Characterization of a novel Y2K-type dehydrin VrDhn1 from Vigna radiata

Plant dehydrins and dehydrin-like proteins: characterization and participation in abiotic stress response

Abiotic stress has a significant impact on plant growth and development. It causes changes in the subcellular organelles, which, due to their stress sensitivity, can be affected. Cellular components involved in the abiotic stress response include dehydrins, widely distributed proteins forming a class II of late embryogenesis abundant protein family with characteristic properties including the presence of evolutionarily conserved sequence motifs (including lysine-rich K-segment, N-terminal Y-segment, and often phosphorylated S motif) and high hydrophilicity and disordered structure in the unbound state. Selected dehydrins and few poorly characterized dehydrin-like proteins participate in cellular stress acclimation and are also shown to interact with organelles. Through their functioning in stabilizing biological membranes and binding reactive oxygen species, dehydrins and dehydrin-like proteins contribute to the protection of fragile organellar structures under adverse conditions. Our review characterizes the participation of plant dehydrins and dehydrin-like proteins (including some organellar proteins) in plant acclimation to diverse abiotic stress conditions and summarizes recent updates on their structure (the identification of dehydrin less conserved motifs), classification (new proposed subclasses), tissue- and developmentally specific accumulation, and key cellular activities (including organellar protection under stress acclimation). Recent findings on the subcellular localization (with emphasis on the mitochondria and plastids) and prospective applications of dehydrins and dehydrin-like proteins in functional studies to alleviate the harmful stress consequences by means of plant genetic engineering and a genome editing strategy are also discussed.

Molecular Characterization of Dehydrin in Azraq Saltbush among Related Atriplex Species

Atriplex spp. (saltbush) is known to survive extremely harsh environmental stresses such as salinity and drought. It mitigates such conditions based on specialized physiological and biochemical characteristics. Dehydrin genes (DHNs) are considered major players in this adaptation. In this study, a novel DHN gene from Azrak (Jordan) saltbush was characterized along with other Atriplex species from diverse habitats. Intronless DHN-expressed sequence tags (495-761 bp) were successfully cloned and sequenced. Saltbush dehydrins contain one S-segment followed by three K-segments: an arrangement called SK3-type. Two substantial insertions were detected including three copies of the K2-segemnet in A. canescens. New motif variants other than the six-serine standard were evident in the S-segment. AhaDHN1 (A. halimus) has a cysteine residue (SSCSSS), while AgaDHN1 (A. gardneri var. utahensis) has an isoleucine residue (SISSSS). In contrast to the conserved K1-segment, both the K2- and K3-segment showed several substitutions, particularly in AnuDHN1 (A. nummularia). In addition, a parsimony phylogenetic tree based on homologs from related genera was constructed. The phylogenetic tree resolved DHNs for all of the investigated Atriplex species in a superclade with an 85% bootstrap value. Nonetheless, the DHN isolated from Azraq saltbush was uniquely subclustred with a related genera Halimione portulacoides. The characterized DHNs revealed tremendous diversification among the Atriplex species, which opens a new venue for their functional analysis.

Involvement of dehydrin proteins in mitigating the negative effects of drought stress in plants

Drought stress-induced crop loss has been considerably increased in recent years because of global warming and changing rainfall pattern. Natural drought-tolerant plants entail the recruitment of a variety of metabolites and low molecular weight proteins to negate the detrimental effects of drought stress. Dehydrin (DHN) proteins are one such class of proteins that accumulate in plants during drought and associated stress conditions. These proteins are highly hydrophilic and perform multifaceted roles in the protection of plant cells during drought stress conditions. Evidence gathered over the years suggests that DHN proteins impart drought stress tolerance by enhancing the water retention capacity, elevating chlorophyll content, maintaining photosynthetic machinery, activating ROS detoxification, and promoting the accumulation of compatible solutes, among others. Overexpression studies have indicated that these proteins can be effectively targeted to mitigate the negative effects of drought stress and for the development of drought stress-tolerant crops to feed the ever-growing population in the near future. In this review, we describe the mechanism of DHNs mediated drought stress tolerance in plants and their interaction with several phytohormones to provide an in-depth understanding of DHNs function.

The Disordered Dehydrin and Its Role in Plant Protection: A Biochemical Perspective

Dehydrins are intrinsically disordered proteins composed of several well conserved sequence motifs known as the Y-, S-, F-, and K-segments, the latter of which is a defining feature of all dehydrins. These segments are interspersed by regions of low sequence conservation and are organized modularly, which results in seven different architectures: Kn, SKn, YnSKn, YnKn, KnS, FnK and FnSKn. Dehydrins are expressed ubiquitously throughout the plant kingdom during periods of low intracellular water content, and are capable of improving desiccation tolerance in plants. In vitro evidence of dehydrins shows that they are involved in the protection of membranes, proteins and DNA from abiotic stresses. However, the molecular mechanisms by which these actions are achieved are as of yet somewhat unclear. With regards to macromolecule cryoprotection, there is evidence to suggest that a molecular shield-like protective effect is primarily influenced by the hydrodynamic radius of the dehydrin and to a lesser extent by the charge and hydrophobicity. The interaction between dehydrins and membranes is thought to be a surface-level, charge-based interaction that may help to lower the transition temperature, allowing membranes to maintain fluidity at low temperatures and preventing membrane fusion. In addition, dehydrins are able to protect DNA from damage, showing that these abiotic stress protection proteins have multiple roles.

The ethylene-responsive transcription factor of durum wheat, TdSHN1, confers cadmium, copper, and zinc tolerance to yeast and transgenic tobacco plants

Cadmium (Cd), copper (Cu), and zinc (Zn) are among the most common heavy metals (HMs) present in polluted soils. While some HMs are required for key biological processes, they are toxic when present in excess. This toxicity damages plant health, decreases crop yields, and can impact human health via the food chain. For example, durum wheat is a staple food that is known to accumulate Cd when grown on polluted soils. Plant response to HM stress is complex and involves several transcription factors (TFs) among which members of the ERF family. Although roles of SHINE-type ERF transcription factors in abiotic stress tolerance have been thoroughly investigated, there is little information concerning their role in HM stress tolerance. In the present study, we investigated the role of durum wheat TdSHN1 TF in HM response and tolerance. Results showed that TdSHN1 expression was strongly induced by Cd, Cu, and Zn in durum wheat seedlings. In addition, TdSHN1 gene promoter directed HM-inducible GUS gene expression in transgenic tobacco. Overexpression of TdSHN1 encoding cDNA in transgenic yeast and tobacco conferred Cd, Cu, and Zn tolerances. Interestingly, transgenic tobacco lines exhibited longer roots and greater biomass accumulation, retained more chlorophyll, and produced less ROS than WT plants, when subjected to excess HMs. In addition, transgenic tobacco lines had higher activities of ROS-scavenging enzymes (SOD and CAT) which might have contributed to their HM tolerance. This study suggested that TdSHN1 is a potential candidate for improving HM tolerance in plants and phytoremediation of HM-contaminated soils.

AnDHN, a Dehydrin Protein From Ammopiptanthus nanus, Mitigates the Negative Effects of Drought Stress in Plants

Dehydrins (DHNs) play crucial roles in a broad spectrum of abiotic stresses in model plants. However, the evolutionary role of DHNs has not been explored, and the function of DHN proteins is largely unknown in Ammopiptanthus nanus (A. nanus), an ancient and endangered legume species from the deserts of northwestern China. In this study, we isolated a drought-response gene (c195333_g1_i1) from a drought-induced RNA-seq library of A. nanus. Evolutionary bioinformatics showed that c195333_g1_i1 is an ortholog of Arabidopsis DHN, and we renamed it AnDHN. Moreover, DHN proteins may define a class of proteins that are evolutionarily conserved in all angiosperms that have experienced a contraction during the evolution of legumes. Arabidopsis plants overexpressing AnDHN exhibited morpho-physiological changes, such as an increased germination rate, higher relative water content (RWC), higher proline (PRO) content, increased peroxidase (POD) and catalase (CAT) activities, lower contents of malondialdehyde (MDA), H₂O₂ and O₂ ^-, and longer root length. Our results showed that the transgenic lines had improved drought resistance with deep root system architecture, excellent water retention, increased osmotic adjustment, and enhanced reactive oxygen species (ROS) scavenging. Furthermore, the transgenic lines also had enhanced salt and cold tolerance. Our findings demonstrate that AnDHN may be a good candidate gene for improving abiotic stress tolerance in crops. Key Message: Using transcriptome analysis in Ammopiptanthus nanus, we isolated a drought-responsive gene, AnDHN, that plays a key role in enhancing abiotic stress tolerance in plants, with strong functional diversification in legumes.

Quantitative analysis of differential dehydrin regulation in pine and spruce seedlings under water deficit

Dehydrins are well-known components of plant responses to different stresses that cause dehydration, including drought, freezing, salinity, etc. In conifers, the dehydrin gene family is very large, implying that the members of this family have important physiological functions in conifer stress tolerance. However, dehydrin gene expression displays a wide range of responses to stress, from thousand-fold increased expression to decreased expression, and it is generally unknown how regulatory systems are connected at the mRNA and protein levels. Therefore, we studied these aspects of dehydrin regulation in Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) H. Karst) seedlings under polyethylene glycol 6000-induced osmotic stress ranging from relatively low (culture medium water potential of -0.15 MPa) to very high (-1.0 MPa) intensities. In pine, the major dehydrin protein was Dhn1 in both the roots and needles, and in spruce, two isoforms of the Dhn4 protein were the major dehydrins; both of these proteins are AESK-type dehydrins. The genes encoding these major proteins were highly expressed even under control conditions; surprisingly, we also observed several highly expressed dehydrin genes that were not abundantly translated. Under osmotic stress, the most prominent expression changes were observed for the dehydrin genes with low basal expression levels, whereas highly expressed genes generally demonstrated rather modest changes in expression. We report proposed constitutive physiological functions of the AESK-type dehydrins in Pinaceae plants.

CaDHN3, a Pepper (Capsicum annuum L.) Dehydrin Gene Enhances the Tolerance against Salt and Drought Stresses by Reducing ROS Accumulation

Dehydrins (DHNs) play an important role in abiotic stress tolerance in a large number of plants, but very little is known about the function of DHNs in pepper plants. Here, we isolated a Y₁SK₂-type DHN gene “CaDHN3” from pepper. To authenticate the function of CaDHN3 in salt and drought stresses, it was overexpressed in Arabidopsis and silenced in pepper through virus-induced gene silencing (VIGS). Sub-cellular localization showed that CaDHN3 was located in the nucleus and cell membrane. It was found that CaDHN3-overexpressed (OE) in Arabidopsis plants showed salt and drought tolerance phenotypic characteristics, i.e., increased the initial rooting length and germination rate, enhanced chlorophyll content, lowered the relative electrolyte leakage (REL) and malondialdehyde (MDA) content than the wild-type (WT) plants. Moreover, a substantial increase in the activities of antioxidant enzymes; including the superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), and lower hydrogen peroxide (H₂O₂) contents and higher O₂^•− contents in the transgenic Arabidopsis plants. Silencing of CaDHN3 in pepper decreased the salt- and drought-stress tolerance, through a higher REL and MDA content, and there was more accumulation of reactive oxygen species (ROS) in the CaDHN3-silenced pepper plants than the control plants. Based on the yeast two-hybrid (Y2H) screening and Bimolecular Fluorescence Complementation (BiFC) results, we found that CaDHN3 interacts with CaHIRD11 protein in the plasma membrane. Correspondingly, the expressions of four osmotic-related genes were significantly up-regulated in the CaDHN3-overexpressed lines. In brief, our results manifested that CaDHN3 may play an important role in regulating the relative osmotic stress responses in plants through the ROS signaling pathway. The results of this study will provide a basis for further analyses of the function of DHN genes in pepper.

Functional Characteristics Analysis of Dehydrins in Larix kaempferi under Osmotic Stress

Dehydrins (DHN) belong to the late embryogenesis abundant II family and have been found to enhance plant tolerance to abiotic stress. In the present study, we reported four DHNs in Larix kaempferi (LkDHN) which were identified from the published transcriptome. Alignment analysis showed that these four LkDHNs shared close relationships and belonged to SK3-type DHNs. The electrophoretic mobility shift assay indicated that these four LkDHNs all possess sequence-independent binding capacity for double-strands DNAs. The subcellular localizations of the four LkDHNs were in both the nucleus and cytoplasm, indicating that these LkDHNs enter the nucleus to exert the ability to bind DNA. The preparation of tobacco protoplasts with different concentrations of mannitol showed that LkDHNs enhanced the tolerance of plant cells under osmotic stress. The overexpression of LkDHNs in yeasts enhanced their tolerance to osmotic stress and helped the yeasts to survive severe stress. In addition, LkDHNs in the nucleus of salt treated tobacco increased. All of these results indicated that the four LkDHNs help plants survive from heavy stress by participating in DNA protection. These four LKDHNs played similar roles in the response to osmotic stress and assisted in the adaptation of L. kaempferi to the arid and cold winter of northern China.

Effect of K-/S- segments on subcellular localization and dimerization of wheat dehydrin WZY1-2

Dehydrins (DHNs) belong to group Ⅱ late embryogenesis abundant (LEA) proteins which perform multiple functions in plants during stress conditions. Both K- and S-segments are conserved domains in the dehydrin protein family; however, there are only a few in vivo functional studies for these two conserved segments. In this study, the DHN gene wzy1-2 was isolated from Triticum aestivum and its K-/S-segment-truncated derivatives were generated. In order to explore the biological function of these two conserved fragments, subcellular localization and dimerization detection assays were performed for the K-/S-segment-truncated derivatives. Results of GFP fusion and bimolecular fluorescence complementation (BiFC) assays indicated that WZY1-2 localized to nucleus as a homologous dimer. The S-segment partially regulated the nuclear localization of WZY1-2 but did not affect its dimerization, while the K-segment influenced neither the dimer formation nor the subcellular localization.

Lysine, Lysine-Rich, Serine, and Serine-Rich Proteins: Link Between Metabolism, Development, and Abiotic Stress Tolerance and the Role of ncRNAs in Their Regulation

Lysine (Lys) is indispensable nutritionally, and its levels in plants are modulated by both transcriptional and post-transcriptional control during plant ontogeny. Animal glutamate receptor homologs have been detected in plants, which may participate in several plant processes through the Lys catabolic products. Interestingly, a connection between Lys and serotonin metabolism has been established recently in rice. 2-Aminoadipate, a catabolic product of Lys appears to play a critical role between serotonin accumulation and the color of rice endosperm/grain. It has also been shown that expression of some lysine-methylated proteins and genes encoding lysine-methyltransferases (KMTs) are regulated by cadmium even as it is known that Lys biosynthesis and its degradation are modulated by novel mechanisms. Three complex pathways co-exist in plants for serine (Ser) biosynthesis, and the relative preponderance of each pathway in relation to plant development or abiotic stress tolerance are being unfolded slowly. But the phosphorylated pathway of L-Ser biosynthesis (PPSB) appears to play critical roles and is essential in plant metabolism and development. Ser, which participates indirectly in purine and pyrimidine biosynthesis and plays a pivotal role in plant metabolism and signaling. Also, L-Ser has been implicated in plant responses to both biotic and abiotic stresses. A large body of information implicates Lys-rich and serine/arginine-rich (SR) proteins in a very wide array of abiotic stresses. Interestingly, a link exists between Lys-rich K-segment and stress tolerance levels. It is of interest to note that abiotic stresses largely influence the expression patterns of SR proteins and also the alternative splicing (AS) patterns. We have checked if any lncRNAs form a cohort of differentially expressed genes from the publicly available PPSB, sequence read archives of NCBI GenBank. Finally, we discuss the link between Lys and Ser synthesis, catabolism, Lys-proteins, and SR proteins during plant development and their myriad roles in response to abiotic stresses.

CaDHN4, a Salt and Cold Stress-Responsive Dehydrin Gene from Pepper Decreases Abscisic Acid Sensitivity in Arabidopsis

Dehydrins play an important role in improving plant resistance to abiotic stresses. In this study, we isolated a dehydrin gene from pepper (Capsicum annuum L.) leaves, designated as CaDHN4. Sub-cellular localization of CaDHN4 was to be found in the nucleus and membrane. To authenticate the function of CaDHN4 in cold- and salt-stress responses and abscisic acid (ABA) sensitivity, we reduced the CaDHN4 expression using virus-induced gene silencing (VIGS), and overexpressed the CaDHN4 in Arabidopsis. We found that silencing of CaDHN4 reduced the growth of pepper seedlings and CaDHN4-silenced plants exhibited more serious wilting, higher electrolyte leakage, and more accumulation of ROS in the leaves compared to pTRV2:00 plants after cold stress, and lower chlorophyll contents and higher electrolyte leakage compared to pTRV2:00 plants under salt stress. However, CaDHN4-overexpressing Arabidopsis plants had higher seed germination rates and post-germination primary root growth, compared to WT plants under salt stress. In response to cold and salt stresses, the CaDHN4-overexpressed Arabidopsis exhibited lower MDA content, and lower relative electrolyte leakage compared to the WT plants. Under ABA treatments, the fresh weight and germination rates of transgenic plants were higher than WT plants. The transgenic Arabidopsis expressing a CaDHN4 promoter displayed a more intense GUS staining than the normal growth conditions under treatment with hormones including ABA, methyl jasmonate (MeJA), and salicylic acid (SA). Our results suggest that CaDHN4 can protect against cold and salt stresses and decrease ABA sensitivity in Arabidopsis.

Binding of a Vitis riparia dehydrin to DNA

Plants must protect themselves from abiotic stresses such as drought, cold, and high salinity. The common thread of all three stresses is that they cause dehydration, which in turn promotes the formation of reactive oxygen species (ROS). Dehydrin proteins (dehydrins) are a large family of proteins that have been identified in nearly all land plants, and whose presence is correlated with plant protection from abiotic stresses. Several dehydrin studies have shown that some dehydrins localize to the nucleus, as well as the cytoplasm, but a functional role for nuclear dehydrins has not yet been determined. We show here that the Vitis riparia dehydrin VrDHN1 localizes to the nucleus and is able to bind to DNA to protect it from damage caused by hydrogen peroxide, an ROS source. We also show that the binding to DNA is not DNA-sequence specific, suggesting that the protein is able to protect any exposed DNA without interfering with its normal function. NMR studies show that the binding is largely driven by the lysine-rich nature of dehydrins located in the conserved K-segments. Unlike other, previously studied dehydrins, VrDHN1 binding to DNA is not enhanced through the presence of metals. Lastly, we demonstrate that the Y-segment does not bind ATP, as has long been proposed.

Evolution of the modular, disordered stress proteins known as dehydrins

Dehydrins, plant proteins that are upregulated during dehydration stress conditions, have modular sequences that can contain three conserved motifs (the Y-, S-, and K-segments). The presence and order of these motifs are used to classify dehydrins into one of five architectures: Kn, SKn, KnS, YnKn, and YnSKn, where the subscript n describes the number of copies of that motif. In this study, an architectural and phylogenetic analysis was performed on 426 dehydrin sequences that were identified in 53 angiosperm and 3 gymnosperm genomes. It was found that angiosperms contained all five architectures, while gymnosperms only contained Kn and SKn dehydrins. This suggests that the ancestral dehydrin in spermatophytes was either Kn or SKn, and the Y-segment containing dehydrins first arose in angiosperms. A high-level split between the YnSKn dehydrins from either the Kn or SKn dehydrins could not be confidently identified, however, two lower level architectural divisions appear to have occurred after different duplication events. The first likely occurred after a whole genome duplication, resulting in the duplication of a Y3SK2 dehydrin; the duplicate subsequently lost an S- and K- segment to become a Y3K1 dehydrin. The second split occurred after a tandem duplication of a Y1SK2 dehydrin, where the duplicate lost both the Y- and S- segment and gained four K-segments, resulting in a K6 dehydrin. We suggest that the newly arisen Y3K1 dehydrin is possibly on its way to pseudogenization, while the newly arisen K6 dehydrin developed a novel function in cold protection.

Genome-scale identification, classification, and tissue specific expression analysis of late embryogenesis abundant (LEA) genes under abiotic stress conditions in Sorghum bicolor L

Late embryogenesis abundant (LEA) proteins, the space fillers or molecular shields, are the hydrophilic protective proteins which play an important role during plant development and abiotic stress. The systematic survey and characterization revealed a total of 68 LEA genes, belonging to 8 families in Sorghum bicolor. The LEA-2, a typical hydrophobic family is the most abundant family. All of them are evenly distributed on all 10 chromosomes and chromosomes 1, 2, and 3 appear to be the hot spots. Majority of the S. bicolor LEA (SbLEA) genes are intron less or have fewer introns. A total of 22 paralogous events were observed and majority of them appear to be segmental duplications. Segmental duplication played an important role in SbLEA-2 family expansion. A total of 12 orthologs were observed with Arabidopsis and 13 with Oryza sativa. Majority of them are basic in nature, and targeted by chloroplast subcellular localization. Fifteen miRNAs targeted to 25 SbLEAs appear to participate in development, as well as in abiotic stress tolerance. Promoter analysis revealed the presence of abiotic stress-responsive DRE, MYB, MYC, and GT1, biotic stress-responsive W-Box, hormone-responsive ABA, ERE, and TGA, and development-responsive SKn cis-elements. This reveals that LEA proteins play a vital role during stress tolerance and developmental processes. Using microarray data, 65 SbLEA genes were analyzed in different tissues (roots, pith, rind, internode, shoot, and leaf) which show clear tissue specific expression. qRT-PCR analysis of 23 SbLEA genes revealed their abundant expression in various tissues like roots, stems and leaves. Higher expression was noticed in stems compared to roots and leaves. Majority of the SbLEA family members were up-regulated at least in one tissue under different stress conditions. The SbLEA3-2 is the regulator, which showed abundant expression under diverse stress conditions. Present study provides new insights into the formation of LEAs in S. bicolor and to understand their role in developmental processes under stress conditions, which may be a valuable source for future research.

Analysis of Brassica napus dehydrins and their Co-Expression regulatory networks in relation to cold stress

Dehydrins (DHNs) are plant specific cold and drought stress-responsive proteins that belong to late embryogenesis abundant (LEA) protein families. B. napus DHNs (BnDHNs) were computationally analyzed to establish gene regulatory- and protein-protein interaction networks. Promoter analyses suggested functionality of phytohormones in BnDHNs gene network. The relative expressions of some BnDHNs were analyzed using qRT-PCR in seedling leaves of both cold-tolerant (Zarfam) and -sensitive (Sari Gul) canola treated/untreated by cold. Our expression data were indicative of the importance of BnDHNs in cold tolerance in Zarfam. BnDHNs were classified into three classes according to the expression pattern. Moreover, expression of three BnDHN types, SK_n (BnLEA10 and BnLEA18), Y_nK_n (BnLEA90) and Y_nSK_n (BnLEA104) were significantly high in the tolerant cultivar at 12 h of cold treatment. Our findings put forward the possibility of considering these genes as screening biomarker to determine cold-tolerant breeding lines; something that needs to be further corroborated. Furthermore, these genes may have some implications in developing such tolerant lines via transgenesis.

An Atypical Late Embryogenesis Abundant Protein OsLEA5 Plays a Positive Role in ABA-Induced Antioxidant Defense in Oryza sativa L

OsLEA5 acts as a co-regulator of a transcriptional fact ZFP36 to enhance the expression and the activity of ascorbate peroxidase OsAPX1 to regulate seed germination in rice, but it it unknown whether OsLEA5 is also crucial in plant seedlings under stress conditions. To determine this, we generated OsLEA5 overexpression and knockdown rice plants. We found that overexpression of OsLEA5 in rice plants enhanced the tolerance to drought and salt stress; in contrast, an RNA interference (RNAi) mutant of OsLEA5 rice plants was more sensitive to drought and salinity. Further investigation found that various stimuli and ABA could induce OsLEA5 expression, and OsLEA5 acted downstream of ZFP36 to be involved in ABA-induced generation of hydrogen peroxide (H2O2), and the regulation of the expression and the activities of antioxidant defense enzymes in plants leaves, and OsLEA5 contributed to stabilize ZFP36. Additionally, OsLEA5 participates in the accumulation of ABA by up-regulating ABA biosynthesis genes and down-regulating ABA metabolism genes. Moreover, we found that two homologs of OsLEA5 (5C700, short for Os05g0526700; and 5C300, short for Os05g0584300) which were induced by ABA also interacted with ZFP36 separately; interestingly, the nuclear-located 5C700 could also act as a co-activator of ZFP36 to modulate OsAPX1, while 5C300 which was down-regulated by ABA induction acted as an ABA-induced inhibitor of ZFP36 to regulate OsAPX1. Hence, our conclusion is that OsLEA5 participates in the ABA-mediated antioxidant defense to function in drought and salt stress response in rice, and the 5C subgroup of LEAs contribute by acting as co-regulators of the transcription factor ZFP36.

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.

Expression of CdDHN4, a Novel YSK2-Type Dehydrin Gene from Bermudagrass, Responses to Drought Stress through the ABA-Dependent Signal Pathway

Dehydrin improves plant resistance to many abiotic stresses. In this study, the expression profiles of a dehydrin gene, CdDHN4, were estimated under various stresses and abscisic acid (ABA) treatments in two bermudagrasses (Cynodon dactylon L.): Tifway (drought-tolerant) and C299 (drought-sensitive). The expression of CdDHN4 was up-regulated by high temperatures, low temperatures, drought, salt and ABA. The sensitivity of CdDHN4 to ABA and the expression of CdDHN4 under drought conditions were higher in Tifway than in C299. A 1239-bp fragment, CdDHN4-P, the partial upstream sequence of the CdDHN4 gene, was cloned by genomic walking from Tifway. Bioinformatic analysis showed that the CdDHN4-P sequence possessed features typical of a plant promoter and contained many typical cis elements, including a transcription initiation site, a TATA-box, an ABRE, an MBS, a MYC, an LTRE, a TATC-box and a GT1-motif. Transient expression in tobacco leaves demonstrated that the promoter CdDHN4-P can be activated by ABA, drought and cold. These results indicate that CdDHN4 is regulated by an ABA-dependent signal pathway and that the high sensitivity of CdDHN4 to ABA might be an important mechanism enhancing the drought tolerance of bermudagrass.

Multifunctional Roles of Plant Dehydrins in Response to Environmental Stresses

To respond to environmental changes, plants have developed complex mechanisms that allow them to rapidly perceive and respond to abiotic stresses. Late embryogenesis abundant (LEA) proteins are a large and diverse family that play important roles in environmental stress tolerance in plants. Dehydrins belong to group II LEA proteins, which are considered stress proteins involved in the formation of plants' protective reactions to dehydration. Some studies have demonstrated that dehydrins could binding metal ions or lipid vesicles. In vitro experiments revealed that dehydrins could protect the activity of enzyme from damage caused by environmental stress. Although many studies have been conducted to understand their roles in abiotic stresses, the molecular function of dehydrins is still unclear. In this review, to generate new ideas for elucidating dehydrins' functions, we highlight the functional characteristics of dehydrins to understand their roles under environmental stress in plants.

Effect of HbDHN1 and HbDHN2 Genes on Abiotic Stress Responses in Arabidopsis

Dehydrin is a type of late embryogenesis abundant (LEA) protein. The dehydrin genes, HbDHN1 and HbDHN2, in Hevea brasiliensis were previously found to be induced at the wounding site of epicormic shoots, with local tissue dehydration identified as the key signal for laticifer differentiation. However, the exact role of the HbDHNs remains unknown. In this study, HbDHN1 and HbDHN2 expression was examined under multiple abiotic stresses; namely, cold, salt, drought, wounding, abscisic acid (ABA), ethylene (ET), and jasmonic acid (JA) treatment. Although, both HbDHNs were defined as SK2-type dehydrin, they showed different cellular localizations. Overexpression of the HbDHNs in Arabidopsis thaliana further revealed a significant increase in tolerance to salt, drought and osmotic stresses. Increased accumulation of proline and a reduction in electrolyte leakage were also observed under salt and drought stress, and a higher water content was indicated under osmotic stress. The transgenic plants also showed higher activity levels of ascorbate peroxidase (APX), superoxide dismutase (SOD) and catalase, and accumulated less hydrogen peroxide (H₂O₂) and superoxide ([Formula: see text]). Given that reactive oxygen species (ROS) are thought to be a key signal for laticifer differentiation, these findings suggest that HbDHNs act as ROS scavengers, directly or indirectly affecting laticifer differentiation. Both HbDHNs therefore influence physiological processes, improving plant tolerance to multiple abiotic stresses.

Salinity and High Temperature Tolerance in Mungbean [Vigna radiata (L.) Wilczek] from a Physiological Perspective

Biotic and abiotic constraints seriously affect the productivity of agriculture worldwide. The broadly recognized benefits of legumes in cropping systems-biological nitrogen fixation, improving soil fertility and broadening cereal-based agro-ecologies, are desirable now more than ever. Legume production is affected by hostile environments, especially soil salinity and high temperatures (HTs). Among legumes, mungbean has acceptable intrinsic tolerance mechanisms, but many agro-physiological characteristics of the Vigna species remain to be explored. Mungbean has a distinct advantage of being short-duration and can grow in wide range of soils and environments (as mono or relay legume). This review focuses on salinity and HT stresses on mungbean grown as a fallow crop (mungbean-rice-wheat to replace fallow-rice-wheat) and/or a relay crop in cereal cropping systems. Salinity tolerance comprises multifaceted responses at the molecular, physiological and plant canopy levels. In HTs, adaptation of physiological and biochemical processes gradually may lead to improvement of heat tolerance in plants. At the field level, managing or manipulating cultural practices can mitigate adverse effects of salinity and HT. Greater understanding of physiological and biochemical mechanisms regulating these two stresses will contribute to an evolving profile of the genes, proteins, and metabolites responsible for mungbean survival. We focus on abiotic stresses in legumes in general and mungbean in particular, and highlight gaps that need to be bridged through future mungbean research. Recent findings largely from physiological and biochemical fronts are examined, along with a few agronomic and farm-based management strategies to mitigate stress under field conditions.

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.

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.

Differential regulation of dehydrin expression and trehalose levels in Cardinal table grape skin by low temperature and high CO2

Dehydrins and trehalose are multifunctional protective biomolecules that play a role in counteracting cellular damage during dehydrative stresses. In this paper, we studied dehydrin isoform patterns, dehydrin gene expression and trehalose levels in the skin of Cardinal (Vitis vinifera L.) table grapes, along with their regulation by different cold postharvest storage conditions. Immunoanalysis with K-segment antibody recognizes four constitutive dehydrins (from 17 to 44 kDa) that are tightly regulated by low temperature and high CO2. Phosphatase treatment showed that DHN44 and DHN22 isoforms are phosphorylated polypeptides, while MALDI-TOF MS and MS/MS analysis suggested that 44 kDa polypeptide may be a dehydrin homodimer. At the transcriptional level, dehydrins are also regulated by low temperature and high CO2, showing a fairly good correlation with their mRNA levels. Trehalose was quantified by high performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD), revealing a progressive increase of this metabolite throughout storage at 0 °C and the sudden transitory increases in short-term high CO2-treated fruit. We propose that the constitutive presence and up-regulation of dehydrins and trehalose during low temperature postharvest storage could be positively correlated with the relative chilling tolerance of table grapes and the adaptive responses activated by high CO2 levels to preserve cell water status and to counteract the disruption of physiological processes during cold storage.

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.

The crucial role of Φ- and K-segments in the in vitro functionality of Vitis vinifera dehydrin DHN1a

Dehydrins (DHNs), group II LEA (Late Embryogenesis Abundant) proteins, are among the most commonly observed proteins which accumulate in plants in response to cold and any other environmental factors, causing the dehydration of cells. In previous studies, we isolated a YSK2-type VvcDHN1a gene from table grapes (Vitis vinifera cv. Cardinal) which presented two spliced variants (the spliced, DHN1a_s and the unspliced, DHN1a_u). Their expression was induced by low temperature storage and CO2, although with different accumulation patterns. DHN1a_u codifies for a truncated YS protein lacking Ф- and K-segments, which might affect its functionality. In this work, we expressed both DHN1a_s and DHN1a_u recombinant proteins in Escherichia coli. We carried out a number of in vitro assays to analyze the implications that Ф- and K-segments have in the protective role of VvcDHN1 against different abiotic stresses and their antifungal activity against the fungal pathogen Botrytis cinerea. Our results showed that unlike DHN1a_u, DHN1a_s has a potent cryoprotective effect on lactate dehydrogenase activity, protects malate dehydrogenase against dehydration and partially inhibits B. cinerea growth. Moreover, the DHN1a promoter presented cis-regulatory elements related to cold and drought, as well as biotic stress-related elements. We also observed that both spliced variants interact weakly with DNA, suggesting that K-segments are not involved in DNA binding. Overall, this work highlights the crucial role of Ф- and K-segments in DHNs function in plant response to abiotic stress showing for the first time, the potential role of the V. vinifera DHN1a_s in the protection against freezing and dehydration as well as inhibiting B. cinerea growth.

Transplastomic Nicotiana benthamiana plants expressing multiple defence genes encoding protease inhibitors and chitinase display broad-spectrum resistance against insects, pathogens and abiotic stresses

Plastid engineering provides several advantages for the next generation of transgenic technology, including the convenient use of transgene stacking and the generation of high expression levels of foreign proteins. With the goal of generating transplastomic plants with multiresistance against both phytopathogens and insects, a construct containing a monocistronic patterned gene stack was transformed into Nicotiana benthamiana plastids harbouring sweet potato sporamin, taro cystatin and chitinase from Paecilomyces javanicus. Transplastomic lines were screened and characterized by Southern/Northern/Western blot analysis for the confirmation of transgene integration and respective expression level. Immunogold localization analyses confirmed the high level of accumulation proteins that were specifically expressed in leaf and root plastids. Subsequent functional bioassays confirmed that the gene stacks conferred a high level of resistance against both insects and phytopathogens. Specifically, larva of Spodoptera litura and Spodoptera exigua either died or exhibited growth retardation after ingesting transplastomic plant leaves. In addition, the inhibitory effects on both leaf spot diseases caused by Alternaria alternata and soft rot disease caused by Pectobacterium carotovorum subsp. carotovorum were markedly observed. Moreover, tolerance to abiotic stresses such as salt/osmotic stress was highly enhanced. The results confirmed that the simultaneous expression of sporamin, cystatin and chitinase conferred a broad spectrum of resistance. Conversely, the expression of single transgenes was not capable of conferring such resistance. To the best of our knowledge, this is the first study to demonstrate an efficacious stacked combination of plastid-expressed defence genes which resulted in an engineered tolerance to various abiotic and biotic stresses.

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.

Purification and biochemical characterization of Arabidopsis At-NEET, an ancient iron-sulfur protein, reveals a conserved cleavage motif for subcellular localization

CDGSH iron-sulfur domain-containing proteins (CISDs) are newly discovered proteins with electron-accepting and electron-donating moieties. Although the CISDs of plants and animals show high sequence similarity in their CDGSH domain at the C-terminus, their N-terminal peptides have low sequence homology. Here, we show that At-NEET, a recently identified Arabidopsis CISD, contains a cleavable N-terminal peptide for chloroplast targeting, which is different from the uncleavable N-terminal peptide of mammal CISDs for mitochondrial outer membrane localization. Using affinity purification to isolate endogenous At-NEET, we identified a consensus sequence for the chloroplast transit peptide cleavage site of V-[R/K]↓A-E in At-NEET as well as other plant CISDs. Moreover, chloroplast subfractionation and immunogold labeling experiments showed that At-NEET localizes to the stroma of chloroplast. In addition, biochemical characterization revealed that At-NEET contains a conserved Cys(3)-His(1) ligand in the CDGSH domain, which is essential for coordination of 2Fe-2S clusters and protein folding. Our findings suggest that plant and animal CISDs contain an evolutionarily conserved CDGSH domain. However, they show different subcellular localization patterns that may result in distinct physiological functions.

ZmLEA3, a multifunctional group 3 LEA protein from maize (Zea mays L.), is involved in biotic and abiotic stresses

Late embryogenesis abundant (LEA) proteins accumulate to high levels during the late stage of seed maturation and in response to water deficit, and are involved in protecting higher plants from damage caused by environmental stresses, especially drought. In the present study, a novel maize (Zea mays L.) group 3 LEA gene, ZmLEA3, was identified and later characterized using transgenic tobacco plants to investigate its functions in abiotic and biotic stresses. Transcript accumulation demonstrated that ZmLEA3 was induced in leaves by high salinity, low temperature, osmotic and oxidative stress as well as by signaling molecules such as ABA, salicylic acid (SA) and methyl jasmonate (MeJA). The transcript of ZmLEA3 could also be induced by pathogens [Pseudomonas syringae pv. tomato DC3000 (pst dc3000)]. ZmLEA3 is located in the cytosol and the nucles. Further study indicated that the ZmLEA3 protein could bind Mn(2+), Fe(3+), Cu(2+) and Zn(2+). Overexpression of ZmLEA3 in transgenic tobacco (Nicotiana tabacum) and yeast (GS115) conferred tolerance to osmotic and oxidative stresses. Interestingly, we also found that overexpression of ZmLEA3 in transgenic tobacco increased the hypersensitive cell death triggered by pst dc3000 and enhanced the expression of PR1a, PR2 and PR4 when compared with the wild type. Thus, we proposed that the ZmLEA3 protein plays a role in protecting plants from damage by protecting protein structure and binding metals under osmotic and oxidative stresses. In addition, ZmLEA3 may also enhance transgenic plant tolerance to biotic stress.

Mining genes involved in the stratification of Paris polyphylla seeds using high-throughput embryo transcriptome sequencing

Background

Paris polyphylla var. yunnanensis is an important medicinal plant. Seed dormancy is one of the main factors restricting artificial cultivation. The molecular mechanisms of seed dormancy remain unclear, and little genomic or transcriptome data are available for this plant.

Results

In this study, massive parallel pyrosequencing on the Roche 454-GS FLX Titanium platform was used to generate a substantial sequence dataset for the P. polyphylla embryo. 369,496 high quality reads were obtained, ranging from 50 to 1146 bp, with a mean of 219 bp. These reads were assembled into 47,768 unigenes, which included 16,069 contigs and 31,699 singletons. Using BLASTX searches of public databases, 15,757 (32.3%) unique transcripts were identified. Gene Ontology and Cluster of Orthologous Groups of proteins annotations revealed that these transcripts were broadly representative of the P. polyphylla embryo transcriptome. The Kyoto Encyclopedia of Genes and Genomes assigned 5961 of the unique sequences to specific metabolic pathways. Relative expression levels analysis showed that eleven phytohormone-related genes and five other genes have different expression patterns in the embryo and endosperm in the seed stratification process.

Conclusions

Gene annotation and quantitative RT-PCR expression analysis identified 464 transcripts that may be involved in phytohormone catabolism and biosynthesis, hormone signal, seed dormancy, seed maturation, cell wall growth and circadian rhythms. In particular, the relative expression analysis of sixteen genes (CYP707A, NCED, GA20ox2, GA20ox3, ABI2, PP2C, ARP3, ARP7, IAAH, IAAS, BRRK, DRM, ELF1, ELF2, SFR6, and SUS) in embryo and endosperm and at two temperatures indicated that these related genes may be candidates for clarifying the molecular basis of seed dormancy in P. polyphlla var. yunnanensis.

A KS-type dehydrin and its related domains reduce Cu-promoted radical generation and the histidine residues contribute to the radical-reducing activities

Dehydrin is a plant disordered protein whose functions are not yet totally understood. Here it is reported that a KS-type dehydrin can reduce the formation of reactive oxygen species (ROS) from Cu. AtHIRD11, which is the Arabidopsis KS-type dehydrin, inhibited generation of hydrogen peroxide and hydroxyl radicals in the Cu-ascorbate system. The radical-reducing activity of AtHIRD11 was stronger than those of radical-silencing peptides such as glutathione and serum albumin. The addition of Cu(2+) reduced the disordered state, decreased the trypsin susceptibility, and promoted the self-association of AtHIRD11. Domain analyses indicated that the five domains containing histidine showed ROS-reducing activities. Histidine/alanine substitutions indicated that histidine is a crucial residue for reducing ROS generation. Using the 27 peptides which are related to the KnS-type dehydrins of 14 plant species, it was found that the strengths of ROS-reducing activities can be determined by two factors, namely the histidine contents and the length of the peptides. The degree of ROS-reducing activities of a dehydrin can be predicted using these indices.

Late Embryogenesis Abundant (LEA) proteins in legumes

Plants are exposed to different external conditions that affect growth, development, and productivity. Water deficit is one of these adverse conditions caused by drought, salinity, and extreme temperatures. Plants have developed different responses to prevent, ameliorate or repair the damage inflicted by these stressful environments. One of these responses is the activation of a set of genes encoding a group of hydrophilic proteins that typically accumulate to high levels during seed dehydration, at the last stage of embryogenesis, hence named Late Embryogenesis Abundant (LEA) proteins. LEA proteins also accumulate in response to water limitation in vegetative tissues, and have been classified in seven groups based on their amino acid sequence similarity and on the presence of distinctive conserved motifs. These proteins are widely distributed in the plant kingdom, from ferns to angiosperms, suggesting a relevant role in the plant response to this unfavorable environmental condition. In this review, we analyzed the LEA proteins from those legumes whose complete genomes have been sequenced such as Phaseolus vulgaris, Glycine max, Medicago truncatula, Lotus japonicus, Cajanus cajan, and Cicer arietinum. Considering their distinctive motifs, LEA proteins from the different groups were identified, and their sequence analysis allowed the recognition of novel legume specific motifs. Moreover, we compile their transcript accumulation patterns based on publicly available data. In spite of the limited information on these proteins in legumes, the analysis and data compiled here confirm the high correlation between their accumulation and water deficit, reinforcing their functional relevance under this detrimental conditions.