The natural alkaloid sanguinarine promotes the expression of heat shock protein genes in Arabidopsis

Small-molecule heat shock response inducers are known to enhance heat tolerance in plants. In this paper, we report that a plant alkaloid enhances the heat tolerance of Arabidopsis. We investigated 12 commercially available alkaloids to determine whether they enhance the heat tolerance of Arabidopsis seedlings using an in vitro assay system with geldanamycin, which is a known heat shock response inducer, as a positive control. Accordingly we found that the isoquinoline alkaloid sanguinarine can enhance heat tolerance in Arabidopsis. No such effect was shown for the other 11 alkaloids. The sanguinarine treatment increased the expression of heat shock protein genes such as HSP17.6C-CI, HSP70, and HSP90.1, which were up-regulated by geldanamycin. Treatments with other isoquinoline alkaloids (berberine and papaverine), which showed few heat tolerance-enhancing effects, did not promote the expression of the heat shock protein genes. These results suggest that sanguinarine influenced the heat tolerance of Arabidopsis by enhancing the expression of heat shock protein genes.     

Heat shock and light activation of aChlamydomonas HSP70 gene are mediated by independent regulatory pathways

Induction ofHSP70 heat shock genes by light has been demonstrated inChlamydomonas. Our aim was to establish whether this induction by light is mediated by the heat stress sensing pathway or by an independent signal chain. Inhibitors of cytoplasmic protein synthesis revealed an initial difference. Cycloheximide and other inhibitors of protein synthesis preventedHSP70A induction upon illumination but not during heat stress. Analysis ofHSP70A induction in cells that had differentiated into gametes revealed a second difference. While heat shock resulted in elevatedHSP70A mRNA levels, light was no longer able to serve as an inducer in gametes. To identify the regulatory sequences that mediate the response of theHSP70A gene to either heat stress or light we introduced a series of progressive 5′ truncations into its promoter sequence. Analyses of the levels of mRNA transcribed from these deletion constructs showed that in most of them the responses to heat shock and light were similar, suggesting that light induction is mediated by a light-activated heat shock factor. However, we show that theHSP70A promoter also containscis-acting sequences involved in light induction that do not participate in induction by heat stress. Together, these results provide evidence for a regulation ofHSP70A gene expression by light through a heat shock-independent signal pathway.     

Menin links the stress response to genome stability in Drosophila melanogaster

Background

The multiple endocrine neoplasia type I gene functions as a tumor suppressor gene in humans and mouse models. In Drosophila melanogaster, mutants of the menin gene (Mnn1) are hypersensitive to mutagens or gamma irradiation and have profound defects in the response to several stresses including heat shock, hypoxia, hyperosmolarity and oxidative stress. However, it is not known if the function of menin in the stress response contributes to genome stability. The objective of this study was to examine the role of menin in the control of the stress response and genome stability.

Methodology/Principal Findings

Using a test of loss-of-heterozygosity, we show that Drosophila strains lacking a functional Mnn1 gene or expressing a Mnn1 dsRNA display increased genome instability in response to non-lethal heat shock or hypoxia treatments. This is also true for strains lacking all Hsp70 genes, implying that a precise control of the stress response is required for genome stability. While menin is required for Hsp70 expression, the results of epistatic studies indicate that the increase in genome instability observed in Mnn1 lack-of-function mutants cannot be accounted for by mis-expression of Hsp70. Therefore, menin may promote genome stability by controlling the expression of other stress-responsive genes. In agreement with this notion, gene profiling reveals that Mnn1 is required for sustained expression of all heat shock protein genes but is dispensable for early induction of the heat shock response.

Conclusions/Significance

Mutants of the Mnn1 gene are hypersensitive to several stresses and display increased genome instability when subjected to conditions, such as heat shock, generally regarded as non-genotoxic. In this report, we describe a role for menin as a global regulator of heat shock gene expression and critical factor in the maintenance of genome integrity. Therefore, menin links the stress response to the control of genome stability in Drosophila melanogaster.     

Effects of cis and trans regulatory variations on the expression divergence of heat shock response genes between yeast strains

Phenotypic variation among individuals in a population can be due to DNA sequence variation in protein coding regions or in regulatory elements. Recently, many studies have indicated that mutations in regulatory elements may be the major cause of phenotypic evolution. However, the mechanisms for evolutionary changes in gene expression are still not well understood. Here, we studied the relative roles of cis and trans regulatory changes in Saccharomyces cerevisiae cells to cope with heat stress. It has been found that the expression level of ~ 300 genes was induced at least two fold and that of ~ 500 genes was repressed at least two fold in response to heat shock. From the former set of genes, we randomly selected 65 genes that showed polymorphism(s) between the BY and RM strains for pyrosequencing analysis to explore the relative contributions of cis and trans regulatory variations to the expression divergence between BY and RM. Our data indicated that the expression divergence between BY and RM was mainly due to trans regulatory variations under either the normal condition or the heat stress condition. However, the relative contribution of trans regulatory variation was decreased from 76.9% to 61.5% after the heat shock stress. These results indicated that the cis regulatory variation may play an important role in the adaption to heat stress. In our data, 43.1% (28 genes) of the 65 genes showed the same trend of cis or trans variation effect after the heat shock stress, 35.4% (23 genes) showed an increased cis variation effect and 21.5% (14 genes) showed an increased trans variation effect after the heat shock stress. Thus, our data give insights into the relative roles of cis and trans variations in response to heat shock in yeast.     

Thermal stress responses in Antarctic yeast, Glaciozyma antarctica PI12, characterized by real-time quantitative PCR

Living organisms have some common and unique strategies to response to thermal stress. However, the amount of data on thermal stress response of certain organism is still lacking, especially psychrophilic yeast from the extreme habitat. Therefore, it is not known whether psychrophilic yeast shares the common responses of other organisms when exposed to thermal stresses. In this work, the cold shock and heat shock responses in Antarctic psychrophilic yeast Glaciozyma antarctica PI12 which had an optimal growth temperature of 12 °C were determined. The expression levels of 14 thermal stress-related genes were measured using real-time quantitative PCR (qPCR) when the yeast cells were exposed to cold shock (0 °C), mild cold shock (5 °C), and heat shock (22 °C) conditions. The expression profiles of the 14 genes at these three temperatures varied indicating that these genes had their specific roles to ensure the survival of the yeast. Under cold shock condition, the afp4 and fad genes were over-expressed possibly as a way for the G. antarctica PI12 to avoid ice crystallization in the cell and to maintain the membrane fluidity. Under the heat shock condition, hsp70 was significantly up-regulated possibly to ensure the proteins fold properly. Among the six oxidative stress-related genes, MnSOD and prx were up-regulated under cold shock and heat shock, respectively, possibly to reduce the negative effects caused by oxidative stress. Interestingly, it was found that the trehalase gene, nth1 that plays a role in degrading excess trehalose, was down-regulated under the heat shock condition possibly as an alternative way to accumulate trehalose in the cells to protecting them from being damaged.     

Effects of heat stress on ovarian development and the expression of HSP genes in mice

Heat stress reduces oocyte competence, thereby causing lower fertility in animals. Chronic and acute heat stresses cause extensive morphological damage in animals, but few reports have focused on the effects of chronic and acute heat stresses on ovarian function and heat shock protein (HSP) gene expression during ovarian injury. In this study, we subjected female mice to chronic and acute heat stresses; we then calculated the ovary index, examined ovary microstructure, and measured the expression of multiple HSP family genes. Chronic heat stress reduced whole-body and ovarian growth but had little effect on the ovarian index; acute heat stress did not alter whole-body or ovarian weight. Both chronic and acute heat stresses impaired ovary function by causing the dysfunction of granular cells. Small HSP genes increased rapidly after heat treatment, and members of the HSP40, HSP70, and HSP90 families were co-expressed to function in the regulation of the heat stress response. We suggest that the HSP chaperone machinery may regulate the response to heat stress in the mouse ovary.     

Heat Shock Protein-Mediated Resistance to High Hydrostatic Pressure in Escherichia coli

A random library of Escherichia coli MG1655 genomic fragments fused to a promoterless green fluorescent protein (GFP) gene was constructed and screened by differential fluorescence induction for promoters that are induced after exposure to a sublethal high hydrostatic pressure stress. This screening yielded three promoters of genes belonging to the heat shock regulon (dnaK, lon, clpPX), suggesting a role for heat shock proteins in protection against, and/or repair of, damage caused by high pressure. Several further observations provide additional support for this hypothesis: (i) the expression of rpoH, encoding the heat shock-specific sigma factor σ³², was also induced by high pressure; (ii) heat shock rendered E. coli significantly more resistant to subsequent high-pressure inactivation, and this heat shock-induced pressure resistance followed the same time course as the induction of heat shock genes; (iii) basal expression levels of GFP from heat shock promoters, and expression of several heat shock proteins as determined by two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis of proteins extracted from pulse-labeled cells, was increased in three previously isolated pressure-resistant mutants of E. coli compared to wild-type levels.     

Heat shock proteins do not influence wet heat resistance of Bacillus subtilis spores

Spores of Bacillus subtilis are significantly more resistant to wet heat than are their vegetative cell counterparts. Analysis of the effects of mutations in and the expression of fusions of a coding gene for a thermostable β-galactosidase to a number of heat shock genes has shown that heat shock proteins play no significant role in the wet heat resistance of B. subtilis spores.