Calmodulin is involved in heat shock signal transduction in wheat

Cell-specific association of heat shock-induced proton flux with actin ring formation in Chenopodium cells: comparison of auto- and heterotroph cultures

A comparison of the responses of extracellular pH, buffering capacity and actin cytoskeleton in autotroph and heterotroph Chenopodium rubrum cells to heat shock revealed cell-specific reactions: alkalinization caused by the heat shock at 25-35 degrees C was higher in heterotroph cells and characterized by heat shock-induced changes in the actin cytoskeleton and ring formation at 35-37 degrees C. Rings (diameter up to 3 mum) disappeared and extracellular pH recovered after the heat-shocked cells were transferred into control medium. At 41 degrees C, no rings but a network of coarse actin filaments were induced; at higher temperatures, fragmentation of the actin cytoskeleton and release of buffering compounds occurred, indicating sudden membrane leakage at 45-47 degrees C. The calcium chelator EGTA [ethylene-glycol-bis(beta-aminoethyl-ether)-N,N,N',N'-tetraacetic-acid] increased the frequency of heat shock-induced rings. Ionophore (10 microM nigericin) and the sodium/proton antiport blocker [100 microM 5-(N-ethyl-N-isopropyl)-amiloride] mimicked the effect of the 37 degrees C heat shock. The cytoskeleton inhibitors latrunculin B, cytochalasin D and 2,3-butanedione monoxime inhibited ring formation but not alkalinization. In autotroph cells, the treatment with nigericin (10 microM) produced rings, although the actin cytoskeleton was not affected by temperatures up to 45 degrees C. We conclude that Chenopodium cells express a specific temperature sensor that has ascendancy over the organization of the actin cytoskeleton; this is probably a temperature- and potential-sensitive proton-transporting mechanism that is dependent on the culture conditions of the heterotroph cells.

Heat stress-responsive transcriptome analysis in heat susceptible and tolerant wheat (Triticum aestivum L.) by using Wheat Genome Array

Background

Wheat is a major crop in the world, and the high temperature stress can reduce the yield of wheat by as much as 15%. The molecular changes in response to heat stress are poorly understood. Using GeneChip^® Wheat Genome Array, we analyzed genome-wide gene expression profiles in the leaves of two wheat genotypes, namely, heat susceptible 'Chinese Spring' (CS) and heat tolerant 'TAM107' (TAM).

Results

A total of 6560 (~10.7%) probe sets displayed 2-fold or more changes in expression in at least one heat treatment (false discovery rate, FDR, α = 0.001). Except for heat shock protein (HSP) and heat shock factor (HSF) genes, these putative heat responsive genes encode transcription factors and proteins involved in phytohormone biosynthesis/signaling, calcium and sugar signal pathways, RNA metabolism, ribosomal proteins, primary and secondary metabolisms, as well as proteins related to other stresses. A total of 313 probe sets were differentially expressed between the two genotypes, which could be responsible for the difference in heat tolerance of the two genotypes. Moreover, 1314 were differentially expressed between the heat treatments with and without pre-acclimation, and 4533 were differentially expressed between short and prolonged heat treatments.

Conclusion

The differences in heat tolerance in different wheat genotypes may be associated with multiple processes and mechanisms involving HSPs, transcription factors, and other stress related genes. Heat acclimation has little effects on gene expression under prolonged treatments but affects gene expression in wheat under short-term heat stress. The heat stress responsive genes identified in this study will facilitate our understanding of molecular basis for heat tolerance in different wheat genotypes and future improvement of heat tolerance in wheat and other cereals.

The calmodulin-binding protein kinase 3 is part of heat-shock signal transduction in Arabidopsis thaliana

Based on our previous findings, we proposed a pathway for the participation of Ca(2+)/calmodulin (CaM) in heat-shock (HS) signal transduction. The specific mechanism by which CaM regulates activation of heat-shock transcription factors (HSFs) is not known. CaM-binding protein kinases (CBK) are the most poorly understood of the CaM target proteins in plants. In this study, using a yeast two-hybrid assay, we found that AtCBK3 interacts with AtHSFA1a. Fluorescence resonance energy transfer was used to confirm the interaction between AtCBK3-YFP and AtHSFA1a-CFP. Furthermore, we demonstrate that purified recombinant AtCBK3 phosphorylated recombinant AtHSFA1a in vitro. We also describe the results of both downregulation of AtCBK3 expression and ectopic overexpression in Arabidopsis thaliana. The T-DNA insertion AtCBK3 knockout lines had impaired basal thermotolerance, which could be complemented by transformation of plants with the native gene. Overexpression of AtCBK3 resulted in plants with increased basal thermotolerance. Results from real-time quantitative PCR and protein gel-blot analyses suggest that AtCBK3 regulates transcription of heat-shock protein (HSP) genes and synthesis of HSPs. The binding activity of HSF to the heat-shock element (HSE), the mRNA level of HSP genes and synthesis of HSPs were upregulated in AtCBK3-overexpressing lines after HS, but downregulated in AtCBK3 null lines. These results indicate that AtCBK3 controls the binding activity of HSFs to HSEs by phosphorylation of AtHSFA1a, and is an important component of the HS signal transduction pathway.

A comprehensive analysis of the combined effects of high light and high temperature stresses on gene expression in sunflower

BACKGROUND AND AIMS

Although high light (HL) and high temperature (HT) stresses have been extensively investigated, a global analysis of their combined effects on the transcriptome of any plant species has not yet been described. Sunflower is an agronomically important oil crop frequently subjected to these stress factors. Because results in model plants may not always translate well to crop plants, responses of sunflower (Helianthus annuus) to HL, HT and a combination of both stresses were analysed by profiling gene expression in leaves and immature seeds.

METHODS

Plants were grown in HL (600 microE m(-2) s(-1)), HT (35 degrees C) and a combination of HL and HT (HL + HT), and gene expression in leaves and immature seeds was profiled using cDNA microarrays containing more than 8000 putative unigenes.

KEY RESULTS

Using two-way analysis of variance, 105, 55 and 129 cDNA clones were identified showing significant changes in steady-state transcript levels, across the two tissues, in response to HL, HT and HL + HT, respectively. A significant number of these transcripts were found to be specific to each stress. Comparing gene expression profiles between leaves and immature seeds revealed that 89, 113 and 186 cDNA clones can be considered as differentially expressed in response to HL, HT and HL + HT, respectively. More than half of the cDNA clones showing significant differences between embryo and leaf tissues in response to HL + HT were specific to this stress. Significant differences between leaves and seeds shared by all three stress treatments were observed for only eight genes.

CONCLUSIONS

Taken together, these results indicate that vegetative and reproductive tissues employ different transcriptome responses to these stress treatments. Careful examination of the putative functions of these genes revealed novel and specific responses. The potential roles of many of the differentially expressed genes in stress tolerance are mentioned and discussed.

Interaction network of proteins associated with abiotic stress response and development in wheat

Wheat is the most widely adapted crop to abiotic stresses and considered an excellent system to study stress tolerance in spite of its genetic complexity. Recent studies indicated that several hundred genes are either up- or down-regulated in response to stress treatment. To elucidate the function of some of these genes, an interactome of proteins associated with abiotic stress response and development in wheat was generated using the yeast two-hybrid GAL4 system and specific protein interaction assays. The interactome is comprised of 73 proteins, generating 97 interactions pairs. Twenty-one interactions were confirmed by bimolecular fluorescent complementation in Nicotiana benthamiana. A confidence-scoring system was elaborated to evaluate the significance of the interactions. The main feature of this interactome is that almost all bait proteins along with their interactors were interconnected, creating a spider web-like structure. The interactome revealed also the presence of a "cluster of proteins involved in flowering control" in three- and four-protein interaction loops. This network provides a novel insight into the complex relationships among transcription factors known to play central roles in vernalization, flower initiation and abscisic acid signaling, as well as associations that tie abiotic stress with other regulatory and signaling proteins. This analysis provides useful information in elucidating the molecular mechanism associated with abiotic stress response in plants.

Calmodulin-binding protein phosphatase PP7 is involved in thermotolerance in Arabidopsis

PP7 is the first protein Ser/Thr phosphatase to be found to interact with calmodulin (CaM) in plants. The T-DNA insertion AtPP7 knockout line and AtPP7 overexpression lines were employed to study the specific function of AtPP7. The AtPP7 knockout impaired the thermotolerance of Arabidopsis seedlings while the overexpression of AtPP7 resulted in plants with increased thermotolerance. Results from real-time polymerase chain reaction (PCR) showed that the expression of AtHSP70 and AtHSP101 genes was up-regulated in AtPP7 overexpression lines after heat shock (HS) at 37 degrees C for 1 h. Protein gel blot analysis showed that HSP70 protein levels increased in AtPP7 overexpression lines after HS at 37 degrees C for 2 h. The expression of the AtPP7 gene was also induced by HS at 37 degrees C in wild-type Arabidopsis. Using a yeast two-hybrid screen, we showed an interaction between AtPP7 and CaM. In addition, we found that AtPP7 interacts with an HS transcription factor (HSF), suggesting a possible role for AtPP7 in regulating the expression of heat shock protein (HSP) genes.

Calcium-calmodulin is required for abscisic acid-induced antioxidant defense and functions both upstream and downstream of H2O2 production in leaves of maize (Zea mays) plants

* Using pharmacological and biochemical approaches, the role of calmodulin (CaM) and the relationship between CaM and hydrogen peroxide (H(2)O(2)) in abscisic acid (ABA)-induced antioxidant defense in leaves of maize (Zea mays) plants were investigated. * Treatment with ABA or H(2)O(2) led to significant increases in the concentration of cytosolic Ca(2+) in the protoplasts of mesophyll cells and in the expression of the calmodulin 1 (CaM1) gene and the content of CaM in leaves of maize plants, and enhanced the expression of the antioxidant genes superoxide dismutase 4 (SOD4), cytosolic ascorbate peroxidase (cAPX), and glutathione reductase 1 (GR1) and the activities of the chloroplastic and cytosolic antioxidant enzymes. The up-regulation of the antioxidant enzymes was almost completely blocked by pretreatments with two CaM antagonists. * Pretreatments with CaM antagonists almost completely inhibited ABA-induced H(2)O(2) production throughout ABA treatment, but pretreatment with an inhibitor or scavenger of reactive oxygen species (ROS) did not affect the initial increase in the contents of CaM induced by ABA. * Our results suggest that Ca(2+)-CaM is involved in ABA-induced antioxidant defense, and that cross-talk between Ca(2+)-CaM and H(2)O(2) plays a pivotal role in ABA signaling.

Influx of extracellular Ca2+ involved in jasmonic-acid-induced elevation of [Ca2+]cyt and JR1 expression in Arabidopsis thaliana

The changes in cytosolic Ca2+ levels play important roles in the signal transduction pathways of many environmental and developmental stimuli in plants and animals. We demonstrated that the increase in cytosolic free Ca2+ concentration ([Ca2+]cyt) of Arabidopsis thaliana leaf cells was induced by exogenous application of jasmonic acid (JA). The elevation of [Ca2+]cyt was detected within 1 min after JA treatment by the fluorescence intensity using laser scanning confocal microscopy, and the elevated level of fluorescence was maintained during measuring time. With pretreatment of nifedipine (Nif), a nonpermeable L-type channel blocker, the fluorescence of [Ca2+]cyt induced by JA was inhibited in a dose-dependent manner. In contrast, verapamil, another L-type channel blocker, had no significant effect. Furthermore, Nif repressed JA-induced gene expression of JR1 but verapamil did not. JA-induced gene expression could be mimicked by higher concentration of extracellular Ca2+. W-7 [N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide], an antagonist of calmodulin (CaM), blocked the JA induction of JR1 expression while W-5 [N-(6-aminohexyl)-1-naphthalenesulfonamide], its inactive antagonist, had no apparent effect. These data provide the evidence that the influx of extracellular Ca2+ through Nif sensitive plasma membrane Ca2+ channel may be responsible for JA-induced elevation of [Ca2+]cyt and downstream gene expression, CaM may be also involved in JA signaling pathway.

Lipopolysaccharide-responsive phosphoproteins in Nicotiana tabacum cells

Mounting evidence is merging to affirm the effectiveness of bacterial lipopolysaccharides (LPS) as biological control agents, inducers of innate immunity, and to stimulate/potentiate the development of defense responses in plants through protein phosphorylation-mediated signal perception/transduction responses. In vivo labeling of protein phosphorylation events during signal transduction indicated the rapid phosphorylation of several proteins. Substantial differences and de novo LPS-induced phosphorylation were also observed with two-dimensional analysis. In this study, qualitative and quantitative changes in phosphoproteins of Nicotiana tabacum suspension cells during elicitation by LPS from the Gram-negative bacteria, Burkholderia cepacia, were analyzed using two-dimensional electrophoresis in combination with a phosphoprotein-specific gel stain. Trypsin digested phosphoproteins were analyzed by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF/MS) and nano-electrospray-ionization liquid chromatography tandem mass spectrometry (nano-ESI-LC/MS/MS). A total of 27 phosphoproteins were identified from 23 excised gel spots. The identified phosphoproteins indicate that LPS(B.cep)-induced signal perception/transduction involves G-protein coupled receptor signaling, Ca(2+)/calmodulin-dependent signaling pathways, H(+)-ATPase regulation of intracellular pH, thioredoxin-mediated signaling and phosphorylation of 14-3-3 regulatory proteins. Other targets of LPS(B.cep)-responsive phosphorylation included NTP pool maintenance, heat shock proteins, protein biosynthesis and chaperones as well as cytoskeletal tubulin. The results add novel insights into the biochemical process of LPS perception and resulting signal transduction.

Primary evidence for involvement of IP3 in heat-shock signal transduction in Arabidopsis

The role of inositol 1,4,5-trisphosphate (IP(3)) in transducing heat-shock (HS) signals was examined in Arabidopsis. The whole-plant IP(3) level increased within 1 min of HS at 37 degrees C. After 3 min of HS, the IP(3) level reached a maximum 2.5 fold increase. Using the transgenic Arabidopsis plants that have AtHsp18.2 promoter-beta-glucuronidase (GUS) fusion gene, it was found that the level of GUS activity was up-regulated by the addition of caged IP(3) at both non-HS and HS temperatures and was down-regulated by the phospholipase C (PLC) inhibitors {1-[6-((17beta-3-Methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl]-2,5-pyrrolidinedione}(U-73122). The intracellular-free calcium ion concentration ([Ca(2+)](i)) increased during HS at 37 degrees C in suspension-cultured Arabidopsis cells expressing apoaequorin. Treatment with U-73122 prevented the increase of [Ca(2+)](i) to some extent. Above results provided primary evidence for the possible involvement of IP(3) in HS signal transduction in higher plants.

Plant-specific calmodulin-binding proteins

Calmodulin CaM is the most prominent Ca2+ transducer in eukaryotic cells, regulating the activity of numerous proteins with diverse cellular functions. Many features of CaM and its downstream targets are similar in plants and other eukaryotes. However, plants possess a unique set of CaM-related proteins, and several unique CaM target proteins. This review discusses recent progress in identifying plant-specific CaM-binding proteins and their roles in response to biotic and abiotic stresses and development. The review also addresses aspects emerging from recent structural studies of CaM interactions with target proteins relevant to plants.

Characterization of the genomic structures and selective expression profiles of nine class I small heat shock protein genes clustered on two chromosomes in rice (Oryza sativa L.)

The cytosolic class I small heat shock proteins (sHSP-CI) represent the most abundant sHSP in plants. Here, we report the characterization and the expression profile of nine members of the sHSP-CI gene family in rice (Oryza sativa Tainung No.67), of which Oshsp16.9A, Oshsp16.9B, Oshsp16.9C, Oshsp16.9D and Oshsp17.9B are clustered on chromosome 1, and Oshsp17.3, Oshsp17.7, Oshsp17.9A and Oshsp18.0 are clustered on chromosome 3. Oshsp17.3 and Oshsp18.0 are linked by a 356-bp putative bi-directional promoter. Individual gene products were identified from the protein subunits of a heat shock complex (HSC) and from in vitro transcription/ translation products by two-dimensional gel electrophoreses (2-DE). All sHSP-CI genes except Oshsp17.9B were induced strongly after a 2-h heat shock treatment. The genes on chromosome 3 were induced rapidly at 32 and 41 degrees C, whereas those on chromosome 1 were induced slowly by similar conditions. Seven of these genes, except Oshsp16.9D and Oshsp17.9B, were induced by arsenite (As), but only genes on chromosome 3 were strongly induced by azetidine-2-carboxylic acid (Aze, a proline analog) and cadmium (Cd). A similar expression profile of all sHSP-CI genes at a lower level was evoked by ethanol, H2O2 and CuCl2 treatments. Transient expression assays of the promoter activity by linking to GUS reporter gene also supported the in vivo selective expression of the sHSP-CI genes by Aze treatment indicating the differential induction of rice sHSP-CI genes is most likely regulated at the transcriptional level. Only Oshsp16.9A abundantly accumulated in mature dry seed also suggested additionally prominent roles played by this HSP in development.

Ca(2+) and calmodulin modulate DNA-binding activity of maize heat shock transcription factor in vitro

DNA-binding activity of a maize heat shock transcription factor (HSF) was induced by heat shock of a whole cell extract at 44 degrees C. Addition of the calcium ion chelator EGTA reduced the binding of the HSF to heat shock element (HSE) in vitro. Re-addition of CaCl(2) to the sample pretreated with EGTA restored the ability of the HSF to bind to DNA. DNA-binding activity of the HSF was also induced by directly adding CaCl(2) to a whole cell extract at non-heat-shock temperature, but not by MgCl(2). During HS at 44 degrees C, calmodulin (CaM) antagonists chlorpromazine (CPZ) and N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W7) inhibited DNA-binding activity of the HSF in a concentration-dependent manner, but N-(6-aminohexyl)-1-naphthalenesulfonamide (W5), an inactive structural analogue of W7, did not. Addition of antiserum specific to CaM reduced the binding of the HSF to HSE. Re-addition of CaM to the sample pretreated with antiserum could restore the binding activity of the HSF. DNA-binding activity of the HSF was promoted by directly adding CaM to a whole cell extract at 44 degrees C, but not by BSA. Moreover, at non-heat-shock temperature, DNA-binding activity of the HSF was also induced by directly adding CaM to a whole cell extract, but not by BSA. Our observations further confirm the role of Ca(2+) in activation of the HSF in plant and provide the first example of the role of CaM in regulation of DNA-binding activity of the HSF. These results suggest that Ca(2+) and CaM are involved in HSP gene expression likely through regulating the activity of the HSF.

Calcium/calmodulin-mediated signal network in plants

Various extracellular stimuli elicit specific calcium signatures that can be recognized by different calcium sensors. Calmodulin, the predominant calcium receptor, is one of the best-characterized calcium sensors in eukaryotes. In recent years, completion of the Arabidopsis genome project and advances in functional genomics have helped to identify and characterize numerous calmodulin-binding proteins in plants. There are some similarities in Ca(2+)/calmodulin-mediated signaling in plants and animals. However, plants possess multiple calmodulin genes and many calmodulin target proteins, including unique protein kinases and transcription factors. Some of these proteins are likely to act as "hubs" during calcium signal transduction. Hence, a better understanding of the function of these calmodulin target proteins should help in deciphering the Ca(2+)/calmodulin-mediated signal network and its role in plant growth, development and response to environmental stimuli.