Overexpression of MtCAS31 enhances drought tolerance in transgenic Arabidopsis by reducing stomatal density

The superior allele LEA12OR in wild rice enhances salt tolerance and yield

Soil salinity has negative impacts on food security and sustainable agriculture. Ion homeostasis, osmotic adjustment and reactive oxygen species scavenging are the main approaches utilized by rice to resist salt stress. Breeding rice cultivars with high salt tolerance (ST) and yield is a significant challenge due to the lack of elite alleles conferring ST. Here, we report that the elite allele LEA12OR, which encodes a late embryogenesis abundant (LEA) protein from the wild rice Oryza rufipogon Griff., improves osmotic adjustment and increases yield under salt stress. Mechanistically, LEA12OR, as the early regulator of the LEA12OR-OsSAPK10-OsbZIP86-OsNCED3 functional module, maintains the kinase stability of OsSAPK10 under salt stress, thereby conferring ST by promoting abscisic acid biosynthesis and accumulation in rice. The superior allele LEA12OR provides a new avenue for improving ST and yield via the application of LEA12OR in current rice through molecular breeding and genome editing.

Dehydrin CaDHN2 Enhances Drought Tolerance by Affecting Ascorbic Acid Synthesis under Drought in Peppers

Peppers (Capsicum annuum L.), as a horticultural crop with one of the highest ascorbic acid contents, are negatively affected by detrimental environmental conditions both in terms of quality and productivity. In peppers, the high level of ascorbic acid is not only a nutrient substance but also plays a role in environmental stress, i.e., drought stress. When suffering from drought stress, plants accumulate dehydrins, which play important roles in the stress response. Here, we isolated an SK3-type DHN gene CaDHN2 from peppers. CaDHN2 was located in the nucleus, cytoplasm, and cell membrane. In CaDHN2-silenced peppers, which are generated by virus-induced gene silencing (VIGS), the survival rate is much lower, the electrolytic leakage is higher, and the accumulation of reactive oxygen species (ROS) is greater when compared with the control under drought stress. Moreover, when CaDHN2 (CaDHN2-OE) is overexpressed in Arabidopsis, theoverexpressing plants show enhanced drought tolerance, increased antioxidant enzyme activities, and lower ROS content. Based on yeast two-hybrid (Y2H), GST-pull down, and bimolecular fluorescence complementation (BiFC) results, we found that CaDHN2 interacts with CaGGP1, the key enzyme in ascorbic acid (AsA) synthesis, in the cytoplasm. Accordingly, the level of ascorbic acid is highly reduced in CaDHN2-silenced peppers, indicating that CaDHN2 interacts with CaGGP1 to affect the synthesis of ascorbic acid under drought stress, thus improving the drought tolerance of peppers. Our research provides a basis for further study of the function of DHN genes.

Transcription Factor ZmNAC20 Improves Drought Resistance by Promoting Stomatal Closure and Activating Expression of Stress-Responsive Genes in Maize

Drought is a major environmental threat that limits crop growth, development, and productivity worldwide. Improving drought resistance with genetic engineering methods is necessary to tackle global climate change. It is well known that NAC (NAM, ATAF and CUC) transcription factors play a critical role in coping with drought stress in plants. In this study, we identified an NAC transcription factor ZmNAC20, which regulates drought stress response in maize. ZmNAC20 expression was rapidly upregulated by drought and abscisic acid (ABA). Under drought conditions, the ZmNAC20-overexpressing plants had higher relative water content and survival rate than the wild-type maize inbred B104, suggesting that overexpression of ZmNAC20 improved drought resistance in maize. The detached leaves of ZmNAC20-overexpressing plants lost less water than those of wild-type B104 after dehydration. Overexpression of ZmNAC20 promoted stomatal closure in response to ABA. ZmNAC20 was localized in the nucleus and regulated the expression of many genes involved in drought stress response using RNA-Seq analysis. The study indicated that ZmNAC20 improved drought resistance by promoting stomatal closure and activating the expression of stress-responsible genes in maize. Our findings provide a valuable gene and new clues on improving crop drought resistance.

Identification of the BcLEA Gene Family and Functional Analysis of the BcLEA73 Gene in Wucai (Brassica campestris L.)

Late embryogenesis abundant (LEA) proteins are important developmental proteins in the response of plants to abiotic stress. In our previous study, BcLEA73 was differentially expressed under low-temperature stress. Herein, we combined bioinformatics analysis, subcellular localization, expression assays, and stress experiments (including salt, drought, and osmotic stress) to identify and analyze the BcLEA gene family. Gene cloning and functional analysis of BcLEA73 were performed in tobacco and Arabidopsis. Based on the sequence homology and the available conservative motif, 82 BrLEA gene family members were identified and were divided into eight subfamilies in the genome-wide database of Chinese cabbage. The analysis showed that the BrLEA73 gene was located on chromosome A09 and belonged to the LEA_6 subfamily. Quantitative real-time PCR analysis indicated that the BcLEA genes were differentially expressed to varying degrees in the roots, stems, leaves, and petioles of Wucai. The overexpressed BcLEA73 transgenic plants exhibited no significant differences in root length and seed germination rates compared to the wild-type (WT) plants under control conditions. Under salt and osmotic stress treatment, the root length and seed germination rates of the BcLEA73-OE strain were significantly greater than those of WT plants. Under salt stress, the total antioxidant capacity (T-AOC) of the BcLEA73-OE lines increased significantly, and the relative conductivity, (REL), hydrogen peroxide (H2O2) content, and superoxide anion (O2-) production rate decreased significantly. Under drought treatment, the survival rate of the BcLEA73-OE lines was significantly higher than that of WT plants. These results showed that the BcLEA73 gene of Wucai functions in enhancing the tolerance of plants to salt, drought, and osmotic stress. This study provides a theoretical basis to explore the relevant functions of the BcLEA gene family members of Wucai.

How Does Stomatal Density and Residual Transpiration Contribute to Osmotic Stress Tolerance?

Osmotic stress that is induced by salinity and drought affects plant growth and development, resulting in significant losses to global crop production. Consequently, there is a strong need to develop stress-tolerant crops with a higher water use efficiency through breeding programs. Water use efficiency could be improved by decreasing stomatal transpiration without causing a reduction in CO2 uptake under osmotic stress conditions. The genetic manipulation of stomatal density could be one of the most promising strategies for breeders to achieve this goal. On the other hand, a substantial amount of water loss occurs across the cuticle without any contribution to carbon gain when the stomata are closed and under osmotic stress. The minimization of cuticular (otherwise known as residual) transpiration also determines the fitness and survival capacity of the plant under the conditions of a water deficit. The deposition of cuticular wax on the leaf epidermis acts as a limiting barrier for residual transpiration. However, the causal relationship between the frequency of stomatal density and plant osmotic stress tolerance and the link between residual transpiration and cuticular wax is not always straightforward, with controversial reports available in the literature. In this review, we focus on these controversies and explore the potential physiological and molecular aspects of controlling stomatal and residual transpiration water loss for improving water use efficiency under osmotic stress conditions via a comparative analysis of the performance of domesticated crops and their wild relatives.

GlPS1 overexpression accumulates coumarin secondary metabolites in transgenic Arabidopsis

The dried root of Glehnia littoralis is a traditional Chinese herbal medicine mainly used to treat lung diseases and plays an important role in fighting coronavirus disease 2019 pneumonia in China. This study focused on the key enzyme gene GlPS1 for furanocoumarin synthesis in G. littoralis. In the 35S:GlPS1 transgenic Arabidopsis study, the Arabidopsis thaliana-overexpressing GlPS1 gene was more salt-tolerant than Arabidopsis in the blank group. Metabolomics analysis showed 30 differential metabolites in Arabidopsis, which overexpressed the GlPS1 gene. Twelve coumarin compounds were significantly upregulated, and six of these coumarin compounds were not detected in the blank group. Among these differential coumarin metabolites, isopimpinellin and aesculetin have been annotated by the Kyoto Encyclopedia of Genes and Genomes and isopimpinellin was not detected in the blank group. Through structural comparison, imperatorin was formed by dehydration and condensation of zanthotoxol and a molecule of isoprenol, and the difference between them was only one isoprene. Results showed that the GlPS1 gene positively regulated the synthesis of coumarin metabolites in A. thaliana and at the same time improved the salt tolerance of A. thaliana.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s11240-022-02427-w.

Tolerant mechanism of model legume plant Medicago truncatula to drought, salt, and cold stresses

Legume plants produce one-third of the total yield of primary crops and are important food sources for both humans and animals worldwide. Frequent exposure to abiotic stresses, such as drought, salt, and cold, greatly limits the production of legume crops. Several morphological, physiological, and molecular studies have been conducted to characterize the response and adaptation mechanism to abiotic stresses. The tolerant mechanisms of the model legume plant Medicago truncatula to abiotic stresses have been extensively studied. Although many potential genes and integrated networks underlying the M. truncatula in responding to abiotic stresses have been identified and described, a comprehensive summary of the tolerant mechanism is lacking. In this review, we provide a comprehensive summary of the adaptive mechanism by which M. truncatula responds to drought, salt, and cold stress. We also discuss future research that need to be explored to improve the abiotic tolerance of legume plants.

Citrus FRIGIDA cooperates with its interaction partner dehydrin to regulate drought tolerance

Drought is a major environmental stress that severely affects plant growth and crop productivity. FRIGIDA (FRI) is a key regulator of flowering time and drought tolerance in model plants. However, little is known regarding its functions in woody plants, including citrus. Thus, we explored the functional role of the citrus FRI ortholog (CiFRI) under drought. Drought treatment induced CiFRI expression. CiFRI overexpression enhanced drought tolerance in transgenic Arabidopsis and citrus, while CiFRI suppression increased drought susceptibility in citrus. Moreover, transcriptomic profiling under drought conditions suggested that CiFRI overexpression altered the expression of numerous genes involved in the stress response, hormone biosynthesis, and signal transduction. Mechanistic studies revealed that citrus dehydrin likely protects CiFRI from stress-induced degradation, thereby enhancing plant drought tolerance. In addition, a citrus brassinazole-resistant (BZR) transcription factor family member (CiBZR1) directly binds to the CiFRI promoter to activate its expression under drought conditions. CiBZR1 also enhanced drought tolerance in transgenic Arabidopsis and citrus. These findings further our understanding of the molecular mechanisms underlying the CiFRI-mediated drought stress response in citrus.

Improving Drought Stress Tolerance in Ramie (Boehmeria nivea L.) Using Molecular Techniques

Ramie is one of the most significant fiber crops and contributes to good quality fiber. Drought stress (DS) is one of the most devastating abiotic factors which is accountable for a substantial loss in crop growth and production and disturbing sustainable crop production. DS impairs growth, plant water relation, and nutrient uptake. Ramie has evolved a series of defense responses to cope with DS. There are numerous genes regulating the drought tolerance (DT) mechanism in ramie. The morphological and physiological mechanism of DT is well-studied; however, modified methods would be more effective. The use of novel genome editing tools like clustered regularly interspaced short palindromic repeats (CRISPR) is being used to edit the recessive genes in crops to modify their function. The transgenic approaches are used to develop several drought-tolerant varieties in ramie, and further identification of tolerant genes is needed for an effective breeding plan. Quantitative trait loci (QTLs) mapping, transcription factors (TFs) and speed breeding are highly studied techniques, and these would lead to the development of drought-resilient ramie cultivars. The use of hormones in enhancing crop growth and development under water scarcity circumstances is critical; however, using different concentrations and testing genotypes in changing environments would be helpful to sort the tolerant genotypes. Since plants use various ways to counter DS, investigating mechanisms of DT in plants will lead to improved DT in ramie. This critical review summarized the recent advancements on DT in ramie using novel molecular techniques. This information would help ramie breeders to conduct research studies and develop drought tolerant ramie cultivars.

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.

Genome-wide survey of the dehydrin genes in bread wheat (Triticum aestivum L.) and its relatives: identification, evolution and expression profiling under various abiotic stresses

BACKGROUND

Bread wheat (Triticum aestivum) is an important staple cereal grain worldwide. The ever-increasing environmental stress makes it very important to mine stress-resistant genes for wheat breeding programs. Therefore, dehydrin (DHN) genes can be considered primary candidates for such programs, since they respond to multiple stressors.

RESULTS

In this study, we performed a genome-wide analysis of the DHN gene family in the genomes of wheat and its three relatives. We found 55 DHN genes in T. aestivum, 31 in T. dicoccoides, 15 in T. urartu, and 16 in Aegilops tauschii. The phylogenetic, synteny, and sequence analyses showed we can divide the DHN genes into five groups. Genes in the same group shared similar conserved motifs and potential function. The tandem TaDHN genes responded strongly to drought, cold, and high salinity stresses, while the non-tandem genes respond poorly to all stress conditions. According to the interaction network analysis, the cooperation of multiple DHN proteins was vital for plants in combating abiotic stress.

CONCLUSIONS

Conserved, duplicated DHN genes may be important for wheat being adaptable to a different stress conditions, thus contributing to its worldwide distribution as a staple food. This study not only highlights the role of DHN genes help the Triticeae species against abiotic stresses, but also provides vital information for the future functional studies in these crops.

Plant Dehydrins: Expression, Regulatory Networks, and Protective Roles in Plants Challenged by Abiotic Stress

Dehydrins, also known as Group II late embryogenesis abundant (LEA) proteins, are classic intrinsically disordered proteins, which have high hydrophilicity. A wide range of hostile environmental conditions including low temperature, drought, and high salinity stimulate dehydrin expression. Numerous studies have furnished evidence for the protective role played by dehydrins in plants exposed to abiotic stress. Furthermore, dehydrins play important roles in seed maturation and plant stress tolerance. Hence, dehydrins might also protect plasma membranes and proteins and stabilize DNA conformations. In the present review, we discuss the regulatory networks of dehydrin gene expression including the abscisic acid (ABA), mitogen-activated protein (MAP) kinase cascade, and Ca²⁺ signaling pathways. Crosstalk among these molecules and pathways may form a complex, diverse regulatory network, which may be implicated in regulating the same dehydrin.

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.

Macroscopic variation in Arabidopsis mutants despite stomatal uniformity across soil nutrient environments

Stomata are essential pores flanked by guard cells that control gas exchange in plants. We can utilize stomatal size and density measurements as a proxy for a plant's capacity for gas exchange. While stomatal responses to stressful environments are well studied; data are lacking in the responses across mutant genotypes of the same species in these trait and treatment interactions or genetic variation in phenotypic plasticity. We evaluated the effects of soil nutrient variation on macroscopic and stomatal traits of Arabidopsis thaliana T-DNA insertion mutants for which prior performance in a single benign growing condition were available. Nutrient-induced stress significantly impacted traits including plant biomass, height, fruit number, and leaf number which we denote as macroscopic traits. We found evidence that genotype by environment effects exist for macroscopic traits, yet total stomatal area variation, or "microscopic variation" across environments was modest. Divergence from the wildtype line varied by mutant background and these responses were variable among traits. These findings suggest that Arabidopsis employs a strategy of physiological compensation, sacrificing morphological traits to maintain stomatal production.

Overexpression of MtRAV3 enhances osmotic and salt tolerance and inhibits growth of Medicago truncatula

Related to ABI3/VP1 (RAV) transcription factors play important roles in regulating plant growth and stress tolerance, which have been studied in many plant species, but have remained largely unidentified in legumes. To functionally characterize RAV in legumes, MtRAV3 from legume model plant Medicago truncatula was isolated and its function was investigated by overexpressing MtRAV3 in M. truncatula. Expression analysis demonstrated that MtRAV3 was markedly induced by NaCl and polyethylene glycol (PEG). MtRAV3 overexpression enhanced tolerance of transgenic M. truncatula to mannitol, drought and salt stresses, and induced the expression of adversity-related genes, including MtWRKY76, MtMYB61, cold-acclimation specific protein 31 (MtCAS31), alternative oxidase 1 (MtAOX1) and ethylene response factor 1 (MtERF1). There were lower relative electrolyte leakage and higher chlorophyll content of leaves in the MtRAV3 overexpression plants than in wild type plants under both salt and drought stress. MtRAV3 overexpression M. truncatula were featured by some phenotypes of dwarfing, late flowering, more branches, smaller flower and leaf organs. Further investigations showed that the expression levels of DWARF14 (MtD14), CAROTENOID CLEAVAGE DIOXYGENASES 7 (MtCCD7) and GA3-oxidase1 (MtGA3ox1), which related to dwarf and branch phenotype, were obviously reduced, as well as MtGA3ox1' (MTR_1g011580), GA20-oxidase1 (MtGA20ox1), MtGA20ox1' (MTR_1g102070) and GA20-oxidase2 (MtGA20ox2) involved in gibberellins (GAs) pathway. Overall, our results revealed that MtRAV3 exerted an important role in adversity response and plant growth, was a multifunctional gene in M. truncatula, which provided reference for genetic improvement of alfalfa (Medicago sativa).

Genetic mapping and identification of a QTL determining tolerance to freezing stress in Fragaria vesca L

Extreme cold and frost cause significant stress to plants which can potentially be lethal. Low temperature freezing stress can cause significant and irreversible damage to plant cells and can induce physiological and metabolic changes that impact on growth and development. Low temperatures cause physiological responses including winter dormancy and autumn cold hardening in strawberry (Fragaria) species, and some diploid F. vesca accessions have been shown to have adapted to low-temperature stresses. To study the genetics of freezing tolerance, a F. vesca mapping population of 143 seedlings segregating for differential responses to freezing stress was raised. The progeny was mapped using ‘Genotyping-by-Sequencing’ and a linkage map of 2,918 markers at 851 loci was resolved. The mapping population was phenotyped for freezing tolerance response under controlled and replicated laboratory conditions and subsequent quantitative trait loci analysis using interval mapping revealed a single significant quantitative trait locus on Fvb2 in the physical interval 10.6 Mb and 15.73 Mb on the F. vesca v4.0 genome sequence. This physical interval contained 896 predicted genes, several of which had putative roles associated with tolerance to abiotic stresses including freezing. Differential expression analysis of the 896 QTL-associated gene predictions in the leaves and crowns from ‘Alta’ and ‘NCGR1363’ parental genotypes revealed genotype-specific changes in transcript accumulation in response to low temperature treatment as well as expression differences between genotypes prior to treatment for many of the genes. The putative roles, and significant interparental differential expression levels of several of the genes reported here identified them as good candidates for the control of the effects of freezing tolerance at the QTL identified in this investigation and the possible role of these candidate genes in response to freezing stress is discussed.

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.

DcABF3, an ABF transcription factor from carrot, alters stomatal density and reduces ABA sensitivity in transgenic Arabidopsis

Abscisic acid-responsive element (ABRE)-binding factors (ABFs) are important transcription factors involved in various physiological processes in plants. Stomata are micro channels for water and gas exchange of plants. Previous researches have demonstrated that ABFs can modulate the stomatal development in some plants. However, little is known about stomata-related functions of ABFs in carrots. In our study, DcABF3, a gene encoding for ABF transcription factor, was isolated from carrot. The open reading frame of DcABF3 was 1329 bp, encoding 442 amino acids. Expression profiles of DcABF3 indicated that DcABF3 can respond to drought, salt or ABA treatment in carrots. Overexpressing DcABF3 in Arabidopsis led to the increase of stomatal density which caused severe water loss. Expression assay indicated that overexpression of DcABF3 caused high expression of stomatal development-related transcription factor genes, SPCH, FAMA, MUTE and SCRMs. Increased antioxidant enzyme activities and higher expression levels of stress-related genes were also found in transgenic lines after water deficit treatment. Changes in expression of ABA synthesis-related genes and AtABIs indicated the potential role of DcABF3 in ABA signaling pathway. Under the treatment of exogenous ABA, DcABF3-overexpression Arabidopsis seedlings exhibited increased root length and germination rate. Our findings demonstrated that heterologous overexpression of DcABF3 positively affected stomatal development and also reduced ABA sensitivity in transgenic Arabidopsis.

The SUPPRESSOR of MAX2 1 (SMAX1)-Like SMXL6, SMXL7 and SMXL8 Act as Negative Regulators in Response to Drought Stress in Arabidopsis

Drought represents a major threat to crop growth and yields. Strigolactones (SLs) contribute to regulating shoot branching by targeting the SUPPRESSOR OF MORE AXILLARY GROWTH2 (MAX2)-LIKE6 (SMXL6), SMXL7 and SMXL8 for degradation in a MAX2-dependent manner in Arabidopsis. Although SLs are implicated in plant drought response, the functions of the SMXL6, 7 and 8 in the SL-regulated plant response to drought stress have remained unclear. Here, we performed transcriptomic, physiological and biochemical analyses of smxl6, 7, 8 and max2 plants to understand the basis for SMXL6/7/8-regulated drought response. We found that three D53 (DWARF53)-Like SMXL members, SMXL6, 7 and 8, are involved in drought response as the smxl6smxl7smxl8 triple mutants showed markedly enhanced drought tolerance compared to wild type (WT). The smxl6smxl7smxl8 plants exhibited decreased leaf stomatal index, cuticular permeability and water loss, and increased anthocyanin biosynthesis during dehydration. Moreover, smxl6smxl7smxl8 were hypersensitive to ABA-induced stomatal closure and ABA responsiveness during and after germination. In addition, RNA-sequencing analysis of the leaves of the D53-like smxl mutants, SL-response max2 mutant and WT plants under normal and dehydration conditions revealed an SMXL6/7/8-mediated network controlling plant adaptation to drought stress via many stress- and/or ABA-responsive and SL-related genes. These data further provide evidence for crosstalk between ABA- and SL-dependent signaling pathways in regulating plant responses to drought. Our results demonstrate that SMXL6, 7 and 8 are vital components of SL signaling and are negatively involved in drought responses, suggesting that genetic manipulation of SMXL6/7/8-dependent SL signaling may provide novel ways to improve drought resistance.

Late Embryogenesis Abundant Protein-Client Protein Interactions

The intrinsically disordered proteins belonging to the LATE EMBRYOGENESIS ABUNDANT protein (LEAP) family have been ascribed a protective function over an array of intracellular components. We focus on how LEAPs may protect a stress-susceptible proteome. These examples include instances of LEAPs providing a shield molecule function, possibly by instigating liquid-liquid phase separations. Some LEAPs bind directly to their client proteins, exerting a holdase-type chaperonin function. Finally, instances of LEAP-client protein interactions have been documented, where the LEAP modulates (interferes with) the function of the client protein, acting as a surreptitious rheostat of cellular homeostasis. From the examples identified to date, it is apparent that client protein modulation also serves to mitigate stress. While some LEAPs can physically bind and protect client proteins, some apparently bind to assist the degradation of the client proteins with which they associate. Documented instances of LEAP-client protein binding, even in the absence of stress, brings to the fore the necessity of identifying how the LEAPs are degraded post-stress to render them innocuous, a first step in understanding how the cell regulates their abundance.

Over-expression of a γ-tocopherol methyltransferase gene in vitamin E pathway confers PEG-simulated drought tolerance in alfalfa

BACKGROUND

α-Tocopherol is one of the most important vitamin E components present in plant. α-Tocopherol is a potent antioxidant, which can deactivate photoproduced reactive oxygen species (ROS) and prevent lipids from oxidation when plants suffer drought stress. γ-Tocopherol methyltransferase (γ-TMT) catalyzes the formation of α-tocopherol in the tocopherol biosynthetic pathway. Our previous studies showed that over-expression of γ-TMT gene can increase the accumulation of α-tocopherol in alfalfa (Medicago sativa). However, whether these transgenic plants confer increased drought tolerance and the underlying mechanism are still unknown.

RESULTS

In the present study, we further evaluate transgenic alfalfa lines, and found that over-expression of MsTMT led to an increase in α-tocopherol and total tocopherol level in the transgenic lines compared with the control plant. It was revealed that drought tolerance of the transgenic alfalfa was remarkably increased, with alleviated oxidative damage and accumulation of more osmolytic substances. The stomatal development in transgenic plants was significantly inhibited on both sides of leaves, which may be resulted from the repression of MsSPCHLESS (MsSPCH) gene. The reduced stomatal density of transgenic plants contributes to a lower stomatal conductance and higher water use efficiency (WUE). Moreover, both RNA-seq and qRT-PCR analyses indicate that regulatory mechanism of MsTMT in drought involved in both ABA-dependent and ABA-independent pathways.

CONCLUSION

Our results suggest that MsTMT gene plays a positive role in regulating alfalfa response to PEG-simulated drought stress, which might involve complex mechanisms, including ROS scavenging system, stomatal development and multiple phytohormone signaling pathways. This study will broaden our view on the function of γ-TMT gene and provide new strategy for genetic engineering in alfalfa breeding.

Down Regulation and Loss of Auxin Response Factor 4 Function Using CRISPR/Cas9 Alters Plant Growth, Stomatal Function and Improves Tomato Tolerance to Salinity and Osmotic Stress

Auxin controls multiple aspects of plant growth and development. However, its role in stress responses remains poorly understood. Auxin acts on the transcriptional regulation of target genes, mainly through Auxin Response Factors (ARF). This study focuses on the involvement of SlARF4 in tomato tolerance to salinity and osmotic stress. Using a reverse genetic approach, we found that the antisense down-regulation of SlARF4 promotes root development and density, increases soluble sugars content and maintains chlorophyll content at high levels under stress conditions. Furthermore, ARF4-as displayed higher tolerance to salt and osmotic stress through reduced stomatal conductance coupled with increased leaf relative water content and Abscisic acid (ABA) content under normal and stressful conditions. This increase in ABA content was correlated with the activation of ABA biosynthesis genes and the repression of ABA catabolism genes. Cu/ZnSOD and mdhar genes were up-regulated in ARF4-as plants which can result in a better tolerance to salt and osmotic stress. A CRISPR/Cas9 induced SlARF4 mutant showed similar growth and stomatal responses as ARF4-as plants, which suggest that arf4-cr can tolerate salt and osmotic stresses. Our data support the involvement of ARF4 as a key factor in tomato tolerance to salt and osmotic stresses and confirm the use of CRISPR technology as an efficient tool for functional reverse genetics studies.

Characterization of a novel cotton MYB gene, GhMYB108-like responsive to abiotic stresses

Transcriptional factors are the major regulators of plant signaling pathways in response to environmental stresses i.e., drought, salinity and cold. Hereby, the GhMYB108-like was characterized to determine whether it regulate these stresses. The GhMYB108-like cDNA consisted of 1107 base pairs (bp) with 807 open reading frame encoded a protein of 268 amino acids. Its isoelectric point and molecular weight are 5.51 and 30.3 kDa respectively. Phylogenetic analysis and online databases revealed that GhMYB108-like proteins are closely related with the Arabidopsis thaliana MYB2. Important cis-elements were detected in the promotor region of GhMYB108-like responding to stresses and phytohormones. The 3D structure of GhMYB108-like protein has been predicted. In addition, various physico-chemical properties of GhMYB108-like have been determined. Subcellular localization confirmed that GhMYB108-like are nuclear localized protein. Quantitative expression analysis showed that polyethylene glycol and salt treatments significantly induced the expression of GhMYB108-like. Overall, our findings suggest that GhMYB108-like is an important gene that would plays important regulatory role in response to drought and salt stresses.

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.

Knockdown of GhIQD31 and GhIQD32 increases drought and salt stress sensitivity in Gossypium hirsutum

Drought, salinity and cold stresses have a major impact on cotton production, thus identification and utilization of plant genes vital for plant improvement Whole-genome identification and functional characterizations of the IQ67-domain (IQD) protein family was carried out in which 148, 77, and 79 IQD genes were identified in Gossypium hirsutum, G. raimondii, and G. arboreum. The entire IQD proteins had varied physiochemical properties, however; their grand hydropathy values were negative, which demonstrated that the proteins were hydrophilic, a property common among the proteins encoded by various stresses responsive genes, such as the late embryogenesis abundant (LEA) proteins. The IQD proteins were predicted to be majorly sublocalized in the nucleus; moreover, various cis-regulatory elements with higher role in enhancing abiotic stress tolerance were detected. RNA-seq and RT-qPCR analysis revealed two key genes, Gh_D06G0014 and Gh_A09G1608 with significantly higher upregulation across the various tissues under drought, salt and cold stress. Knockdown of the two genes negatively affected the ability of G. hirsutum to tolerate the effects of the three stress factors, being all the antioxidant assayed were significantly low concentrations compared to the oxidizing enzymes in VIGS plants under stress, furthermore, morphological and physiological traits were all negatively affected in VIGS plants. Expression levels of GhLEA2, GhCDK_F4, GPCR (TOM1) and Gh_A05G2067 (TH), the stress responsive genes were all downregulated in the VIGS plants, but significantly upregulated in WT and positively controlled plants. The results demonstrated that the IQD genes could be responsible for enhancing drought, salt and cold stress tolerance in cotton.

RNAi mediated silencing of dehydrin gene WZY2 confers osmotic stress intolerance in transgenic wheat

Dehydrins are involved in the prevention of osmotic damage in plants. Many studies have shown that overexpression of dehydrin genes can enhance the osmotic stress tolerance in transgenic plants. Our previous studies showed a YnSKn-type dehydrin gene WZY2 could be induced by polyethylene glycol (PEG), cold, indole-3-acetic acid (IAA), salicylic acid (SA) and abscisic acid (ABA). In the present study, we examined the phenotype and physiological indices in a dehydrin gene WZY2 RNA interference (RNAi) lines in wheat. Real-time PCR indicated a depressed WZY2 gene expression in transformed wheat. Furthermore, transgenic wheat showed lower relative water content, oxidative-related enzyme activities and higher malondialdehyde (MDA) content than wild-type bread wheat (Zhengyin No.1) under osmotic stress. Overexpression of the WZY2 in Arabidopsis thaliana (L.) Heynh. revealed a significant increase in tolerance to drought stress. Further studies also showed that WZY2 could participate in ABA-induced stomatal closure. These results demonstrated a key function of WZY2 in plant response to osmotic stress.

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.

Dehydrin MtCAS31 promotes autophagic degradation under drought stress

Drought stress seriously affects crop yield, and the mechanism underlying plant resistance to drought stress via macroautophagy/autophagy is not clear. Here, we show that a dehydrin, Medicago truncatula MtCAS31 (cold acclimation-specific 31), a positive regulator of drought response, plays a key role in autophagic degradation. A GFP cleavage assay and treatment with an autophagy-specific inhibitor indicated that MtCAS31 participates in the autophagic degradation pathway and that overexpressing MtCAS31 promotes autophagy under drought stress. Furthermore, we discovered that MtCAS31 interacts with the autophagy-related protein ATG8a in the AIM-like motif YXXXI, supporting its function in autophagic degradation. In addition, we identified a cargo protein of MtCAS31, the aquaporin MtPIP2;7, by screening an M. truncatula cDNA library. We found that MtPIP2;7 functions as a negative regulator of drought response. Under drought stress, MtCAS31 facilitated the autophagic degradation of MtPIP2;7 and reduced root hydraulic conductivity, thus reducing water loss and improving drought tolerance. Taken together, our results reveal a novel function of dehydrins in promoting the autophagic degradation of proteins, which extends our knowledge of the function of dehydrins.Abbreviations: AIM: ATG8-interacting motif; ATG: autophagy-related; ATI1: ATG8-interacting protein1; BiFC: Biomolecular fluorescence complementation; CAS31: cold acclimation-specific 31; ConcA: concanamycin A; DSK2: dominant suppressor of KAR2; ER: endoplasmic reticulum; ERAD: ER-associated degradation; NBR1: next to BRCA1 gene 1; PM: plasma membrane; PIPs: plasma membrane intrinsic proteins; TALEN: transcription activator-like effector nuclease; TSPO: tryptophan-rich sensory protein/translocator; UPR: unfolded protein response; VC: vector control.

Contrasting Effects of Wild Arachis Dehydrin Under Abiotic and Biotic Stresses

Plant dehydrins (DNHs) belong to the LEA (Late Embryogenesis Abundant) protein family and are involved in responses to multiple abiotic stresses. DHNs are classified into five subclasses according to the organization of three conserved motifs (K-; Y-; and S-segments). In the present study, the DHN protein family was characterized by molecular phylogeny, exon/intron organization, protein structure, and tissue-specificity expression in eight Fabaceae species. We identified 20 DHN genes, encompassing three (YnSKn, SKn, and Kn) subclasses sharing similar gene organization and protein structure. Two additional low conserved DHN Φ-segments specific to the legume SKn-type of proteins were also found. The in silico expression patterns of DHN genes in four legume species (Arachis duranensis, A. ipaënsis, Glycine max, and Medicago truncatula) revealed that their tissue-specific regulation is associated with the presence or absence of the Y-segment. Indeed, DHN genes containing a Y-segment are mainly expressed in seeds, whereas those without the Y-segment are ubiquitously expressed. Further qRT-PCR analysis revealed that, amongst stress responsive dehydrins, a SKn-type DHN gene from A. duranensis (AdDHN1) showed opposite response to biotic and abiotic stress with a positive regulation under water deficit and negative regulation upon nematode infection. Furthermore, transgenic Arabidopsis lines overexpressing (OE) AdDHN1 displayed improved tolerance to multiple abiotic stresses (freezing and drought) but increased susceptibility to the biotrophic root-knot nematode (RKN) Meloidogyne incognita. This contradictory role of AdDHN1 in responses to abiotic and biotic stresses was further investigated by qRT-PCR analysis of transgenic plants using a set of stress-responsive genes involved in the abscisic acid (ABA) and jasmonic acid (JA) signaling pathways and suggested an involvement of DHN overexpression in these stress-signaling pathways.

Overexpression of the RNA binding protein MhYTP1 in transgenic apple enhances drought tolerance and WUE by improving ABA level under drought condition

MhYTP1 is involved in post-transcriptional regulation as a member of YT521-homology (YTH) domain-containing RNA-binding proteins. We previously cloned MhYTP1 and found it participated in various biotic and abiotic stress responses. However, its function in long-term moderate drought has not been verified. Thus, we explored its biological role in response to drought. Under drought condition, the net photosynthesis rate (P_n) and water use efficiency (WUE) were significantly elevated in MhYTP1-overexpressing (OE) apple plants when compared with the non-transgenic (NT) controls. Further analysis indicated MhYTP1 expression was associated with elevated ABA content, increased stomatal density and reduced stomatal aperture. In addition, to gain insight into the function of stem-specific expression of MhYTP1, grafting experiments were performed. Interestingly, lower transpiration rate (T_r) and higher WUE were observed when transgenic plants were used as scions as opposed to rootstocks and when transgenic rather than NT plants were used as rootstocks, indicating MhYTP1 plays crucial roles in grafted plants. These results define a function for MhYTP1 in promoting tolerance to drought conditions, and suggest that MhYTP1 can serve as a candidate gene for future apple drought resistance breeding with the help of biotechnology.

Evidence for in vivo interactions between dehydrins and the aquaporin AtPIP2B

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

Dissecting interplays between Vitis vinifera L. and grapevine virus B (GVB) under field conditions

Plant virus infections are often difficult to characterize as they result from a complex molecular and physiological interplay between a pathogen and its host. In this study, the impact of the phloem-limited grapevine virus B (GVB) on the Vitis vinifera L. wine-red cultivar Albarossa was analysed under field conditions. Trials were carried out over two growing seasons by combining agronomic, molecular, biochemical and ecophysiological approaches. The data showed that GVB did not induce macroscopic symptoms on 'Albarossa', but affected the ecophysiological performances of vines in terms of assimilation rates, particularly at the end of the season, without compromising yield and vigour. In GVB-infected plants, the accumulation of soluble carbohydrates in the leaves and transcriptional changes in sugar- and photosynthetic-related genes seemed to trigger defence responses similar to those observed in plants infected by phytoplasmas, although to a lesser extent. In addition, GVB activated berry secondary metabolism. In particular, total anthocyanins and their acetylated forms accumulated at higher levels in GVB-infected than in GVB-free berries, consistent with the expression profiles of the related biosynthetic genes. These results contribute to improve our understanding of the multifaceted grapevine-virus interaction.

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

BACKGROUND

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

RESULTS

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

CONCLUSIONS

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

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.

Overexpression of Rosea1 From Snapdragon Enhances Anthocyanin Accumulation and Abiotic Stress Tolerance in Transgenic Tobacco

The co-expression of Rosea1 (Ros1) and Delila (Del) regulates anthocyanin levels in snapdragon flowers, as well as in tomato, petunia, and tobacco. However, there is little information on how Ros1 expression alone controls anthocyanin regulation and whether it is involved in the mechanism that leads to abiotic stress tolerance. In the present study, tobacco (Nicotiana tabacum 'Xanthi') transgenic plants overexpressing Ros1 (T2-Ros1-1, T2-Ros1-2, T2-Ros1-3, and T2-Ros1-4) promoted accumulation of anthocyanin in leaves and flowers by elevating the transcription of all key genes involved in the biosynthesis of this pigment. This promotion largely occurred through the upregulation of dihydroflavonol 4-reductase (DFR), and anthocyanidin synthase genes in leaves and upregulation of DFR in flowers. Under normal conditions, the transgenic lines and wild type (WT) plants showed well-developed broad leaves and regular roots, whereas a reduction in plant growth was observed under cold and drought stresses. However, the transgenic T2-Ros1 lines were able to tolerate the stresses better than the WT line by inducing reactive oxygen species scavenging activities, and the expression of antioxidant-related and stress-responsive genes. In addition, phylogenetic analysis clustered Ros1 with many transcription factors (TFs) that confer tolerance to different abiotic stresses. Overall, the results obtained here suggest that Ros1 overexpression upregulates anthocyanin biosynthetic, antioxidant-related, and stress-responsive genes thereby enhancing anthocyanin accumulation and abiotic stress tolerance.

Overexpression of 9-cis-Epoxycarotenoid Dioxygenase Cisgene in Grapevine Increases Drought Tolerance and Results in Pleiotropic Effects

9-cis-epoxycarotenoid dioxygenase (NCED) is a key enzyme involved in the biosynthesis of abscisic acid (ABA), which is associated with drought tolerance in plants. An osmotic-inducible VaNCED1 gene was isolated from a drought-resistant cultivar of Vitis amurensis and constitutively overexpressed in a drought-sensitive cultivar of Vitis vinifera. Transgenic plants showed significantly improved drought tolerance, including a higher growth rate and better drought resistant under drought conditions, compared to those of wild-type (WT) plants. After water was withheld for 50 days, the upper leaves of transgenic plants remained green, whereas most leaves of WT plants turned yellow and fell. Besides the increase in ABA content, overexpression of VaNCED1 induced the production of jasmonic acid (JA) and accumulation of JA biosynthesis-related genes, including allene oxide cyclase (AOC) and 12-oxophytodienoate reductase (OPR3). Moreover, transgenic plants possessed advantageous physiological indices, including lower leaf stomatal density, lower photosynthesis rate, and lower accumulation of proline and superoxide dismutase (SOD), compared to those of WT plants, indicating increased resistance to drought stress. Quantitative real time polymerase chain reaction (RT-qPCR) analysis revealed that overexpression of VaNCED1 enhanced the expression of drought-responsive genes, such as ABA-responsive element1 (ABRE1), ABRE binding factors 2 (ABF2), plasma membrane intrinsic proteins 2 (PIP2), C-repeat/DRE-Binding Factor 4 (VvCBF4) and ABA-insensitive 5 (ABI5). Although the development of transgenic plants was delayed by 4 months than WT plants, because of seed dormancy and abnormal seedlings, the surviving transgenic plants provided a solid method for protection of woody plants from drought stress.

A novel cotton WRKY gene, GhWRKY6-like, improves salt tolerance by activating the ABA signaling pathway and scavenging of reactive oxygen species

WRKY transcription factors are transcriptional regulators of signaling pathways involved in biotic and abiotic stress responses. In this study, we report that ectopic expression of the GhWRKY6-like gene significantly improved salt tolerance in Arabidopsis thaliana while silencing the GhWRKY6-like increase the sensitivity to abiotic stresses in cotton. GhWRKY6-like was localized to the nucleus. Expression of GhWRKY6-like was remarkably induced by salt, polyethylene glycol (PEG) and abscisic acid (ABA) treatments. For further characterization, the GhWRKY6-like gene was cloned and transformed into Arabidopsis. Our findings showed that the germination rate and root length were significantly improved in plants overexpressing GhWRKY6-like vs wild type (WT) under salt, mannitol and ABA treatments. Additionally, the overexpressing lines showed greater salt tolerance than WT plants in soil. In addition, overexpressing plants accumulated less H₂ O₂ and malondialdehyde (MDA), while higher proline content, superoxide dismutase (SOD) and peroxidase (POD) activities were detected under salt and osmotic stresses. In contrast, virus-induced gene silencing (VIGS) of GhWRKY6-like in cotton showed enhanced sensitivity compared to WT plants during salt and drought stresses. Additionally, expression analysis of stress-responsive genes in GhWRKY6-like Arabidopsis revealed that there was increased expression of genes involved in the ABA signaling pathway (AtABF4, AtABI5 and AtMYC2) and osmotic stress (AtSOS2, AtRD29a and AtRD29b). Our results revealed that GhWRKY6-like enhanced salt tolerance in Arabidopsis by scavenging reactive oxygen species and regulating the ABA signaling pathway. We suggest that overexpression of the GhWRKY6-like gene in cotton will enhance tolerance against salt, drought and osmotic stresses.

MtCAS31 Aids Symbiotic Nitrogen Fixation by Protecting the Leghemoglobin MtLb120-1 Under Drought Stress in Medicago truncatula

Symbiotic nitrogen fixation (SNF) in legume root nodules injects millions of tons of nitrogen into agricultural lands and provides ammonia to non-legume crops under N-deficient conditions. During plant growth and development, environmental stresses, such as drought, salt, cold, and heat stress are unavoidable. This raises an interesting question as to how the legumes cope with the environmental stress along with SNF. Under drought stress, dehydrin proteins are accumulated, which function as protein protector and osmotic substances. In this study, we found that the dehydrin MtCAS31 (cold-acclimation-specific 31) functions in SNF in Medicago truncatula during drought stress. We found that MtCAS31 is expressed in nodules and interacts with leghemoglobin MtLb120-1. The interaction between the two proteins protects MtLb120-1 from denaturation under thermal stress in vivo. Compared to wild type, cas31 mutants display a lower nitrogenase activity, a lower ATP/ADP ratio, higher expression of nodule senescence genes and higher accumulation of amyloplasts under dehydration conditions. The results suggested that MtCAS31 protects MtLb120-1 from the damage of drought stress. We identified a new function for dehydrins in SNF under drought stress, which enriches the understanding of the molecular mechanism of dehydrins.

Overexpression of a SDD1-Like Gene From Wild Tomato Decreases Stomatal Density and Enhances Dehydration Avoidance in Arabidopsis and Cultivated Tomato

Stomata are microscopic valves formed by two guard cells flanking a pore, which are located on the epidermis of most aerial plant organs and are used for water and gas exchange between the plant and the atmosphere. The number, size and distribution of stomata are set during development in response to changing environmental conditions, allowing plants to minimize the impact of a stressful environment. In Arabidopsis, STOMATAL DENSITY AND DISTRIBUTION 1 (AtSDD1) negatively regulates stomatal density and optimizes transpiration and water use efficiency (WUE). Despite this, little is known about the function of AtSDD1 orthologs in crop species and their wild stress-tolerant relatives. In this study, SDD1-like from the stress-tolerant wild tomato Solanum chilense (SchSDD1-like) was identified through its close sequence relationship with SDD1-like from Solanum lycopersicum and AtSDD1. Both Solanum SDD1-like transcripts accumulated in high levels in young leaves, suggesting that they play a role in early leaf development. Arabidopsis sdd1-3 plants transformed with SchSDD1-like under a constitutive promoter showed a significant reduction in stomatal leaf density compared with untransformed sdd1-3 plants. Additionally, a leaf dehydration shock test demonstrated that the reduction in stomatal abundance of transgenic plants was sufficient to slow down dehydration. Overexpression of SchSDD1-like in cultivated tomato plants decreased the stomatal index and density of the cotyledons and leaves, and resulted in higher dehydration avoidance. Taken together, these results indicate that SchSDD1-like functions in a similar manner to AtSDD1 and suggest that Arabidopsis and tomatoes share this component of the stomatal development pathway that impinges on water status.

Overexpression of snapdragon Delila (Del) gene in tobacco enhances anthocyanin accumulation and abiotic stress tolerance

BACKGROUND

Rosea1 (Ros1) and Delila (Del) co-expression controls anthocyanin accumulation in snapdragon flowers, while their overexpression in tomato strongly induces anthocyanin accumulation. However, little data exist on how Del expression alone influences anthocyanin accumulation.

RESULTS

In tobacco (Nicotiana tabacum 'Xanthi'), Del expression enhanced leaf and flower anthocyanin production through regulating NtCHS, NtCHI, NtF3H, NtDFR, and NtANS transcript levels. Transgenic lines displayed different anthocyanin colors (e.g., pale red: T0-P, red: T0-R, and strong red: T0-S), resulting from varying levels of biosynthetic gene transcripts. Under salt stress, the T2 generation had higher total polyphenol content, radical (DPPH, ABTS) scavenging activities, antioxidant-related gene expression, as well as overall greater salt and drought tolerance than wild type (WT).

CONCLUSION

We propose that Del overexpression elevates transcript levels of anthocyanin biosynthetic and antioxidant-related genes, leading to enhanced anthocyanin production and antioxidant activity. The resultant increase of anthocyanin and antioxidant activity improves abiotic stress tolerance.

Molecular cloning, characterization, heterologous expression and in-silico analysis of disordered boiling soluble stress-responsive wBsSRP protein from drought tolerant wheat cv.PBW 175

The structural and physico-chemical properties that account for the multi-functionality of dehydrins remain largely unknown. In this study, we identified, sequenced and cloned a stress regulated cDNA encoding a dehydrin-like boiling stable protein (designated as wBsSRP; wheat boiling stable stress responsive protein) from drought stressed seedlings of drought tolerant cultivar of wheat (PBW 175). qRT-PCR analysis documented high transcripts levels of wBsSRP during drought and cold conditions in the tolerant cv. PBW 175 as a part of adaptive response to stress while the levels were significantly lower in the sensitive cv. PBW 343. We also describe in-silico characterization and molecular modeling of wBsSRP through homology search, motif analysis, secondary structure prediction, active site prediction and 3D structure analysis. The physico-chemical properties and theoretical data of wBsSRP depicts that it is a canonical group 2 LEA protein. The recombinant wBsSRP protein when expressed in E. coli detected a specific differential band (∼11 kDa) on SDS- PAGE after IPTG induction. The functional analysis of wBsSRP in E. coli revealed that wBsSRP is essential for the survival of E. coli as well as for maintaining bacterial growth under various stress conditions. In vitro peroxidase protection assay during heat stress (50 and 100 °C) showed that in the presence of wBsSRP, peroxidase activity was significantly retained and/or increased. Based upon the findings, it is suggested that wBsSRP accentuated the effects of stress by acting as a protectant and by the stabilization of membranes, thereby contributing to the improved stress tolerance of the recombinant E. coli under various abiotic stress conditions. We suggest that these findings might provide the rationale for the mechanism of how these proteins obviate the adverse effects of dehydration stress.

Overexpression of MpCYS4, A Phytocystatin Gene from Malus prunifolia (Willd.) Borkh., Enhances Stomatal Closure to Confer Drought Tolerance in Transgenic Arabidopsis and Apple

Phytocystatins (PhyCys) comprise a group of inhibitors for cysteine proteinases in plants. They play a wide range of important roles in regulating endogenous processes and protecting plants against various environmental stresses, but the underlying mechanisms remain largely unknown. Here, we detailed the biological functions of MpCYS4, a member of cystatin genes isolated from Malus prunifolia. This gene was activated under water deficit, heat (40°C), exogenous abscisic acid (ABA), or methyl viologen (MV) (Tan et al., 2014a). At cellular level, MpCYS4 protein was found to be localized in the nucleus, cytoplasm, and plasma membrane of onion epidermal cells. Recombinant MpCYS4 cystatin expressed in Escherichia coli was purified and it exhibited cysteine protease inhibitor activity. Transgenic overexpression of MpCYS4 in Arabidopsis (Arabidopsis thaliana) and apple (Malus domestica) led to ABA hypersensitivity and series of ABA-associated phenotypes, such as enhanced ABA-induced stomatal closing, altered expression of many ABA/stress-responsive genes, and enhanced drought tolerance. Taken together, our results demonstrate that MpCYS4 is involved in ABA-mediated stress signal transduction and confers drought tolerance at least in part by enhancing stomatal closure and up-regulating the transcriptional levels of ABA- and drought-related genes. These findings provide new insights into the molecular mechanisms by which phytocystatins influence plant growth, development, and tolerance to stress.

Different dehydrins perform separate functions in Physcomitrella patens

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

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.

Comparison of full-length and conserved segments of wheat dehydrin DHN-5 overexpressed in Arabidopsis thaliana showed different responses to abiotic and biotic stress

Dehydrins (DHNs) are among the most common proteins accumulated in plants under water-related stress. They typically contain at least three conserved sequences designated as the Y-, S- and K-segments. The present work aims to highlight the role of the K-segments in plant tolerance to biotic and abiotic stresses. For this purpose, transgenic Arabidopsis thaliana (L.) Heyhn. lines expressing distinct wheat (Triticum aestivum L.) DHN-5 truncated constructs with or without the K-segments were generated. Our results showed that unlike the derivative lacking a K-segment, constructs containing only one or two K-segments enhanced the tolerance of A. thaliana to diverse stresses and were similar to the full-length wheat DHN-5. Moreover, compared with the wild-type and the YS form, the transgenic plants overexpressing wheat DHN-5 with K-segments maintained higher superoxide dismutase, catalase and peroxide dismutase enzymatic activity, and accumulated lower levels of H2O2 and malondialdehyde. In addition, we demonstrated that lines like A. thaliana overexpressing wheat DHN-5 showed increased resistance to fungal infections caused by Botrytis cinerea and Alternaria solani. Finally, the overexpression of the different forms of wheat DHN-5 led to the regulation of the expression of several genes involved in the jasmonic acid signalling pathway.

Novel functional microRNAs from virus-free and infected Vitis vinifera plants under water stress

MicroRNAs (miRNAs) are small non-coding RNAs that regulate the post-transcriptional control of several pathway intermediates, thus playing pivotal roles in plant growth, development and response to biotic and abiotic stresses. In recent years, the grapevine genome release, small(s)-RNAseq and degradome-RNAseq together has allowed the discovery and characterisation of many miRNA species, thus rendering the discovery of additional miRNAs difficult and uncertain. Taking advantage of the miRNA responsiveness to stresses and the availability of virus-free Vitis vinifera plants and those infected only by a latent virus, we have analysed grapevines subjected to drought in greenhouse conditions. The sRNA-seq and other sequence-specific molecular analyses have allowed us to characterise conserved miRNA expression profiles in association with specific eco-physiological parameters. In addition, we here report 12 novel grapevine-specific miRNA candidates and describe their expression profile. We show that latent viral infection can influence the miRNA profiles of V. vinifera in response to drought. Moreover, study of eco-physiological parameters showed that photosynthetic rate, stomatal conductance and hydraulic resistance to water transport were significantly influenced by drought and viral infection. Although no unequivocal cause–effect explanation could be attributed to each miRNA target, their contribution to the drought response is discussed.

Comparative Physiological and Transcriptional Analyses of Two Contrasting Drought Tolerant Alfalfa Varieties

Drought is one of major environmental determinants of plant growth and productivity. Alfalfa (Medicago sativa) is a legume perennial forage crop native to the arid and semi-arid environment, which is an ideal candidate to study the biochemical and molecular mechanisms conferring drought resistance in plants. In this study, drought stress responses of two alfalfa varieties, Longdong and Algonquin, were comparatively assayed at the physiological, morphological, and transcriptional levels. Under control condition, the drought-tolerant Longdong with smaller leaf size and lower stomata density showed less water loss than the drought-sensitive Algonquin. After exposing to drought stress, Longdong showed less severe cell membrane damage, more proline, and ascorbate (ASC) contents and less accumulation of H2O2 than Algonquin. Moreover, significantly higher antioxidant enzymes activities after drought treatment were found in Longdong when compared with Algonquin. In addition, transcriptional expression analysis showed that Longdong exhibited significantly higher transcripts of drought-responsive genes in leaf and root under drought stress condition. Taken together, these results indicated that Longdong variety was more drought-tolerant than Algonquin variety as evidenced by less leaf firing, more lateral root number, higher relative aboveground/underground biomass per plant and survival rate.