraction of metals from various sulfide ores. With metal demand and energy prices on the rise and the concurrent decline in quality and availability of mineral resources, there is an increasing interest in applying biomining technology, in particular for leaching metals from low grade minerals and wastes. However, bioprocessing is often hampered by the presence of inhibitory compounds that originate from complex ores. Synthetic biology could provide tools to improve the tolerance of biomining microbes to various stress factors that are present in biomining environments, which would ultimately increase bioleaching efficiency. This paper reviews the state-of-the-art tools to genetically modify acidophilic biomining microorganisms and the limitations of these tools. The first part of this review discusses resilience pathways that can be engineered in acidophiles to enhance their robustness and tolerance in harsh environments that prevail in bioleaching. The second part of the paper reviews the efforts that have been carried out towards engineering robust microorganisms and developing metabolic modelling tools. Novel synthetic biology tools have the potential to transform the biomining industry and facilitate the extraction of value from ores and wastes that cannot be processed with existing biomining microorganisms.

Heterologous expression of AgsA enhances Escherichia coli tolerance to the combined effect of elevated temperature and Zinc toxicity

Small heat shock proteins (sHSPs) are ubiquitous stress proteins that are able to protect the cells against cellular insults from temperature, heavy metal etc. However, the molecular chaperone roles of sHSPs in enhancing growth and adaptation under combined temperature and metal stresses in Escherichia coli cells have been poorly understood. Here, we analyze the function of recombinant AgsA, a small heat shock protein from Salmonella enterica serovar Typhimurium under combined temperature and zinc stress in E. coli. Our results show that the heterologous expression of AgsA significantly increases the tolerance of E. coli cells to the combined effect of temperature stress and zinc toxicity by maintaining the stability of soluble proteins. Furthermore, there was remarkable and significant difference in the half effect concentration (EC50) of zinc at all temperatures treatments in both test cells. The EC50s of zinc at 37 °C, 42 °C and 50 °C were 15.24 mg/L, 29.30 mg/L, and 5.98 mg/L respectively in the AgsA-transformed E. coli cells, and 3.03 mg/L, 2.38 mg/L, and 0.373 mg/L, respectively in the control cells lacking AgsA. Together, our data indicate a good concentration-response relationship between all three temperatures treatment and zinc toxicity in E. coli, and establish for the first time the combined effects of temperature and zinc toxicity on E. coli cells. Also, the AgsA protein response to combined thermal and metal stress could serve as a molecular biomarker for the assessment of interactive stress damage to the cells.

Heterogeneous expression of DnaK gene from Alicyclobacillus acidoterrestris improves the resistance of Escherichia coli against heat and acid stress

Alicyclobacillus acidoterrestris, an acidophilic and thermophilic bacteria, is an important microbial resource for stress resistance genes screening. In this study, DnaK gene from A. acidoterrestris was subcloned to construct the recombinant plasmid pET28a-DnaK. The successful construction of the plasmid was verified by double-enzyme digestion and sequencing analysis. The recombinant plasmid was transformed into Escherichia coli BL21 and isopropy-β-D-thiogalactoside (IPTG) was used to induce recombinant E. coli to express DnaK gene. A 70 kD fusion protein was identified by SDS-PAGE, which suggested that DnaK gene from A. acidoterrestris was successfully expressed. The recombinant and wild BL21 were treated with high temperatures of 54, 56 and 58 °C at pH values of 5.0-7.0 to compare the effects of heterogeneous expression of the DnaK gene from A. acidoterrestris on the stress resistance. The experimental results showed that survival rate of recombinant BL21-DnaK has been improved considerably under heat and acid stresses in contrast with the wild BL21, and D-values of recombinant BL21 were 14.7-72% higher than that of wild BL21, which demonstrated that heterogeneous expression of DnaK gene from A. acidoterrestris could significantly enhance the resistance of host bacteria E. coli against heat and acid stresses.

Heterologous expression of an engineered protein domain acts as chaperone and enhances thermotolerance of Escherichia coli

Heat shock proteins (HSPs) are known to confer protection to the stressed cells by rescuing vital host cell proteins. In the present study we have demonstrated that heterologous expression of N-terminal domain of hyperthermophilic L-asparaginase (NPfA) confers thermotolerance to E. coli. The recombinant expression of NPfA enabled E. coli to demonstrate typical growth behavior at 52°C and survive a thermal shock up to 62°C, both being the highest reported temperatures for growth and heat shock survival. To understand the basis of protection proteome analysis of these cells was carried out which showed that NPfA guards a battery of proteins, especially related to gene regulations and repair, providing definite survival advantage to the stressed cells. Thus NPfA a non-canonical, non-natural chaperone has been shown to render E. coli cells with selective growth advantage under extremes of conditions. We propose that such modified, heat stabilized hosts could be utilized in developing heat-induced expression systems as well for the recombinant expression of thermophilic proteins.

A novel plant E3 ligase stabilizes Escherichia coli heat shock factor σ32

The heat shock response is crucial for organisms against heat-damaged proteins and maintaining homeostasis at a high temperature. Heterologous expression of eukaryotic molecular chaperones protects Escherichia coli from heat stress. Here we report that expression of the plant E3 ligase BnTR1 significantly increases the thermotolerance of E. coli. Different from eukaryotic chaperones, BnTR1 expression induces the accumulation of heat shock factor σ³² and heat shock proteins. The active site of BnTR1 in E. coli is the zinc fingers of the RING domain, which interacts with DnaK resulting in stabilizing σ³². Our findings indicate the expression of BnTR1 confers thermoprotective effects on E. coli cells, and it may provide useful clues to engineer thermophilic bacterial strains.

Genome-wide identification and analysis of biotic and abiotic stress regulation of small heat shock protein (HSP20) family genes in bread wheat

Small Heat Shock Proteins (sHSPs)/HSP20 are molecular chaperones that protect plants by preventing protein aggregation during abiotic stress conditions, especially heat stress. Due to global climate change, high temperature is emerging as a major threat to wheat productivity. Thus, the identification of HSP20 and analysis of HSP transcriptional regulation under different abiotic stresses in wheat would help in understanding the role of these proteins in abiotic stress tolerance. We used sequences of known rice and Arabidopsis HSP20 HMM profiles as queries against publicly available wheat genome and wheat full length cDNA databases (TriFLDB) to identify the respective orthologues from wheat. 163 TaHSP20 (including 109 sHSP and 54 ACD) genes were identified and classified according to the sub-cellular localization and phylogenetic relationship with sequenced grass genomes (Oryza sativa, Sorghum bicolor, Zea mays, Brachypodium distachyon and Setaria italica). Spatio-temporal, biotic and abiotic stress-specific expression patterns in normalized RNA seq and wheat array datasets revealed constitutive as well as inductive responses of HSP20 in different tissues and developmental stages of wheat. Promoter analysis of TaHSP20 genes showed the presence of tissue-specific, biotic, abiotic, light-responsive, circadian and cell cycle-responsive cis-regulatory elements. 14 TaHSP20 family genes were under the regulation of 8 TamiRNA genes. The expression levels of twelve HSP20 genes were studied under abiotic stress conditions in the drought- and heat-tolerant wheat genotype C306. Of the 13 TaHSP20 genes, TaHSP16.9H-CI showed high constitutive expression with upregulation only under salt stress. Both heat and salt stresses upregulated the expression of TaHSP17.4-CI, TaHSP17.7A-CI, TaHSP19.1-CIII, TaACD20.0B-CII and TaACD20.6C-CIV, while TaHSP23.7-MTI was specifically induced only under heat stress. Our results showed that the identified TaHSP20 genes play an important role under different abiotic stress conditions. Thus, the results illustrate the complexity of the TaHSP20 gene family and its stress regulation in wheat, and suggest that sHSPs as attractive breeding targets for improvement of the heat tolerance of wheat.

Identification and characterization of the GhHsp20 gene family in Gossypium hirsutum

In higher plants, Heat Shock Protein 20 (Hsp20) plays crucial roles in growth, development and responses to abiotic stresses. In this study, 94 GhHsp20 genes were identified in G. hirsutum, and these genes were phylogenetically clustered into 14 subfamilies. Out of these, 73 paralogous gene pairs remained in conserved positions on segmental duplicated blocks and only 14 genes clustered into seven tandem duplication event regions. Transcriptome analysis showed that 82 GhHsp20 genes were expressed in at least one tested tissues, indicating that the GhHsp20 genes were involved in physiological and developmental processes of cotton. Further, expression profiles under abiotic stress exhibited that two-thirds of the GhHsp20 genes were responsive to heat stress, while 15 genes were induced by multiple stresses. In addition, qRT-PCR confirmed that 16 GhHsp20 genes were hot-induced, and eight genes were up-regulated under multiple abiotic stresses and stress-related phytohormone treatments. Taken together, our results presented here would be helpful in laying the foundation for understanding the complex mechanisms of GhHsp20 mediated developmental processes and abiotic stress signaling transduction pathways in cotton.

Global transcriptional analysis of Escherichia coli expressing IrrE, a regulator from Deinococcus radiodurans, in response to NaCl shock

Improving the microbial tolerance to stresses is very important for bioprocesses. Our previous study showed that IrrE, a global regulator from the extremely radioresistant bacterium Deinococcus radiodurans, dramatically enhanced the multi-stress tolerance of Escherichia coli when expressed exogenously. However, the function of IrrE is still unclear. In this study, we used whole-genome microarray assays to profile the global gene expression of the IrrE-expressing E. coli strain MGE and the control strain MGT with or without salt shock. The analysis showed that IrrE expression led to many differentially expressed genes in E. coli, which were responsible for the transport and metabolism of trehalose and glycerol, nucleotide biosynthesis, carbon source utilization, amino acid utilization, and acid resistance, including many RpoS-dependent genes, e.g., the trehalose biosynthesis genes otsAB, the acid-resistance genes gadABC and uspB, the osmotic and oxidative stress response genes katE (response to DNA damage stimulus and stress) and osmBC (response to stress), and gadWX (which controls the transcription of pH-inducible genes). The intracellular content of trehalose and glycerol increased significantly in the IrrE-expressing strain after NaCl treatment for 0 and 60 min as determined by HPLC. These results indicated the possibility that IrrE regulates the global regulator RpoS. Interestingly, we found that although IrrE did not affect the level of the rpoS transcript, it enhanced the accumulation of the RpoS protein by increasing the expression of the antiadaptors, AppY, IraM and IraD, which inhibit RpoS degradation, suggesting that the accumulation of RpoS due to IrrE regulation is an important way to improve tolerance to salt and other stresses in E. coli.

Characterization of rice small heat shock proteins targeted to different cellular organelles

Small heat shock proteins (sHSPs) are a family of ATP-independent molecular chaperones which prevent cellular protein aggregation by binding to misfolded proteins. sHSPs form large oligomers that undergo drastic rearrangement/dissociation in order to execute their chaperone activity in protecting substrates from stress. Substrate-binding sites on sHSPs have been predominantly mapped on their intrinsically disordered N-terminal arms. This region is highly variable in sequence and length across species, and has been implicated in both oligomer formation and in mediating chaperone activity. Here, we present our results on the functional and structural characterization of five sHSPs in rice, each differing in their subcellular localisation, viz., cytoplasm, nucleus, chloroplast, mitochondria and peroxisome. We performed activity assays and dynamic light scattering studies to highlight differences in the chaperone activity and quaternary assembly of sHSPs targeted to various organelles. By cloning constructs that differ in the length and sequence of the tag in the N-terminal region, we have probed the sensitivity of sHSP oligomer assembly and chaperone activity to the length and amino acid composition of the N-terminus. In particular, we have shown that the incorporation of an N-terminal tag has significant consequences on sHSP quaternary structure.

Molecular Cloning and Differential Expression of Cytosolic Class I Small Hsp Gene Family in Pennisetum glaucum (L.)

Small heat shock protein (Hsp) family genes have been reported in several plant species that function as molecular chaperones to protect proteins from being denatured in extreme conditions. As a first step towards the isolation and characterization of genes that contribute to combating abiotic stresses particularly heat stress, construction and screening of the subtracted complementary DNA (cDNA) library is reported here. In this study, a subtractive heat stress cDNA library was constructed that was used to isolate members of small Hsps (sHsps) using PgsHsp17.9A gene as a probe. As a result, a total of 150 cDNA clones were isolated from the subtracted cDNA library screening, leading to 121 high-quality expressed sequence tags (ESTs), with an average size of 450 bp, comprising of 15 contigs, and majority of these isolated sHsp genes belong to cytosolic class I (CI) family. In silico sequence analysis of CI-sHsp family genes revealed that the length of sHsp proteins varied from 151 to 159 amino acids and showed large variation in isoelectric point value (5.03 to 10.05) and a narrow range of molecular weight (16.09 to 17.94 kDa). The real-time PCR results demonstrated that CI-sHsp genes are differentially expressed in Pennisetum leaves under different abiotic stress conditions particularly at high temperature. The results presented in this study provide basic information on PgCI-sHsp family genes and form the foundation for future functional studies of these genes.

A novel mechanism for small heat shock proteins to function as molecular chaperones

Small heat shock proteins (sHSPs) are molecular chaperones ubiquitously present in all forms of life, but their function mechanisms remain controversial. Here we show by cryo-electron microscopy and single particle 3D reconstruction that, at the low temperatures (4-25°C), CeHSP17 (a sHSP from Caenorhabditis elegans) exists as a 24-subunit spherical oligomer with tetrahedral symmetry. Our studies demonstrate that CeHSP17 forms large sheet-like super-molecular assemblies (SMAs) at the high temperatures (45-60°C), and such SMAs are apparently the form that exhibits chaperone-like activity. Our findings suggest a novel molecular mechanism for sHSPs to function as molecular chaperones.

Overexpression of the HspL Promotes Agrobacterium tumefaciens Virulence in Arabidopsis Under Heat Shock Conditions

Agrobacterium tumefaciens transfers a specific DNA fragment from the resident tumor-inducing (Ti) plasmid and effector virulence (Vir) proteins to plant cells during infection. A. tumefaciens VirB1-11 and VirD4 proteins assemble as the type IV secretion system (T4SS), which mediates transfer of the T-DNA and effector Vir protein into plant cells, thus resulting in crown gall disease in plants. Previous studies revealed that an α-crystallin-type, small heat-shock protein (HspL) is a more effective VirB8 chaperone than three other small heat-shock proteins (HspC, HspAT1, and HspAT2). Additionally, HspL contributes to efficient T4SS-mediated DNA transfer and tumorigenesis under room-temperature growth. In this study, we aimed to characterize the impact of HspL on Agrobacterium-mediated transformation efficiency under heat-shock treatment. During heat shock, transient transformation efficiency and VirB8 protein accumulation were lower in the hspL deletion mutant than in the wild type. Overexpression of HspL in A. tumefaciens enhanced the transient transformation efficiency in root explants of both susceptible and recalcitrant Arabidopsis ecotypes. In addition, the reduced transient transformation efficiency during heat stress was recovered by overexpression of HspL in A. tumefaciens. HspL may help maintain VirB8 homeostasis and elevate Agrobacterium-mediated transformation efficiency under both heat-shock and nonheat-shock growth.

Expression of a gene encoding a rice RING zinc-finger protein, OsRZFP34, enhances stomata opening

By oligo microarray expression profiling, we identified a rice RING zinc-finger protein (RZFP), OsRZFP34, whose gene expression increased with high temperature or abscisic acid (ABA) treatment. As compared with the wild type, rice and Arabidopsis with OsRZFP34 overexpression showed increased relative stomata opening even with ABA treatment. Furthermore, loss-of-function mutation of OsRZFP34 and AtRZFP34 (At5g22920), an OsRZFP34 homolog in Arabidopsis, decreased relative stomata aperture under nonstress control conditions. Expressing OsRZFP34 in atrzfp34 reverted the mutant phenotype to normal, which indicates a conserved molecular function between OsRZFP34 and AtRZFP34. Analysis of water loss and leaf temperature under stress conditions revealed a higher evaporation rate and cooling effect in OsRZFP34-overexpressing Arabidopsis and rice than the wild type, atrzfp34 and osrzfp34. Thus, stomata opening, enhanced leaf cooling, and ABA insensitivity was conserved with OsRZFP34 expression. Transcription profiling of transgenic rice overexpressing OsRZFP34 revealed many genes involved in OsRZFP34-mediated stomatal movement. Several genes upregulated or downregulated in OsRZFP34-overexpressing plants were previously implicated in Ca(2+) sensing, K(+) regulator, and ABA response. We suggest that OsRZFP34 may modulate these genes to control stomata opening.

Chaperone function and mechanism of small heat-shock proteins

Small heat-shock proteins (sHSPs) are ubiquitous ATP-independent molecular chaperones that play crucial roles in protein quality control in cells. They are able to prevent the aggregation and/or inactivation of various non-native substrate proteins and assist the refolding of these substrates independently or under the help of other ATP-dependent chaperones. Substrate recognition and binding by sHSPs are essential for their chaperone functions. This review focuses on what natural substrate proteins an sHSP protects and how it binds the substrates in cells under fluctuating conditions. It appears that sHSPs of prokaryotes, although being able to bind a wide range of cellular proteins, preferentially protect certain classes of functional proteins, such as translation-related proteins and metabolic enzymes, which may well explain why they could increase the resistance of host cells against various stresses. Mechanistically, the sHSPs of prokaryotes appear to possess numerous multi-type substrate-binding residues and are able to hierarchically activate these residues in a temperature-dependent manner, and thus act as temperature-regulated chaperones. The mechanism of hierarchical activation of substrate-binding residues is also discussed regarding its implication for eukaryotic sHSPs.

A small heat shock protein enables Escherichia coli to grow at a lethal temperature of 50°C conceivably by maintaining cell envelope integrity

It is essential for organisms to adapt to fluctuating growth temperatures. Escherichia coli, a model bacterium commonly used in research and industry, has been reported to grow at a temperature lower than 46.5°C. Here we report that the heterologous expression of the 17-kDa small heat shock protein from the nematode Caenorhabditis elegans, CeHSP17, enables E. coli cells to grow at 50°C, which is their highest growth temperature ever reported. Strikingly, CeHSP17 also rescues the thermal lethality of an E. coli mutant deficient in degP, which encodes a protein quality control factor localized in the periplasmic space. Mechanistically, we show that CeHSP17 is partially localized in the periplasmic space and associated with the inner membrane of E. coli, and it helps to maintain the cell envelope integrity of the E. coli cells at the lethal temperatures. Together, our data indicate that maintaining the cell envelope integrity is crucial for the E. coli cells to grow at high temperatures and also shed new light on the development of thermophilic bacteria for industrial application.

Multilevel structural characteristics for the natural substrate proteins of bacterial small heat shock proteins

Small heat shock proteins (sHSPs) are ubiquitous molecular chaperones that prevent the aggregation of various non-native proteins and play crucial roles for protein quality control in cells. It is poorly understood what natural substrate proteins, with respect to structural characteristics, are preferentially bound by sHSPs in cells. Here we compared the structural characteristics for the natural substrate proteins of Escherichia coli IbpB and Deinococcus radiodurans Hsp20.2 with the respective bacterial proteome at multiple levels, mainly by using bioinformatics analysis. Data indicate that both IbpB and Hsp20.2 preferentially bind to substrates of high molecular weight or moderate acidity. Surprisingly, their substrates contain abundant charged residues but not abundant hydrophobic residues, thus strongly indicating that ionic interactions other than hydrophobic interactions also play crucial roles for the substrate recognition and binding of sHSPs. Further, secondary structure prediction analysis indicates that the substrates of low percentage of β-sheets or coils but high percentage of α-helices are un-favored by both IbpB and Hsp20.2. In addition, IbpB preferentially interacts with multi-domain proteins but unfavorably with α + β proteins as revealed by SCOP analysis. Together, our data suggest that bacterial sHSPs, though having broad substrate spectrums, selectively bind to substrates of certain structural features. These structural characteristic elements may substantially participate in the sHSP-substrate interaction and/or increase the aggregation tendency of the substrates, thus making the substrates more preferentially bound by sHSPs.

In vivo substrate diversity and preference of small heat shock protein IbpB as revealed by using a genetically incorporated photo-cross-linker

Small heat shock proteins (sHSPs), as ubiquitous molecular chaperones found in all forms of life, are known to be able to protect cells against stresses and suppress the aggregation of a variety of model substrate proteins under in vitro conditions. Nevertheless, it is poorly understood what natural substrate proteins are protected by sHSPs in living cells. Here, by using a genetically incorporated photo-cross-linker (p-benzoyl-l-phenylalanine), we identified a total of 95 and 54 natural substrate proteins of IbpB (an sHSP from Escherichia coli) in living cells with and without heat shock, respectively. Functional profiling of these proteins (110 in total) suggests that IbpB, although binding to a wide range of cellular proteins, has a remarkable substrate preference for translation-related proteins (e.g. ribosomal proteins and amino-acyl tRNA synthetases) and moderate preference for metabolic enzymes. Furthermore, these two classes of proteins were found to be more prone to aggregation and/or inactivation in cells lacking IbpB under stress conditions (e.g. heat shock). Together, our in vivo data offer novel insights into the chaperone function of IbpB, or sHSPs in general, and suggest that the preferential protection on the protein synthesis machine and metabolic enzymes may dominantly contribute to the well known protective effect of sHSPs on cell survival against stresses.

ZmHSP16.9, a cytosolic class I small heat shock protein in maize (Zea mays), confers heat tolerance in transgenic tobacco

Various organisms produce HSPs in response to high temperature and other stresses. The function of heat shock proteins, including small heat shock protein (sHSP), in stress tolerance is not fully explored. To improve our understanding of sHSPs, we isolated ZmHSP16.9 from maize. Sequence alignments and phylogenetic analysis reveal this to be a cytosolic class I sHSP. ZmHSP16.9 expressed in root, leaf and stem tissues under 40 °C treatment, and was up-regulated by heat stress and exogenous H₂O₂. Overexpression of ZmHSP16.9 in transgenic tobacco conferred tolerance to heat and oxidative stresses by increased seed germination rate, root length, and antioxidant enzyme activities compared with WT plants. These results support the positive role of ZmHSP16.9 in response to heat stress in plant.

KEY MESSAGE

The overexpression of ZmHSP16.9 enhanced tolerance to heat and oxidative stress in transgenic tobacco.

The oligomer plasticity of the small heat-shock protein Lo18 from Oenococcus oeni influences its role in both membrane stabilization and protein protection

The ability of the small Hsp (heat-shock protein) Lo18 from Oenococcus oeni to modulate the membrane fluidity of liposomes or to reduce the thermal aggregation of proteins was studied as a function of the pH in the range 5-9. We have determined by size-exclusion chromatography and analytical ultracentrifugation that Lo18 assembles essentially as a 16-mer at acidic pH. Its quaternary structure evolves to a mixture of lower molecular mass oligomers probably in dynamic equilibrium when the pH increases. The best Lo18 activities are observed at pH 7 when the particle distribution contains a major proportion of dodecamers. At basic pH, particles corresponding to a dimer prevail and are thought to be the building blocks leading to oligomerization of Lo18. At acidic pH, the dimers are organized in a double-ring of stacked octamers to form the 16-mer as shown by the low-resolution structure determined by electron microscopy. Experiments performed with a modified protein (A123S) shown to preferentially form dimers confirm these results. The α-crystallin domain of Methanococcus jannaschii Hsp16.5, taken as a model of the Lo18 counterpart, fits with the electron microscopy envelope of Lo18.

Proteomics of rice in response to heat stress and advances in genetic engineering for heat tolerance in rice

Rice is the most important food crop worldwide. Global warming inevitably affects the grain yields of rice. Recent proteomics studies in rice have provided evidence for better understanding the mechanisms of thermal adaptation. Heat stress response in rice is complicated, involving up- or down-regulation of numerous proteins related to different metabolic pathways. The heat-responsive proteins mainly include protection proteins, proteins involved in protein biosynthesis, protein degradation, energy and carbohydrate metabolism, and redox homeostasis. In addition, increased thermotolerance in transgenic rice was obtained by overexpression of rice genes and genes from other plants. On the other hand, heterologous expression of some rice proteins led to enhanced thermotolerance in bacteria and other easily transformed plants. In this paper, we review the proteomic characterization of rice in response to high temperature and achievements of genetic engineering for heat tolerance in rice.

Proteome analysis of maize seeds: the effect of artificial ageing

Previous understanding of the mechanism of seed ageing is largely based on observations on imbibed seeds rather than dry seeds. The present research was conducted to investigate whether seed ageing has effects on the dry seeds through proteome analysis. Maize (Zea mays cv. Dabaitou) seeds were artificially aged at 50°C (13.58% moisture content) for 5 or 13 days, and the total protein was extracted from embryos of the dry seeds. Two-dimensional electrophoresis was performed and the differentially expressed proteins were identified by matrix-assisted laser desorption ionization-time of flight mass spectrometry. A total of 40 proteins were identified, in which 16 proteins were upregulated, indicating that artificial ageing affected the proteome of the dry seeds. Proteomic studies revealed that the signal transduction and transcription were disturbed by artificial ageing, which might lead to reduced protection against ageing. Artificial ageing also increased proteases and broke down stored proteins, impaired metabolism and energy supply, and ultimately resulted in seed deterioration. Proteins involved in metabolism and energy were the largest downregulated protein group, with regard to glycolysis, tricarboxylic acid cycle, the electron transport chain and oxidative phosphorylation. The downregulation of these proteins, together with reduction in the specific activity of glucose-6-phosphate dehydrogenase, and the content of glucose 6-phosphate, pyruvic acid and ATP in aged seeds, suggested the important roles of the mobilization of stored carbohydrates and energy supply in seed ageing and seed vigor. The present work provides new information about the proteomic changes during seed ageing and provides a possible mechanism for seed deterioration.

Laboratory-evolved mutants of an exogenous global regulator, IrrE from Deinococcus radiodurans, enhance stress tolerances of Escherichia coli

Background

The tolerance of cells toward different stresses is very important for industrial strains of microbes, but difficult to improve by the manipulation of single genes. Traditional methods for enhancing cellular tolerances are inefficient and time-consuming. Recently, approaches employing global transcriptional or translational engineering methods have been increasingly explored. We found that an exogenous global regulator, irrE from an extremely radiation-resistant bacterium, Deinococcus radiodurans, has the potential to act as a global regulator in Escherichia coli, and that laboratory-evolution might be applied to alter this regulator to elicit different phenotypes for E. coli.

Methodology/Principal Findings

To extend the methodology for strain improvement and to obtain higher tolerances toward different stresses, we here describe an approach of engineering irrE gene in E. coli. An irrE library was constructed by randomly mutating the gene, and this library was then selected for tolerance to ethanol, butanol and acetate stresses. Several mutants showing significant tolerances were obtained and characterized. The tolerances of E. coli cells containing these mutants were enhanced 2 to 50-fold, based on cell growth tests using different concentrations of alcohols or acetate, and enhanced 10 to 100-fold based on ethanol or butanol shock experiments. Intracellular reactive oxygen species (ROS) assays showed that intracellular ROS levels were sharply reduced for cells containing the irrE mutants. Sequence analysis of the mutants revealed that the mutations distribute cross all three domains of the protein.

Conclusions

To our knowledge, this is the first time that an exogenous global regulator has been artificially evolved to suit its new host. The successes suggest the possibility of improving tolerances of industrial strains by introducing and engineering exogenous global regulators, such as those from extremophiles. This new approach can be applied alone or in combination with other global methods, such as global transcriptional machinery engineering (gTME) for strain improvements.

Human pancreas-specific protein disulfide-isomerase (PDIp) can function as a chaperone independently of its enzymatic activity by forming stable complexes with denatured substrate proteins

Members of the PDI (protein disulfide-isomerase) family are critical for the correct folding of secretory proteins by catalysing disulfide bond formation as well as by serving as molecular chaperones to prevent protein aggregation. In the present paper, we report that the chaperone activity of the human pancreas-specific PDI homologue (PDIp) is independent of its enzymatic activity on the basis of the following lines of evidence. First, alkylation of PDIp by iodoacetamide fully abolishes its enzymatic activity, whereas it still retains most of its chaperone activity in preventing the aggregation of reduced insulin B chain and denatured GAPDH (glyceraldehyde-3-phosphate dehydrogenase). Secondly, mutation of the cysteine residues in PDIp's active sites completely abolishes its enzymatic activity, but does not affect its chaperone activity. Thirdly, the b-b' fragment of PDIp, which does not contain the active sites and is devoid of enzymatic activity, still has chaperone activity. Mechanistically, we found that both the recombinant PDIp expressed in Escherichia coli and the natural PDIp present in human or monkey pancreas can form stable complexes with thermal-denatured substrate proteins independently of their enzymatic activity. The high-molecular-mass soluble complexes between PDIp and GAPDH are formed in a stoichiometric manner (subunit ratio of 1:3.5-4.5), and can dissociate after storage for a certain time. As a proof-of-concept for the biological significance of PDIp in intact cells, we demonstrated that its selective expression in E. coli confers strong protection of these cells against heat shock and oxidative-stress-induced death independently of its enzymatic activity.

Distinct amino acids of the Oenococcus oeni small heat shock protein Lo18 are essential for damaged protein protection and membrane stabilization

The small heat shock protein (smHsp) Lo18 from lactic acid bacteria Oenococcus oeni reduces in vitro thermal aggregation of proteins and modulates the membrane fluidity of native liposomes. An absence of information relating to the way in which the smHsp demonstrates a stabilizing effect for both proteins and membranes prompted this study. We expressed three Lo18 proteins with amino acid substitutions in Escherichia coli to investigate their ability to prevent E. coli protein aggregation and their capacity to stabilize E. coli whole-cell membranes. Our results showed that the alanine 123 to serine substitution induces a decrease in chaperone activity in denaturated proteins, and that the tyrosine 107 is required for membrane stabilization. Moreover, this study revealed that the oligomeric structures of proteins with amino acid substitutions do not appear to be modified. Our data strongly suggest that different amino acids are involved in the thermostabilization of proteins and in membrane fluidity regulation and are localized in the alpha-crystallin domain.

Isolation and expression of heat shock protein 30 gene from Penicillium marneffei

Penicillium marneffei is a dimorphic fungus that can cause disseminated mycosis, especially in AIDS patients. The role of heat shock proteins and stress response-related proteins in P. marneffei remains unknown. In this study, we isolated a cDNA encoding for heat shock protein 30 (Hsp30) of P. marneffei using an antibody screening method. The DNA sequence and deduced amino acid sequence analysis showed high homology to other fungal hsp30 genes. Expression of P. marneffei hsp30 in response to temperature increase was determined by Northern blot analysis. A high level of hsp30 transcript was detected in yeast cells grown at 37 degrees C, whereas a very low or undetectable transcript level was observed in mycelial cells at 25 degrees C. A recombinant Hsp30 protein was produced and tested preliminarily for its immunoreactivity with sera from P. marneffei-infected AIDS patients using Western blot analysis. The positive immunoblot result, with some serum samples, confirmed the antigenic property of the Hsp30. Collectively, the high response of hsp30 to temperature increase could indicate it may play a role in heat stress response and cell adaptation. This is the first report showing that this small heat shock protein could elicit the human immune response.

Rice sHsp genes: genomic organization and expression profiling under stress and development

Background

Heat shock proteins (Hsps) constitute an important component in the heat shock response of all living systems. Among the various plant Hsps (i.e. Hsp100, Hsp90, Hsp70 and Hsp20), Hsp20 or small Hsps (sHsps) are expressed in maximal amounts under high temperature stress. The characteristic feature of the sHsps is the presence of α-crystallin domain (ACD) at the C-terminus. sHsps cooperate with Hsp100/Hsp70 and co-chaperones in ATP-dependent manner in preventing aggregation of cellular proteins and in their subsequent refolding. Database search was performed to investigate the sHsp gene family across rice genome sequence followed by comprehensive expression analysis of these genes.

Results

We identified 40 α-crystallin domain containing genes in rice. Phylogenetic analysis showed that 23 out of these 40 genes constitute sHsps. The additional 17 genes containing ACD clustered with Acd proteins of Arabidopsis. Detailed scrutiny of 23 sHsp sequences enabled us to categorize these proteins in a revised scheme of classification constituting of 16 cytoplasmic/nuclear, 2 ER, 3 mitochondrial, 1 plastid and 1 peroxisomal genes. In the new classification proposed herein nucleo-cytoplasmic class of sHsps with 9 subfamilies is more complex in rice than in Arabidopsis. Strikingly, 17 of 23 rice sHsp genes were noted to be intronless. Expression analysis based on microarray and RT-PCR showed that 19 sHsp genes were upregulated by high temperature stress. Besides heat stress, expression of sHsp genes was up or downregulated by other abiotic and biotic stresses. In addition to stress regulation, various sHsp genes were differentially upregulated at different developmental stages of the rice plant. Majority of sHsp genes were expressed in seed.

Conclusion

We identified twenty three sHsp genes and seventeen Acd genes in rice. Three nucleocytoplasmic sHsp genes were found only in monocots. Analysis of expression profiling of sHsp genes revealed that these genes are differentially expressed under stress and at different stages in the life cycle of rice plant.