Prokaryotic expression, purification, and the in vitro and in vivo protection study of dehydrin WDHN2 from Triticum aestivum

Dehydrins proteins accumulate and play important protective roles in most plants during abiotic stresses. The objective of this study was to characterize a YSK2-type dehydrin gene, WDHN2, isolated from Triticum aestivum previously. In this work, wheat dehydrin WDHN2 was expressed in Escherichia coli and purified by immobilized metal affinity chromatography, which exhibited as a single band by sodium dodecyl sulfonate polyacrylamide gel electrophoresis and western blotting. We show that WDHN2 is capable of alleviating lactate dehydrogenase inactivation from heat and desiccation in vitro enzyme activity protection assay. In vivo assay of Escherichia coli viability demonstrates the enhancement of cell survival by the overexpression of WDHN2. The protein aggregation prevention assay explores that WDHN2 has a broad protective effect on the cellular proteome. The results show that WDHN2 is mainly accumulated in the nucleus and cytosol, suggesting that this dehydrin may exert its function in both cellular compartments. Our data suggest that WDHN2 acts as a chaperone molecular in vivo.

Protein Disorder in Plant Stress Adaptation: From Late Embryogenesis Abundant to Other Intrinsically Disordered Proteins

Global climate change has caused severe abiotic and biotic stresses, affecting plant growth and food security. The mechanical understanding of plant stress responses is critical for achieving sustainable agriculture. Intrinsically disordered proteins (IDPs) are a group of proteins without unique three-dimensional structures. The environmental sensitivity and structural flexibility of IDPs contribute to the growth and developmental plasticity for sessile plants to deal with environmental challenges. This article discusses the roles of various disordered proteins in plant stress tolerance and resistance, describes the current mechanistic insights into unstructured proteins such as the disorder-to-order transition for adopting secondary structures to interact with specific partners (i.e., cellular membranes, membrane proteins, metal ions, and DNA), and elucidates the roles of liquid-liquid phase separation driven by protein disorder in stress responses. By comparing IDP studies in animal systems, this article provides conceptual principles of plant protein disorder in stress adaptation, reveals the current research gaps, and advises on the future research direction. The highlighting of relevant unanswered questions in plant protein disorder research aims to encourage more studies on these emerging topics to understand the mechanisms of action behind their stress resistance phenotypes.

Expression, Purification, and Preliminary Protection Study of Dehydrin PicW1 From the Biomass of Picea wilsonii

Dehydrins (DHNs) belong to group II of late embryogenesis-abundant (LEA) proteins, which are up-regulated in most plants during cold, drought, heat, or salinity stress. Despite the importance of dehydrins for the plants to resist abiotic stresses, it is necessary to obtain plant-derived dehydrins from different biomass. Generally, dehydrin PicW1 from Picea wilsonii is involved in Kn-type dehydrin with five K-segments, which has a variety of biological activities. In this work, Picea wilsonii dehydrin PicW1 was expressed in Escherichia coli and purified by chitin-affinity chromatography and size-exclusion chromatography, which showed as a single band by SDS-PAGE. A cold-sensitive enzyme of lactate dehydrogenase (LDH) is used to explore the protective activities of other proteins. Temperature stress assays showed that PicW1 had an effective protective effect on LDH activity, which was better than that of bovine serum albumin (BSA). This study provides insights into the purification and protective activity of K5 DHNs for the advancement of dehydrin structure and function from biomass.

The N-Terminal Region of Soybean PM1 Protein Protects Liposomes during Freeze-Thaw

Late embryogenesis abundant (LEA) group 1 (LEA_1) proteins are intrinsically disordered proteins (IDPs) that play important roles in protecting plants from abiotic stress. Their protective function, at a molecular level, has not yet been fully elucidated, but several studies suggest their involvement in membrane stabilization under stress conditions. In this paper, the soybean LEA_1 protein PM1 and its truncated forms (PM1-N: N-terminal half; PM1-C: C-terminal half) were tested for the ability to protect liposomes against damage induced by freeze-thaw stress. Turbidity measurement and light microscopy showed that full-length PM1 and PM1-N, but not PM1-C, can prevent freeze-thaw-induced aggregation of POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) liposomes and native thylakoid membranes, isolated from spinach leaves (Spinacia oleracea). Particle size distribution analysis by dynamic light scattering (DLS) further confirmed that PM1 and PM1-N can prevent liposome aggregation during freeze-thaw. Furthermore, PM1 or PM1-N could significantly inhibit membrane fusion of liposomes, but not reduce the leakage of their contents following freezing stress. The results of proteolytic digestion and circular dichroism experiments suggest that PM1 and PM1-N proteins bind mainly on the surface of the POPC liposome. We propose that, through its N-terminal region, PM1 functions as a membrane-stabilizing protein during abiotic stress, and might inhibit membrane fusion and aggregation of vesicles or other endomembrane structures within the plant cell.

Evidence for in vivo interactions between dehydrins and the aquaporin AtPIP2B

Plants have developed mechanisms that allow them to tolerate different abiotic stresses. Among these mechanisms, the accumulation of specific proteins such as dehydrins (DHNs) and aquaporins (AQPs) can protect other proteins from damage during dehydration and may allow the control of water loss, respectively. Although both types of proteins are involved in plant protection against dehydration stress, a direct interaction between them has not been explored. A previous screen to identify potential OpsDHN1 protein interactions revealed an aquaporin as a possible candidate. Here, we used the Bimolecular Fluorescence Complementation (BiFC) approach to investigate the direct interaction of the cactus OpsDHN1 protein with the Arabidopsis plasma membrane PIP family aquaporin AtPIP2B (At2G37170). Since AtPIP2B is a membrane protein and OpsDHN1 is a cytosolic protein that may be peripherally associated with membranes, we propose that OpsDHN1/AtPIP2B interaction takes place at cellular membranes. Furthermore, we also demonstrate the interaction of AtPIP2B with the three Arabidopsis dehydrins COR47 (AT1G20440), ERD10 (At1g20450), and RAB18 (At5g66400).

Characterization of Dehydrin protein, CdDHN4-L and CdDHN4-S, and their differential protective roles against abiotic stress in vitro

BACKGROUND

Dehydrins play positive roles in regulating plant abiotic stress responses. The objective of this study was to characterize two dehydrin genes, CdDHN4-L and CdDHN4-S, generated by alternative splicing of CdDHN4 in bermudagrass.

RESULTS

Overexpression of CdDHN4-L with φ-segment and CdDHN4-S lacking of φ-segment in Arabidopsis significantly increased tolerance against abiotic stresses. The growth phenotype of Arabidopsis exposed to NaCl at 100 mM was better in plants overexpressing CdDHN4-L than those overexpressing CdDHN4-S, as well as better in E.coli cells overexpressing CdDHN4-L than those overexpressing CdDHN4-S in 300 and 400 mM NaCl, and under extreme temperature conditions at - 20 °C and 50 °C. The CdDHN4-L had higher disordered characterization on structures than CdDHN4-S at temperatures from 10 to 90 °C. The recovery activities of lactic dehydrogenase (LDH) and alcohol dehydrogenase (ADH) in presence of CdDHN4-L and CdDHN4-S were higher than that of LDH and ADH alone under freeze-thaw damage and heat. Protein-binding and bimolecular fluorescence complementation showed that both proteins could bind to proteins with positive isoelectric point via electrostatic forces.

CONCLUSIONS

These results indicate that CdDHN4-L has higher protective ability against abiotic stresses due to its higher flexible unfolded structure and thermostability in comparison with CdDHN4-S. These provided direct evidence of the function of the φ-segment in dehydrins for protecting plants against abiotic stress and to show the electrostatic interaction between dehydrins and client proteins.

Mining Late Embryogenesis Abundant (LEA) Family Genes in Cleistogenes songorica, a Xerophyte Perennial Desert Plant

Plant growth and development depends on its ability to maintain optimal cellular homeostasis during abiotic and biotic stresses. Cleistogenes songorica, a xerophyte desert plant, is known to have novel drought stress adaptation strategies and contains rich pools of stress tolerance genes. Proteins encoded by Late Embryogenesis Abundant (LEA) family genes promote cellular activities by functioning as disordered molecules, or by limiting collisions between enzymes during stresses. To date, functions of the LEA family genes have been heavily investigated in many plant species except perennial monocotyledonous species. In this study, 44 putative LEA genes were identified in the C. songorica genome and were grouped into eight subfamilies, based on their conserved protein domains and domain organizations. Phylogenetic analyses indicated that C. songorica Dehydrin and LEA_2 subfamily proteins shared high sequence homology with stress responsive Dehydrin proteins from Arabidopsis. Additionally, promoter regions of CsLEA_2 or CsDehydrin subfamily genes were rich in G-box, drought responsive (MBS), and/or Abscisic acid responsive (ABRE) cis-regulatory elements. In addition, gene expression analyses indicated that genes from these two subfamilies were highly responsive to heat stress and ABA treatment, in both leaves and roots. In summary, the results from this study provided a comprehensive view of C. songoricaLEA genes and the potential applications of these genes for the improvement of crop tolerance to abiotic stresses.

Structural and Functional Dynamics of Dehydrins: A Plant Protector Protein under Abiotic Stress

Abiotic stress affects the growth and development of crops tremendously, worldwide. To avoid adverse environmental effects, plants have evolved various efficient mechanisms to respond and adapt to harsh environmental factors. Stress conditions are associated with coordinated changes in gene expressions at a transcriptional level. Dehydrins have been extensively studied as protectors in plant cells, owing to their vital roles in sustaining the integrity of membranes and lactate dehydrogenase (LDH). Dehydrins are highly hydrophilic and thermostable intrinsically disordered proteins (IDPs), with at least one Lys-rich K-segment. Many dehydrins are induced by multiple stress factors, such as drought, salt, extreme temperatures, etc. This article reviews the role of dehydrins under abiotic stress, regulatory networks of dehydrin genes, and the physiological functions of dehydrins. Advances in our understanding of dehydrin structures, gene regulation and their close relationships with abiotic stresses demonstrates their remarkable ability to enhance stress tolerance in plants.

Cryptic Disorder Out of Disorder: Encounter between Conditionally Disordered CP12 and Glyceraldehyde-3-Phosphate Dehydrogenase

Among intrinsically disordered proteins, conditionally disordered proteins undergo dramatic structural disorder rearrangements upon environmental changes and/or post-translational modifications that directly modulate their function. Quantifying the dynamics of these fluctuating proteins is extremely challenging but paramount to understanding the regulation of their function. The chloroplast protein CP12 is a model of such proteins and acts as a redox switch by formation/disruption of its two disulfide bridges. It regulates the Calvin cycle by forming, in oxidized conditions, a supramolecular complex with glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and then phosphoribulokinase. In this complex, both enzymes are inactive. The highly dynamic nature of CP12 has so far hindered structural characterization explaining its mode of action. Thanks to a synergistic combination of small-angle X-ray scattering, nuclear magnetic resonance and circular dichroism that drove the molecular modeling of structural ensembles, we deciphered the structural behavior of Chlamydomonas reinhardtii oxidized CP12 alone and in the presence of GAPDH. Contrary to sequence-based structural predictions, the N-terminal region is unstable, oscillates at the ms timescale between helical and random conformations, and is connected through a disordered linker to its C-terminus, which forms a stable helical turn. Upon binding to GAPDH, oxidized CP12 undergoes an induced unfolding of its N-terminus. This phenomenon called cryptic disorder contributes to decrease the entropy cost and explains CP12 unusual high affinity for its partners.

Dehydrins Impart Protection against Oxidative Stress in Transgenic Tobacco Plants

Environmental stresses generate reactive oxygen species (ROS) which might be detrimental to the plants when produced in an uncontrolled way. However, the plants ameliorate such stresses by synthesizing antioxidants and enzymes responsible for the dismutation of ROS. Additionally, the dehydrins were also able to protect the inactivation of the enzyme lactate dehydrogenase against hydroxyl radicals (OH^⋅) generated during Fenton's reaction. SbDhn1 and SbDhn2 overexpressing transgenic tobacco plants were able to protect against oxidative damage. Transgenic tobacco lines showed better photosynthetic efficiency along with high chlorophyll content, soluble sugar and proline. However, the malonyl dialdehyde (MDA) content was significantly lower in transgenic lines. Experimental evidence demonstrates the protective effect of dehydrins on electron transport chain in isolated chloroplast upon methyl viologen (MV) treatment. The transgenic tobacco plants showed significantly lower superoxide radical generation () upon MV treatment. The accumulation of the H₂O₂ was also lower in the transgenic plants. Furthermore, in the transgenic plants the expression of ROS scavenging enzymes was higher compared to non-transformed (NT) or vector transformed (VT) plants. Taken together these data, during oxidative stress dehydrins function by scavenging the () directly and also by rendering protection to the enzymes responsible for the dismutation of () thereby significantly reducing the amount of hydrogen peroxides formed. Increase in proline content along with other antioxidants might also play a significant role in stress amelioration. Dehydrins thus function co-operatively with other protective mechanisms under oxidative stress conditions rendering protection in stress environment.

Chilling susceptibility in mungbean varieties is associated with their differentially expressed genes

BACKGROUND

Mungbean (Vigna radiata L. Wilczek) is an economically important legume of high nutritional value, however, its cultivation is limited by susceptibility to chilling. Varieties NM94 and VC1973A, with differential susceptibility to stress, serve as good materials for uncovering how they differ in chilling tolerance. This study aimed to identify the ultrastructural, physiological and molecular changes to provide new insights on the differential susceptibility to chilling between varieties VC1973A and NM94.

RESULTS

Chilling stress caused a greater reduction in relative growth rate, a more significant decrease in maximum photochemical efficiency of PSII and DPPH scavenging activity and more-pronounced ultrastructural changes in VC1973A than in NM94 seedlings. Comparative analyses of transcriptional profiles in NM94 and VC1973A revealed that the higher expression of chilling regulated genes (CORs) in NM94. The transcript levels of lipid transfer protein (LTP), dehydrin (DHN) and plant defensin (PDF) in NM94 seedlings after 72 h at 4 °C was higher than that in its parental lines VC1973A, 6601 and VC2768A.

CONCLUSIONS

Our results suggested that LTP, DHN and PDF may mediate chilling tolerance in NM94 seedlings.

Overexpression of CsLEA11, a Y3SK2-type dehydrin gene from cucumber (Cucumis sativus), enhances tolerance to heat and cold in Escherichia coli

As the group II LEA (late embryogenesis abundant) proteins, dehydrins (DHNs) play an important role in plant growth and development, as well as in response to abiotic or biotic stress challenges. In this study, a DHN gene named CsLEA11 was identified and characterized from Cucumis sativus. Sequence analysis of CsLEA11 showed that it is a Y₃SK₂-type DHN protein rich in hydrophilic amino acids. Expression analyses revealed that the transcription of CsLEA11 could be significantly induced by heat and cold stress. The recombinant plasmid was transformed into Escherichia coli BL21 and isopropy-β-D-thiogalactoside (IPTG) was used to induce recombinant E. coli to express CsLEA11 gene. Overexpression of CsLEA11 in E. coli enhanced cell viability and conferred tolerance to heat and cold stress. Furthermore, CsLEA11 protein could protect the activity of lactate dehydrogenase (LDH) under heat stress. Taken together, our data demonstrate that CsLEA11 might function in tolerance of cucumber to heat and cold stress.

Group 4 late embryogenesis abundant proteins as a model to study intrinsically disordered proteins in plants

Late Embryogenesis Abundant (LEA) proteins comprise a heterogeneous group of proteins that accumulate to high levels in the dry seed and in vegetative plant tissues under water deficit. We recently reported that group 4 LEA proteins from Arabidopsis thaliana, regardless of their structural disorder prevalent in aqueous solution, are able to fold into α-helix when subjected to water deficit and/or macromolecular crowding environments. Interestingly, the ability to gain structure under water limiting conditions is circumscribed to the N-terminal conserved region. This environment- driven conformational plasticity has a functional impact because the conserved N-terminal region is necessary and sufficient to prevent the inactivation and/or aggregation of reporter enzymes, when they are subjected to partial dehydration or freeze-thaw treatments. In this addendum we present a broader analysis of the data and propose that the mechanism by which group 4 LEA proteins exert their chaperone-like activity occurs via a selection of particular LEA structural conformations favored by water deficit environments. In addition, we include further observations regarding the abundance and conservation of histidine residues in LEA proteins of this group, particularly at the C-terminal variable region, supporting the presence of an additional function in the same polypeptides as metal ion sequesters. The structural characteristics of group 4 LEA proteins together with their conceivable multifunctionality, a widespread feature in Intrinsically Disordered Proteins (IDPs), raises the possibility of using this set of proteins as a model to investigate the structure-function relationship of IDPs in plants.

Involvement of C-Terminal Histidines in Soybean PM1 Protein Oligomerization and Cu2+ Binding

Late embryogenesis abundant (LEA) proteins are widely distributed among plant species, where they contribute to abiotic stress tolerance. LEA proteins can be classified into seven groups according to conserved sequence motifs. The PM1 protein from soybean, which belongs to the Pfam LEA_1 group, has been shown previously to be at least partially natively unfolded, to bind metal ions and potentially to stabilize proteins and membranes. Here, we investigated the role of the PM1 C-terminal domain and in particular the multiple histidine residues in this half of the protein. We constructed recombinant plasmids expressing full-length PM1 and two truncated forms, PM1-N and PM1-C, which represent the N- and C-terminal halves of the protein, respectively. Immunoblotting and cross-linking experiments showed that full-length PM1 forms oligomers and high molecular weight (HMW) complexes in vitro and in vivo, while PM1-C, but not PM1-N, also formed oligomers and HMW complexes in vitro. When the histidine residues in PM1 and PM1-C were chemically modified, oligomerization was abolished, suggesting that histidines play a key role in this process. Furthermore, we demonstrated that high Cu2+ concentrations promote oligomerization and induce PM1 and PM1-C to form HMW complexes. Therefore, we speculate that PM1 proteins not only maintain ion homeostasis in the cytoplasm, but also potentially stabilize and protect other proteins during abiotic stress by forming a large, oligomeric molecular shield around biological targets.

Folding of intrinsically disordered plant LEA proteins is driven by glycerol-induced crowding and the presence of membranes

Late embryogenesis abundant (LEA) proteins are related to cellular dehydration tolerance. Most LEA proteins are predicted to have no stable secondary structure in solution, i.e., to be intrinsically disordered proteins (IDPs), but they may acquire α-helical structure upon drying. In the model plant Arabidopsis thaliana, the LEA proteins COR15A and COR15B are highly induced upon cold treatment and are necessary for the plants to attain full freezing tolerance. Freezing leads to increased intracellular crowding due to dehydration by extracellular ice crystals. In vitro, crowding by high glycerol concentrations induced partial folding of COR15 proteins. Here, we have extended these investigations to two related proteins, LEA11 and LEA25. LEA25 is much longer than LEA11 and COR15A, but shares a conserved central sequence domain with the other two proteins. We have created two truncated versions of LEA25 (2H and 4H) to elucidate the structural and functional significance of this domain. Light scattering and CD spectroscopy showed that all five proteins were largely unstructured and monomeric in dilute solution. They folded in the presence of increasing concentrations of trifluoroethanol and glycerol. Additional folding was observed in the presence of glycerol and membranes. Fourier transform infra red spectroscopy revealed an interaction of the LEA proteins with membranes in the dry state leading to a depression in the gel to liquid-crystalline phase transition temperature. Liposome stability assays revealed a cryoprotective function of the proteins. The C- and N-terminal extensions of LEA25 were important in cryoprotection, as the central domain itself (2H, 4H) only provided a low level of protection.

Physcomitrella Patens Dehydrins (PpDHNA and PpDHNC) Confer Salinity and Drought Tolerance to Transgenic Arabidopsis Plants

Dehydrins (DHNs) as a member of late-embryogenesis-abundant (LEA) proteins are involved in plant abiotic stress tolerance. Two dehydrins PpDHNA and PpDHNC were previously characterized from the moss Physcomitrella patens, which has been suggested to be an ideal model plant to study stress tolerance due to its adaptability to extreme environment. In this study, functions of these two genes were analyzed by heterologous expressions in Arabidopsis. Phenotype analysis revealed that overexpressing PpDHN dehydrin lines had stronger stress resistance than wild type and empty-vector control lines. These stress tolerance mainly due to the up-regulation of stress-related genes expression and mitigation to oxidative damage. The transgenic plants showed strong scavenging ability of reactive oxygen species(ROS), which was attributed to the enhancing of the content of antioxidant enzymes like superoxide dismutase (SOD) and catalase (CAT). Further analysis showed that the contents of chlorophyll and proline tended to be the appropriate level (close to non-stress environment) and the malondialdehyde (MDA) were repressed in these transgenic plants after exposure to stress. All these results suggest the PpDHNA and PpDHNC played a crucial role in response to drought and salt stress.

Structural and Functional Insights into the Cryoprotection of Membranes by the Intrinsically Disordered Dehydrins

Dehydration can be due to desiccation caused by a lack of environmental water or to freezing caused by a lack of liquid water. Plants have evolved a large family of proteins called LEA (late embryogenesis abundant) proteins, which include the intrinsically disordered dehydrin (dehydration protein) family, to combat these abiotic stresses. Although transcription and translation studies have shown a correlation between dehydration stress and the presence of dehydrins, the biochemical mechanisms have remained somewhat elusive. We examine here the effect and structure of a small model dehydrin (Vitis riparia K2) on the protection of membranes from freeze-thaw stress. This protein is able to bind to liposomes containing phosphatidic acid and protect the liposomes from fusing after freeze-thaw treatment. The presence of K2 did not measurably affect liposome surface accessibility or lipid mobility but did lower its membrane transition temperature by 3 °C. Using sodium dodecyl sulfate as a membrane model, we examined the NMR structure of K2 in the presence and absence of the micelle. Biochemical and NMR experiments show that the conserved, lysine-rich segments are involved in the binding of the dehydrin to a membrane, whereas the poorly conserved φ segments play no role in binding or protection.

Wheat dehydrin K-segments ensure bacterial stress tolerance, antiaggregation and antimicrobial effects

Dehydrins are a group of plant proteins that have been shown to be involved in the tolerance of various abiotic stresses such as dehydration, salinity, and low temperature. We have previously shown that the K-segments of the wheat dehydrin DHN-5 are essential for the protection of enzyme activities in vitro. In this study, we further investigate the role of the K-segments in the growth of Escherichia coli under various stresses, and we tested their antibacterial and antifungal activities. Our results showed that the truncated forms of DHN-5 containing the two K-segments enhanced tolerance of E. coli against diverse stresses by protecting proteins against aggregation. In addition, we demonstrated that the K-segments have antibacterial and antifungal activities against Gram-positive and Gram-negative bacteria and fungi. Based on these results, we propose that the K-segments may play a protective role in plants not only under abiotic stress conditions but also most likely during defense mechanisms.

The K-segments of wheat dehydrin WZY2 are essential for its protective functions under temperature stress

Dehydrins (DHNs), group 2 of late embryogenesis abundant (LEA) proteins, are up-regulated in most plants during cold, drought, heat, or salinity stress. All DHNs contain at least one K-segment, which is believed to play a significant role in DHN function by forming an amphipathic helix. In previous studies, wzy2, an YSK2-type DHN gene, was isolated from the Zhengyin 1 cultivar of Triticum aestivum under cold and drought stress treatment conditions. Four WZY2 truncated derivatives were constructed to knock out the K-, Y- or S-segment, which potentially affect the function of the protein. In vivo assays of Escherichia coli viability enhancement, in vitro lactate dehydrogenase (LDH) activity protection and ex vivo protein aggregation prevention assays revealed that WZY2 acted as a protectant and improved stress tolerance during temperature variation. The results also showed that unlike the truncated derivative without K-segments, the derivative containing two K-segments had remarkable effects that were similar to those of full-length WZY2, indicating that the K-segment is the major functional component of WZY2. Moreover, compared with the other segments, the first K-segment might be the most critical contributor to WZY2 functionality. In general, this work highlights the behavior of DHNs in relieving cold stress ex vivo and the contribution of the K-segment to DHN function.

The K-segments of wheat dehydrin WZY2 are essential for its protective functions under temperature stress

Dehydrins (DHNs), group 2 of late embryogenesis abundant (LEA) proteins, are up-regulated in most plants during cold, drought, heat, or salinity stress. All DHNs contain at least one K-segment, which is believed to play a significant role in DHN function by forming an amphipathic helix. In previous studies, wzy2, an YSK2-type DHN gene, was isolated from the Zhengyin 1 cultivar of Triticum aestivum under cold and drought stress treatment conditions. Four WZY2 truncated derivatives were constructed to knock out the K-, Y- or S-segment, which potentially affect the function of the protein. In vivo assays of Escherichia coli viability enhancement, in vitro lactate dehydrogenase (LDH) activity protection and ex vivo protein aggregation prevention assays revealed that WZY2 acted as a protectant and improved stress tolerance during temperature variation. The results also showed that unlike the truncated derivative without K-segments, the derivative containing two K-segments had remarkable effects that were similar to those of full-length WZY2, indicating that the K-segment is the major functional component of WZY2. Moreover, compared with the other segments, the first K-segment might be the most critical contributor to WZY2 functionality. In general, this work highlights the behavior of DHNs in relieving cold stress ex vivo and the contribution of the K-segment to DHN function.

Identification and expression of different dehydrin subclasses involved in the drought response of Trifolium repens

Reverse transcribed RNAs coding for YnKn, YnSKn, SKn, and KS dehydrin types in drought-stressed white clover (Trifolium repens) were identified and characterized. The nucleotide analyses revealed the complex nature of dehydrin-coding sequences, often featured with alternative start and stop codons within the open reading frames, which could be a prerequisite for high variability among the transcripts originating from a single gene. For some dehydrin sequences, the existence of natural antisense transcripts was predicted. The differential distribution of dehydrin homologues in roots and leaves from a single white clover stolon under normal and drought conditions was evaluated by semi-quantitative RT-PCR and immunoblots with antibodies against the conserved K-, Y- and S-segments. The data suggest that different dehydrin classes have distinct roles in the drought stress response and vegetative development, demonstrating some specific characteristic features. Substantial levels of YSK-type proteins with different molecular weights were immunodetected in the non-stressed developing leaves. The acidic SK2 and KS dehydrin transcripts exhibited some developmental gradient in leaves. A strong increase of YK transcripts was documented in the fully expanded leaves and roots of drought-stressed individuals. The immunodetected drought-induced signals imply that Y- and K-segment containing dehydrins could be the major inducible Late Embryogenesis Abundant class 2 proteins (LEA 2) that accumulate predominantly under drought.

Disorder and function: a review of the dehydrin protein family

Dehydration proteins (dehydrins) are group 2 members of the late embryogenesis abundant (LEA) protein family. The protein architecture of dehydrins can be described by the presence of three types of conserved sequence motifs that have been named the K-, Y-, and S-segments. By definition, a dehydrin must contain at least one copy of the lysine-rich K-segment. Abiotic stresses such as drought, cold, and salinity cause the upregulation of dehydrin mRNA and protein levels. Despite the large body of genetic and protein evidence of the importance of these proteins in stress response, the in vivo protective mechanism is not fully known. In vitro experimental evidence from biochemical assays and localization experiments suggests multiple roles for dehydrins, including membrane protection, cryoprotection of enzymes, and protection from reactive oxygen species. Membrane binding by dehydrins is likely to be as a peripheral membrane protein, since the protein sequences are highly hydrophilic and contain many charged amino acids. Because of this, dehydrins in solution are intrinsically disordered proteins, that is, they have no well-defined secondary or tertiary structure. Despite their disorder, dehydrins have been shown to gain structure when bound to ligands such as membranes, and to possibly change their oligomeric state when bound to ions. We review what is currently known about dehydrin sequences and their structures, and examine the various ligands that have been shown to bind to this family of proteins.

A dehydrin-dehydrin interaction: the case of SK3 from Opuntia streptacantha

Dehydrins belongs to a large group of highly hydrophilic proteins known as Late Embryogenesis Abundant (LEA) proteins. It is well known that dehydrins are intrinsically disordered plant proteins that accumulate during the late stages of embryogenesis and in response to abiotic stresses; however, the molecular mechanisms by which their functions are carried out are still unclear. We have previously reported that transgenic Arabidopsis plants overexpressing an Opuntia streptacantha SK3 dehydrin (OpsDHN1) show enhanced tolerance to freezing stress. Herein, we show using a split-ubiquitin yeast two-hybrid system that OpsDHN1 dimerizes. We found that the deletion of regions containing K-segments and the histidine-rich region in the OpsDHN1 protein affects dimer formation. Not surprisingly, in silico protein sequence analysis suggests that OpsDHN1 is an intrinsically disordered protein, an observation that was confirmed by circular dichroism and gel filtration of the recombinantly expressed protein. The addition of zinc triggered the association of recombinantly expressed OpsDHN1 protein, likely through its histidine-rich motif. These data brings new insights about the molecular mechanism of the OpsDHN1 SK3-dehydrin.

The importance of size and disorder in the cryoprotective effects of dehydrins

Dehydrins protect plant proteins and membranes from damage during drought and cold. Vitis riparia K2 is a 48-residue protein that can protect lactate dehydrogenase from freeze-thaw damage by preventing the aggregation and denaturation of the enzyme. To further elucidate its mechanism, we used a series of V. riparia K2 concatemers (K4, K6, K8, and K10) and natural dehydrins (V. riparia YSK2, 60 kilodalton peach dehydrin [PCA60], barley dehydrin5 [Dhn5], Thellungiella salsuginea dehydrin2 [TsDHN-2], and Opuntia streptacantha dehydrin1 [OpsDHN-1]) to test the effect of the number of K-segments and dehydrin size on their ability to protect lactate dehydrogenase from freeze-thaw damage. The results show that the larger the hydrodynamic radius of the dehydrin, the more effective the cryoprotection. A similar trend is observed with polyethylene glycol, which would suggest that the protection is simply a nonspecific volume exclusion effect that can be manifested by any protein. However, structured proteins of a similar range of sizes did not show the same pattern and level of cryoprotection. Our results suggest that with respect to enzyme protection, dehydrins function primarily as molecular shields and that their intrinsic disorder is required for them to be an effective cryoprotectant. Lastly, we show that the cryoprotection by a dehydrin is not due to any antifreeze protein-like activity, as has been reported previously.

Dehydrin-like proteins in the necrotrophic fungus Alternaria brassicicola have a role in plant pathogenesis and stress response

In this study, the roles of fungal dehydrin-like proteins in pathogenicity and protection against environmental stresses were investigated in the necrotrophic seed-borne fungus Alternaria brassicicola. Three proteins (called AbDhn1, AbDhn2 and AbDhn3), harbouring the asparagine-proline-arginine (DPR) signature pattern and sharing the characteristic features of fungal dehydrin-like proteins, were identified in the A. brassicicola genome. The expression of these genes was induced in response to various stresses and found to be regulated by the AbHog1 mitogen-activated protein kinase (MAPK) pathway. A knock-out approach showed that dehydrin-like proteins have an impact mainly on oxidative stress tolerance and on conidial survival upon exposure to high and freezing temperatures. The subcellular localization revealed that AbDhn1 and AbDhn2 were associated with peroxisomes, which is consistent with a possible perturbation of protective mechanisms to counteract oxidative stress and maintain the redox balance in AbDhn mutants. Finally, we show that the double deletion mutant ΔΔabdhn1-abdhn2 was highly compromised in its pathogenicity. By comparison to the wild-type, this mutant exhibited lower aggressiveness on B. oleracea leaves and a reduced capacity to be transmitted to Arabidopsis seeds via siliques. The double mutant was also affected with respect to conidiation, another crucial step in the epidemiology of the disease.

LEA proteins: IDPs with versatile functions in cellular dehydration tolerance

LEA (late embryogenesis abundant) proteins were originally described almost 30 years ago as accumulating late in plant seed development. They were later found to be induced in vegetative plant tissues under environmental stress conditions and also in desiccation-tolerant micro-organisms and invertebrates. Although they are widely assumed to play crucial roles in cellular dehydration tolerance, their physiological and biochemical functions are largely unknown. Most LEA proteins are predicted to be intrinsically disordered and this has been experimentally verified in several cases. In addition, some LEA proteins partially fold, mainly into α-helices, during drying or in the presence of membranes. Recent studies have concentrated on the potential roles of LEA proteins in stabilizing membranes or sensitive enzymes during freezing or drying, and the present review concentrates on these two possible functions of LEA proteins in cellular dehydration tolerance.

Interactions of Thellungiella salsuginea dehydrins TsDHN-1 and TsDHN-2 with membranes at cold and ambient temperatures-surface morphology and single-molecule force measurements show phase separation, and reveal tertiary and quaternary associations

Dehydrins (group 2 late embryogenesis abundant proteins) are intrinsically-disordered proteins that are expressed in plants experiencing extreme environmental conditions such as drought or low temperature. Their roles include stabilizing cellular proteins and membranes, and sequestering metal ions. Here, we investigate the membrane interactions of the acidic dehydrin TsDHN-1 and the basic dehydrin TsDHN-2 derived from the crucifer Thellungiella salsuginea that thrives in the Canadian sub-Arctic. We show using compression studies with a Langmuir-Blodgett trough that both dehydrins can stabilize lipid monolayers with a lipid composition mimicking the composition of the plant outer mitochondrial membrane, which had previously been shown to induce ordered secondary structures (disorder-to-order transitions) in the proteins. Ellipsometry of the monolayers during compression showed an increase in monolayer thickness upon introducing TsDHN-1 (acidic) at 4°C and TsDHN-2 (basic) at room temperature. Atomic force microscopy of supported lipid bilayers showed temperature-dependent phase transitions and domain formation induced by the proteins. These results support the conjecture that acidic dehydrins interact with and potentially stabilize plant outer mitochondrial membranes in conditions of cold stress. Single-molecule force spectroscopy of both proteins pulled from supported lipid bilayers indicated the induced formation of tertiary conformations in both proteins, and potentially a dimeric association for TsDHN-2.

Computational and statistical analyses of amino acid usage and physico-chemical properties of the twelve late embryogenesis abundant protein classes

Late Embryogenesis Abundant Proteins (LEAPs) are ubiquitous proteins expected to play major roles in desiccation tolerance. Little is known about their structure - function relationships because of the scarcity of 3-D structures for LEAPs. The previous building of LEAPdb, a database dedicated to LEAPs from plants and other organisms, led to the classification of 710 LEAPs into 12 non-overlapping classes with distinct properties. Using this resource, numerous physico-chemical properties of LEAPs and amino acid usage by LEAPs have been computed and statistically analyzed, revealing distinctive features for each class. This unprecedented analysis allowed a rigorous characterization of the 12 LEAP classes, which differed also in multiple structural and physico-chemical features. Although most LEAPs can be predicted as intrinsically disordered proteins, the analysis indicates that LEAP class 7 (PF03168) and probably LEAP class 11 (PF04927) are natively folded proteins. This study thus provides a detailed description of the structural properties of this protein family opening the path toward further LEAP structure - function analysis. Finally, since each LEAP class can be clearly characterized by a unique set of physico-chemical properties, this will allow development of software to predict proteins as LEAPs.

Phosphorylation of Thellungiella salsuginea dehydrins TsDHN-1 and TsDHN-2 facilitates cation-induced conformational changes and actin assembly

Group 2 late embryogenesis abundant (LEA) proteins, also known as dehydrins, are intrinsically disordered proteins that are expressed in plants experiencing extreme environmental conditions such as drought or low temperatures. These proteins are characterized by the presence of at least one conserved, lysine-rich K-segment and sometimes by one or more serine-rich S-segments that are phosphorylated. Dehydrins may stabilize proteins and membrane structures during environmental stress and can sequester and scavenge metal ions. Here, we investigate how the conformations of two dehydrins from Thellungiella salsuginea, denoted as TsDHN-1 (acidic) and TsDHN-2 (basic), are affected by pH, interactions with cations and membranes, and phosphorylation. Both TsDHN-1 and TsDHN-2 were expressed as SUMO fusion proteins for in vitro phosphorylation by casein kinase II (CKII), and structural analysis by circular dichroism and attenuated total reflection-Fourier transform infrared spectroscopy. We show that the polyproline II conformation can be induced in the dehydrins by their environmental conditions, including changes in the concentration of divalent cations such as Ca(2+). The assembly of actin by these dehydrins was assessed by sedimentation assays and viewed by transmission electron and atomic force microscopy. Phosphorylation allowed both dehydrins to polymerize actin filaments. These results support the hypothesis that dehydrins stabilize the cytoskeleton under stress conditions and further that phosphorylation may be an important feature of this stabilization.

Structural transitions in the intrinsically disordered plant dehydration stress protein LEA7 upon drying are modulated by the presence of membranes

Dehydration stress-related late embryogenesis abundant (LEA) proteins have been found in plants, invertebrates and bacteria. Most LEA proteins are unstructured in solution, but some fold into amphipathic α-helices during drying. The Pfam LEA_4 (Group 3) protein LEA7 from the higher plant Arabidopsis thaliana was predicted to be 87% α-helical, while CD spectroscopy showed it to be largely unstructured in solution and only 35% α-helical in the dry state. However, the dry protein contained 15% β-sheets. FTIR spectroscopy revealed the β-sheets to be largely due to aggregation. β-Sheet content was reduced and α-helix content increased when LEA7 was dried in the presence of liposomes with secondary structure apparently influenced by lipid composition. Secondary structure was also affected by the presence of membranes in the fully hydrated state. A temperature-induced increase in the flexibility of the dry protein was also only observed in the presence of membranes. Functional interactions of LEA7 with membranes in the dry state were indicated by its influence on the thermotropic phase transitions of the lipids and interactions with the lipid headgroup phosphates.

Zinc induces disorder-to-order transitions in free and membrane-associated Thellungiella salsuginea dehydrins TsDHN-1 and TsDHN-2: a solution CD and solid-state ATR-FTIR study

Dehydrins are intrinsically unstructured proteins that are expressed in plants experiencing extreme environmental conditions such as drought or low temperature. Although their role is not completely understood, it has been suggested that they stabilize proteins and membrane structures during environmental stress and also sequester metals such as zinc. Here, we investigate two dehydrins (denoted as TsDHN-1 and TsDHN-2) from Thellungiella salsuginea. This plant is a crucifer that thrives in the Canadian sub-Arctic (Yukon Territory) where it grows on saline-rich soils and experiences periods of both extreme cold and drought. We show using circular dichroism and attenuated total reflection-Fourier transform infrared spectroscopy that ordered secondary structure is induced and stabilized in these proteins, both in free and vesicle-bound form, by association with zinc. In membrane-associated form, both proteins have an increased proportion of β-strand conformation induced by the cation, in addition to the amphipathic α-helices formed by their constituent K-segments. These results support the hypothesis that dehydrins stabilize plant plasma and organellar membranes in conditions of stress, and further that zinc may be an important co-factor in stabilization. Whereas dehydrins in the cytosol of a plant cell undergoing dehydration or temperature stress form bulk hydrogels and remain primarily disordered, dehydrins with specific membrane- or protein-associations will have induced ordered secondary structures.