Small Heat Shock Protein Research Articles

Genome-Wide Identification and Characterization of Heat Shock Protein 20 Genes in Maize.

Maize is an important cereal crop worldwide and is sensitive to abiotic stresses in fluctuant environments that seriously affect its growth, yield, and quality. The small heat shock protein (HSP20) plays a crucial role in protecting plants from abiotic stress. However, little is known about HSP20 in maize (ZmHSP20). In this study, 44 ZmHSP20s were identified, which were unequally distributed over 10 chromosomes, and 6 pairs of ZmHSP20s were tandemly presented. The gene structure of ZmHSP20s was highly conserved, with 95% (42) of the genes having no more than one intron. The analysis of the cis-element in ZmHSP20s promoter demonstrated large amounts of elements related to hormonal and abiotic stress responses, including abscisic acid (ABA), high temperature, and hypoxia. The ZmHSP20s protein had more than two conserved motifs that were predictably localized in the cytoplasm, nucleus, endoplasmic reticulum, peroxisome, mitochondria, and plasma. Phylogenetic analysis using HSP20s in Arabidopsis, rice, maize, and Solanum tuberosum indicated that ZmHSP20s were classified into 11 categories, of which each category had unique subcellular localization. Approximately 80% (35) of ZmHSP20 were upregulated under heat stress at the maize seedling stage, whereas the opposite expression profiling of 10 genes under 37 and 48 °C was detected. A total of 20 genes were randomly selected to investigate their expression under treatments of ABA, gibberellin (GA), ethylene, low temperature, drought, and waterlogging, and the results displayed that more than half of these genes were downregulated while ZmHSP20-3, ZmHSP20-7, ZmHSP20-24, and ZmHSP20-44 were upregulated under 1 h treatment of ethylene. A yeast-one-hybrid experiment was conducted to analyze the binding of four heat stress transcription factors (ZmHSFs) with eight of the ZmHSP20s promoter sequences, in which ZmHSF3, ZmHSF13, and ZmHSF17 can bind to most of these selected ZmHSP20s promoters. Our results provided a valuable resource for studying HSP20s function and offering candidates for genetic improvement under abiotic stress.

Legionella pneumophila Cas2 Promotes the Expression of Small Heat Shock Protein C2 That Is Required for Thermal Tolerance and Optimal Intracellular Infection.

Previously, we demonstrated that Cas2 encoded within the CRISPR-Cas locus of Legionella pneumophila strain 130b promotes the ability of the Legionella pathogen to infect amoebal hosts. Given that L. pneumophila Cas2 has RNase activity, we posited that the cytoplasmic protein is regulating the expression of another Legionella gene(s) that fosters intracellular infection. Proteomics revealed 10 proteins at diminished levels in the cas2 mutant, and reverse transcription-quantitative (qRT-PCR) confirmed the reduced expression of a gene encoding putative small heat shock protein C2 (HspC2), among several others. As predicted, the gene was expressed more highly at 37°C to 50°C than that at 30°C, and an hspC2 mutant, but not its complemented derivative, displayed ~100-fold reduced CFU following heat shock at 55°C. Compatible with the effect of Cas2 on hspC2 expression, strains lacking Cas2 also had impaired thermal tolerance. The hspC2 mutant, like the cas2 mutant before it, was greatly impaired for infection of Acanthamoeba castellanii, a frequent host for legionellae in waters. HspC2 and Cas2 were not required for entry into these host cells but promoted the replicative phase of intracellular infection. Finally, the hspC2 mutant exhibited an additional defect during the infection of macrophages, which are the primary host for legionellae during lung infection. In summary, hspC2 is upregulated by the presence of Cas2, and HspC2 uniquely promotes both L. pneumophila extracellular survival at high temperatures and infection of amoebal and human host cells. To our knowledge, these findings also represent the first genetic proof linking Cas2 to thermotolerance, expanding the repertoire of noncanonical functions associated with CRISPR-Cas proteins.

The cytoprotective sequestration activity of small heat shock proteins is evolutionarily conserved.

The chaperone-mediated sequestration of misfolded proteins into inclusions is a pivotal cellular strategy to maintain proteostasis in Saccharomyces cerevisiae, executed by small heat shock proteins (sHsps) Hsp42 and Btn2. Direct homologs of Hsp42 and Btn2 are absent in other organisms, questioning whether sequestration represents a conserved proteostasis strategy and, if so, which factors are involved. We examined sHsps from Escherchia coli, Caenorhabditis elegans, and humans for their ability to complement the defects of yeast sequestrase mutants. We show that sequestration of misfolded proteins is an original and widespread activity among sHsps executed by specific family members. Sequestrase positive C. elegans' sHsps harbor specific sequence features, including a high content of aromatic and methionine residues in disordered N-terminal extensions. Those sHsps buffer limitations in Hsp70 capacity in C. elegans WT animals and are upregulated in long-lived daf-2 mutants, contributing to lifespan extension. Cellular protection by sequestration of misfolded proteins is, therefore, an evolutionarily conserved activity of the sHsp family.

Heat Shock Protein 27 Affects Myeloid Cell Activation and Interaction with Prostate Cancer Cells

Heat shock proteins are cytoprotective molecules induced by environmental stresses. The small heat shock protein 27 (Hsp27) is highly expressed under oxidative stress conditions, mediating anti-oxidative effects and blocking apoptosis. Since medical gas plasma treatment subjects cancer cells to a multitude of reactive oxygen species (ROS), inducing apoptosis and immunomodulation, probable effects of Hsp27 should be investigated. To this end, we quantified the extracellular Hsp27 in two prostate cancer cell lines (LNCaP, PC-3) after gas plasma-induced oxidative stress, showing a significantly enhanced release. To investigate immunomodulatory effects, two myeloid cell lines (THP-1 and HL-60) were also exposed to Hsp27. Only negligible effects on viability, intracellular oxidative milieu, and secretion profiles of the myeloid cells were found when cultured alone. Interestingly, prostate cancer-myeloid cell co-cultures showed altered secretion profiles with a significant decrease in vascular endothelial growth factor (VEGF) release. Furthermore, the myeloid surface marker profiles were changed, indicating an enhanced differentiation in co-culture upon Hsp27 treatment. Finally, we investigated morphological changes, proliferation, and interaction with prostate cancer cells, and found significant alterations in the myeloid cells, supporting the tendency to differentiate. Collectively, our results suggest an ambiguous effect of Hsp27 on myeloid cells in the presence of prostate cancer cells which needs to be further investigated.

The in vivo performance of a heat shock transcription factor from Populus euphratica, PeHSFA2, promises a prospective strategy to alleviate heat stress damage in poplar

Heat stress driven by global warming has affected forest yields and survival at a larger scale in recent decades, hence breeding heat-tolerant tree species has become imperative. We here investigated the role of PeHSFA2, a crucial gene in plant heat shock response from Populus euphratica, in regulating plant heat stress protection. PeHSFA2 is localized to the cytoplasm and nucleus and can be transported from the cytoplasm into the nucleus under detrimental high-temperature conditions. Poplar plants with overexpressed PeHSFA2 outperformed the control group when subjected to severe heat stress, for they had higher leaf water content, lower leaf relative electrolyte leakage, and better photosynthetic activity after heat treatment. The results of qRT-PCR analyses revealed that PeHSFA2 regulates the transcription of a group of heat-protective genes including small heat shock protein, GALACTINOL SYNTHASE 2.2, and ASCORBATE PEROXIDASE 2 in white poplar. Transactivation assays confirmed that PeHSFA2 activated the expression of PtoHSP19.9, PtoHSP21.3, PtoHSP21.8, PtoHSP22.0, PtoGOLS2.2, and PtoAPX2 via binding to the promoter regions of these genes. These results emphasize the point that PeHSFA2 can vehemently reinforce plant thermotolerance via regulating the transcription of a set of heat shock response genes, and PeHSFA2 possesses enormous potential in breeding poplar plants with substantially enhanced thermotolerance.

Heat-shock chaperone HSPB1 regulates cytoplasmic TDP-43 phase separation and liquid-to-gel transition.

While acetylated, RNA-binding-deficient TDP-43 reversibly phase separates within nuclei into complex droplets (anisosomes) comprised of TDP-43-containing liquid outer shells and liquid centres of HSP70-family chaperones, cytoplasmic aggregates of TDP-43 are hallmarks of multiple neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS). Here we show that transient oxidative stress, proteasome inhibition or inhibition of the ATP-dependent chaperone activity of HSP70 provokes reversible cytoplasmic TDP-43 de-mixing and transition from liquid to gel/solid, independently of RNA binding or stress granules. Isotope labelling mass spectrometry was used to identify that phase-separated cytoplasmic TDP-43 is bound by the small heat-shock protein HSPB1. Binding is direct, mediated through TDP-43's RNA binding and low-complexity domains. HSPB1 partitions into TDP-43 droplets, inhibits TDP-43 assembly into fibrils, and is essential for disassembly of stress-induced TDP-43 droplets. A decrease in HSPB1 promotes cytoplasmic TDP-43 de-mixing and mislocalization. HSPB1 depletion was identified in spinal motor neurons of patients with ALS containing aggregated TDP-43. These findings identify HSPB1 to be a regulator of cytoplasmic TDP-43 phase separation and aggregation.

High mRNA Expression Levels of Heat Shock Protein Family B Member 2 (HSPB2) Are Associated with Breast Cancer Patients' Relapse and Poor Survival.

Small heat shock proteins (sHSPs) are ubiquitous ATP-independent chaperones that contribute to the maintenance of proteome integrity and functionality. Recent evidence suggests that sHSPs are ubiquitously expressed in numerous types of tumors and have been proposed to be implicated in oncogenesis and malignant progression. Heat shock protein family B member 2 (HSPB2) is a member of the sHSPs, which is found to be expressed, among others, in human breast cancer cell lines and constitutes an inhibitor of apical caspase activation in the extrinsic apoptotic pathway. In this study, we investigated the potential prognostic significance of HSPB2 mRNA expression levels in breast cancer, which represents the most frequent malignancy in females and one of the three most common cancer types worldwide. To this end, malignant breast tumors along with paired non-cancerous breast tissue specimens were used. HSPB2 expression levels were quantified in these two cohorts using a sensitive and accurate SYBR green-based quantitative real-time polymerase chain reaction (q-RT-PCR). Extensive biostatistical analyses were performed including Kaplan–Meier and Cox regression survival analyses for the assessment of the results. The significant downregulation of HSPB2 gene expression was revealed in breast tumors compared to their adjacent non-cancerous breast tissues. Notably, high HSPB2 mRNA expression predicts poor disease-free survival and overall survival of breast cancer patients. Multivariate Cox regression analysis revealed that HSPB2 mRNA overexpression is a significant predictor of poor prognosis in breast cancer, independent of other clinicopathological factors. In conclusion, high HSPB2 mRNA expression levels are associated with breast cancer patients’ relapse and poor survival.

The Role of the Heat-Shock Proteins in Esophagogastric Cancer.

Heat-shock proteins (HSPs) are a family of proteins that have received considerable attention over the last several years. They have been classified into six prominent families: high-molecular-mass HSP, 90, 70, 60, 40, and small heat shock proteins. HSPs participate in protein folding, stability, and maturation of several proteins during stress, such as in heat, oxidative stress, fever, and inflammation. Due to the immunogenic host’s role in the combat against cancer cells and the role of the inflammation in the cancer control or progression, abnormal expression of these proteins has been associated with many types of cancer, including esophagogastric cancer. This study aims to review all the evidence concerning the role of HSPs in the pathogenesis and prognosis of esophagogastric cancer and their potential role in future treatment options. This narrative review gathers scientific evidence concerning HSPs in relation to esophagus and gastric cancer. All esophagogastric cancer subtypes are included. The role of HSPs in carcinogenesis, prognostication, and therapy for esophagogastric cancer are discussed. The main topics covered are premalignant conditions for gastric cancer atrophic gastritis, Barrett esophagus, and some viral infections such as human papillomavirus (HPV) and Epstein–Barr virus (EBV). HSPs represent new perspectives on the development, prognostication, and treatment of esophagogastric cancer.

Regulation and physiological function of proteins for heat tolerance in cowpea (Vigna unguiculata) genotypes under controlled and field conditions.

The expression of heat shock proteins is considered a central adaptive mechanism to heat stress. This study investigated the expression of heat shock proteins (HSPs) and other stress-protective proteins against heat stress in cowpea genotypes under field (IT-96D-610 and IT-16) and controlled (IT-96D-610) conditions. Heat stress response analysis of proteins at 72 h in the controlled environment showed 270 differentially regulated proteins identified using label-free quantitative proteomics in IT-96D-610 plants. These plants expressed HSPs and chaperones [BAG family molecular chaperone 6 (BAG6), Multiprotein bridging factor1c (MBF1C) and cold shock domain protein 1 (CSDP1) in the controlled environment]. However, IT-96D-610 plants expressed a wider variety of small HSPs and more HSPs in the field. IT-96D-610 plants also responded to heat stress by exclusively expressing chaperones [DnaJ chaperones, universal stress protein and heat shock binding protein (HSBP)] and non-HSP proteins (Deg1, EGY3, ROS protective proteins, temperature-induced lipocalin and succinic dehydrogenase). Photosynthesis recovery and induction of proteins related to photosynthesis were better in IT-96D-610 because of the concurrent induction of heat stress response proteins for chaperone functions, protein degradation for repair and ROS scavenging proteins and PSII operating efficiency (Fq’/Fm′) than IT-16. This study contributes to identification of thermotolerance mechanisms in cowpea that can be useful in knowledge-based crop improvement.

Conformational Changes of α-Crystallin Proteins Induced by Heat Stress.

α-crystallin is a major structural protein in the eye lenses of vertebrates that is composed of two relative subunits, αA and αB crystallin, which function in maintaining lens transparency. As a member of the small heat-shock protein family (sHsp), α-crystallin exhibits chaperone-like activity to prevent the misfolding or aggregation of critical proteins in the lens, which is associated with cataract disease. In this study, high-purity αA and αB crystallin proteins were expressed from E. coli and purified by affinity and size-exclusion chromatography. The size-exclusion chromatography experiment showed that both αA and αB crystallins exhibited oligomeric complexes in solution. Here, we present the structural characteristics of α-crystallin proteins from low to high temperature by combining circular dichroism (CD) and small-angle X-ray scattering (SAXS). Not only the CD data, but also SAXS data show that α-crystallin proteins exhibit transition behavior on conformation with temperature increasing. Although their protein sequences are highly conserved, the analysis of their thermal stability showed different properties in αA and αB crystallin. In this study, taken together, the data discussed were provided to demonstrate more insights into the chaperone-like activity of α-crystallin proteins.

Is the small heat shock protein HSPB7 (cvHsp) a genuine actin-binding protein?

It is postulated that the small heat shock proteins directly interact with actin, affect formation and stabilize actin filaments. To verify this suggestion, we have analyzed interaction of recombinant human small heat shock protein HspB7 with skeletal muscle actin. In blot overlay HspB7 binds both G- and F-actin. The sites of interaction are located in the C-terminal large core domain of actin. In the course of ultracentrifugation F-actin and F-actin/tropomyosin complexes were pelleted and trapped HspB7. However, HspB7 pelleting was nonspecific and saturation was not achieved even at very high HspB7 concentration. HspB7 was unable to retard or prevent heat-induced F-actin aggregation. Native gel electrophoresis and chemical crosslinking failed to detect interaction of G-actin with HspB7, although both these methods clearly demonstrated formation of complexes formed by G-actin with DNAse I and cofilin-2. It is concluded that HspB7 is not a genuine actin-binding protein and its effect on actin filaments seems to be determined by interaction of HspB7 with minor regulatory proteins of actin filaments.

The division protein FtsZ interacts with the small heat shock protein IbpA in Acholeplasma laidlawii

Small heat shock proteins (sHSPs) control the proteins stability in the cell preventing their irreversible denaturation. While many mycoplasmas possess the sHSP gene in the genome, Acholeplasma laidlawii is the only mycoplasma capable of surviving in the environment. Here we report that the sHSP IbpA directly interacts with the key division protein FtsZ in A. laidlawii, representing the first example of such interaction in prokaryotes. FtsZ co-immunoprecipitates with IbpA from A. laidlawii crude extract and in vitro binds IbpA with KD ~ 1 μM. Proteins co-localize in the soluble fraction of the cell at 30–37 °C and in the non-soluble fraction after 1 h exposition to cold stress (4 °C). Under heat shock conditions (42 °C) the amount of FtsZ decreases and the protein remains in both soluble and non-soluble fractions. Furthermore, in vitro, FtsZ co-elutes with IbpAHis6 from A. laidlawii crude extract at any temperatures from 4 to 42 °C, with highest yield at 42 °C. Moreover, in vitro FtsZ retains its GTPase activity in presence of IbpA, and the filaments and bundles formation seems to be even improved by sHSP at 30–37 °C. At extreme temperatures, either 4 or 42 °C, IbpA facilitates FtsZ polymerization, although filaments under 4 °C appears shorter and with lower density, while at 42 °C IbpA sticks around the bundles, preventing their destruction by heat. Taken together, these data suggest that sHSP IbpA in A. laidlawii contributes to the FtsZ stability control and may be assisting appropriate cell division under unfavorable conditions.

Heat shock proteins: Biological functions, pathological roles, and therapeutic opportunities.

The heat shock proteins (HSPs) are ubiquitous and conserved protein families in both prokaryotic and eukaryotic organisms, and they maintain cellular proteostasis and protect cells from stresses. HSP protein families are classified based on their molecular weights, mainly including large HSPs, HSP90, HSP70, HSP60, HSP40, and small HSPs. They function as molecular chaperons in cells and work as an integrated network, participating in the folding of newly synthesized polypeptides, refolding metastable proteins, protein complex assembly, dissociating protein aggregate dissociation, and the degradation of misfolded proteins. In addition to their chaperone functions, they also play important roles in cell signaling transduction, cell cycle, and apoptosis regulation. Therefore, malfunction of HSPs is related with many diseases, including cancers, neurodegeneration, and other diseases. In this review, we describe the current understandings about the molecular mechanisms of the major HSP families including HSP90/HSP70/HSP60/HSP110 and small HSPs, how the HSPs keep the protein proteostasis and response to stresses, and we also discuss their roles in diseases and the recent exploration of HSP related therapy and diagnosis to modulate diseases. These research advances offer new prospects of HSPs as potential targets for therapeutic intervention.

Role of Small Heat Shock Proteins in the Remodeling of Actin Microfilaments.

Small heat shock proteins (sHsps) play an important role in the maintenance of proteome stability and, particularly, in stabilization of the cytoskeleton and cell contractile apparatus. Cell exposure to different types of stress is accompanied by the translocation of sHsps onto actin filaments; therefore, it is commonly believed that the sHsps are true actin-binding proteins. Investigations of last years have shown that this assumption is incorrect. Stress-induced translocation of sHsp to actin filaments is not the result of direct interaction of these proteins with intact actin, but results from the chaperone-like activity of sHsps and their interaction with various actin-binding proteins. HspB1 and HspB5 interact with giant elastic proteins titin and filamin thus providing an integrity of the contractile apparatus and its proper localization in the cell. HspB6 binds to the universal adapter protein 14-3-3 and only indirectly affects the structure of actin filament. HspB7 interacts with filamin C and controls actin filament assembly. HspB8 forms tight complex with the universal regulatory and adapter protein Bag3 and participates in the chaperone-assisted selective autophagy (CASA) of actin-binding proteins (e.g., filamin), as well as in the actin-depending processes taking place in mitoses. Hence, the mechanisms of sHsp participation in the maintenance of the contractile apparatus and cytoskeleton are much more complicated and diverse than it has been postulated earlier and are not limited to direct interactions of sHsps with actin. The old hypothesis on the direct binding of sHsps to intact actin should be revised and further detailed investigation on the sHsp interaction with minor proteins participating in the formation and remodeling of actin filaments is required.

HSPB8 Overexpression Ameliorates Cognitive Impairment in Diabetic Mice via Inhibiting NLRP3 Inflammation Activation

Type 2 diabetes mellitus (T2DM) is associated with an elevated risk of cognitive impairment. And the underlying mechanism remains unillustrated. HSPB8 is a member of the small heat shock protein family. In this study, we found that the expression of HSPB8 was upregulated in the hippocampus of high − fat diet (HFD) + streptozotocin (STZ) − induced diabetic mice and N2a cells exposed to high glucose. Overexpression of HSPB8 relieved cognitive decline in DM mice. Mechanically, HSPB8 overexpression in the hippocampus of diabetic mice inhibited NOD-like receptor protein 3 (NLRP3) inflammasome activation via dephosphorylating mitochondrial fission-associated protein dynamin-related protein 1 (DRP1) at the phosphorylated site Ser616 (p-Drp1S616). Furthermore, HSPB8 overexpression increased mitochondrial membrane potential (MMP) and reduced oxidative stress. These results indicate a protective effect of HSPB8 in the hippocampus of diabetic mice and N2a cells exposed to high glucose. Overexpression of HSPB8 might be a useful strategy for treating T2DM-related cognitive decline.

Protective effects of small heat shock proteins in Daphnia magna against heavy metal exposure

Daphnia magna is one of the most commonly used model organisms to assess toxicity of heavy metal and other xenobiotics. However, the lack of knowledge about important stress-resistant molecules limits our understanding of the alteration of phenotypic and physiological traits of D. magna upon stress exposures. In this study, we focused on a chaperone family of small heat shock protein (sHSP) that has been found in archaea, bacteria and eukaryotes and plays an important role in stress tolerance. A total of eleven sHSP genes (termed DmsHSP1 - DmsHSP11) were identified from the D. magna genome, whose expression profiles during exposure to heavy metal (Cd2+, Cu2+ and Zn2+) and a few other potential pollutants were evaluated via qRT-PCR and RNA-Seq analysis. The results highlighted the predominant role of DmsHSP1 with the highest basal expression level in adults and robust upregulation upon exposure to heavy metals (Cu2+ > Cd2+ > Zn2+). In vivo, recombinant protein rDmsHSP1–21 and rDmsHSP11–12.8 could not only prevent model substrates agglutination induced by heavy metals or reducer dithiotreitol (DTT), but also protect tissue proteins and enzymes from denaturation and inactivation caused by heavy metals or high temperature. Ectopically expression of DmsHSP1–21 or DmsHSP11–12.8 in E. coli conferred host enhanced resistance against various abiotic stresses including Cd2+, Cu2+ and phenazine methosulfate (PMS). Knockdown of DmsHSP1–21 by RNAi, but not for DmsHSP11–12.8, significantly increased the vulnerability of D. magna to heavy metal exposure. Our work provides systematic information on the evolution and function of sHSPs in D. magna and leads to important insights into the mechanisms by which D. magna survive in adverse environments.

Deletion of NTH1 and HSP12 increases the freeze–thaw resistance of baker’s yeast in bread dough

BackgroundThe intracellular molecule trehalose in Saccharomyces cerevisiae may have a major protective function under extreme environmental conditions. NTH1 is one gene which expresses trehalase to degrade trehalose. Small heat shock protein 12 (HSP12 expressed) plays a role in protecting membranes and enhancing freezing stress tolerance.ResultsAn optimized S. cerevisiae CRISPR-Cpf1 genome-editing system was constructed. Multiplex genome editing using a single crRNA array was shown to be functional. NTH1 or/and HSP12 knockout in S. cerevisiae enhanced the freezing stress tolerance and improved the leavening ability after freezing and thawing.ConclusionsDeleting NTH1 in the combination with deleting HSP12 would strengthen the freezing tolerance and protect the cell viability from high rates of death in longer-term freezing. It provides valuable insights for breeding novel S. cerevisiae strains for the baking industry through a more precise, speedy, and economic genome-editing system.

Are casein micelles extracellular condensates formed by liquid-liquid phase separation?

Casein micelles are extracellular polydisperse assemblies of unstructured casein proteins. Caseins are the major component of milk. Within casein micelles, casein molecules are stabilised by binding to calcium phosphate nanoclusters and, by acting as molecular chaperones, through multivalent interactions. In the light of such interactions, we discuss whether casein micelles can be considered as extracellular condensates formed by liquid-liquid phase separation. We analyse the sequence, structure and interactions of caseins in comparison with proteins forming intracellular condensates. Furthermore, we review the similarities between caseins and small heat-shock proteins whose chaperone activity is linked to phase separation of proteins. By bringing these observations together, we describe a regulatory mechanism for protein condensates, as exemplified by casein micelles.

Characterization of Spermidine Synthase (SPDS) Gene and RNA−Seq Based Identification of Spermidine (SPD) and Spermine (SPM) Involvement in Improving High Temperature Stress Tolerance in Gracilariopsis lemaneiformis (Rhodophyta)

Gracilariopsis lemaneiformis, an important commercial red macroalga, is facing significant impacts from global warming, which limits algal growth and yield in China. Polyamines (PAs), spermidine (SPD) and spermine (SPM), are ubiquitous polycations important for growth and environmental stress responses including high temperature (HT) tolerance. Spermidine synthase (SPDS) gene is one of the important genes in higher PA biosynthesis, which plays critical roles in HT stress response. Here, we isolated an SPDS gene from G. lemaneiformis and further analyzed its phylogenetic tree, subcellular localization, and gene expression patterns under stress conditions. Meanwhile, supplemented with SPD and SPM were used to study the effects of PAs on HT tolerance in G. lemaneiformis. It showed exogenous 0.5 mM SPD and SPM, respectively, remarkably improved the algal relative growth rate (RGR) compared to those in the CK treatment groups under HT conditions. In addition, they both significantly elevated the activities of antioxidant enzymes and significantly upregulated the expression of genes encoding antioxidant enzymes, triggered transcription factors (TFs) signaling, and improved the expression of genes encoding small heat shock proteins (sHSP20s) during HT stress. Moreover, exogenous PA also enhanced the expression of genes involved in pyruvate metabolism, ascorbate and aldarate metabolism, and nucleotide excision repair in G. lemaneiformis, which helped to maintain better energy supply, redox homeostasis, and genome integrity under HT stress. Taken together, these data provided valuable information for functional characterization of specific gene in endogenous PA synthesis and uncovered the importance of exogenous PAs in promoting algae adaptation to HT stress.

Small heat shock protein (Hsp20) gene family in Phaseolus vulgaris L.: Genome-wide identification, evolutionary and expression analysis

Understanding the mechanisms responsible for plant tolerance under various abiotic stresses is linked to understanding heat shock proteins (Hsps). The Hsp20 subfamily is the main family of heat shock proteins, but little is known about this family in common bean (Phaseolus vulgaris L.), an important agricultural crop sensitive to temperature and salt stress. We identified 41 candidate common bean Hsp20 genes (PvHsp20). We mapped the PvHsp20 genes according to their chromosomal locations and found 49 duplications, 35 segmental and 14 tandem. Subsequent gene structure analysis identified regions of exons, introns, and conserved motifs. In the phylogenetic analysis, all PvHsp20 genes were grouped into 11 subfamilies, except for two genes that could not be classified. Synteny analysis revealed that Hsp20 genes from the common bean are highly related to soybean. Promoter analysis of PvHsp20 genes showed the presence of hormone-related, light-responsive and stress-responsive cis-regulatory elements. 8 PvHsp20 genes were under the regulation of 8 PvmiRNA genes. The in silico expression profile showed that PvHsp20 was differentially expressed. The gene expression of the PvHsp20-31, PvHsp20-27, PvHsp-2, and PvHsp20-39 genes in the roots of the Ispir genotype suggested that these genes might play a vital role in the salt tolerance mechanism. Our results provide new information, contribute to understanding PvHsp20 genes, and validate their role in mitigating the adverse effects triggered by abiotic stresses.