Evolution of the modular, disordered stress proteins known as dehydrins

Order in Chaos: Lesser-Conserved and Repeat Structures in Dehydrins

Dehydrins (Dhns) are a group of intrinsically disordered land plant proteins that are closely associated with tolerance of dehydrative stress. Dhns are recognized and classified by the presence and sequence of five different conserved segments, varying in length from 8 to 15 residues, separated by highly variable disordered regions. In addition to one or more copies of the diagnostic, fifteen-residue K segment, most Dhns can be classified into one of three major groups based on the mutually exclusive presence of three other conserved segments (H, Y, or F), with all three groups typically incorporating multi-serine S segments. Many Dhns also include repeat structures. From an input library of 8675 non-redundant candidate sequences, a specialized R script identified and classified 2658 complete and 236 partial Dhn sequences in all major green plant (Viridiplantae) lineages, including a few green algal genera. An examination of the connecting segments bridging the conserved segments identified additional conserved patterns, suggesting that multi-Y, S-K, and K-S domains may act as functional units. Dhn Decoder identified 857 Dhns with repeat structures, ranging from 3 short, simple repeats to elaborate variations with up to 45 repeats or repeats of up to 85 residues comprising 1 or more of the conserved segments, suggesting that internal sequence duplication is an important mode of evolution in Dhns.

New Insights into Involvement of Low Molecular Weight Proteins in Complex Defense Mechanisms in Higher Plants

Dynamic climate changes pose a significant challenge for plants to cope with numerous abiotic and biotic stressors of increasing intensity. Plants have evolved a variety of biochemical and molecular defense mechanisms involved in overcoming stressful conditions. Under environmental stress, plants generate elevated amounts of reactive oxygen species (ROS) and, subsequently, modulate the activity of the antioxidative enzymes. In addition, an increase in the biosynthesis of important plant compounds such as anthocyanins, lignin, isoflavonoids, as well as a wide range of low molecular weight stress-related proteins (e.g., dehydrins, cyclotides, heat shock proteins and pathogenesis-related proteins), was evidenced. The induced expression of these proteins improves the survival rate of plants under unfavorable environmental stimuli and enhances their adaptation to sequentially interacting stressors. Importantly, the plant defense proteins may also have potential for use in medical applications and agriculture (e.g., biopesticides). Therefore, it is important to gain a more thorough understanding of the complex biological functions of the plant defense proteins. It will help to devise new cultivation strategies, including the development of genotypes characterized by better adaptations to adverse environmental conditions. The review presents the latest research findings on selected plant defense proteins.

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.

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.

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.

Flooding and herbivory: the effect of concurrent stress factors on plant volatile emissions and gene expression in two heirloom tomato varieties

BACKGROUND

In nature and in cultivated fields, plants encounter multiple stress factors. Nonetheless, our understanding of how plants actively respond to combinatorial stress remains limited. Among the least studied stress combination is that of flooding and herbivory, despite the growing importance of these stressors in the context of climate change. We investigated plant chemistry and gene expression changes in two heirloom tomato varieties: Cherokee Purple (CP) and Striped German (SG) in response to flooding, herbivory by Spodoptera exigua, and their combination.

RESULTS

Volatile organic compounds (VOCs) identified in tomato plants subjected to flooding and/or herbivory included several mono- and sesquiterpenes. Flooding was the main factor altering VOCs emission rates, and impacting plant biomass accumulation, while different varieties had quantitative differences in their VOC emissions. At the gene expression levels, there were 335 differentially expressed genes between the two tomato plant varieties, these included genes encoding for phenylalanine ammonia-lyase (PAL), cinnamoyl-CoA-reductase-like, and phytoene synthase (Psy1). Flooding and variety effects together influenced abscisic acid (ABA) signaling genes with the SG variety showing higher levels of ABA production and ABA-dependent signaling upon flooding. Flooding downregulated genes associated with cytokinin catabolism and general defense response and upregulated genes associated with ethylene biosynthesis, anthocyanin biosynthesis, and gibberellin biosynthesis. Combining flooding and herbivory induced the upregulation of genes including chalcone synthase (CHS), PAL, and genes encoding BAHD acyltransferase and UDP-glucose iridoid glucosyltransferase-like genes in one of the tomato varieties (CP) and a disproportionate number of heat-shock proteins in SG. Only the SG variety had measurable changes in gene expression due to herbivory alone, upregulating zeatin, and O-glucosyltransferase and thioredoxin among others.

CONCLUSION

Our results suggest that both heirloom tomato plant varieties differ in their production of secondary metabolites including phenylpropanoids and terpenoids and their regulation and activation of ABA signaling upon stress associated with flooding. Herbivory and flooding together had interacting effects that were evident at the level of plant chemistry (VOCs production), gene expression and biomass markers. Results from our study highlight the complex nature of plant responses to combinatorial stresses and point at specific genes and pathways that are affected by flooding and herbivory combined.

The Effect of Positive Charge Distribution on the Cryoprotective Activity of Dehydrins

Dehydrins are intrinsically disordered proteins expressed ubiquitously throughout the plant kingdom in response to desiccation. Dehydrins have been found to have a cryoprotective effect on lactate dehydrogenase (LDH) in vitro, which is in large part influenced by their hydrodynamic radius rather than the order of the amino acids within the sequence (alternatively, this may be a sequence specific effect). However, it seems that a different mechanism may underpin the cryoprotection that they confer to the cold-labile yeast frataxin homolog-1 (Yfh1). Circular dichroism spectroscopy (CD) was used to assess the degree of helicity of Yfh1 at 1 °C, both alone and in the presence of several dehydrin constructs. Three constructs were compared to the wild type: YSK₂-K→R (lysine residues substituted with arginine), YSK₂-Neutral (locally neutralized charge), and YSK₂-SpaceK (evenly distributed positive charge). The results show that sequence rearrangements and minor substitutions have little impact on the ability of the dehydrin to preserve LDH activity. However, when the positive charge of the dehydrin is locally neutralized or evenly distributed, the dehydrin becomes less efficient at promoting structure in Yfh1 at low temperatures. This suggests that a stabilizing, charge-based interaction occurs between dehydrins and Yfh1. Dehydrins are intrinsically disordered proteins, expressed by certain organisms to improve desiccation tolerance. These proteins are thought to serve many cellular roles, such as the stabilization of membranes, DNA, and proteins. However, the molecular mechanisms underlying the function of dehydrins are not well understood. Here, we examine the importance of positive charges in dehydrin sequences by making substitutions and comparing their effects in the cryoprotection of two different proteins.

Distinct Tomato Cultivars Are Characterized by a Differential Pattern of Biochemical Responses to Drought Stress

Future climate scenarios suggest that crop plants will experience environmental changes capable of affecting their productivity. Among the most harmful environmental stresses is drought, defined as a total or partial lack of water availability. It is essential to study and understand both the damage caused by drought on crop plants and the mechanisms implemented to tolerate the stress. In this study, we focused on four cultivars of tomato, an economically important crop in the Mediterranean basin. We investigated the biochemical mechanisms of plant defense against drought by focusing on proteins specifically involved in this stress, such as osmotin, dehydrin, and aquaporin, and on proteins involved in the general stress response, such as HSP70 and cyclophilins. Since sugars are also known to act as osmoprotectants in plant cells, proteins involved in sugar metabolism (such as RuBisCO and sucrose synthase) were also analyzed. The results show crucial differences in biochemical behavior among the selected cultivars and highlight that the most tolerant tomato cultivars adopt quite specific biochemical strategies such as different accumulations of aquaporins and osmotins. The data set also suggests that RuBisCO isoforms and aquaporins can be used as markers of tolerance/susceptibility to drought stress and be used to select tomato cultivars within breeding programs.

Physiological, Structural, and Functional Insights Into the Cryoprotection of Membranes by the Dehydrins

Plants can be exposed to cold temperatures and have therefore evolved several mechanisms to prevent damage caused by freezing. One of the most important targets are membranes, which are particularly susceptible to cold damage. To protect against such abiotic stresses, plants express a family of proteins known as late embryogenesis abundant (LEA) proteins. Many LEA proteins are intrinsically disordered, that is, they do not contain stable secondary or tertiary structures alone in solution. These proteins have been shown in a number of studies to protect plants from damage caused by cold, drought, salinity, and osmotic stress. In this family, the most studied proteins are the type II LEA proteins, better known as dehydrins (dehydration-induced proteins). Many physiological studies have shown that dehydrins are often located near the membrane during abiotic stress and that the expression of dehydrins helps to prevent the formation of oxidation-modified lipids and reduce the amount of electrolyte leakage, two hallmarks of damaged membranes. One of the earliest biophysical clues that dehydrins are involved in membrane cryoprotection came from in vitro studies that demonstrated a binding interaction between the protein and membranes. Subsequent work has shown that one conserved motif, known as K-segments, is involved in binding, while recent studies have used NMR to explore the residue specific structure of dehydrins when bound to membranes. The biophysical techniques also provide insight into the mechanism by which dehydrins protect the membrane from cold stress, which appears to mainly involve the lowering of the transition temperature.

The Halophyte Dehydrin Sequence Landscape

Dehydrins (DHNs) belong to the LEA (late embryogenesis abundant) family group II, that comprise four conserved motifs (the Y-, S-, F-, and K-segments) and are known to play a multifunctional role in plant stress tolerance. Based on the presence and order of these segments, dehydrins are divided into six subclasses: YnSKn, FnSKn, YnKn, SKn, Kn, and KnS. DHNs are rarely studied in halophytes, and their contribution to the mechanisms developed by these plants to survive in extreme conditions remains unknown. In this work, we carried out multiple genomic analyses of the conservation of halophytic DHN sequences to discover new segments, and examine their architectures, while comparing them with their orthologs in glycophytic plants. We performed an in silico analysis on 86 DHN sequences from 10 halophytic genomes. The phylogenetic tree showed that there are different distributions of the architectures among the different species, and that FSKn is the only architecture present in every plant studied. It was found that K-, F-, Y-, and S-segments are highly conserved in halophytes and glycophytes with a few modifications, mainly involving charged amino acids. Finally, expression data collected for three halophytic species (Puccinillia tenuiflora, Eutrema salsugenium, and Hordeum marinum) revealed that many DHNs are upregulated by salt stress, and the intensity of this upregulation depends on the DHN architecture.

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.

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.

Evolutionary analysis of angiosperm dehydrin gene family reveals three orthologues groups associated to specific protein domains

Dehydrins (DHNs) are a family of plant proteins that play important roles on abiotic stress tolerance and seed development. They are classified into five structural subgroups: K-, SK-, YK-, YSK-, and KS-DHNs, according to the presence of conserved motifs named K-, Y- and S- segments. We carried out a comparative structural and phylogenetic analysis of these proteins, focusing on the less-studied KS-type DHNs. A search for conserved motifs in DHNs from 56 plant genomes revealed that KS-DHNs possess a unique and highly conserved N-terminal, 15-residue amino acid motif, not previously described. This novel motif, that we named H-segment, is present in DHNs of angiosperms, gymnosperms and lycophytes, suggesting that HKS-DHNs were present in the first vascular plants. Phylogenetic and microsynteny analyses indicate that the five structural subgroups of angiosperm DHNs can be assigned to three groups of orthologue genes, characterized by the presence of the H-, F- or Y- segments. Importantly, the hydrophilin character of DHNs correlate with the phylogenetic origin of the DHNs rather than to the traditional structural subgroups. We propose that angiosperm DHNs can be ultimately subdivided into three orthologous groups, a phylogenetic framework that should help future studies on the evolution and function of this protein family.

Comparative Genomics, Evolution, and Drought-Induced Expression of Dehydrin Genes in Model Brachypodium Grasses

Dehydration proteins (dehydrins, DHNs) confer tolerance to water-stress deficit in plants. We performed a comparative genomics and evolutionary study of DHN genes in four model Brachypodium grass species. Due to limited knowledge on dehydrin expression under water deprivation stress in Brachypodium, we also performed a drought-induced gene expression analysis in 32 ecotypes of the genus' flagship species B. distachyon showing different hydric requirements. Genomic sequence analysis detected 10 types of dehydrin genes (Bdhn) across the Brachypodium species. Domain and conserved motif contents of peptides encoded by Bdhn genes revealed eight protein architectures. Bdhn genes were spread across several chromosomes. Selection analysis indicated that all the Bdhn genes were constrained by purifying selection. Three upstream cis-regulatory motifs (BES1, MYB124, ZAT) were detected in several Bdhn genes. Gene expression analysis demonstrated that only four Bdhn1-Bdhn2, Bdhn3, and Bdhn7 genes, orthologs of wheat, barley, rice, sorghum, and maize genes, were expressed in mature leaves of B. distachyon and that all of them were more highly expressed in plants under drought conditions. Brachypodium dehydrin expression was significantly correlated with drought-response phenotypic traits (plant biomass, leaf carbon and proline contents and water use efficiency increases, and leaf water and nitrogen content decreases) being more pronounced in drought-tolerant ecotypes. Our results indicate that dehydrin type and regulation could be a key factor determining the acquisition of water-stress tolerance in grasses.

Plant Group II LEA Proteins: Intrinsically Disordered Structure for Multiple Functions in Response to Environmental Stresses

In response to various environmental stresses, plants have evolved a wide range of defense mechanisms, resulting in the overexpression of a series of stress-responsive genes. Among them, there is certain set of genes that encode for intrinsically disordered proteins (IDPs) that repair and protect the plants from damage caused by environmental stresses. Group II LEA (late embryogenesis abundant) proteins compose the most abundant and characterized group of IDPs; they accumulate in the late stages of seed development and are expressed in response to dehydration, salinity, low temperature, or abscisic acid (ABA) treatment. The physiological and biochemical characterization of group II LEA proteins has been carried out in a number of investigations because of their vital roles in protecting the integrity of biomolecules by preventing the crystallization of cellular components prior to multiple stresses. This review describes the distribution, structural architecture, and genomic diversification of group II LEA proteins, with some recent investigations on their regulation and molecular expression under various abiotic stresses. Novel aspects of group II LEA proteins in Phoenix dactylifera and in orthodox seeds are also presented. Genome-wide association studies (GWAS) indicated a ubiquitous distribution and expression of group II LEA genes in different plant cells. In vitro experimental evidence from biochemical assays has suggested that group II LEA proteins perform heterogenous functions in response to extreme stresses. Various investigations have indicated the participation of group II LEA proteins in the plant stress tolerance mechanism, spotlighting the molecular aspects of group II LEA genes and their potential role in biotechnological strategies to increase plants' survival in adverse environments.

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).

Effects of Exogenous Salicylic Acid on Drought Response and Characterization of Dehydrins in Impatiens walleriana

Impatiens walleriana is a valued ornamental plant sensitive to drought stress. We investigated whether the foliar application of 2mM salicylic acid (SA) can protect potted I. walleriana plants from drought stress. The plants were divided into: watered plants, drought-stressed plants, watered plants treated with SA and drought-stressed plants treated with SA. The number of flowers and flower buds, relative water content (RWC), contents of malondialdehyde (MDA) and proline (Pro) and the activities of superoxide dismutases, catalases and peroxidases were recorded at different time points. Three dehydrin sequences were identified in de novo assembled leaf transcriptome: IwDhn1, IwDhn2.1 and IwDhn2.2. Drought stress caused wilting, floral abortion, reduction of RWC and increased MDA-an indicator of lipid peroxidation. In response to drought, Impatiens accumulated Pro and induced chloroplastic Cu/ZnSOD and two peroxidase isoforms. The most remarkable drought response was strong induction of IwDhn2.1 and IwDhn2.2. Rehydration restored RWC, Pro level, Cu/ZnSOD activity and dehydrins expression in drought-stressed plants approximately to the values of watered plants.SA had ameliorating effects on plants exposed to drought, including prevention of wilting, preservation of RWC, increased Pro accumulation, modulation of antioxidative activities and remarkable decrease of lipid peroxidation, but without effects on flowers' preservation.

Conserved sequence motifs in the abiotic stress response protein late embryogenesis abundant 3

LEA3 proteins, a family of abiotic stress proteins, are defined by the presence of a tryptophan-containing motif, which we name the W-motif. We use Pfam LEA3 sequences to search the Phytozome database to create a W-motif definition and a LEA3 sequence dataset. A comprehensive analysis of these sequences revealed four N-terminal motifs, as well as two previously undiscovered C-terminal motifs that contain conserved acidic and hydrophobic residues. The general architecture of the LEA3 sequences consisted of an N-terminal motif with a potential mitochondrial transport signal and the twin-arginine motif cut-site, followed by a W-motif and often a C-terminal motif. Analysis of species distribution of the motifs showed that one architecture was found exclusively in Commelinids, while two were distributed fairly evenly over all species. The physiochemical properties of the different architectures showed clustering in a relatively narrow range compared to the previously studied dehydrins. The evolutionary analysis revealed that the different sequences grouped into clades based on architecture, and that there appear to be at least two distinct groups of LEA3 proteins based on their architectures and physiochemical properties. The presence of LEA3 proteins in non-vascular plants but their absence in algae suggests that LEA3 may have arisen in the evolution of land plants.

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.

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.