Plant dehydrins — Tissue location, structure and function

Dehydrins (DHNs) are part of a large group of highly hydrophilic proteins known as LEA (Late Embryogenesis Abundant). They were originally identified as group II of the LEA proteins. The distinctive feature of all DHNs is a conserved, lysine-rich 15-amino acid domain, EKKGIMDKIKEKLPG, named the K-segment. It is usually present near the C-terminus. Other typical dehydrin features are: a track of Ser residues (the S-segment); a consensus motif, T/VDEYGNP (the Y-segment), located near the N-terminus; and less conserved regions, usually rich in polar amino acids (the Φ-segments). They do not display a well-defined secondary structure. The number and order of the Y-, S-and K-segments define different DHN sub-classes: Y_nSK_n, Y_nKn, SK_n, K_n and K_nS. Dehydrins are distributed in a wide range of organisms including the higher plants, algae, yeast and cyanobacteria. They accumulate late in embryogenesis, and in nearly all the vegetative tissues during normal growth conditions and in response to stress leading to cellular dehydration (e.g. drought, low temperature and salinity). DHNs are localized in different cell compartments, such as the cytosol, nucleus, mitochondria, vacuole, and the vicinity of the plasma membrane; however, they are primarily localized to the cytoplasm and nucleus. The precise function of dehydrins has not been established yet, but in vitro experiments revealed that some DHNs (YSK_n-type) bind to lipid vesicles that contain acidic phospholipids, and others (K_nS) were shown to bind metals and have the ability to scavenge hydroxyl radicals [Asghar, R. et al. Protoplasma 177 (1994) 87–94], protect lipid membranes against peroxidation or display cryoprotective activity towards freezing-sensitive enzymes. The SK_n-and K-type seem to be directly involved in cold acclimation processes. The main question arising from the in vitro findings is whether each DHN structural type could possess a specific function and tissue distribution. Much recent in vitro data clearly indicates that dehydrins belonging to different subclasses exhibit distinct functions. An erratum to this article is available at .     

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.     

Identification and transcriptional analysis of dehydrin gene family in cucumber (<Emphasis Type="Italic">Cucumis sativus</Emphasis>)

Dehydrins (DHNs) are a group II late embryogenesis abundant (LEA) proteins that play essential roles in plant growth, development and responses to diverse environmental stimuli. Here, four DHNs in cucumber genome were identified using bioinformatics-based methods according to the highly conserved K-, Y- and S-segments, including 1 Y_nK_n-type, 2 Y_nSK_n-type, and 1 SK_n-type DHNs. All of them are intrinsically disordered proteins (IDPs) and possess a large number of disorder-promoting amino acids. Secondary structure prediction revealed that each of them is composed of high proportion of alpha helix and random coil. Gene structure and phylogenetic analyses with DHNs from cucumber and several other species revealed that some closely related DHN genes had similar gene structures. A number of cis-elements involved in stress responses and phytohormones were found in each CsDHN promoter. The tissue expression profiles suggested that the CsDHN genes have overlapping, but different expression patterns. qRT-PCR results showed that three selected CsDHN genes could respond to heat, cold, osmotic and salt stresses, as well as to signaling molecules such as H₂O₂ and ABA. These results lay a solid foundation for future functional investigation of the cucumber dehydrin gene family in tissue development and stress responses in plants.     

Potato dehydrins present high intrinsic disorder and are differentially expressed under ABA and abiotic stresses

Dehydrins (DHNs) correspond to late embryogenesis abundant proteins (LEA) of group 2, they are known as glycin rich proteins. Despite their expression during the late seed maturation stages, they are also involved in plant response to a number of abiotic stresses such as drought, salinity and cold. In the present study, we identified five full-length cDNAs encoding dehydrins (designated StDHN2a, StDHN1, TAS14, StDHN25 and StLEA27) isolated from potato. These dehydrins were composed of serine amino acids called S domain and lysine-rich segment corresponding to a K domain. Three DHNs (StDHN1, TAS14 and StLEA27) contained Y segments. In silico analysis showed that these StDHN sequences share high homology with other Solanum dehydrin proteins species. The analysis of gene expression using quantitative RT-PCR showed that they were upregulated by dehydration and salinity. Moreover, the search for putative regulatory element in the promoter sequence of dehydrin genes was investigated.     

A dehydrin cognate protein from pea (Pisum sativum L.) with an atypical pattern of expression

Dehydrins are a family of proteins characterised by conserved amino acid motifs, and induced in plants by dehydration or treatment with ABA. An antiserum was raised against a synthetic oligopeptide based on the most highly conserved dehydrin amino acid motif, the lysine-rich block (core sequence KIKEK-LPG). This antiserum detected a novel M _r 40 000 polypeptide and enabled isolation of a corresponding cDNA clone, pPsB61 (B61). The deduced amino acid sequence contained two lysine-rich blocks, however the remainder of the sequence differed markedly from other pea dehydrins. Surprisingly, the sequence contained a stretch of serine residues, a characteristic common to dehydrins from many plant species but which is missing in pea dehydrin.The expression patterns of B61 mRNA and polypeptide were distinctively different from those of the pea dehydrins during seed development, germination and in young seedlings exposed to dehydration stress or treated with ABA. In particular, dehydration stress led to slightly reduced levels of B61 RNA, and ABA application to young seedlings had no marked effect on its abundance.The M _r 40 000 polypeptide is thus related to pea dehydrin by the presence of the most highly conserved amino acid sequence motifs, but lacks the characteristic expression pattern of dehydrin. By analogy with heat shock cognate proteins we refer to this protein as a dehydrin cognate.     

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.     

Dehydrin genes and their expression in recalcitrant oak (<Emphasis Type="Italic">Quercus robur</Emphasis>) embryos

In this work, three dehydrin genes, QrDhn1, QrDhn2, QrDhn3, were isolated from recalcitrant oak (Quercus robur). Their expression pattern was analyzed in both zygotic and somatic embryos as well as in vegetative tissues exposed to different kinds of abiotic stresses including desiccation, osmotic stress, and chilling. The QrDhn1 gene encoding for Y_nSK_n type dehydrin was expressed during later stages of zygotic embryo development but in somatic embryos only when exposed to osmotic or desiccation stress. In contrast, the other two oak dehydrin genes encoding for putative K_n type dehydrins were expressed only in somatic embryos (both not-treated and osmotically stressed) and leaves of oak seedlings exposed to desiccation. Behavior of these genes suggests that different dehydrins are involved in processes of seed maturation and response to altered osmotic (water status) conditions in somatic embryos. Revealing further members of dehydrin gene family in recalcitrant oak might contribute to clarify non-orthodox seed behavior as well as identify mechanisms contributing to desiccation tolerance in plants.     

Oxidative stress protective function of ApY2SK2 dehydrin: a late embryogenesis abundant protein in embryogenic callus of Agapanthus praecox to promote post-cryopreservation survival

Dehydrins (DHNs) as the member of the late embryogenesis abundant protein family, play critical roles in seed dehydration protection and plant adaptation to multiple abiotic stresses. As an important method of germplasm preservation, cryopreservation is also an ideal research system to study compound stress. Oxidative stress, as the critical stress in cryopreservation, directly affects cell viability. Our previous in vitro tests indicated that ApY₂SK₂ DHN can effectively protect enzyme activity and almost double the survival rate of Arabidopsis thaliana seedlings after cryopreservation, but the in vivo protective effect of ApY₂SK₂ on cryopreservation have not yet been elucidated. In this study, ApY₂SK₂ type DHN was genetically transformed into embryogenic callus (EC) of Agapanthus praecox by overexpression (OE) and RNA interference (RNAi) techniques to evaluate the in vivo oxidative stress protective effect of DHNs during cryopreservation. The results showed that the cell viability had a completely opposite trend between OE and RNAi cell lines, and the cell relative death ratio of ApY₂SK₂-OE EC was significantly decreased 18.5% and ApY₂SK₂-RNAi cells was significantly increased 23.5% after cryopreservation. Overexpression ApY₂SK₂ increased non-enzymatic antioxidant (AsA and GSH) contents, antioxidant enzyme (POD and SOD) activities and up-regulated CAT, POD and GPX expression, while ApY₂SK₂-RNAi cells decreased CAT, FeSOD, POD and GPX expression during cryopreservation. These findings suggested that ApY₂SK₂ can affect ROS metabolism, alleviate H₂O₂ and OH·excessive generation, activate the antioxidant system, improve cellular REDOX balance and reduce membrane lipid peroxidation damage of plant cells during cryopreservation. DHNs can effectively improve cell stress tolerance and have great potential for in vivo or in vitro applications in plant cryopreservation.

     

Plant dehydrins and stress tolerance: Versatile proteins for complex mechanisms

Dehydrins (DHNs), or group 2 LEA (Late Embryogenesis Abundant) proteins, play a fundamental role in plant response and adaptation to abiotic stresses. They accumulate typically in maturing seeds or are induced in vegetative tissues following salinity, dehydration, cold and freezing stress. The generally accepted classification of dehydrins is based on their structural features, such as the presence of conserved sequences, designated as Y, S and K segments. The K segment representing a highly conserved 15 amino acid motif forming amphiphilic a-helix is especially important since it has been found in all dehydrins. Since more than 20 y, they are thought to play an important protective role during cellular dehydration but their precise function remains unclear. This review outlines the current status of the progress made toward the structural, physico-chemical and functional characterization of plant dehydrins and how these features could be exploited in improving stress tolerance in plants.Key words: abiotic stress, dehydration stress, drought, cold acclimation, freezing tolerance, LEA proteins, dehydrins     

Genome-wide Identification and Characterization of a Dehydrin Gene Family in Poplar (Populus trichocarpa)

Dehydrins (DHNs) define a complex group of stress inducible proteins characterized by the presence of one or more lysine-rich motifs. DHNs are present in multiple copies in the genome of plant species. Although genome-wide analysis of DHNs composition and chromosomal distribution has been conducted in herbaceous species, it remains unexplored in woody plants. Here, we report on the identification of ten genes encoding eleven putative DHN polypeptides in Populus. We document that DHN genes occur as duplicated blocks distributed over seven of the 19 poplar chromosomes likely as a result of segmental and tandem duplication events. Based on conserved motifs, poplar DHNs were assigned to four subgroups with the K_n subgroup being the most frequent. One putative DHN polypeptide (PtrDHN-10) with a SKS arrangement could originate from a recombination between SK_n and K_nS genes. In silico analysis of microarray data showed that in unstressed poplar, DHN genes are expressed in all vegetative tissues except for mature leaves. This exhaustive survey of DHN genes in poplar provides important information that will assist future studies on their functional role in poplar.     

大麦Dhn6基因的克隆、蛋白质结构预测与干旱胁迫表达模式

脱水素(Dehydrins,DHNs)是高等植物胚胎发育晚期产生的一类特异多肽,其表达累积程度与植物的发育阶段、低温、ABA和脱水信号调节等因素密切相关。为了解脱水素的结构与干旱胁迫表达累积反应,文章从六棱大麦分离到序列全长为1 767 bp的Dhn6基因,序列分析结果表明,该基因含一个92 bp内含子,90~1 759 bp为一个开放阅读框,与裸大麦Dhn6基因(GenBank登录号:AF043091)的同源性最高,达93.18%,编码523个氨基酸残基的多肽,预测蛋白质的分子量为49.68 kDa,理论等电点为8.04。结构分析发现,蛋白质具有3个螺旋区,无规则卷曲构成二级结构的主要组分,亲水氨基酸比例超过83%;三维结构预测发现,多肽链自身反向平行排列成松散的亲水索链,K-片段参与兼性?-螺旋结构域的形成,意味着该脱水素具有束缚自由水、稳定细胞膜相结构的功能。实时定量RT-PCR检测结果表明,Dhn6基因的相对表达水平在干旱处理8 h快速累积,推测DHN6在大麦对干旱胁迫的早期响应中发挥重要功能。     

Expression analysis of dehydrin multigene family across tolerant and susceptible barley (Hordeum vulgare L.) genotypes in response to terminal drought stress

Dehydrins are one of the characteristic families of plant proteins that usually accumulate in response to drought. In the present study, gene expressions of dehydrin multigene family (13 genes) were examined in flag leaves of tolerant (Yousef) and susceptible (Moroco) barley varieties under terminal drought to characterize the involvement of dehydrins in the adaptive processes. The stomatal conductance, RWC, and Chl a, b contents had more reduction in Moroco than the Yousef which has more elevated osmotic adjustment. Drought stress increased significantly MDA and electrolyte leakage levels, but greater in Moroco, indicating a poor protection of cell and cytoplasmic membrane in this variety. Yousef variety had no reduction in grain yield under drought condition. Five genes (Dhn1, Dhn3, Dhn5, Dhn7 and Dhn9) were exclusively induced in Yousef under drought stress. In the stress condition, relative gene expression of Dhn3, Dhn9 had the direct correlations (P < 0.05) with Chl a, b contents, osmotic adjustment, stomatal conductance, plant biomass and grain yield, and the negative correlations (P < 0.05) with MDA and electrolyte leakage levels. The results supported the impending functional roles of dehydrin K_n and particularly Y_nSK_n types in dehydration tolerance of barley during the reproductive stage.