AmDHN4, a winter accumulated SKn-type dehydrin from Ammopiptanthus mongolicus, and regulated by AmWRKY45, enhances the tolerance of Arabidopsis to low temperature and osmotic stress

Ammopiptanthus mongolicus, a rare temperate evergreen broadleaf shrub, exhibits remarkable tolerance to low temperature and drought stress in winter. Late embryogenesis abundant (LEA) proteins, a kind of hydrophilic protein with a protective function, play significant roles in enhancing plant tolerance to abiotic stress. In this present study, we analyzed the evolution and expression of LEA genes in A. mongolicus, and investigated the function and regulatory mechanism of dehydrin under abiotic stresses. Evolutionary analysis revealed that 14 AmLEA genes underwent tandem duplication events, and 36 AmLEA genes underwent segmental duplication events Notably, an expansion in SKn-type dehydrins was observed. Expression analysis showed that AmDHN4, a SKn-type dehydrin, was up-regulated in winter and under low temperature and osmotic stresses. Functional analysis showcased that the heterologous expression of the AmDHN4 enhanced the tolerance of yeast and tobacco to low temperature stress. Additionally, the overexpression of AmDHN4 significantly improved the tolerance of transgenic Arabidopsis to low temperature, drought, and osmotic stress. Further investigations identified AmWRKY45, a downstream transcription factor in the jasmonic acid signaling pathway, binding to the AmDHN4 promoter and positively regulating its expression. In summary, these findings contribute to a deeper understanding of the functional and regulatory mechanisms of dehydrin.

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.

Plant biomarkers as early detection tools in stress management in food crops: a review

MAIN CONCLUSION

Plant Biomarkers are objective indicators of a plant's cellular state in response to abiotic and biotic stress factors. They can be explored in crop breeding and engineering to produce stress-tolerant crop species. Global food production safely and sustainably remains a top priority to feed the ever-growing human population, expected to reach 10 billion by 2050. However, abiotic and biotic stress factors negatively impact food production systems, causing between 70 and 100% reduction in crop yield. Understanding the plant stress responses is critical for developing novel crops that can adapt better to various adverse environmental conditions. Using plant biomarkers as measurable indicators of a plant's cellular response to external stimuli could serve as early warning signals to detect stresses before severe damage occurs. Plant biomarkers have received considerable attention in the last decade as pre-stress indicators for various economically important food crops. This review discusses some biomarkers associated with abiotic and biotic stress conditions and highlights their importance in developing stress-resilient crops. In addition, we highlighted some factors influencing the expression of biomarkers in crop plants under stress. The information presented in this review would educate plant researchers, breeders, and agronomists on the significance of plant biomarkers in stress biology research, which is essential for improving plant growth and yield toward sustainable food production.

Isolation and molecular characterization of an FSK2-type dehydrin from Atriplex halimus

Dehydrins form the group II LEA protein family and are known to play multiple roles in plant stress tolerance and enzyme protection. They harbor a variable number of conserved lysine rich motifs (K-segments) and may also contain three additional conserved motifs (Y-, F- and S-segments). In this work, we report the isolation and characterization of an FSK₂-type dehydrin from the halophytic species Atriplex halimus, which we designate as AhDHN1. In silico analysis of the protein sequence revealed that AhDHN1 contains large number of hydrophilic residues, and is predicted to be intrinsically disordered. In addition, it has an FSK₂ architecture with one F-segment, one S-segment, and two K-segments. The expression analysis showed that the AhDHN1 transcript is induced by salt and water stress treatments in the leaves of Atriplex seedlings. Moreover, circular dichroism spectrum performed on recombinant AhDHN1 showed that the dehydrin lacks any secondary structure, confirming its intrinsic disorder nature. However, there is a gain of α-helicity in the presence of membrane-like SDS micelles. In vitro assays revealed that AhDHN1 is able to effectively protect enzymatic activity of the lactate dehydrogenase against cold, heat and dehydration stresses. Our findings strongly suggest that AhDHN1 can be involved in the adaptation mechanisms of halophytes to adverse environments.

The cationic nature of lysine-rich segments modulates the structural and biochemical properties of wild potato FSK3 dehydrin

Dehydrins are hydrophilic stress-induced proteins that are thought to protect cellular machinery from the adverse effect of dehydration caused by low temperature, drought, or salinity. In the previous study, acidic FSK₃ dehydrin DHN24 from Solanum sogarandinum was found to accumulate at multiple sites in phloem cells in response to cold treatment. This study investigated the biochemical and structural properties of recombinant DHN24. It was shown that the overexpression of DHN24 in Escherichia coli led to the inhibition of bacterial growth. The purified DHN24 was found to protect lactate dehydrogenase from freeze-induced denaturation. Circular dichroism (CD) analysis showed that DHN24 was disordered in aqueous solutions, but adopted α-helical conformation in a membrane-mimetic environment using sodium dodecyl sulfate micelles. DHN24 also interacted with anionic phosphatidic acid (PA). DHN24 contains four lysine-rich regions including three K-segments and a region upstream of the S-segment. The role of their local cationic nature is unknown. These segments are predicted to form helical structures. The CD analysis of mutant proteins in the membrane-mimetic environment matched these predictions most closely, revealing that the positively charged lysine residues in these regions promoted disorder-to-order transitions. Moreover, the inhibition of bacterial growth and interactions with PA were regulated by the local cationic nature of DHN24, while no such regulation was observed for its cryoprotective activity. The importance of the positive charge of the lysine-rich segments and disordered structure for DHN24 activity is discussed in relation to its possible biological function.

Increased dehydrin level decreases leaf rolling grade by altering the reactive oxygen species homeostasis and abscisic acid content in maize subjected to osmotic stress

Dehydrins (DHNs) are stress proteins involved in the development of protective reactions in plants against dehydration. The relationship between DHNs and morphological responses such as leaf rolling in plants exposed to water deficit is not well known. In this study, we detected how variations in DHN levels affect the leaf rolling response in maize exposed to osmotic stress in relation to the antioxidant system and ABA level. In this context, we altered the DHN levels in maize seedlings by treatment with bio-regulators (salicylic acid and abscisic acid) under PEG6000-free and PEG6000-induced osmotic stress. When the DHN levels were increased by the bio-regulators (25 µM SA and 100 µM ABA), the relative expression level of the Zea mays dehydrin COR410 gene increased in the seedlings, while reactive oxygen species (ROS) and leaf rolling grade decreased. Moreover, induction of DHNs caused increases in the antioxidant enzyme activity and content of antioxidant substances, and very high amounts of endogenous abscisic acid. When DHN level was suppressed by a bio-regulator (200 µM SA) in the maize seedlings, dehydrin COR410 expression level decreased, while ROS and the leaf rolling grade increased. Moreover, the antioxidant enzyme activity and content of antioxidant substances decreased in the seedlings, while the amount of abscisic acid increased. Taken all together, an increase in DHN level by bio-regulator treatment can stimulate the antioxidant system, enable abscisic acid regulation, and thus reduce leaf rolling through decreased ROS levels. The results also indicated that DHNs may be involved in the signal pathways inducing expression of some genes related to leaf rolling response, possibly by modulating ROS levels, in maize seedlings exposed to osmotic stress.

Linking genome wide RNA sequencing with physio-biochemical and cytological responses to catalogue key genes and metabolic pathways for alkalinity stress tolerance in lentil (Lens culinaris Medikus)

BACKGROUND

Alkaline soils cause low productivity in crop plants including lentil. Alkalinity adaptation strategies in lentil were revealed when morpho-anatomical and physio-biochemical observations were correlated with transcriptomics analysis in tolerant (PDL-1) and sensitive (L-4076) cultivars at seedling stage.

RESULTS

PDL-1 had lesser salt injury and performed better as compared to L-4076. Latter showed severe wilting symptoms and higher accumulation of Na⁺ and lower K⁺ in roots and shoots. PDL-1 performed better under high alkalinity stress which can be attributed to its higher mitotic index, more accumulation of K⁺ in roots and shoots and less aberrantly dividing cells. Also, antioxidant enzyme activities, osmolytes' accumulation, relative water content, membrane stability index and abscisic acid were higher in this cultivar. Differentially expressed genes (DEGs) related to these parameters were upregulated in tolerant genotypes compared to the sensitive one. Significantly up-regulated DEGs were found to be involved in abscisic acid (ABA) signalling and secondary metabolites synthesis. ABA responsive genes viz. dehydrin 1, 9-cis-epoxycarotenoid dioxygenase, ABA-responsive protein 18 and BEL1-like homeodomain protein 1 had log₂fold change above 4.0. A total of 12,836 simple sequence repeats and 4,438 single nucleotide polymorphisms were identified which can be utilized in molecular studies.

CONCLUSIONS

Phyto-hormones biosynthesis-predominantly through ABA signalling, and secondary metabolism are the most potent pathways for alkalinity stress tolerance in lentil. Cultivar PDL-1 exhibited high tolerance towards alkalinity stress and can be used in breeding programmes for improving lentil production under alkalinity stress conditions.

Inhibition of cryoaggregation of phospholipid liposomes by an Arabidopsis intrinsically disordered dehydrin and its K-segment

Dehydrin is an intrinsically disordered protein involved in the cold tolerance of plants. Although dehydrins have been thought to protect biomembranes under cold conditions, the underlying protective mechanism has not been confirmed. Here we report that Arabidopsis dehydrin AtHIRD11 inhibited the aggregation of phospholipid liposomes after freezing and thawing. AtHIRD11 showed significantly greater cryoaggregation-prevention activity than cryoprotective agents such as trehalose, proline, and polyethylene glycols. Amino acid sequence segmentation analysis indicated that the K-segment of AtHIRD11 inhibited the cryoaggregation of phosphatidylcholine (PC) liposomes but other segments did not. This showed that K-segments conserved in all dehydrins were likely to be the cryoprotective sites of dehydrins. Amino acid replacement for a typical K-segment (TypK for short) sequence demonstrated that both hydrophobic and charged amino acids were required for the cryoaggregation-prevention activity of PC liposomes. The amino acid shuffling of TypK remarkably reduced cryoprotective activity. Although TypK did not bind to PC liposomes in solution, the addition of liposomes reduced its disordered content under crowded conditions. Together, these results suggested that dehydrins protected biomembranes via conserved K-segments whose sequences were optimized for cryoprotective activities.

Overexpression of ZmDHN11 could enhance transgenic yeast and tobacco tolerance to osmotic stress

KEY MESSAGE

Maize group II LEA protein ZmDHN11 could protect protein activity and confer resistance to osmotic stress on transgenic yeast and tobacco. Late embryogenesis abundant (LEA) proteins are widely assumed to play crucial roles in environmental stress tolerance, but their function has remained obscure. Dehydrins are group II LEA proteins, which are highly hydrophilic plant stress proteins. In the present study, a novel group II LEA protein, ZmDHN11, was cloned and identified from maize. The expression of ZmDHN11 was induced by high osmotic stress, low temperature, salinity, and ABA (abscisic acid). The ZmDHN11 protein specifically accumulated in the nuclei and cytosol. Further study indicated that ZmDHN11 is phosphorylated by the casein kinase CKII. ZmDHN11 protected the activity of LDH under water-deficit stress. The overexpression of ZmDHN11 endows transgenic yeast and tobacco with tolerance to osmotic stress.

An intrinsically disordered radish vacuolar calcium-binding protein (RVCaB) showed cryoprotective activity for lactate dehydrogenase with its hydrophobic region

A soluble protein fraction from radish (Raphanus sativus L.) taproot had cryoprotective activity for lactate dehydrogenase (LDH). The activity was found mainly in the heat-stable fractions of soluble proteins. The cryoprotective protein, whose molecular mass was 43 kDa in sodium dodecyl sulfate polyacrylamide gel electrophoresis, was obtained by successive chromatographies on TOYOPEARL SuperQ and TOYOPEARL DEAE. MALDI-TOF MS/MS analysis indicated that the purified protein was a radish vacuolar calcium-binding protein (RVCaB), which is reportedly related to calcium storage in the vacuoles of radish taproot. The purified RVCaB inhibited the cryoinactivation, cryodenaturation, and cryoaggregation of LDH. RVCaB had greater cryoprotective activity than general cryoprotectants. When RVCaB was divided into 15 segments (Seg01 to Seg15, 15 amino acids each), Seg03, which had a high hydrophobicity scale, showed remarkable cryoprotective activity. This indicated that RVCaB protected LDH from freezing and thawing damage presumably through a specific hydrophobic area (i.e., Seg03).

Functional characterization of VviDHN2 and VviDHN4 dehydrin isoforms from Vitis vinifera (L.): An in silico and in vitro approach

Dehydrins, a family of hydrophilic and intrinsically disordered proteins, are a subgroup of late embryogenesis abundant proteins that perform different protective roles in plants. Although the transition from a disordered to an ordered state has been associated with dehydrin function or interactions with specific partner molecules, the question of how the primary and secondary dehydrin protein structure is related to specific functions or target molecule preferences remains unresolved. This work addresses the in silico sequencing analysis and in vitro functional characterization of two dehydrin isoforms, VviDHN2 and VviDHN4, from Vitis vinifera. Conformational changes suggest potential interactions with a broad range of molecules and could point to more than one function. The in silico analysis showed differences in conserved segments, specific amino acid binding sequences, heterogeneity of structural properties and predicted sites accessible for various post-translational modifications between the sequence of both dehydrins. Moreover, in vitro functional analysis revealed that although they both showed slight antifungal activity, only VviDHN4 acts as a molecular shield that protects proteins from freezing and dehydration. VviDHN4 also demonstrated high potential as a chaperone and reactive oxygen species scavenger, in addition to presenting antifreeze activity, all of which confirms its multifunctional nature. Our findings highlight the significant role of Y-segments and the differential and specific amino acid composition of less conserved segments that are rich in polar/charged residues between S- and K-segments, coupled with post-translational modifications, in modulating and switching dehydrin biological function.

Oxidative stress level and dehydrin gene expression pattern differentiate two contrasting cucumber F1 hybrids under high fertigation treatment

Two cucumber F1 cultivar hybrids were investigated for stress tolerance markers upon application of different strength of Hoagland fertigation solutions (HG). 'Joker' and 'Oitol' cultivar hybrids were studied, representing typically field grown and greenhouse cultivated genotypes, respectively. At standard fertigation level (0.5 × HG) in controlled environment young 'Joker' plants displayed slower growth than 'Oitol' based on total leaf area. At this basal nutrient concentration leaves of 'Joker' plants had significantly lower antioxidant capacity and higher malondialdehyde (MDA, an indicator of lipid peroxidation) level than 'Oitol'. According to RT-qPCR transcript levels of several antioxidant enzymes' genes (ascorbate peroxidase, glutathione reductase and glutathione peroxidase) were significantly higher in 'Joker' compared to 'Oitol'. At increased HG concentrations (1.0, 1.5, 2.0, and 2.5 × HG) growth didn't change significantly in either hybrid. Osmotic potential declined at higher fertigation levels. Antioxidant capacity increased in both hybrids with strong characteristic differences favouring 'Oitol' plants. Higher MDA content of leaves testified more oxidative burden in 'Joker' plants at all and especially at the more concentrated HG treatments. This trend was also approved by results of bio photon emission imaging, which is a powerful method to quantify stress level in living tissues with autoluminescence detection technology. Gene expression for antioxidant enzymes followed HG concentration-dependent increase in both hybrids, at a substantially higher level in 'Joker'. Expression of the dehydrin gene DHN3 was preferentially induced at elevated fertigation levels in 'Oitol' plants, which could contribute to the lower oxidative stress detected in this hybrid. Results presented in this report demonstrate differences in shoot growth, antioxidant capacity, level of oxidative stress and antioxidant gene expression in two contrasting cucumber hybrids at basal fertigation. Furthermore, excessive HG fertigation was found to increase oxidative stress in a genotype-specific way. This effect may be due to different antioxidant capacity and differential expression of stress protective genes, such as the DHN3 dehydrin.

An ERF-type transcription factor is involved in the regulation of the dehydrin wzy1-2 gene in wheat

As stress-inducible proteins, dehydrins exert functional protective role by alleviating the cell damage when plants are suffering from the stresses. However, the upstream regulatory mechanism of these proteins is not very clear. To unravel the regulatory mechanism of dehydrin, a screen of wheat cDNA library from cold and PEG-treated wheat seedlings was performed and a transcription factor TaERF4a (GenBank NO. AFP49822.1) interacting with wheat dehydrin wzy1-2 gene (Gene ID: 100037544) promoter was identified by yeast one-hybrid assay. The regulator TaERF4a and the wzy1-2 gene can respond to the abiotic stress, the induced transcripts of these two genes exhibit a similar expression trend under adverse environmental conditions. In planta, the dual luciferase transient assay analysis showed that TaERF4a can positively regulate the expression of WZY1-2 dehydrin. Therefore, the obtained results suggest that ERF transcription factor can regulate the expression level of the dehydrin gene in wheat.

Cryoprotective activity of Arabidopsis KS-type dehydrin depends on the hydrophobic amino acids of two active segments

Dehydrins are intrinsically disordered proteins which are related to cold tolerance in plants. Dehydrins show potent cryoprotective activities for freeze-sensitive enzymes such as lactate dehydrogenase (LDH). Previous studies demonstrated that K-segments conserved in dehydrins had cryoprotective activities and that K-segment activities depended on the hydrophobic amino acids in the segment. However, the cryoprotective roles of hydrophobic amino acids in dehydrin itself have not been reported. Here, we demonstrated that hydrophobic amino acids were required for the cryoprotective activity of Arabidopsis dehydrin AtHIRD11. Cryoprotective activities were compared between AtHIRD11 and the corresponding mutant in which all hydrophobic residues were changed to T (AtHIRD11Φ/T) by using LDH. The change strikingly reduced AtHIRD11 activity. A segmentation analysis indicated that the conserved K-segment (Kseg) and a previously unidentified segment (non-K-segment 1, NK1) showed cryoprotective activities. Circular dichroism indicated that the secondary structures of all peptides showed disorder, but only cryoprotective peptides changed to the ordered forms by sodium dodecyl sulfate. Ultracentrifuge analysis indicated that AtHIRD11 and AtHIRD11Φ/T had similar molecular sizes in solution. These results suggest that not only structural disorder but also hydrophobic amino acids contributed to the cryoprotective activity of AtHIRD11. A possible mechanism based on an extended molecular shield model is proposed.

Transcription factor TabHLH49 positively regulates dehydrin WZY2 gene expression and enhances drought stress tolerance in wheat

BACKGROUND

As functional proteins, dehydrins are found in many maturing seeds and vegetable tissues under adverse environmental conditions. However, the regulation of dehydrin expression remains unclear.

RESULTS

In this study, a novel drought stress-related bHLH transcription factor, TabHLH49, was isolated from a wheat cDNA library treated with the drought and cold stress by using yeast one-hybrid system. TabHLH49 protein possesses a typical conserved bHLH domain and is a Myc-type bHLH transcription factor. TabHLH49 was detected in the nucleus of tobacco epidermal cells, and the amino acid sequences at the C-terminus (amino acids 323-362) is necessary for its transactivation activity. Real-time PCR analyses revealed the tissue-specific expression and drought stress-responsive expression of TabHLH49 in wheat. In addition, the verification in Y1H and electrophoretic mobility shift assays illustrated that TabHLH49 protein can bind and interact with the promoter of the wheat WZY2 dehydrin. Furthermore, the dual-luciferase assays showed that TabHLH49 can positively regulate the expression of WZY2 dehydrin. The transient expression and BSMV-mediated gene silencing of TabHLH49 also showed that TabHLH49 positively regulates the expression of WZY2 dehydrin and improves drought stress resistance in wheat.

CONCLUSIONS

These results provide direct evidences that TabHLH49 positively regulates expression level of dehydrin WZY2 gene and improves drought tolerance of wheat.

Protective functions of alternative splicing transcripts (CdDHN4-L and CdDHN4-S) of CdDHN4 from bermudagrass under multiple abiotic stresses

Dehydrins (DHNs) play critical roles in plant adaptation to abiotic stresses. The objective of this study was to characterize DHNs in bermudagrass (Cynodon spp.). CdDHN4 gene was cloned from bermudagrass ‘Tifway’. Two CdDHN4 transcripts were detected due to alternative splicing (the nonspliced CdDHN4-L and the spliced CdDHN4-S) and both the CdDHN4-S and CdDHN4-L proteins are YSK₂-type DHNs, the Φ-segment is present in CdDHN4-L and absent in CdDHN4-S. Transgenic Arabidopsis thaliana expressing CdDHN4-L or CdDHN4-S exhibited improved tolerance to salt, osmotic, low temperature and drought stress compared to the wild type (WT). The two transgenic lines did not differ in salt or drought tolerance, while plants expressing CdDHN4-S grew better under osmotic stress than those expressing CdDHN4-L. Both transgenic lines exhibited reduced content of malondialdehyde (MDA) and reactive oxygen species (ROS); and higher antioxidant enzymatic activities than the wild type plants under salt or drought stress. CdDHN4-S exhibited a higher ROS-scavenging capacity than CdDHN4-L.

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Two CdDHN4 transcripts (CdDHN4-L and CdDHN4-S) were detected due to alternative splicing in bermudagrass ‘Tifway’.

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CdDHN4s transgenic Arabidopsis thaliana exhibited higher tolerance to multiple abiotic stress compared to the wild type.

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CdDHN4s transgenic lines has lower content of ROS than the wild type under salt or drought stress.

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CdDHN4-S had a higher ROS-scavenging capacity than CdDHN4-L.

Characterization of the nucellus-specific dehydrin MdoDHN11 demonstrates its involvement in the tolerance to water deficit

MdoDHN11 acts in the nucellus layer to protect the embryo and the endosperm from limited water availability during apple seed development. Dehydrins (DHNs) are protective proteins related to several plant developmental responses that involve dehydration such as seed desiccation and abiotic stresses. In apple (Malus × domestica Borkh.), the seed-specific MdoDHN11 was suggested to play important roles against dehydration during seed development. However, this hypothesis has not yet been evaluated. Within this context, several experiments were performed to functionally characterize MdoDHN11. In situ hybridization analysis during apple seed development showed that MdoDHN11 expression is confined to a maternal tissue called nucellus, a central mass of parenchyma between the endosperm and the testa. The MdoDHN11 protein was localized in the cytosol and nucleus. Finally, transgenic Arabidopsis plants expressing MdoDHN11 were generated and exposed to a severe water-deficit stress, aiming to mimic a situation that can occurs during seed development. All transgenic lines showed increased tolerance to water deficit in relation to wild-type plants. Taken together, our results provide evidences that MdoDHN11 plays important roles during apple seed development by protecting the embryo and the endosperm from limited water availability, and the mechanism of action probably involves the interaction of MdoDHN11 with proteins and other components in the cell.

Y2SK2 and SK3 type dehydrins from Agapanthus praecox can improve plant stress tolerance and act as multifunctional protectants

Two dehydrins from Agapanthus praecox (ApY₂SK₂ and ApSK₃) show important protective effects under complex stresses. Both ApY₂SK₂ and ApSK₃ contain one intron and consist of a full-length cDNA of 981 bp and 1057 bp encoding 186 and 215 amino acids, respectively. ApY₂SK₂ and ApSK₃ transgenic Arabidopsis thaliana show reduced plasma membrane damage and ROS levels and higher antioxidant activity and photosynthesis capability under salt, osmotic, cold and drought stresses compared with the wild-type. ApY₂SK₂ and ApSK₃ are mainly located in the cytoplasm and cell membrane, and ApY₂SK₂ can even localize in the nucleus. In vitro tests indicate that ApY₂SK₂ and ApSK₃ can effectively protect enzyme activity during the freeze-thaw process, and ApY₂SK₂ also exhibits this function during desiccation treatment. Furthermore, ApY₂SK₂ and ApSK₃ can significantly inhibit hydroxyl radical generation. These two dehydrins can bind metal ions with a binding affinity of Co²⁺> Ni²⁺> Cu²⁺> Fe³⁺; the binding affinity of ApSK₃ is higher than that of ApY₂SK₂. Thus, ApY₂SK₂ has a better protective effect on enzyme activity, and ApSK₃ has stronger metal ion binding function and effect on ROS metabolism. Moreover, plant cryopreservation evaluation tests indicate that ApY₂SK₂ and ApSK₃ transformation can enhance the seedling survival ratio from 23% to 47% and 55%, respectively; the addition of recombinant ApY₂SK₂ and ApSK₃ to plant vitrification solution may increase the survival ratio of wild-type A. thaliana seedlings from 24% to 50% and 46%, respectively. These findings suggest that ApY₂SK₂ and ApSK₃ can effectively improve cell stress tolerance and have great potential for in vivo or in vitro applications.

PEST sequences from a cactus dehydrin regulate its proteolytic degradation

Dehydrins (DHNs) are intrinsically disordered proteins expressed under cellular dehydration-related stresses. In this study, we identified potential proteolytic PEST sequences located at the central and C-terminal regions from the Opuntia streptacantha OpsDHN1 protein. In order to evaluate these PEST sequences as proteolytic tags, we generated a translational fusion with the GUS reporter protein and OpsDHN1 coding sequence. We found a GUS degradation effect in tobacco agro-infiltrated leaves and Arabidopsis transgenic lines that expressed the fusion GUS::OpsDHN1 full-length. Also, two additional translational fusions between OpsDHN1 protein fragments that include the central (GUS::PEST-1) or the C-terminal (GUS::PEST-2) PEST sequences were able to decrease the GUS activity, with PEST-2 showing the greatest reduction in GUS activity. GUS signal was abated when the OpsDHN1 fragment that includes both PEST sequences (GUS::PEST-1-2) were fused to GUS. Treatment with the MG132 proteasome inhibitor attenuated the PEST-mediated GUS degradation. Point mutations of phosphorylatable residues in PEST sequences reestablished GUS signal, hence these sequences are important during protein degradation. Finally, in silico analysis identified potential PEST sequences in other plant DHNs. This is the first study reporting presence of PEST motifs in dehydrins.

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).

Interspecies evolutionary divergence in Liriodendron, evidence from the nucleotide variations of LcDHN-like gene

Background

Liriodendron is a genus of Magnoliaceae, which consists of two relict species, Liriodendron chinense and L. tulipifera. Although the morphologies are highly similar, the two species exhibit different adaptive capacity. Dehydrins (DHNs) are abiotic stresses resistant proteins in planta, which are associated with adaptive evolution. To better understand the evolution divergence between L. chinense and L. tulipifera and how DHN genes are associated with adaptation evolution, we firstly investigated the DNA polymorphisms of the LcDHN-like gene in 21 L. chinense and 6 L. tulipifera populations.

Results

A 707 bp LcDHN-like gene was cloned, which included a 477 bp open reading frame (ORF) and coding 158 amino acids. 311 LcDHN-like gDNA sequences were obtained from 70 L. chinense and 35 L. tulipifera individuals. The AMOVA and phylogenetic relationship analysis showed significant differences between the two species. A higher genetic diversity was observed in L. tulipifera compared to L. chinense, in consistent with the higher adaptive capacity of L. tulipifera. Our data also suggested that the LcDHN-like genes’ polymorphisms were under neutral mutation and purifying selection model in the L. chinense and L. tulipifera populations, respectively. The distinct expanding range and rate between the two species, haplotypes shared only in L.chinense’s nearby populations, and wide dispersals in L. tulipifera could contribute to the obscure east-west separation in L. chinense and entirely unordered phylogeny in L. tulipifera. The completely separated nonsynonymous substitution at position 875 and the higher range scope of aliphatic index in L. tulipifera populations may be related with its higher adaptive capacity. Taken together, our study suggests LcDHN-like gene is a potential mark gene responsible for adaptive evolution divergence in Liriodendron.

Conclusions

Significant differences and completely distinct haplogroups between L. chinense and L. tulipifera showed that the two species have evolved into different directions. The more widely distribution, earlier haplogroups divergence events, and richer SNPs variations in L. tulipifera could imply its stronger adaptation in this species. And potential effect of the allelic variations in LcDHN-like gene may reflect the difference of water stress and chill tolerance between L. chinense and L. tulipifera, which could provide some information for further adaption evolution studies of Liriodendron.

Electronic supplementary material

The online version of this article (10.1186/s12862-018-1318-7) contains supplementary material, which is available to authorized users.

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.

Transgenic creeping bentgrass plants expressing a Picea wilsonii dehydrin gene (PicW) demonstrate improved freezing tolerance

Agrostis stolonifera L. 'Penn A-4' is a common creeping bentgrass species that is widely used in urban landscaping and golf courses. To prolong the green stage of this grass, a dehydrin gene PicW isolated from Wilson's spruce (Picea wilsonii) was transformed into plants of 'Penn A-4' cultivar via a straightforward stolon node infection system. A putative transgenic plant was obtained and its tolerance to low-temperature stress was evaluated. When the transgenic line was subjected to a freezing (- 5 °C) treatment, it showed better viability and more robust physiology than wild type, as evidenced by higher soluble sugar and proline contents, and lower relative electrical conductivity and malondialdehyde content. The transgenic line also showed tolerance to a chilling treatment (5 °C), although its performance was not significantly different from that of wild-type plants. Overall, the research here clearly revealed the explicit role of PicW in increasing freezing tolerance of grass at the whole-plant level, and demonstrated that the straightforward stolon node transformation method could be well used to genetically modify turfgrass. The obtained transgenic line might be as genetic resource for breeding program and practiced to grow in cold temperate zones.

Ascophyllum nodosum extract biostimulants and their role in enhancing tolerance to drought stress in tomato plants

Global changes in climate are leading to increased occurrence and duration of drought episodes with concurrent reduction in crop yields. Expansion of the irrigated land area does not appear to be a viable solution in many regions to deliver crop productivity. The development of crop drought tolerance traits by either genetic modification or plant breeding represent the principal approaches to meeting this challenge to date. Biostimulants are an emerging category of crop management products which can enhance crop productivity under abiotic stress conditions. The ability of some biostimulant products such as Ascophyllum nodosum extracts (ANE) to enhance the tolerance of crops to drought stress has been observed by growers. The objective of this study was to investigate if different commercial ANE biostimulants provided the same tolerance to tomato plants (cv. Moneymaker) subjected to a defined drought period. A compositional characterisation of the key macromolecules of ANEs was performed. In addition, the role of ANE biostimulants in inducing changes of chlorophyll and osmolytes levels, MDA production, dehydrin isoform pattern and dehydrin gene expression levels was assessed. The three ANE biostimulants evaluated were found to provide different levels of tolerance to drought stressed tomato plants. The level of drought tolerance provided was related to changes in the concentration of osmolytes and expression of tas14 dehydrin gene. Taken together, our results highlight that despite the fact all ANE biostimulants were manufactured from the same raw material, their ability to maintain crop productivity during and after drought stress was not the same.

Effect of photoperiod prior to cold acclimation on freezing tolerance and carbohydrate metabolism in alfalfa (Medicago sativa L.)

Cold acclimation proceeds sequentially in response to decreases in photoperiod and temperature. This study aimed at assessing the impact of photoperiod prior to cold acclimation on freezing tolerance and related biochemical and molecular responses in two alfalfa cultivars. The fall dormant cultivar Evolution and semi-dormant cultivar 6010 were grown in growth chambers under different photoperiods (8, 10, 12, 14 or 16h) prior to cold acclimation. Freezing tolerance was evaluated as well as carbohydrate concentrations, levels of transcripts encoding enzymes of carbohydrate metabolism as well as a K-3dehydrin, before and after cold acclimation. The fall dormant cultivar Evolution had a better freezing tolerance than the semi-dormant cultivar 6010. The effect of photoperiod prior to cold acclimation on the level of freezing tolerance differed between the two cultivars: an 8h-photoperiod induced the highest level of freezing tolerance in Evolution and the lowest in 6010. In Evolution, the 8h-induced superior freezing tolerance was associated with higher concentration of raffinose-family oligosaccharides (RFO). The transcript levels of sucrose synthase (SuSy) decreased whereas those of sucrose phosphatase synthase (SPS) and galactinol synthase (GaS) increased in response to cold acclimation in both cultivars. Our results indicate that RFO metabolism could be involved in short photoperiod-induced freezing tolerance in dormant alfalfa cultivars.

Patterns of low temperature induced accumulation of dehydrins in Rosaceae crops-Evidence for post-translational modification in apple

Important crop plants of Rosaceae family are often damaged during winter due to the lack of acclimation and cold hardiness. One of the cellular responses of plants to cold stress is the accumulation of dehydrin proteins. We studied the expression of dehydrins in several Rosaceae species during low temperature treatment in vitro. Microshoots of Pyrus communis, Malus×domestica, Fragaria vesca, Fragaria×ananassa, Prunus cerasus and Prunus avium cultivars were grown in low temperature conditions. Genotype -specific accumulation of dehydrins was detected by immunoblot analysis of the extracted proteins. Untargeted difference gel electrophoresis of Malus x domestica microshoots revealed an extensive accumulation of three dehydrins. In a protein phosphatase assay, MdDHN2 and MdDHN4, but not MdDHN6 proteins were found to be extensively phosphorylated. In terms of the amount of protein synthesized, dehydrins are a major protein-level adaptation mechanism to low temperature in M. x domestica. In addition to dehydrins, the induction of proteins involved in the response for oxidative stress were observed. Additionally, a Xero2 -like dehydrin of F. vesca was detected by difference gel electrophoresis and identified by nano LC-MS/MS.

Metal ion - Dehydrin interactions investigated by affinity capillary electrophoresis and computer models

Dehydrins are specialized proteins which are related to environmental stress tolerance in plants. The proteins can bind different metal ions and have versatile other functions such as reduction of reactive oxygen species and acting as transcription factor. The structure determination of proteins from this family is challenging, since they have a high number of disordered structure elements. Consequently, to determine the functionality of these proteins on a molecular basis a computed model is helpful. This work focuses on a model for the Arabidopsis thaliana dehydrin AtHIRD11. To develop a model which reflects experimental data from literature and own binding data from affinity capillary electrophoresis experiments, a more rigid state of this protein was chosen. The Cu²⁺-complex of this protein was formed and evaluated. The model explains some of the properties of the complexes. Possible Cu²⁺-bindings site were found and the change of conformations were investigated via molecular dynamics simulation. The AtHIRD11-Cu²⁺-complex is a first approach towards a complex model for a structural versatile protein, which is already sufficient to explain binding data and possible structure elements.

Plant dehydrins: shedding light on structure and expression patterns of dehydrin gene family in barley

Dehydrins, an important group of late embryogenesis abundant proteins, accumulate in response to dehydration stresses and play protective roles under stress conditions. Herein, phylogenetic analysis of the dehydrin family was performed using the protein sequences of 108 dehydrins obtained from 14 plant species based on plant taxonomy and protein subclasses. Sub-cellular localization and phosphorylation sites of these proteins were also predicted. The protein features distinguishing these dehydrins categories were identified using various attribute weighting and decision tree analyses. The results revealed that the presence of the S motif preceding the K motif (Y_nSK_n, SK_n, and S_nKS) was more evident and the Y_nSK_n subclass was more frequent in monocots. In barley, as one of the most drought-tolerant crops, there are ten members of Y_nSK_n out of 13 HvDhns. In promoter regions, six types of abiotic stress-responsive elements were identified. Regulatory elements in UTR sequences of HvDhns were infrequent while only four miRNA targets were found. Furthermore, physiological parameters and gene expression levels of HvDhns were studied in tolerant (HV1) and susceptible (HV2) cultivars, and in an Iranian tolerant wild barley genotype (Spontaneum; HS) subjected to gradual water stress and after recovery duration at the vegetative stage. The results showed the significant impact of dehydration on dry matter, relative leaf water, chlorophyll contents, and oxidative damages in HV2 compared with the other studied genotypes, suggesting a poor dehydration tolerance, and incapability of recovering after re-watering in HV2. Under severe drought stress, among the 13 HvDhns genes, 5 and 10 were exclusively induced in HV1 and HS, respectively. The gene and protein structures and the expression patterns of HvDhns as well as the physiological data consistently support the role of dehydrins in survival and recovery of barley plants from drought particularly in HS. Overall, this information would be helpful for functional characterization of the Dhn family in plants.

An analysis of the development of cauliflower seed as a model to improve the molecular mechanism of abiotic stress tolerance in cauliflower artificial seeds

The development stages of conventional cauliflower seeds were studied and the accumulation of dehydrin proteins through the maturation stages was investigated with the aim of identifying methods to improve the viability of artificial seeds of cauliflower. While carbohydrate, ash and lipids increased throughout the development of cauliflower traditional seeds, proteins increased with the development of seed and reached the maximum level after 75 days of pollination, however, the level of protein started to decrease after that. A significant increase in the accumulation of small size dehydrin proteins (12, 17, 26 KDa) was observed during the development of cauliflower seeds. Several experiments were conducted in order to increase the accumulation of important dehydrin proteins in cauliflower microshoots (artificial seeds). Mannitol and ABA (Absisic acid) increased the accumulation of dehydrins in cauliflower microshoots while cold acclimation did not have a significant impact on the accumulation of these proteins. Molybdenum treatments had a negative impact on dehydrin accumulation. Dehydrins have an important role in the drought tolerance of seeds and, therefore, the current research helps to improve the accumulation of these proteins in cauliflower artificial seeds. This in turns improves the quality of these artificial seeds. The current results suggest that dehydrins do not play an important role in cold tolerance of cauliflower artificial seeds. This study could have an important role in improving the understanding of the molecular mechanism of abiotic stress tolerance in plants.

The role of hydrophobic amino acids of K-segments in the cryoprotection of lactate dehydrogenase by dehydrins

Dehydrins, which are group 2 late embryogenesis abundant (LEA) proteins, accumulate in plants during the development of the embryo and exposure to abiotic stresses including low temperature. Dehydrins exhibit cryoprotection of freezing-sensitive enzymes, e.g. lactate dehydrogenase (LDH). Although it has been reported that K-segments conserved in dehydrins are related to their cryoprotection activity, it has not been determined which sequence features of the K-segments contribute to the cryoprotection. A cryoprotection assay using LDH indicated that 13 K-segments including 12 K-segments found in Arabidopsis dehydrins and a typical K-segment (TypK, EKKGIMEKIKEKLPG) derived from the K-segments of many plants showed similar cryoprotective activities. Mutation of the TypK sequence demonstrated that hydrophobic amino acids were clearly involved in preventing the cryoinactivation, cryoaggregation, and cryodenaturation of LDH. We propose that the cryoprotective activities of dehydrins may be made possible by the hydrophobic residues of the K-segments.

Different dehydrins perform separate functions in Physcomitrella patens

Dehydrins, PpDHNA and PpDHNB from Physcomitrella patens provide drought and cold tolerance while PpDHNC shows antimicrobial property suggesting different dehydrins perform separate functions in P. patens. The moss Physcomitrella patens can withstand extremes of environmental condition including abiotic stress such as dehydration, salinity, low temperature and biotic stress such as pathogen attack. Osmotic stress is inflicted under both cold and drought stress conditions where dehydrins have been found to play a significant protective role. In this study, a comparative analysis was drawn for the three dehydrins PpDHNA, PpDHNB and PpDHNC from P. patens. Our data shows that PpDHNA and PpDHNB play a major role in cellular protection during osmotic stress. PpDHNB showed several fold upregulation of the gene when P. patens was subjected to cold and osmotic stress in combination. PpDHNA and PpDHNB provide protection to enzyme lactate dehydrogenase under osmotic as well as freezing conditions. PpDHNC possesses antibacterial activity and thus may have a role in biotic stress response. Overexpression of PpDHNA, PpDHNB and PpDHNC in transgenic tobacco showed a better performance for PpDHNB with respect to cold and osmotic stress. These results suggest that specific dehydrins contribute to tolerance of mosses under different stress conditions.

De novo transcriptome sequencing and gene expression profiling of Elymus nutans under cold stress

BACKGROUND

Elymus nutans Griseb., is an important alpine perennial forage of Pooideae subfamily with strong inherited cold tolerance. To get a deeper insight into its molecular mechanisms of cold tolerance, we compared the transcriptome profiling by RNA-Seq in two genotypes of Elymus nutans Griseb. the tolerant Damxung (DX) and the sensitive Gannan (GN) under cold stress.

RESULTS

The new E. nutans transcriptomes were assembled and comprised 200,520 and 181,331 transcripts in DX and GN, respectively. Among them, 5436 and 4323 genes were differentially expressed in DX and GN, with 170 genes commonly expressed over time. Early cold responses involved numerous genes encoding transcription factors and signal transduction in both genotypes. The AP2/EREBP famliy of transcription factors was predominantly expressed in both genotypes. The most significant transcriptomic changes in the later phases of cold stress are associated with oxidative stress, primary and secondary metabolism, and photosynthesis. Higher fold expressions of fructan, trehalose, and alpha-linolenic acid metabolism-related genes were detected in DX. The DX-specific dehydrins may be promising candidates to improve cold tolerance. Twenty-six hub genes played a central role in both genotypes under cold stress. qRT-PCR analysis of 26 genes confirmed the RNA-Seq results.

CONCLUSIONS

The stronger transcriptional differentiation during cold stress in DX explains its better cold tolerance compared to GN. The identified fructan biosynthesis, alpha-linolenic acid metabolism, and DX-specific dehydrin-related genes may provide genetic resources for the improvement of cold-tolerant characters in DX. Our findings provide important clues for further studies of the molecular mechanisms underlying cold stress responses in plants.

Isolation, cloning, and characterization of a novel Sorghum dehydrin (SbDhn2) protein

Plants can produce their own set of defense molecules in an attempt to survive under stressed conditions. Dehydrins play a considerable role in protecting the plants under varied stress situations. We have isolated a novel SK3 type dehydrin from Sorghum capable of protecting the enzyme lactate dehydrogenase in vitro under both cold and high temperature. This protein showed non-canonical migration in a sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) due to the high hydrophilicity of the protein. The high percentage of glycine and histidine residues present in the protein sequence is responsible for the radical scavenging activity of the protein. The protein also exhibited binding affinity to metal ions owing to the histidine-rich motifs, therefore chelating the metal ions and making them unavailable to systems responsible for generation of reactive oxygen species (ROS). In the presence of specific metal ions, the protein showed reversible aggregation with certain degree of protease resistivity along with induction of secondary structures. The resistivity of the protein to degradation might be implicated in stress situations, thus leading to an increase in the shelf life of the protein. Association with metal ions like copper and zinc at a fairly low concentration increased the protective effect of the SbDHN2 protein for lactate dehydrogenase (LDH) activity to a considerable extent. The synthesis of this dehydrin in stressed plants might help the plant in rendering stress tolerance.

Molecular processes induced in primed seeds-increasing the potential to stabilize crop yields under drought conditions

Environmental stress factors such as drought, salinity, temperature extremes and rising CO₂ negatively affect crop growth and productivity. Faced with the scarcity of water resources, drought is the most critical threat to world food security. This is particularly important in the context of climate change and an increasing world population. Seed priming is a very promising strategy in modern crop production management. Although it has been known for several years that seed priming can enhance seed quality and the effectiveness of stress responses of germinating seeds and seedlings, the molecular mechanisms involved in the acquisition of stress tolerance by primed seeds in the germination process and subsequent plant growth remain poorly understood. This review provides an overview of the metabolic changes modulated by priming, such as the activation of DNA repair and the antioxidant system, accumulation of aquaporins and late embryogenesis abundant proteins that contribute to enhanced drought stress tolerance. Moreover, the phenomenon of "priming memory," which is established during priming and can be recruited later when seeds or plants are exposed to stress, is highlighted.

Dose-dependent response of Trichoderma harzianum in improving drought tolerance in rice genotypes

This study demonstrates a dose-dependent response of Trichoderma harzianum Th-56 in improving drought tolerance in rice by modulating proline, SOD, lipid peroxidation product and DHN / AQU transcript level, and the growth attributes. In the present study, the effect of colonization of different doses of T. harzianum Th-56 strain in rice genotypes were evaluated under drought stress. The rice genotypes treated with increasing dose of T. harzianum strain Th-56 showed better drought tolerance as compared with untreated control plant. There was significant change in malondialdehyde, proline, higher superoxide dismutase level, plant height, total dry matter, relative chlorophyll content, leaf rolling, leaf tip burn, and the number of scorched/senesced leaves in T. harzianum Th-56 treated rice genotypes under drought stress. This was corroborated with altered expression of aquaporin and dehydrin genes in T. harzianum Th-56 treated rice genotypes. The present findings suggest that a dose of 30 g/L was the most effective in improving drought tolerance in rice, and its potential exploitation will contribute to the advancement of rice genotypes to sustain crop productivity under drought stress. Interaction studies of T. harzianum with three aromatic rice genotypes suggested that PSD-17 was highly benefitted from T. harzianum colonization under drought stress.

Actin microfilaments are involved in the regulation of HVA1 transcript accumulation in drought-treated barley leaves

Drought is one of the stresses that limit the yield of barley. Despite extensive studies focused on the issue, the molecular mechanism of the response to drought is still not fully understood. In our previous study, we proposed drought-induced signal perception controlled by actin filaments (AFs). To test this hypothesis, we used a chemical inhibitor of AF polarization-latrunculin B. In drought-treated barley leaves, latrunculin B induced AF depolymerization and altered gene expression (mainly those controlling AF formation), notably inhibiting the expression of HVA1, a dehydrin encoding gene whose function in drought tolerance has been widely studied. These results suggest that AFs might be involved in water-deficit signal perception in plant cells.

The Arabidopsis KS-type dehydrin recovers lactate dehydrogenase activity inhibited by copper with the contribution of His residues

Dehydrin, which is one of the late embryogenesis abundant (LEA) proteins, is involved in the ability of plants to tolerate the lack of water. Although many reports have indicated that dehydrins bind heavy metals, the physiological role of this metal binding has not been well understood. Here, we report that the Arabidopsis KS-type dehydrin (AtHIRD11) recovered the lactate dehydrogenase (LDH) activity denatured by Cu(2+). The LDH activity was partially inhibited by 0.93 μM Cu(2+) but totally inactivated by 9.3 μM Cu(2+). AtHIRD11 recovered the activity of LDH treated with 9.3 μM Cu(2+) in a dose-dependent manner. The recovery activity of AtHIRD11 was significantly higher than those of serum albumin and lysozyme. The conversion of His residues to Ala in AtHIRD11 resulted in the loss of the Cu(2+) binding of the protein as well as the disappearance of the conformational change induced by Cu(2+) that is observed by circular dichroism spectroscopy. The mutant protein showed lower recovery activity than the original AtHIRD11. These results indicate that AtHIRD11 can reactivate LDH inhibited by Cu(2+) via the His residues. This function may prevent physiological damage to plants due to heavy-metal stress.

Dehydrins from wheat x Thinopyrum ponticum amphiploid increase salinity and drought tolerance under their own inducible promoters without growth retardation

Dehydrins confer abiotic stress tolerance in seedlings, but few dehydrins have been studied by transgenic analysis under their own promoters in relation to abiotic stress tolerance. Also the inducible promoters for transgenic engineering are limited. In this study, we isolated from wheat three salt-induced YSK2 dehydrin genes and their promoters. The cDNA sequences were 711, 785, and 932 bp in length, encoding proteins containing 133, 166 and 231 amino acids, respectively, and were named TaDHN1, TaDHN2, and TaDHN3. TaDHN2 doesn't contain introns, while the other two genes each contain one. Semi-quantitative reverse transcription PCR analysis revealed all three dehydrin genes are substantially induced by ABA and NaCl, but only TaDHN2 is induced in seedlings by PEG and by cold (4 °C). Regulatory sequences upstream of the first translation codon (775, 1615 and 889 bp) of the three dehydrin genes were also cloned. Cis-element prediction indicated the presence of ABRE and other abiotic-stress-related elements. Histochemical analysis using GUS expression demonstrated that all three promoters were induced by ABA, cold or NaCl. Ectopic over-expression of TaDHN1 or TaDHN3 in Arabidopsis under their own inducible promoters enhanced NaCl- and drought-stress tolerance without growth retardation.

Functional characterization of a dehydrin protein from Fagus sylvatica seeds using experimental and in silico approaches

A strong increase in the level of dehydrin/response ABA transcripts expression reported from the 14th week after flowering coincident with the accumulation of 26 and 44 kDa dehydrins in the embryonic axes of developing beech (Fagus sylvatica L.) seeds. Both transcript and protein levels were strongly correlated with maturation drying. These results suggest that the 44-kDa dehydrin protein is a putative dimer of dehydrin/response ABA protein migrating as a 26-kDa protein. Dehydrins and dehydrin-like proteins form large oligomeric complexes under native conditions and are shown as several spots differing in pI through isoelectrofocusing analyses. Detailed prediction of specific sites accessible for various post-translational modifications (PTMs) in the dehydrin/response ABA protein sequence revealed sites specific to acetylation, amidation, glycosylation, methylation, myristoylation, nitrosylation, O-linked β-N-acetylglucosamination and Yin-O-Yang modification, palmitoylation, phosphorylation, sumoylation, sulfation, and ubiquitination. Thus, these results suggest that specific PTMs might play a role in switching dehydrin function or activity, water binding ability, protein-membrane interactions, transport and subcellular localization, interactions with targeted molecules, and protein stability. Despite the ability of two Cys residues to form a disulfide bond, -SH groups are likely not involved in dimer arrangement. His-rich regions and/or polyQ-tracts are potential candidates as spatial organization modulators. Dehydrin/response ABA protein is an intrinsically disordered protein containing low complexity regions. The lack of a fixed structure and exposition of amino acids on the surface of the protein structure enhances the accessibility to 40 predicted PTM sites, thereby facilitating dehydrin multifunctionality, which is discussed in the present study.

Overexpression of ShDHN, a dehydrin gene from Solanum habrochaites enhances tolerance to multiple abiotic stresses in tomato

Dehydrins (DHNs) play important roles in plant adaptation to abiotic stress. In this study, a cold-induced SK3-type DHN gene (ShDHN) isolated from wild tomato species Solanum habrochaites was characterized for its function in abiotic stress tolerance. ShDHN was constitutively expressed in root, leaf, stem, flower and fruit. ShDHN was continuously up-regulated during cold stress and showed higher expression level in the cold-tolerant S. habrochaites than in the susceptible S. lycopersicum. Moreover, ShDHN expression was also regulated by drought, salt, osmotic stress, and exogenous signaling molecules. Overexpression of ShDHN in cultivated tomato increased tolerance to cold and drought stresses and improved seedling growth under salt and osmotic stresses. Compared with the wild-type, the transgenic plants accumulated more proline, maintained higher enzymatic activities of superoxide dismutase and catalase, and suffered less membrane damage under cold and drought stresses. Moreover, the transgenic plants accumulated lower levels of H2O2 and O2(-) under cold stress, and had higher relative water contents and lower water loss rates under dehydration conditions. Furthermore, overexpression of ShDHN in tomato led to the up- or down-regulated expression of several genes involved in ROS scavenging and JA signaling pathway, including SOD1, GST, POD, LOX, PR1 and PR2. Taken together, these results indicate that ShDHN has pleiotropic effects on improving plant adaptation to abiotic stresses and that it possesses potential usefulness in genetic improvement of stress tolerance in tomato.

Dehydrin expression in seeds and maturation drying: a paradigm change

Dehydrins are well known for being expressed in leaves during the course of developmental processes as well as under drought stress, being part of the protective machinery. Moreover, in seed physiology, dehydrins are classified as late embryogenesis-related proteins (LEA protein), where they are thought to be responsible for persistence and longevity of seeds. Although both topics are a focus of modern plant biology, a direct linkage between these both areas is generally lacking. Based on an alignment of the chain of events, this paper will help to generate understanding that the occurrence of dehydrins in maturing seeds and leaves suffering drought stress is part of the same basic principle: basic principle: dehydrins are expressed in response to water shortage. Unfortunately, the related developmental process in seeds, i.e. maturation drying, has not been adequately considered as a part of this process. As a corresponding implication, the chain of events must be adjusted: the differences in dehydrin expression in orthodox, intermediate and recalcitrant seeds could be directly attributed to the occurrence or absence of maturation drying. The differences in dehydrin expression in orthodox, intermediate and recalcitrant seeds, and thus the differences in longevity, could be attributed to the occurrence or absence of a maturation drying.

Molecular cloning and characterization of a novel SK3-type dehydrin gene from Stipa purpurea

Stipa purpurea, an endemic forage of the grass family in the Tibetan Plateau, is highly resistant to drought. Dehydrins (DHNs) are stress proteins involved in plant protective reactions against environmental stress. In this study, the full-length DHN open reading frame (ORF) cloned from S. purpurea, named SpDHN1, was 816 nucleotides length and encoded a protein of 271 amino acids. Phylogenetic and sequence characterization analysis revealed that the DHN gene was an SK3-type DHNs. Subcellular localization analysis indicated that SpDHN1 was localized in the cytoplasm and the plasma membrane. SpDHN1 function analysis provided new evidence to support the antioxidation of SpDHN1 in plant responses drought stress. Ectopic expression of SpDHN1 in Arabidopsis thaliana plants showed more resistance to drought stress than the wild-type, indicating that SpDHN1 may be a potential candidate gene for genetic improvement of crops to improve stress tolerance.

Classification and expression diversification of wheat dehydrin genes

Dehydrins (DHNs) are late embryonic abundant proteins characterized by the dehydrin domains that are involved in plant abiotic stress tolerance. In this study, fifty-four wheat DHN unigenes were identified in the expressed sequence tags database. These genes encode seven types of dehydrins (KS, SK3, YSK2, Y2SK2, Kn, Y2SK3, and YSK3) and separate in 32 homologous clusters. The gene amplification differed among the dehydrin types, and members of the YSK2- and Kn-type DHNs are more numerous in wheat than in other cereals. The relative expression of all of these DHN clusters was analyzed using an in silico method in seven tissue types (i.e. normal growing shoots, roots, and reproductive tissues; developing and germinating seeds; drought- and cold-stressed shoots) as well as semi-quantitative reverse transcription polymerase chain reaction in seedling leaves and roots treated by dehydration, cold, and salt, respectively. The role of the ABA pathway in wheat DHN expression regulation was analyzed. Transcripts of certain types of DHNs accumulated specifically according to tissue type and treatment, which suggests their differentiated roles in wheat abiotic stress tolerance.

Significant relationships among frost tolerance and net photosynthetic rate, water use efficiency and dehydrin accumulation in cold-treated winter oilseed rapes

Five winter oilseed rape cultivars (Benefit, Californium, Cortes, Ladoga, Navajo) were subjected to 30 days of cold treatment (4 °C) to examine the effect of cold on acquired frost tolerance (FT), dehydrin (DHN) content, and photosynthesis-related parameters. The main aim of this study was to determine whether there are relationships between FT (expressed as LT50 values) and the other parameters measured in the cultivars. While the cultivar Benefit accumulated two types of DHNs (D45 and D35), the other cultivars accumulated three additional DHNs (D97, D47, and D37). The similar-sized DHNs (D45 and D47) were the most abundant; the others exhibited significantly lower accumulations. The highest correlations were detected between LT50 and DHN accumulation (r=-0.815), intrinsic water use efficiency (WUEi; r=-0.643), net photosynthetic rate (r=-0.628), stomatal conductance (r=0.511), and intracellular/intercellular CO2 concentration (r=0.505). Those cultivars that exhibited higher Pn rate in cold (and further a significant increase in WUEi) had higher levels of DHNs and also higher FT. No significant correlation was observed between LT50 and E, PRI, or NDVI. Overall, we have shown the selected physiological parameters to be able to distinguish different FT cultivars of winter oilseed rape.

Dehydrins are highly expressed in overwintering buds and enhance drought and freezing tolerance in Gentiana triflora

Gentians, herbaceous perennials, produce overwintering buds (OWBs) to survive the cold season. Although gentians are known to have strong stress tolerances against drought, cold and freezing, the molecular mechanisms of tolerance are unclear. We explored genes more highly expressed in OWBs than in other tissues and identified two gentian orthologs of dehydrins, denoted GtDHN1 and GtDHN2. These GtDHNs possess several ABA or dehydration responsive elements. Furthermore, GtDHN1 and GtDHN2 transcripts in OWBs accumulated during the winter but decreased prior to spring, suggesting that GtDHNs may be induced by dehydration stress during cold periods and may act as a stress protectant mediated by ABA. Likewise, cultured gentian plantlets accumulated GtDHN transcripts in response to ABA as well as cold and drought stresses. Moreover, transgenic gentian plantlets overexpressing GtDHN1 or GtDHN2 showed improved cold and drought stress tolerance. Metabolome analysis revealed that major antioxidants such as glutathione and ascorbate were accumulated in all transgenic plantlets. Overexpression of GtDHNs also affected the activities of the antioxidant enzymes, ascorbate peroxidase and glutathione peroxidase. Based on the results of this study, GtDHNs are induced by ABA and dehydration stress and have an ability to alleviate dehydration stress, probably via activating antioxidant mechanisms. Accumulation of GtDHNs may be part of the strategy for winter survival of gentian OWBs.

Dehydrin expression in soybean

Soybean (Glycine max) is a relatively cold intolerant plant. In most stress tolerant plants the responsive expression of dehydrin proteins in vegetative tissues can be a significant contributor to protection against environmental stresses. The purpose of this study was to examine the expression of dehydrins in various organs and the cold-responses of dehydrin genes in vegetative tissues of soybean. Examination of the soybean genome indicated the presence of genes encoding ten distinct dehydrins. Levels of dehydrin proteins were probed with several antibodies specific to dehydrins or to the signature K-sequence. A single vegetatively expressed dehydrin protein was detected and the levels were insignificantly altered in response to cold, drought, or salt stress, nor was the transcript responsive to ABA. This SK2-type, acidic dehydrin family member (GmERD14) was purified, identified by mass spectroscopy, and shown to be in vivo phosphorylated; indicating characteristics similar to other known acidic dehydrins. The lack of cold stress-regulated acidic dehydrin expression may contribute to the inability of soybean to cold acclimate. While transcripts for all ten dehydrins could be detected in various tissues, only three accumulated to significant levels in vegetative tissues (two of the KS type and one of SK2 type). One of these transcripts, a KS dehydrin, was accumulated following cold treatments. The accumulation of the KS dehydrin was also responsive to exogenous ABA.