Publications (17)85.42 Total impact
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Article: The plant heat stress transcription factor (Hsf) family: structure, function and evolution.
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ABSTRACT: Ten years after the first overview of a complete plant Hsf family was presented for Arabidopsis thaliana by Nover et al. [1], we compiled data for 252 Hsfs from nine plant species (five eudicots and four monocots) with complete or almost complete genome sequences. The new data set provides interesting insights into phylogenetic relationships within the Hsf family in plants and allows the refinement of their classification into distinct groups. Numerous publications over the last decade document the diversification and functional interaction of Hsfs as well as their integration into the complex stress signaling and response networks of plants. This article is part of a Special Issue entitled: Plant gene regulation in response to abiotic stress.Biochimica et Biophysica Acta 02/2012; 1819(2):104-19. · 4.66 Impact Factor -
Article: Crosstalk between Hsp90 and Hsp70 chaperones and heat stress transcription factors in tomato.
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ABSTRACT: Heat stress transcription factors (Hsfs) regulate gene expression in response to environmental stress. The Hsf network in plants is controlled at the transcriptional level by cooperation of distinct Hsf members and by interaction with chaperones. We found two general mechanisms of Hsf regulation by chaperones while analyzing the three major Hsfs, A1, A2, and B1, in tomato (Solanum lycopersicum). First, Hsp70 and Hsp90 regulate Hsf function by direct interactions. Hsp70 represses the activity of HsfA1, including its DNA binding, and the coactivator function of HsfB1 in the complex with HsfA2, while the DNA binding activity of HsfB1 is stimulated by Hsp90. Second, Hsp90 affects the abundance of HsfA2 and HsfB1 by modulating hsfA2 transcript degradation involved in regulation of the timing of HsfA2 synthesis. By contrast, HsfB1 binding to Hsp90 and to DNA are prerequisites for targeting this Hsf for proteasomal degradation, which also depends on a sequence element in its carboxyl-terminal domain. Thus, HsfB1 represents an Hsp90 client protein that, by interacting with the chaperone, is targeted for, rather than protected from, degradation. Based on these findings, we propose a versatile regulatory regime involving Hsp90, Hsp70, and the three Hsfs in the control of heat stress response.The Plant Cell 02/2011; 23(2):741-55. · 8.99 Impact Factor -
Article: Specific interaction between tomato HsfA1 and HsfA2 creates hetero-oligomeric superactivator complexes for synergistic activation of heat stress gene expression.
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ABSTRACT: In plants, a family of more than 20 heat stress transcription factors (Hsf) controls the expression of heat stress (hs) genes. There is increasing evidence for the functional diversification between individual members of the Hsf family fulfilling distinct roles in response to various environmental stress conditions and developmental signals. In response to hs, accumulation of both heat stress proteins (Hsp) and Hsfs is induced. In tomato, the physical interaction between the constitutively expressed HsfA1 and the hs-inducible HsfA2 results in synergistic transcriptional activation (superactivation) of hs gene expression. Here, we show that the interaction is strikingly specific and not observed with other class A Hsfs. Hetero-oligomerization of the two-component Hsfs is preferred to homo-oligomerization, and each Hsf in the HsfA1/HsfA2 hetero-oligomeric complex has its characteristic contribution to its function as superactivator. Distinct regions of the oligomerization domain are responsible for specific homo- and hetero-oligomeric interactions leading to the formation of hexameric complexes. The results are summarized in a model of assembly and function of HsfA1/A2 superactivator complexes in hs gene regulation.Journal of Biological Chemistry 07/2009; 284(31):20848-57. · 4.77 Impact Factor -
Article: Functional dissection of the cytosolic chaperone network in tomato mesophyll protoplasts.
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ABSTRACT: The heat stress response is universal to all organisms. Upon elevated temperatures, heat stress transcription factors (Hsfs) are activated to up-regulate the expression of molecular chaperones to protect cells against heat damages. In higher plants, the phenomenon is unusually complex both at the level of Hsfs and heat stress proteins (Hsps). Over-expression of both Hsfs and Hsps and the use of RNA interference for gene knock-down in a transient system in tomato protoplasts allowed us to dissect the in vivo chaperone functions of essential components of thermotolerance, such as the cytoplasmic sHsp, Hsp70 and Hsp100 chaperone families, and the regulation of their expression. The results point to specific functions of the different components in protection from protein denaturation and in refolding of denatured proteins.Plant Cell and Environment 03/2009; 32(2):123-33. · 5.22 Impact Factor -
Article: The plant sHSP superfamily: five new members in Arabidopsis thaliana with unexpected properties.
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ABSTRACT: The small heat shock proteins (sHsps), which are ubiquitous stress proteins proposed to act as chaperones, are encoded by an unusually complex gene family in plants. Plant sHsps are classified into different subfamilies according to amino acid sequence similarity and localization to distinct subcellular compartments. In the whole Arabidopsis thaliana genome, 19 genes were annotated to encode sHsps, of which 14 belong to previously defined plant sHsp families. In this paper, we report studies of the five additional sHsp genes in A. thaliana, which can now be shown to represent evolutionarily distinct sHsp subfamilies also found in other plant species. While two of these five sHsps show expression patterns typical of the other 14 genes, three have unusual tissue specific and developmental profiles and do not respond to heat induction. Analysis of intracellular targeting indicates that one sHsp represents a new class of mitochondrion-targeted sHsps, while the others are cytosolic/nuclear, some of which may cooperate with other sHsps in formation of heat stress granules. Three of the five new proteins were purified and tested for chaperone activity in vitro. Altogether, these studies complete our basic understanding of the sHsp chaperone family in plants.Cell Stress and Chaperones 04/2008; 13(2):183-97. · 3.01 Impact Factor -
Article: The diversity of plant heat stress transcription factors.
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ABSTRACT: Compared with other eukaryotes with one to three heat stress transcription factors (Hsf), the plant Hsf family shows a striking multiplicity, with more than 20 members. Despite many conserved features, members of the Hsf family show a strong diversification of expression pattern and function within the family. Research on Arabidopsis Hsfs opened a new era with genome-wide transcriptome profiling in combination with the availability of knockout lines. The output from these analyses provides increasing evidence that individual Hsfs have unique functions as part of different signal transduction pathways operating in response to environmental stress and during development.Trends in Plant Science 11/2007; 12(10):452-7. · 11.05 Impact Factor -
Article: Complexity of the heat stress response in plants.
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ABSTRACT: Plants have evolved a variety of responses to elevated temperatures that minimize damage and ensure protection of cellular homeostasis. New information about the structure and function of heat stress proteins and molecular chaperones has become available. At the same time, transcriptome analysis of Arabidopsis has revealed the involvement of factors other than classical heat stress responsive genes in thermotolerance. Recent reports suggest that both plant hormones and reactive oxygen species also contribute to heat stress signaling. Additionally, an increasing number of mutants that have altered thermotolerance have extended our understanding of the complexity of the heat stress response in plants.Current Opinion in Plant Biology 07/2007; 10(3):310-6. · 9.27 Impact Factor -
Article: Role of heat stress transcription factor HsfA5 as specific repressor of HsfA4.
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ABSTRACT: Unlike other eukaryotes, plants possess a complex family of heat stress transcription factors (Hsfs) with usually more than 20 members. Among them, Hsfs A4 and A5 form a group distinguished from other Hsfs by structural features of their oligomerization domains and by a number of conserved signature sequences. We show that A4 Hsfs are potent activators of heat stress gene expression, whereas A5 Hsfs act as specific repressors of HsfA4 activity. The oligomerization domain of HsfA5 alone is necessary and sufficient to exert this effect. Due to the high specificity of the oligomerization domains, other class A Hsfs are not affected. Pull-down assay and yeast two-hybrid interaction tests demonstrate that the tendency to form HsfA4/A5 heterooligomers is stronger than the formation of homooligomers. The specificity of interaction between Hsfs A4 and A5 was confirmed by bimolecular fluorescence complementation experiments. The major role of the representatives of the HsfA4/A5 group, which are not involved in the conventional heat stress response, may reside in cell type-specific functions connected with the control of cell death triggered by pathogen infection and/or reactive oxygen species.Journal of Biological Chemistry 03/2007; 282(6):3605-13. · 4.77 Impact Factor -
Article: Synthesis, modification and structural binding of heat‐shock proteins in tomato cell cultures
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ABSTRACT: Synthesis of about 30 acidic and 18 basic heat-shock proteins (hsps) is induced in suspension cultures of tomato (Lycopersicon peruvianum) if subjected to supraoptimal temperature conditions (35–40°C). A characteristic aspect of the plant heat-shock response is the formation of cytoplasmic granular aggregates, heat-shock granules, containing distinct heat-shock proteins as major structural components and, in addition, several hitherto undetected minor acidic and basic heat-shock proteins. Structural binding of heat-shock proteins, i.e. assembly of heat-shock granules, is dependent on the persistance of supraoptimal temperature conditions. Despite the ongoing synthesis also at 25°C, e.g. in pulse heat-shocked cultures, these proteins are accumulated exclusively in soluble form.Individual heat-shock proteins are characterized by their kinetics of synthesis and are classified by their compartmentation behaviour into class A proteins (exclusively found in soluble form, e.g. hsps 95 and 80), class B proteins (5–10% bound to heat-shock granules, e.g. hsps 70, 68), class C proteins (30–80% bound to heat-shock granules, e.g. hsps 21, 17, 15) and class D proteins, which are minor heat-shock proteins only detected in structure-bound form. Major representatives are modified proteins, i.e. hsps 95, 80, 70 and 68 are phosphorylated and hsps 80, 74, 70 and 17 are methylated proteins (numbers 70, 80 etc. refer to 10−3Mr).Under heat-shock conditions synthesis of the proteins detected in control cells (25°C proteins) exhibits two patterns. There are proteins with continued and proteins with discontinued synthesis. Synthesis of most of the latter proteins is resumed very rapidly after shift-down to 25°C, even in the presence of actinomycin D. We conclude that reversible segregation of distinct mRNA species from the translation apparatus contributes to the heat-shock-specific pattern of protein synthesis in plants also.European Journal of Biochemistry. 03/2005; 139(2):303 - 313. -
Article: Heat stress response in plants: a complex game with chaperones and more than twenty heat stress transcription factors.
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ABSTRACT: Compared to the overall multiplicity of more than 20 plant Hsfs, detailed analyses are mainly restricted to tomato and Arabidopsis and to three important representatives of the family (Hsfs A1, A2 and B1). The three Hsfs represent examples of striking functional diversification specialized for the three phases of the heat stress (hs) response (triggering, maintenance and recovery). This is best illustrated for the tomato Hsf system: (i) HsfA1a is the master regulator responsible for hs-induced gene expression including synthesis of HsfA2 and HsfB1. It is indispensible for the development of thermotolerance. (ii) Although functionally equivalent to HsfA1a, HsfA2 is exclusively found after hs induction and represents the dominant Hsf, the "working horse" of the hs response in plants subjected to repeated cycles of hs and recovery in a hot summer period. Tomato HsfA2 is tightly integrated into a network of interacting proteins (HsfA1a, Hsp17-CII, Hsp17-CI) influencing its activity and intracellular distribution. (iii) Because of structural peculiarities, HsfB1 acts as coregulator enhancing the activity of HsfA1a and/or HsfA2. But in addition, it cooperates with yet to be identified other transcription factors in maintaining and/or restoring housekeeping gene expression.Journal of Biosciences 01/2005; 29(4):471-87. · 1.65 Impact Factor -
Article: Role of Hsp17.4-CII as coregulator and cytoplasmic retention factor of tomato heat stress transcription factor HsfA2.
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ABSTRACT: HsfA2 is a heat stress (hs)-induced Hsf in peruvian tomato (Lycopersicon peruvianum) and the cultivated form Lycopersicon esculentum. Due to the high activator potential and the continued accumulation during repeated cycles of heat stress and recovery, HsfA2 becomes a dominant Hsf in thermotolerant cells. The formation of heterooligomeric complexes with HsfA1 leads to nuclear retention and enhanced transcriptional activity of HsfA2. This effect seems to represent one part of potential molecular mechanisms involved in its activity control. As shown in this paper, the activity of HsfA2 is also controlled by a network of nucleocytoplasmic small Hsps influencing its solubility, intracellular localization and activator function. By yeast two-hybrid interaction and transient coexpression studies in tobacco (Nicotiana plumbaginifolia) mesophyll protoplasts, we found that tomato (Lycopersicon esculentum) Hsp17.4-CII acts as corepressor of HsfA2. Given appropriate conditions, both proteins together formed large cytosolic aggregates which could be solubilized in presence of class CI sHsps. However, independent of the formation of aggregates or of the nucleocytoplasmic distribution of HsfA2, its transcriptional activity was specifically repressed by interaction of Hsp17.4-CII with the C-terminal activator domain. Although not identical in all aspects, the situation with the highly expressed, heat stress-inducible Arabidopsis HsfA2 was found to be principally similar. In corresponding reporter assays its activity was repressed in presence of AtHsp17.7-CII but not of AtHsp17.6-CII or LpHsp17.4-CII.Plant physiology 08/2004; 135(3):1457-70. · 6.53 Impact Factor -
Article: Tomato heat stress protein Hsp16.1-CIII represents a member of a new class of nucleocytoplasmic small heat stress proteins in plants.
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ABSTRACT: We describe a new class of plant small heat stress proteins (sHsps) with dominant nuclear localization (Hsp17-CIII). The corresponding proteins in tomato, Arabidopsis, and rice are encoded by unique genes containing a short intron in the beta4-encoding region of the alpha-crystallin domain (ACD). The strong nuclear localization results from a cluster of basic amino acid residues in the loop between beta5 and beta6 of the ACD. Using yeast 2-hybrid tests, analyses of native complexes of the sHsps, and immunofluorescence data, we demonstrate that, in contrast to earlier observations (Kirschner et al 2000), proteins of the sHsp classes CI, CII, and CIII interact with each other, thereby influencing oligomerization state and intracellular localization.Cell Stress and Chaperones 02/2003; 8(4):381-94. · 3.01 Impact Factor -
Article: In the complex family of heat stress transcription factors, HsfA1 has a unique role as master regulator of thermotolerance in tomato.
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ABSTRACT: We generated transgenic tomato plants with altered expression of heat stress transcription factor HsfA1. Plants with 10-fold overexpression of HsfA1 (OE plants) were characterized by a single HsfA1 transgene cassette, whereas plants harboring a tandem inverted repeat of the cassette showed cosuppression (CS plants) by posttranscriptional silencing of the HsfA1 gene connected with formation of small interfering RNAs. Under normal growth conditions, major developmental parameters were similar for wild-type (WT), OE, and CS plants. However, CS plants and fruits were extremely sensitive to elevated temperatures, because heat stress-induced synthesis of chaperones and Hsfs was strongly reduced or lacking. Despite the complexity of the plant Hsf family with at least 17 members in tomato, HsfA1 has a unique function as master regulator for induced thermotolerance. Using transient reporter assays with mesophyll protoplasts from WT tomato, we demonstrated that plasmid-encoded HsfA1 and HsfA2 were well expressed. However, in CS protoplasts the cosuppression phenomenon was faithfully reproduced. Only transformation with HsfA2 expression plasmid led to normal expression of the transcription factor and reporter gene activation, whereas even high amounts of HsfA1 expression plasmids were silenced. Thermotolerance in CS protoplasts was restored by plasmid-borne HsfA2, resulting in expression of chaperones, thermoprotection of firefly luciferase, and assembly of heat stress granules.Genes & Development 07/2002; 16(12):1555-67. · 11.66 Impact Factor -
Article: Isolation and characterization of HsfA3, a new heat stress transcription factor of Lycopersicon peruvianum
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ABSTRACT: Stress-induced transcription of heat shock proteins (Hsps) in eukaryotes is mediated by a conserved class of transcription factors called heat stress transcription factors (Hsfs). Here we report the isolation and functional characterization of HsfA3, a new member of the Hsf family. HsfA3 was cloned from a tomato heat stress cDNA library by yeast two-hybrid screening, using HsfA1 as a bait. HsfA3 is a single-copy gene with all the conserved sequence elements characteristic of a heat stress transcription factor. The constitutively expressed HsfA3 is mainly found in the cytoplasm under control conditions and in the nucleus under heat stress conditions. Functionally, HsfA3 behaves similarly to the already known members of tomato Hsf family. It is able to substitute yeast Hsf for viability functions and is a strong activator of Hsf-dependent reporter constructs both in tobacco protoplasts and yeast. Finally, similar to the AHA motifs in HsfA1 and HsfA2, the activator function depends on four short peptide motifs with a central tryptophan residue found in the C-terminal domain of HsfA3.The Plant Journal 12/2001; 22(4):355 - 365. · 6.16 Impact Factor -
Article: Arabidopsis and the heat stress transcription factor world: how many heat stress transcription factors do we need?
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ABSTRACT: Sequencing of the Arabidopsis genome revealed a unique complexity of the plant heat stress transcription factor (Hsf) family. By structural characteristics and phylogenetic comparison, the 21 representatives are assigned to 3 classes and 14 groups. Particularly striking is the finding of a new class of Hsfs (AtHsfC1) closely related to Hsf1 from rice and to Hsfs identified from frequently found expressed sequence tags of tomato, potato, barley, and soybean. Evidently, this new type of Hsf is well expressed in different plant tissues. Besides the DNA binding and oligomerization domains (HR-A/B region), we identified other functional modules of Arabidopsis Hsfs by sequence comparison with the well-characterized tomato Hsfs. These are putative motifs for nuclear import and export and transcriptional activation (AHA motifs). There is intriguing flexibility of size and sequence in certain parts of the otherwise strongly conserved N-terminal half of these Hsfs. We have speculated about possible exon-intron borders in this region in the ancient precursor gene of plant Hsfs, similar to the exon-intron structure of the present mammalian Hsf-encoding genes.Cell Stress and Chaperones 08/2001; · 3.01 Impact Factor -
Article: Heat stress response and heat stress transcription factors
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ABSTRACT: Expression of heat shock protein (HSP)-coding genes is controlled by heat stress transcription factors (Hsfs). They are structurally and functionally conserved throughout the eukaryotic kingdom. In addition to the DNA-binding domain with the helix-turn-helix motif essential for DNA recognition, three functional parts in the C-terminal activator domain were characterized: (i) the HR-A/B region is responsible for oligomerization and activity control, (ii) the nuclear localizing signal (NLS) formed by a cluster of basic amino acid residues which is required and sufficient for nuclear import and (iii) short C-terminal peptide motifs with a central Trp residue (AHA elements). These three parts are indispensible for the activator function. A peculiaritiy of plants is the heat shock-inducible new synthesis of Hsfs. In tomato HsfA1 is constitutively expressed, whereas Hsfs A2 and B1 are heat shock-inducible proteins themselves. We used Hsf knock-out strains of yeast and transient reporter assays in tobacco protoplasts for functional analysis of Hsf-coding cDNA clones and mutants derived from them. HsfA2, which in tomato cell cultures is expressed only after heat shock induction, tends to form large cytoplasmic aggregates together with other HSPs (heat stress granules). In the transient expression assay its relatively low activator potential is evidently due to the inefficient nuclear import. However, the intramolecular shielding of the NLS can be released either by deletion of a short C-terminal fragment or by coexpression with HsfA1, which forms hetero-oligomers with HsfA2.Journal of Biosciences 04/1998; 23(4):313-329. · 1.65 Impact Factor -
Article: Control of ribosome biosynthesis in plant cell cultures under heat shock conditions. II. Ribosomal proteins
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ABSTRACT: The nomenclature and synthesis of acidic and basic ribosomal proteins of plant cell cultures are described, with special regard to ribosome biosynthesis under control and heat-shock conditions. Assembly and processing of preribosomes in the nucleolus require a defined set of ribosomal proteins binding to the nascent pre-rRNA chain. Others are added later on the maturation pathway, mostly in the cytoplasm. Although, under appropriate heat-shock conditions, formation of mature ribosomes is completely blocked, most of the typical ribosomal proteins are still detected in the nuclear fraction. They are constituents of heat-shock preribosomes, which can be processed to normal cytoplasmic ribosomes only if the cells are allowed to recover at 25°C shortly after the labeling period at 40°C. However, if hyperthermic conditions are maintained, the labeled pre-rRNP material is evidently partly broken down. It forms the growing amount of RNP granules (ribosomal wastage) characteristic of the dispersed nucleolus of heat-shocked cells. In addition to the ‘nucleolar’ ribosomal proteins, a few newly formed ribosomal proteins can also be detected in cytoplasmic ribosomes under heat-shock conditions. Most of them belong to the group of exchange proteins whose labeling continues even if pre-rRNA synthesis is blocked by actinomycin D.Biochimica et Biophysica Acta (BBA) - Gene Structure and Expression.
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Institutions
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1998–2012
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Goethe-Universität Frankfurt am Main
Frankfurt am Main, Hesse, Germany
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2009
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Charité Universitätsmedizin Berlin
- Institute of Biochemistry
Berlin, Land Berlin, Germany
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