Monitoring the expression pattern of 1300 Arabidopsis genes under drought and cold stresses by using a full-length cDNA microarray

Regulatory networks in plant responses to drought and cold stress

Drought and cold represent distinct types of abiotic stress, each initiating unique primary signaling pathways in response to dehydration and temperature changes, respectively. However, a convergence at the gene regulatory level is observed where a common set of stress-responsive genes is activated to mitigate the impacts of both stresses. In this review, we explore these intricate regulatory networks, illustrating how plants coordinate distinct stress signals into a collective transcriptional strategy. We delve into the molecular mechanisms of stress perception, stress signaling, and the activation of gene regulatory pathways, with a focus on insights gained from model species. By elucidating both the shared and distinct aspects of plant responses to drought and cold, we provide insight into the adaptive strategies of plants, paving the way for the engineering of stress-resilient crop varieties that can withstand a changing climate.

A comprehensive review of TGA transcription factors in plant growth, stress responses, and beyond

TGA transcription factors (TFs), belonging to the D clade of the basic region leucine zipper (bZIP) family, exhibit a specific ability to recognize and bind to regulatory elements with TGACG as the core recognition sequence, enabling the regulation of target gene expression and participation in various biological regulatory processes. In plant growth and development, TGA TFs influence organ traits and phenotypes, including initial root length and flowering time. They also play a vital role in responding to abiotic stresses like salt, drought, and cadmium exposure. Additionally, TGA TFs are involved in defending against potential biological stresses, such as fungal bacterial diseases and nematodes. Notably, TGA TFs are sensitive to the oxidative-reductive state within plants and participate in pathways that aid in the elimination of reactive oxygen species (ROS) generated during stressful conditions. TGA TFs also participate in multiple phytohormonal signaling pathways (ABA, SA, etc.). This review thoroughly examines the roles of TGA TFs in plant growth, development, and stress response. It also provides detailed insights into the mechanisms underlying their involvement in physiological and pathological processes, and their participation in plant hormone signaling. This multifaceted exploration distinguishes this review from others, offering a comprehensive understanding of TGA TFs.

Comprehensive Identification of the β-Amylase (BAM) Gene Family in Response to Cold Stress in White Clover

White clover (Trifolium repens L.) is an allopolyploid plant and an excellent perennial legume forage. However, white clover is subjected to various stresses during its growth, with cold stress being one of the major limiting factors affecting its growth and development. Beta-amylase (BAM) is an important starch-hydrolyzing enzyme that plays a significant role in starch degradation and responses to environmental stress. In this study, 21 members of the BAM gene family were identified in the white clover genome. A phylogenetic analysis using BAMs from Arabidopsis divided TrBAMs into four groups based on sequence similarity. Through analysis of conserved motifs, gene duplication, synteny analysis, and cis-acting elements, a deeper understanding of the structure and evolution of TrBAMs in white clover was gained. Additionally, a gene regulatory network (GRN) containing TrBAMs was constructed; gene ontology (GO) annotation analysis revealed close interactions between TrBAMs and AMY (α-amylase) and DPE (4-alpha-glucanotransferase). To determine the function of TrBAMs under various tissues and stresses, RNA-seq datasets were analyzed, showing that most TrBAMs were significantly upregulated in response to biotic and abiotic stresses and the highest expression in leaves. These results were validated through qRT-PCR experiments, indicating their involvement in multiple gene regulatory pathways responding to cold stress. This study provides new insights into the structure, evolution, and function of the white clover BAM gene family, laying the foundation for further exploration of the functional mechanisms through which TrBAMs respond to cold stress.

RD29A and RD29B rearrange genetic and epigenetic markers in priming systemic defense responses against drought and salinity

Drought has become the most important limiting factor to crop productions. Research thus far has been devoted to identifying drought-responsive genes (DRGs) via breeding and engineering approaches. Still, these efforts have not resulted in a solution to combat drought's effects because the ectopic expression of most DRGs causes adverse effects that reduce plant growth and yields. Lately, we discovered that two DRGs, Response to Desiccation (RD)29A and RD29B, induced by Paenibacillus polymyxa CR1, a plant growth-promoting rhizobacterium capable of priming drought tolerance and concurrently stimulating plant growth, play pivotal roles in defense responses against drought. In this study, we employ the ChlP and qRT-PCR analyses and further clarify that P. polymyxa CR1 reformats the chromatin/transcriptional memory of RD29s, positioned as upstream controllers that fine-tune the temporal dynamic of stress-regulating transcription factors (TFs) in elaborating induced systemic drought tolerance without growth penalties. Two genes coordinate the upregulation of NAC TFs, while feedback inhibiting CBF TFs, which regulate downstream DRG expressions. This supports that RD29s are unique, feasible transgene candidates for improving plants' survival capacity in both optimal and drought conditions. However, the mode of action of RD29A and RD29B are partly independent, exerting distinct roles in disparate ecological states. When subjected to increasing NaCl concentrations, the KO mutant of RD29A (rd29a) displayed enhanced tolerance compared to WT and rd29b plants, proposing that RD29B, but not RD29A, a key player in conferring WT-like tolerance to salinity stress; further studies will be needed to optimize/maximize their applications in engineering for-profit drought and/or broad-spectrum stress tolerant crops.

Heterologous VvDREB2c Expression Improves Heat Tolerance in Arabidopsis by Inducing Photoprotective Responses

Extreme temperatures limit grape production and sustainability. Dehydration-responsive element-binding (DREB) transcription factors affect plant responses to temperature related stresses. Therefore, we investigated the role of VvDREB2c, a DREB-coding gene, found in grapes (Vitis vinifera L.). Protein characterization revealed that VvDREB2c is localized to the nucleus and that its AP2/ERF domain contains three β-sheets and one α-helix sheet. Analysis of the VvDREB2c promoter region revealed the presence of light-, hormone-, and stress-related cis-acting elements. Furthermore, we observed that the heterologous expression of VvDREB2c in Arabidopsis improved growth, drought tolerance, and heat tolerance. Furthermore, it improved the leaf quantum yield of regulated energy dissipation [Y(NPQ)], elevated the activities of RuBisCO, and phosphoenolpyruvate carboxylase and reduced the quantum yield of non-regulated energy dissipation [Y(NO)] in plants exposed to high temperatures. VvDREB2c-overexpressing lines also specifically upregulated several photosynthesis-related genes (CSD2, HSP21, and MYB102). In addition, VvDREB2c-overexpressing lines reduced light damage and enhanced photoprotective ability by dissipating excess light energy and converting it into heat, which eventually improves tolerance to high temperature. The contents of abscisic acid, jasmonic acid, and salicylic acid and differentially expressed genes (DEGs) in the mitogen-activated protein kinase (MAPK) signaling pathway were affected by heat stress in VvDREB2c-overexpressing lines, which indicated that VvDREB2c positively regulates heat tolerance via a hormonal pathway in Arabidopsis. VvDREB2c promotes heat tolerance in Arabidopsis by exerting effects on photosynthesis, hormones, and growth conditions. This study may provide useful insights into the enrichment of the heat-tolerance pathways in plants.

Overexpression of the cotton trihelix transcription factor GhGT23 in Arabidopsis mediates salt and drought stress tolerance by binding to GT and MYB promoter elements in stress-related genes

Cotton (Gossypium hirsutum L.) is the world's most economically valuable textile crop. However, cotton plants are often subjected to numerous abiotic stresses that can dramatically limit yield. Trihelix transcription factors (TTFs) play important roles in abiotic stress responses in many plant species, and efforts to better understand their roles in cotton abiotic stress responses are ongoing. In this study, a member of the cotton TTF family (GhGT23) was functionally characterized. This protein contains a SANT domain and is a member of the SIP subfamily of TTF proteins. GhGT23 was significantly (p < 0.05) and highly expressed in cotton fiber compared to relatively low expression in other tissues. A significant (p < 0.05) increase in GhGT23 expression occurred in cotton seedlings within 12 hours of drought, salt, and ABA exposure. The GhGT23 protein localized in the nucleus but exhibited no signs of transactivation activity. GhGT23 overexpression in Arabidopsis conferred enhanced drought and salt stress tolerance. The expression of stress-related genes was higher in transgenic Arabidopsis expressing GhGT23 than in wild-type plants subjected to salt stress. The results of electrophoretic mobility shift assay revealed that GhGT23 could bind to the GT cis-elements GT-1Box (Box II), GT2-Box, GT3-Box, GT-3a (Site1-type), GT-3b, and Box as well as the MYB cis-elements MBS1 and MRE4. Our results demonstrate that GhGT23 positively regulates salt and drought stress responses, possibly by enhancing the expression of stress-related genes.

Recent progress and perspectives on physiological and molecular mechanisms underlying cold tolerance of tea plants

Tea is one of the most consumed and widely planted beverage plant worldwide, which contains many important economic, healthy, and cultural values. Low temperature inflicts serious damage to tea yields and quality. To cope with cold stress, tea plants have evolved a cascade of physiological and molecular mechanisms to rescue the metabolic disorders in plant cells caused by the cold stress; this includes physiological, biochemical changes and molecular regulation of genes and associated pathways. Understanding the physiological and molecular mechanisms underlying how tea plants perceive and respond to cold stress is of great significance to breed new varieties with improved quality and stress resistance. In this review, we summarized the putative cold signal sensors and molecular regulation of the CBF cascade pathway in cold acclimation. We also broadly reviewed the functions and potential regulation networks of 128 cold-responsive gene families of tea plants reported in the literature, including those particularly regulated by light, phytohormone, and glycometabolism. We discussed exogenous treatments, including ABA, MeJA, melatonin, GABA, spermidine and airborne nerolidol that have been reported as effective ways to improve cold resistance in tea plants. We also present perspectives and possible challenges for functional genomic studies on cold tolerance of tea plants in the future.

Overexpression of a Malus baccata CBF transcription factor gene, MbCBF1, Increases cold and salinity tolerance in Arabidopsis thaliana

CBFs play a crucial role when plants are in adverse environmental conditions for growth. However, there are few reports on the role of CBF gene in stress responses of Malus plant. In this experiment, a new CBF TF was separated from M. baccata which was named MbCBF1. MbCBF1 protein was found to be localized in the nucleus after subcellular localization. Furthermore, the expression of MbCBF1 was highly accumulated in new leaves and roots due to the high influence of cold and high salt in M. baccata seedlings. After introducing MbCBF1 into A. thaliana, transgenic A. thaliana can better adapt to the living conditions of cold and high salt. The increased expression of MbCBF1 in A. thaliana also increased the contents of proline, remarkablely improved the activities of SOD, POD and CAT, but the content of MDA was decreased. Although the chlorophyll content also decreased, it decreased less in transgenic plants. In short, above date showed that MbCBF1 has a positive effect on improving A. thaliana cold and high salt tolerance. MbCBF1 can regulate the expression of its downstream gene in transgenic lines, up-regulate the expression of key genes COR15a, RD29a/bandCOR6.6/47 related to low temperature under cold conditions and NCED3, CAT1, P5CS1, RD22, DREB2A,PIF1/4, SOS1 and SnRK2.4 related to salt stress under high salt conditions, so as to further improve the adaptability and tolerance of the transgenic plants to low temperature and high salt environment.

Drought and global hunger: biotechnological interventions in sustainability and management

Drought may be efficiently managed using the following strategies: prevention, mitigation, readiness, recovery, and transformation. Biotechnological interventions may become highly important in reducing plants' drought stress in order to address key plant challenges such as population growth and climate change. Drought is a multidimensional construct with several triggering mechanisms or contributing factors working at various spatiotemporal scales, making it one of the known natural catastrophes. Drought is among the causes of hunger and malnutrition, decreasing agricultural output, and poor nutrition. Many deaths caused in children are due to hunger situations, and one in four children face stunted growth. All this hunger and malnutrition may be responsible for the reduction in agricultural productivity caused due to the drought situations affecting food security. Global Hunger Index has been accelerating due to under-nutrition and under-5 deaths. Drought has been covering more than 20% of the world's agricultural areas, leading to significantly less food production than what is required for consumption. Drought reduces soil fertility and adversely affects soil biological activity reducing the inherent capacity of the soil to support vegetation. Recent droughts have had a much greater effect on people's lives, even beyond causing poverty and hunger. Drought may have substantial financial consequences across the globe it may cause a severe impact on the world economy. It is a natural feature of the environment that will appear and disappear as it has in history. Due to increasing temperatures and growing vulnerabilities, it will undoubtedly occur more often and seriously in the coming years. To ensure sustainable socio-economic and social development, it is critical to reducing the effects of potential droughts worldwide using different biotechnological interventions. It's part of a long-term growth plan, and forecasting is essential for early warnings and global hunger management.

mRNA N6 -methyladenosine is critical for cold tolerance in Arabidopsis

Plants respond to low temperatures by altering the mRNA abundance of thousands of genes contributing to numerous physiological and metabolic processes that allow them to adapt. At the post-transcriptional level, these cold stress-responsive transcripts undergo alternative splicing, microRNA-mediated regulation and alternative polyadenylation, amongst others. Recently, m⁶ A, m⁵ C and other mRNA modifications that can affect the regulation and stability of RNA were discovered, thus revealing another layer of post-transcriptional regulation that plays an important role in modulating gene expression. The importance of m⁶ A in plant growth and development has been appreciated, although its significance under stress conditions is still underexplored. To assess the role of m⁶ A modifications during cold stress responses, methylated RNA immunoprecipitation sequencing was performed in Arabidopsis seedlings esposed to low temperature stress (4°C) for 24 h. This transcriptome-wide m⁶ A analysis revealed large-scale shifts in this modification in response to low temperature stress. Because m⁶ A is known to affect transcript stability/degradation and translation, we investigated these possibilities. Interestingly, we found that cold-enriched m⁶ A-containing transcripts demonstrated the largest increases in transcript abundance coupled with increased ribosome occupancy under cold stress. The significance of the m⁶ A epitranscriptome on plant cold tolerance was further assessed using the mta mutant in which the major m⁶ A methyltransferase gene was mutated. Compared to the wild-type, along with the differences in CBFs and COR gene expression levels, the mta mutant exhibited hypersensitivity to cold treatment as determined by primary root growth, biomass, and reactive oxygen species accumulation. Furthermore, and most importantly, both non-acclimated and cold-acclimated mta mutant demonstrated hypersensitivity to freezing tolerance. Taken together, these findings suggest a critical role for the epitranscriptome in cold tolerance of Arabidopsis.

Molecular Cloning and Analysis of an Acetyl-CoA C-acetyltransferase Gene (EkAACT) from Euphorbia kansui Liou

Terpenoids are the largest class of natural products and are essential for cell functions in plants and their interactions with the environment. Acetyl-CoA acetyltransferase (AACT, EC2.3.1.9) can catalyze a key initiation step of the mevalonate pathway (MVA) for terpenoid biosynthesis and is modulated by many endogenous and external stimuli. Here, the function and expression regulation activities of AACT in Euphorbia kansui Liou (EkAACT) were reported. Compared with wild-type Arabidopsis, the root length, whole seedling fresh weight and growth morphology of EkAACT-overexpressing plants were slightly improved. The transcription levels of AtAACT, AtMDC, AtMK, AtHMGR, and AtHMGS in the MVA pathway and total triterpenoid accumulation increased significantly in transgenic Arabidopsis. Under NaCl and PEG treatment, EkAACT-overexpressing Arabidopsis showed a higher accumulation of total triterpenoids, higher enzyme activity of peroxidase (POD) and superoxide dismutase (SOD), increased root length and whole seedling fresh weight, and a decrease in the proline content, which indicated that plant tolerance to abiotic stress was enhanced. Thus, AACT, as the first crucial enzyme, plays a major role in the overall regulation of the MVA pathway.

Transcriptomic Profile Analysis of Populus talassica × Populus euphratica Response and Tolerance under Salt Stress Conditions

A new Populus variety with a strong salt tolerance was obtained from cross breeding P. talassica as the female parent and P. euphratica as the male parent. In order to elucidate the molecular mechanism and find out the major differentially expressed genes of salt tolerance of P. talassica × P. euphratica, after being subjected to salt stress, at 0, 200, and 400 mmol/L NaCl, the root, stem, and leaf transcriptomes (denoted as R0, S0, and L0; R200, S200, and L200; and R400, S400, and L400, respectively) of P. talassica × P. euphratica were sequenced. In total, 41,617 differentially expressed genes (DEGs) were identified in all the comparison groups with 21,603 differentially upregulated genes and 20,014 differentially downregulated genes. Gene Ontology analysis showed that DEGs were significantly enriched in biological processes that may be involved in salt stress, such as ‘cell communication’, ‘ion transport’, ‘signaling’, and signal ‘transmission’. Kyoto Encyclopedia of Genes and Genomes analysis showed that DEGs were mainly enriched in pathways of ‘plant–pathogen interaction’, ‘carbon metabolism’, and ‘plant hormone signal transmission’. The pathways and related gene information formed a basis for future research on the mechanisms of salt stress, the development of molecular markers, and the cloning of key genes in P. talassica × P. euphratica.

Genetic loci associated with freezing tolerance in a European rapeseed (Brassica napus L.) diversity panel identified by genome-wide association mapping

Winter biotypes of rapeseed (Brassica napus L.) require a vernalization treatment to enter the reproductive phase and generally produce greater yields than spring rapeseed. To find genetic loci associated with freezing tolerance in rapeseed, we first performed genotyping-by-sequencing (GBS) on a diversity panel consisting of 222 rapeseed accessions originating primarily from Europe, which identified 69,554 high-quality single-nucleotide polymorphisms (SNPs). Model-based cluster analysis suggested that there were eight subgroups. The diversity panel was then phenotyped for freezing survival (visual damage and Fv/Fo and Fv/Fm) after 2 months of cold acclimation (5°C) and a freezing treatment (-15°C for 4 h). The genotypic and phenotypic data for each accession in the rapeseed diversity panel was then used to conduct a genome-wide association study (GWAS). GWAS results showed that 14 significant markers were mapped to seven chromosomes for the phenotypes scored. Twenty-four candidate genes located within the mapped loci were identified as previously associated with lipid, photosynthesis, flowering, ubiquitination, and cytochrome P450 in rapeseed or other plant species.

Glyphosate-induced GhAG2 is involved in resistance to salt stress in cotton

KEY MESSAGE

The transcription of GhAG2 was strongly enhanced by glyphosate treatment. Overexpression of GhAG2 could improve plant tolerance to salt and salicylic acid stress. Although glyphosate has been widely used as an herbicide over the past decade owing to its high efficacy on weed controls and worldwide commercialization of glyphosate-resistant crops, little is known about the glyphosate-induced responses and transcriptional changes in cotton plants. Here, we report the identification of 26 differentially expressed genes after glyphosate treatment, among which, six highly up-regulated sequences share homology to cotton expressed sequence tags (ESTs) responsive to abiotic stresses. In addition, we cloned GhAG2, a gene whose transcription was strongly enhanced by glyphosate treatment and other abiotic stresses. Transgenic GhAG2 plants showed improved tolerance to salt, and salicylic acid (SA) stress. The results could open the door to exploring the function of the GhAG2 proteins, the glyphosate-induced transcriptional profiles, and the physiological biochemical responses in cotton and other crops. GhAG2 could also be used to improve salt stress tolerance through breeding and biotechnology in crops. Furthermore, these results could provide guidelines to develop a glyphosate-inducible system for controlled expression of targeted genes in plants.

Overexpression of SgDREB2C from Stylosanthes guianensis Leads to Increased Drought Tolerance in Transgenic Arabidopsis

Stylosanthes guianensis is an excellent forage legume in subtropical and tropical regions with drought tolerance, but little is known about its drought tolerance mechanism. Dehydration responsive element binding proteins (DREBs) are responsive to abiotic stresses. A SgDREB2C was cloned from S. guianensis, while SgDREB2C protein was localized at nucleus. SgDREB2C transcript was induced by dehydration treatment. Transgenic Arabidopsis overexpressing SgDREB2C showed enhanced osmotic and drought tolerance with higher levels of relative germination rate, seedlings survival rate and F_v/F_m and lower levels of ion leakage compared with WT after osmotic and drought stress treatments. In addition, higher levels of superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities and stress responsive gene (COR15A, COR47) transcripts were observed in transgenic Arabidopsis than in WT under drought stress. These results suggest that SgDREB2C regulated drought tolerance, which was associated with increased SOD and APX activities and stress-responsive gene expression under drought stress.

ROS1-mediated decrease in DNA methylation and increase in expression of defense genes and stress response genes in Arabidopsis thaliana due to abiotic stresses

BACKGROUND

Small interfering RNAs (siRNAs) target homologous genomic DNA sequences for cytosine methylation, known as RNA-directed DNA methylation (RdDM), plays an important role in transposon control and regulation of gene expression in plants. Repressor of silencing 1 (ROS1) can negatively regulate the RdDM pathway.

RESULTS

In this paper, we investigated the molecular mechanisms by which an upstream regulator ACD6 in the salicylic acid (SA) defense pathway, an ABA pathway-related gene ACO3, and GSTF14, an endogenous gene of the glutathione S-transferase superfamily, were induced by various abiotic stresses. The results demonstrated that abiotic stresses, including water deficit, cold, and salt stresses, induced demethylation of the repeats in the promoters of ACD6, ACO3, and GSTF14 and transcriptionally activated their expression. Furthermore, our results revealed that ROS1-mediated DNA demethylation plays an important role in the process of transcriptional activation of ACD6 and GSTF14 when Arabidopsis plants are subjected to cold stress.

CONCLUSIONS

This study revealed that ROS1 plays an important role in the molecular mechanisms associated with genes involved in defense pathways in response to abiotic stresses.

Investigation of the interaction of a papain-like cysteine protease (RD19c) with selenium-binding protein 1 (SBP1) in Arabidopsis thaliana

AtRD19c is a member of the papain-like cysteine proteases known for its participation in anther development after its maturation by βVPE (vacuolar processing enzyme). This papain-like cysteine protease was identified as an interacting protein of AtSBP1 (selenium binding protein 1) in a yeast two-hybrid screening. To confirm this interaction, we studied AtRD19c with respect to its expression and ability to interact with AtSBP1. The highest gene expression levels of AtRD19c were observed in the roots of 10-day-old seedlings, whereas minimum levels appeared in the hypocotyls of 10-day-old seedlings and flowers. AtRD19c expression was upregulated by selenium, and analysis of its promoter activity showed colocalization of a reporter gene (GUS) with AtSBP1. Additionally, the AtRD19c expression pattern was upregulated in the presence of selenite, indicating its participation in the Se response network. Confocal fluorescence microscopy revealed that AtRD19c localizes in the root tip, lateral roots, and leaf trichomes. Finally, we confirmed the physical interaction between AtRD19c and AtSBP1 and showed the importance of the first 175 aa of the AtSBP1 polypeptide in this interaction. Importantly, the AtRD19c-AtSBP1 interaction was also demonstrated in planta by employing bimolecular fluorescent complementation (BiFC) in a protoplast system.

Functional genomics in plant abiotic stress responses and tolerance: From gene discovery to complex regulatory networks and their application in breeding

Land plants have developed sophisticated systems to cope with severe stressful environmental conditions during evolution. Plants have complex molecular systems to respond and adapt to abiotic stress, including drought, cold, and heat stress. Since 1989, we have been working to understand the complex molecular mechanisms of plant responses to severe environmental stress conditions based on functional genomics approaches with Arabidopsis thaliana as a model plant. We focused on the function of drought-inducible genes and the regulation of their stress-inducible transcription, perception and cellular signal transduction of stress signals to describe plant stress responses and adaptation at the molecular and cellular levels. We have identified key genes and factors in the regulation of complex responses and tolerance of plants in response to dehydration and temperature stresses. In this review article, we describe our 30-year experience in research and development based on functional genomics to understand sophisticated systems in plant response and adaptation to environmental stress conditions.

BaDBL1, a unique DREB gene from desiccation tolerant moss Bryum argenteum, confers osmotic and salt stress tolerances in transgenic Arabidopsis

The dehydration-responsive element-binding (DREB) transcription factors play important roles in regulation of plant responses to abiotic stresses, however, few DREBs have been isolated from a desiccation tolerance moss, and the role of DREBs in the DT mechanism is still unknown. We have functionally characterized a unique DREB transcription factor BaDBL1 from the DT moss Bryum argenteum. Expression pattern analysis revealed that BaDBL1 was induced by dehydration-rehydration, salt, cold, and abscisic acid treatments. BaDBL1 was localized in the nucleus and had a transactivation region in its C-terminal region. Overexpression of BaDBL1 in Arabidopsis resulted in significantly increased osmotic and salt stress tolerance, as illustrated by higher fresh weight and antioxidase activities (SOD, POD and CAT) compared with WT under osmotic and salt stresses. Moreover, the transcription of stress-responsive genes, such as AtRD29A and AtCOR15A, AtLEA in BaDBL1-overexpressing lines were significantly up-regulated under osmotic and salt stresses compared with WT. Transcriptomic analysis revealed that BaDBL1-overexpression affected the lignin biosynthesis pathway by improving lignin content and regulating lignin-biosynthesis-related genes under osmotic stress. The results suggest that BaDBL1 may regulate plant tolerance to stress by enhancing anti-oxidase activities, regulating expression of stress-related genes and effecting the lignin biosynthesis, making BaDBL1 a candidate gene for stress tolerance improvement in crops.

β-Cyclocitral, a Master Regulator of Multiple Stress-Responsive Genes in Solanum lycopersicum L. Plants

β-cyclocitral (βCC), a major apocarotenoid of β-carotene, enhances plants' defense against environmental stresses. However, the knowledge of βCC's involvement in the complex stress-signaling network is limited. Here we demonstrate how βCC reprograms the transcriptional responses that enable Solanum lycopersicum L. (tomato) plants to endure a plethora of environmental stresses. Comparative transcriptome analysis of control and βCC-treated tomato plants was done by generating RNA sequences in the BGISEQ-500 platform. The trimmed sequences were mapped on the tomato reference genome that identifies 211 protein-coding differentially expressed genes. Gene ontology and Kyoto Encyclopedia of Genes and Genomes analysis and their enrichment uncovered that only upregulated genes are attributed to the stress response. Moreover, 80% of the upregulated genes are functionally related to abiotic and biotic stresses. Co-functional analysis of stress-responsive genes revealed a network of 18 genes that code for heat shock proteins, transcription factors (TFs), and calcium-binding proteins. The upregulation of jasmonic acid (JA)-dependent TFs (MYC2, MYB44, ERFs) but not the JA biosynthetic genes is surprising. However, the upregulation of DREB3, an abscisic acid (ABA)-independent TF, validates the unaltered expression of ABA biosynthetic genes. We conclude that βCC treatment upregulates multiple stress-responsive genes without eliciting JA and ABA biosynthesis.

Molecular Mechanisms of Nitric Oxide (NO) Signaling and Reactive Oxygen Species (ROS) Homeostasis during Abiotic Stresses in Plants

Abiotic stressors, such as drought, heavy metals, and high salinity, are causing huge crop losses worldwide. These abiotic stressors are expected to become more extreme, less predictable, and more widespread in the near future. With the rapidly growing human population and changing global climate conditions, it is critical to prevent global crop losses to meet the increasing demand for food and other crop products. The reactive gaseous signaling molecule nitric oxide (NO) is involved in numerous plant developmental processes as well as plant responses to various abiotic stresses through its interactions with various molecules. Together, these interactions lead to the homeostasis of reactive oxygen species (ROS), proline and glutathione biosynthesis, post-translational modifications such as S-nitrosylation, and modulation of gene and protein expression. Exogenous application of various NO donors positively mitigates the negative effects of various abiotic stressors. In view of the multidimensional role of this signaling molecule, research over the past decade has investigated its potential in alleviating the deleterious effects of various abiotic stressors, particularly in ROS homeostasis. In this review, we highlight the recent molecular and physiological advances that provide insights into the functional role of NO in mediating various abiotic stress responses in plants.

ERAD-related E2 and E3 enzymes modulate the drought response by regulating the stability of PIP2 aquaporins

Endoplasmic reticulum-associated degradation (ERAD) is known to regulate plant responses to diverse stresses, yet its underlying molecular mechanisms and links to various stress signaling pathways are poorly understood. Here, we show that the ERAD component ubiquitin-conjugating enzyme UBC32 positively regulates drought tolerance in Arabidopsis thaliana by targeting the aquaporins PIP2;1 and PIP2;2 for degradation. Furthermore, we demonstrate that the RING-type ligase Rma1 acts together with UBC32 and that the E2 activity of UBC32 is essential for the ubiquitination of Rma1. This complex ubiquitinates a phosphorylated form of PIP2;1 at Lys276 to promote its degradation, thereby enhancing plant drought tolerance. Extending these molecular insights into crops, we show that overexpression of Arabidopsis UBC32 also improves drought tolerance in rice (Oryza sativa). Thus, beyond uncovering the molecular basis of an ERAD-regulated stress response, our study suggests multiple potential strategies for engineering crops with improved drought tolerance.

Ectopic expression of a novel cold-resistance protein 1 from Brassica oleracea promotes tolerance to chilling stress in transgenic tomato

Cold stress is considered as one of the major environmental factors that adversely affects the plant growth and distribution. Therefore, there arises an immediate need to cultivate effective strategies aimed at developing stress-tolerant crops that would boost the production and minimise the risks associated with cold stress. In this study, a novel cold-responsive protein1 (BoCRP1) isolated from Brassica oleracea was ectopically expressed in a cold susceptible tomato genotype Shalimar 1 and its function was investigated in response to chilling stress. BoCRP1 was constitutively expressed in all the tissues of B. oleracea including leaf, root and stem. However, its expression was found to be significantly increased in response to cold stress. Moreover, transgenic tomato plants expressing BoCRP1 exhibited increased tolerance to chilling stress (4 °C) with an overall improved rate of seed germination, increased root length, reduced membrane damage and increased accumulation of osmoprotectants. Furthermore, we observed increased transcript levels of stress responsive genes and enhanced accumulation of reactive oxygen species scavenging enzymes in transgenic plants on exposure to chilling stress. Taken together, these results strongly suggest that BoCRP1 is a promising candidate gene to improve the cold stress tolerance in tomato.

An Overview of Abiotic Stress in Cereal Crops: Negative Impacts, Regulation, Biotechnology and Integrated Omics

Abiotic stresses (AbS), such as drought, salinity, and thermal stresses, could highly affect the growth and development of plants. For decades, researchers have attempted to unravel the mechanisms of AbS for enhancing the corresponding tolerance of plants, especially for crop production in agriculture. In the present communication, we summarized the significant factors (atmosphere, soil and water) of AbS, their regulations, and integrated omics in the most important cereal crops in the world, especially rice, wheat, sorghum, and maize. It has been suggested that using systems biology and advanced sequencing approaches in genomics could help solve the AbS response in cereals. An emphasis was given to holistic approaches such as, bioinformatics and functional omics, gene mining and agronomic traits, genome-wide association studies (GWAS), and transcription factors (TFs) family with respect to AbS. In addition, the development of omics studies has improved to address the identification of AbS responsive genes and it enables the interaction between signaling pathways, molecular insights, novel traits and their significance in cereal crops. This review compares AbS mechanisms to omics and bioinformatics resources to provide a comprehensive view of the mechanisms. Moreover, further studies are needed to obtain the information from the integrated omics databases to understand the AbS mechanisms for the development of large spectrum AbS-tolerant crop production.

Morpho-Physiological, Biochemical, and Genetic Responses to Salinity in Medicago truncatula

We used an integrated morpho-physiological, biochemical, and genetic approach to investigate the salt responses of four lines (TN1.11, TN6.18, JA17, and A10) of Medicago truncatula. Results showed that TN1.11 exhibited a high tolerance to salinity, compared with the other lines, recording a salinity induced an increase in soluble sugars and soluble proteins, a slight decrease in malondialdehyde (MDA) accumulation, and less reduction in plant biomass. TN6.18 was the most susceptible to salinity as it showed less plant weight, had elevated levels of MDA, and lower levels of soluble sugars and soluble proteins under salt stress. As transcription factors of the APETALA2/ethylene responsive factor (AP2/ERF) family play important roles in plant growth, development, and responses to biotic and abiotic stresses, we performed a functional characterization of MtERF1 gene. Real-time PCR analysis revealed that MtERF1 is mainly expressed in roots and is inducible by NaCl and low temperature. Additionally, under salt stress, a greater increase in the expression of MtERF1 was found in TN1.11 plants than that in TN6.18. Therefore, the MtERF1 pattern of expression may provide a useful marker for discriminating among lines of M. truncatula and can be used as a tool in breeding programs aiming at obtaining Medicago lines with improved salt tolerance.

Advances in Sensing, Response and Regulation Mechanism of Salt Tolerance in Rice

Soil salinity is a serious menace in rice production threatening global food security. Rice responses to salt stress involve a series of biological processes, including antioxidation, osmoregulation or osmoprotection, and ion homeostasis, which are regulated by different genes. Understanding these adaptive mechanisms and the key genes involved are crucial in developing highly salt-tolerant cultivars. In this review, we discuss the molecular mechanisms of salt tolerance in rice—from sensing to transcriptional regulation of key genes—based on the current knowledge. Furthermore, we highlight the functionally validated salt-responsive genes in rice.

The in vitro structure and functions of the disordered late embryogenesis abundant three proteins

Late embryogenesis abundant (LEA) proteins are produced during seed embryogenesis and in vegetative tissue in response to various abiotic stressors. A correlation has been established between LEA expression and stress tolerance, yet their precise biochemical mechanism remains elusive. LEA proteins are very rich in hydrophilic amino acids, and they have been found to be intrinsically disordered proteins (IDPs) in vitro. Here, we perform biochemical and structural analyses of the four LEA3 proteins from Arabidopsis thaliana (AtLEA3). We show that the LEA3 proteins are disordered in solution but have regions with propensity for order. All LEA3 proteins were effective cryoprotectants of LDH in the freeze/thaw assays, while only one member, AtLEA3-4, was shown to bind Cu²⁺ and Fe³⁺ ions with micromolar affinity. As well, only AtLEA3-4 showed binding and a gain in α-helicity in the presence of the membrane mimic dodecylphosphocholine (DPC). We explored this interaction in greater detail using ¹⁵ N-heteronuclear single quantum coherence (HSQC) nuclear magnetic resonance, and demonstrate that two sets of conserved motifs present in AtLEA3-4 are involved in the interaction with the DPC micelles, which themselves gain α-helical structure.

The Arabidopsis small G-protein AtRAN1 is a positive regulator in chitin-induced stomatal closure and disease resistance

Chitin, a fungal microbial-associated molecular pattern, triggers various defence responses in several plant systems. Although it induces stomatal closure, the molecular mechanisms of its interactions with guard cell signalling pathways are unclear. Based on screening of public microarray data obtained from the ATH1 Affymetrix and Arabidopsis eFP browser, we isolated a cDNA encoding a Ras-related nuclear protein 1 AtRAN1. AtRAN1 expression was enriched in guard cells in a manner consistent with involvement in the control of the stomatal movement. AtRAN1 mutation impaired chitin-induced stomatal closure and accumulation of reactive oxygen species and nitric oxide in guard cells. In addition, Atran1 mutant plants exhibited compromised chitin-enhanced plant resistance to both bacterial and fungal pathogens due to changes in defence-related genes. Furthermore, Atran1 mutant plants were hypersensitive to drought stress compared to Col-0 plants, and had lower levels of stress-responsive genes. These data demonstrate a previously uncharacterized signalling role for AtRAN1, mediating chitin-induced signalling.

Identification of Differentially Expressed Drought-Responsive Genes in Guar [Cyamopsis tetragonoloba (L.) Taub]

Drought remains one of the most serious environmental stresses because of the continuous reduction in soil moisture, which requires the improvement of crops with features such as drought tolerance. Guar [Cyamopsis tetragonoloba (L.) Taub], a forage and industrial crop, is a nonthirsty plant. However, the information on the transcriptome changes that occur under drought stress in guar is very limited; therefore, a gene expression analysis is necessary in this context. Here, we studied the differentially expressed genes (DEGs) in response to drought stress and their metabolic pathways. RNA-Seq via an expectation-maximization algorithm was used to estimate gene abundance. Subsequently, an Empirical Analysis of Digital Gene Expression Data in the R Bioconductor package was used to identify DEGs. Blast2GO, InterProScan, and the Kyoto Encyclopedia of Genes and Genomes were used to explore functional annotation, protein analysis, enzymes, and metabolic pathways. Transcription factors were identified using the PlantTFDB database. Our study identified 499 upregulated and 191 downregulated genes in response to drought stress. Of those, 32 upregulated and six downregulated genes were deemed as novel genes exclusive to guar. An aggregate of 137 protein families, 306 domains, 12 repeats, and two sites were upregulated. The proton-dependent oligopeptide transporter family and transferase, aquaporin transporter, calcium/calmodulin-dependent/calcium-dependent protein kinase, aspartic peptidase A1 family, UDP-glucuronosyl/UDP-glucosyltransferase, and major intrinsic protein were the most upregulated protein families. The upregulated unigenes were associated with 88 enzymes and 77 KEGG pathways. Finally, the MYB-related, MYB, and ERF transcription factor families were upregulated. These data may be useful for understanding the plant molecular response to drought stress.

Identification of salinity responsive genes in lavender through cDNA-AFLP

Currently, a global demand exists forlavender as a significant medicinal plant and source of essential oils. Freshwater and arable lands are two major factors that inhibit extensive farming of medicinal plants in Iran. Saline water from seas and salty soil may be new resources for agricultural use, especially for medicinal plants. We sought to extend our knowledge of the Lavandula angustifolia genome and molecular basis of its salinity tolerance by using cDNA amplified fragment length polymorphism (cDNA-AFLP) to investigate the changes in plant transcriptomes in response to NaCl. All identified transcript derived fragments (TDF) were assigned as novel L. angustifolia genes related to signal transduction, regulation of gene expression, alternative splicing, autophagy, and secondary metabolite biosynthesis. qRT-PCR analysis of the TDFs in response to different concentrations of NaCl revealed various levels of mRNA of the identified genes in this plant. Our findings provided primary insights into the molecular response of L. angustifolia to salinity.

Structure and expression analysis of seven salt-related ERF genes of Populus

Ethylene response factors (ERFs) are plant-specific transcription factors (TFs) that play important roles in plant growth and stress defense and have received a great amount of attention in recent years. In this study, seven ERF genes related to abiotic stress tolerance and response were identified in plants of the Populus genus. Systematic bioinformatics, including sequence phylogeny, genome organisation, gene structure, gene ontology (GO) annotation, etc. were detected. Expression-pattern of these seven ERF genes were analyzed using RT-qPCR and cross validated using RNA-Seq. Data from a phylogenetic tree and multiple alignment of protein sequences indicated that these seven ERF TFs belong to three subfamilies and contain AP2, YRG, and RAYD conserved domains, which may interact with downstream target genes to regulate the plant stress response. An analysis of the structure and promoter region of these seven ERF genes showed that they have multiple stress-related motifs and cis-elements, which may play roles in the plant stress-tolerance process through a transcriptional regulation mechanism; moreover, the cellular_component and molecular_function terms associated with these ERFs determined by GO annotation supported this hypothesis. In addition, the spatio-temporal expression pattern of these seven ERFs, as detected using RT-qPCR and RNA-seq, suggested that they play a critical role in mediating the salt response and tolerance in a dynamic and tissue-specific manner. The results of this study provide a solid basis to explore the functions of the stress-related ERF TFs in Populus abiotic stress tolerance and development process.

Arabidopsis AtMPV17, a homolog of mice MPV17, enhances osmotic stress tolerance

Mutation in the human MPV17 gene or the functional yeast orthologue SYM1 result in mitochondrial DNA depletion. MPV17 homologs are also found in plants including Arabidopsis, but the function of these genes remain unclear. Arabidopsis genome contains 10 MPV17 homologs. Among these, the AtMPV17 protein was localized in mitochondria as MPV17 and SYM1. The yeast sym1 knock out mutant cannot grow on ethanol-containing medium at 37 °C. AtMPV17 complements the ethanol growth defection of sym1 yeast MPV17 ortholog cells at 37 °C, suggesting that AtMPV17 is a functional ortholog of SYM1. AtMPV17 knock out mutant, atmpv17 show similar growth and seed development to those of the wild-type plant on normal growth condition. However, atmpv17 mutant is more sensitive to ABA and mannitol during germination and seedling growth than wild type plants. Growth retardation of the atmpv17 knock out mutant on medium containing ABA and mannitol is complemented by AtMPV17 overexpression. These results suggest that the AtMPV17 contributes to osmotic stress tolerance in plants.

Identification of QTLs for Resistance to Fusarium Head Blight Using a Doubled Haploid Population Derived from Southeastern United States Soft Red Winter Wheat Varieties AGS 2060 and AGS 2035

Fusarium head blight (FHB), caused primarily by the fungus Fusarium graminearum, is one of the most damaging diseases of wheat, causing significant loss of yield and quality worldwide. Warm and wet conditions during flowering, a lack of resistant wheat varieties, and high inoculum pressure from corn stubble contribute to frequent FHB epidemics in the southern United States. The soft red winter wheat variety AGS 2060 is moderately susceptible (as opposed to susceptible) to FHB and regularly found in pedigrees of resistant breeding lines. AGS 2060 does not carry any known resistance genes or quantitative trait loci (QTL). A QTL mapping study was conducted to determine the location and genetic effect of its resistance using a doubled haploid mapping population produced from a cross between wheat varieties AGS 2060 and AGS 2035 (FHB susceptible). The population was genotyped using the Illumina iSelect single nucleotide polymorphism (SNP) array for wheat and phenotyped in Baton Rouge and Winnsboro, Louisiana and Newport, Arkansas in 2018 and 2019. The effect of genotype was significant for Fusarium damaged kernels (FDK) and deoxynivalenol (DON) content across all locations and years, indicating genetic variation in the population. The study detected 13 QTLs (one each on chromosome 1A, 1B, 1D, 2A, 2B, 6A, 6B, 7A, and 7B, and two each on 5A and 5B) responsible for the reduction of FDK and/or DON. Of these, nine QTLs for FHB resistance were identified in Winnsboro, Louisiana, in 2019. QTLs on chromosomes 2A and 7A could be valuable sources of resistance to both DON and FDK over several environments and were likely the best candidates for use in marker-assisted selection. Consistently expressed QTLs on chromosomes 5A, 6B, and 7A were potentially newly identified sources of resistance to FHB in soft red winter wheat.

The wheat E3 ligase TaPUB26 is a negative regulator in response to salt stress in transgenic Brachypodium distachyon

Various abiotic stresses, including high salinity, affect the growth and yield of crop plants. We isolated a gene, TaPUB26, from wheat that encodes a protein containing a U-box domain and armadillo (ARM) repeats. The TaPUB26 transcript levels were upregulated by high salinity, temperature, drought and phytohormones, suggesting the involvement of TaPUB26 in abiotic stress responses. An in vitro ubiquitination assay revealed that TaPUB26 is an E3 ubiquitin ligase. We overexpressed TaPUB26 in Brachypodium distachyon to evaluate TaPUB26 regulation of salt stress tolerance. Compared with the wild type (WT) line, the overexpression lines showed higher salt stress sensitivity under salt stress conditions, but lower chlorophyll (Chl) content, lower photosynthetic levels and overall reduced salt stress tolerance. Additionally, the transgenic plants showed more severe membrane damage, lower antioxidant enzyme activity and more reactive oxygen species (ROS) accumulation than WT plants under salt stress, which might be related to the changes in the expression levels of some antioxidant genes. In addition, the transgenic plants also had higher Na⁺ and lower K⁺ contents, thus maintaining a higher cytosolic Na⁺/K⁺ ratio in leaves and roots than that in WT plants. Further analysis of the molecular mechanisms showed that TaPUB26 interacted with TaRPT2a, an ATPase subunit of the 26S proteasome complex in wheat. We speculated that TaPUB26 negatively regulates salt stress tolerance by interacting with other proteins, such as TaRPT2a, and that this mechanism involves altered antioxidant competition and cytosolic Na⁺/K⁺ equilibrium.

Overexpression of soybean DREB1 enhances drought stress tolerance of transgenic wheat in the field

Drought-response-element binding (DREB)-like transcription factors can significantly enhance plant tolerance to water stress. However, most research on DREB-like proteins to date has been conducted in growth chambers or greenhouses, so there is very little evidence available to support their practical use in the field. In this study, we overexpressed GmDREB1 from soybean in two popular wheat varieties and conducted drought-tolerance experiments across a range of years, sites, and drought-stress regimes. We found that the transgenic plants consistently exhibited significant improvements in yield performance and a variety of physiological traits compared with wild-type plants when grown under limited water conditions in the field, for example showing grain yield increases between 4.79-18.43%. Specifically, we found that the transgenic plants had reduced membrane damage and enhanced osmotic adjustment and photosynthetic efficiency compared to the non-transgenic controls. Three enzymes from the biosynthetic pathway of the phytohormone melatonin were up-regulated in the transgenic plants, and external application of melatonin was found to improve drought tolerance. Together, our results demonstrate the utility of transgenic overexpression of GmDREB1 to improve the drought tolerance of wheat in the field.

Transcriptome sequencing of the apricot (Prunus armeniaca L.) and identification of differentially expressed genes involved in drought stress

Apricot (Prunus armeniaca L.) is an important fruit crop that is widely planted throughout the world. But drought affects both yield and quality of apricot. In order to study the effects of long-term drought on the molecular and physiological mechanisms of apricot, we used transcriptome sequencing and measured physiological indices. First, 322 million high-quality clean reads were obtained, and 74,892 unigenes were generated for the transcriptome. Among the assembled unigenes, 18,671 simple sequence repeats (SSRs) and 5581 differentially expressed genes (DEGs) were identified. The Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis of the DEGs revealed that starch and sucrose metabolism, plant-pathogen interaction and plant hormone signal transduction pathways are enriched. Additionally, we used quantitative real-time PCR (qRT-PCR) to confirm the RNA-seq results with 11 drought-related DEGs. Second, through the physiological analysis of apricot leaves under constant drought stress, and the results show the internal microstructure of apricot leaves changed to withstand drought stress. At the same time, plants exposed to long-term drought stress showed higher degree of membrane damage, which reduced photosynthesis in the damaged leaves. Our findings enrich the genome resources for apricot and refine our understanding of the molecular and physiological mechanisms of drought response in this fruit crop, providing insights into drought adaptation of the apricot.

Biological functions of Arabidopsis thaliana MBP-1-like protein encoded by ENO2 in the response to drought and salt stresses

Arabidopsis thaliana ENO2 (AtENO2) plays an important role in plant growth and development. It encodes two proteins, a full-length AtENO2 and a truncated version, AtMBP-1, alternatively translated from the second start codon of the mRNA. The AtENO2 mutant (eno2^- ) exhibited reduced leaf size, shortened siliques, a dwarf phenotype and higher sensitivity to abiotic stress. The objectives of this study were to analyze the regulatory network of the ENO2 gene in plant growth development and understand the function of AtENO2/AtMBP-1 to abiotic stresses. An eno2^- /35S:AtENO2-GFP line and an eno2^- /35S:AtMBP-1-GFP line of Arabidopsis were obtained. Results of sequencing by 454 GS FLX identified 578 upregulated and 720 downregulated differential expressed genes (DEGs) in a pairwise comparison (WT-VS-eno2^- ). All the high-quality reads were annotated using the Gene Ontology (GO) terms. The DEGs with KEGG pathway annotations occurred in 110 pathways. The metabolic pathways and biosynthesis of secondary metabolites contained more DEGs. Moreover, the eno2^- /35S:AtENO2-GFP line returned to the wild-type (WT) phenotype and was tolerant to drought and salt stresses. However, the eno2^- /35S:AtMBP-1-GFP line was not able to recover the WT phenotype but it has a higher tolerance to drought and salt stresses. Results from this study demonstrate that AtENO2 is critical for the growth and development, and the AtMBP-1 coded by AtENO2 is important in tolerance of Arabidopsis to abiotic stresses.

Regulation of color transition in purple tea (Camellia sinensis)

Comparative proteomics and metabolomics study of juvenile green, light purple and dark purple leaf to identify key proteins and metabolites that putatively govern color transition in Camellia sinensis. Color transition from juvenile green to dark purple leaf in Camellia sinensis is a complex process and thought to be regulated by an intricate balance of genes, proteins and metabolites expression. A molecular-level understanding of proteins and metabolites expression is needed to define metabolic process underpinning color transition in C. sinensis. Here, purple leaf growth of C. sinensis cultivar was divided into three developmental stages viz. juvenile green (JG), light purple (LP) and dark purple (DP) leaf. Scanning electron microscope (SEM) analysis revealed a clear morphological variation such as cell size, shape and texture as tea leaf undergoing color transition. Proteomic and metabolomic analyses displayed the temporal changes in proteins and metabolites that occur in color transition process. In total, 211 differentially expressed proteins (DEPs) were identified presumably involved in secondary metabolic processes particularly, flavonoids/anthocyanin biosynthesis, phytohormone regulation, carbon and nitrogen assimilation and photosynthesis, among others. Subcellular localization of three candidate proteins was further evaluated by their transient expression in planta. Interactome study revealed that proteins involved in primary metabolism, precursor metabolite, photosynthesis, phytohormones, transcription factor and anthocyanin biosynthesis were found to be interact directly or indirectly and thus, regulate color transition from JG to DP leaf. The present study not only corroborated earlier findings but also identified novel proteins and metabolites that putatively govern color transition in C. sinensis. These findings provide a platform for future studies that may be utilized for metabolic engineering/molecular breeding in an effort to develop more desirable traits.

Physiological and Transcriptional Responses of Industrial Rapeseed (Brassica napus) Seedlings to Drought and Salinity Stress

Abiotic stress greatly inhibits crop growth and reduces yields. However, little is known about the transcriptomic changes that occur in the industrial oilseed crop, rapeseed (Brassica napus), in response to abiotic stress. In this study, we examined the physiological and transcriptional responses of rapeseed to drought (simulated by treatment with 15% (w/v) polyethylene glycol (PEG) 6000) and salinity (150 mM NaCl) stress. Proline contents in young seedlings greatly increased under both conditions after 3 h of treatment, whereas the levels of antioxidant enzymes remained unchanged. We assembled transcripts from the leaves and roots of rapeseed and performed BLASTN searches against the rapeseed genome database for the first time. Gene ontology analysis indicated that DEGs involved in catalytic activity, metabolic process, and response to stimulus were highly enriched. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that differentially expressed genes (DEGs) from the categories metabolic pathways and biosynthesis of secondary metabolites were highly enriched. We determined that myeloblastosis (MYB), NAM/ATAF1-2/CUC2 (NAC), and APETALA2/ethylene-responsive element binding proteins (AP2-EREBP) transcription factors function as major switches that control downstream gene expression and that proline plays a role under short-term abiotic stress treatment due to increased expression of synthesis and decreased expression of degradation. Furthermore, many common genes function in the response to both types of stress in this rapeseed.

Overexpression of rice F-box protein OsFBX322 confers increased sensitivity to gamma irradiation in Arabidopsis

Ionizing radiation has a substantial effect on physiological and biochemical processes in plants via induction of transcriptional changes and diverse genetic alterations. Previous microarray analysis showed that rice OsFBX322, which encodes a rice F-box protein, was downregulated in response to three types of ionizing radiation: gamma irradiation, ion beams, and cosmic rays. In order to characterize the radiation-responsive genes in rice, OsFBX322 was selected for further analysis. OsFBX322 expression patterns in response to radiation were confirmed using quantitative RT-PCR. Transient expression of a GFP-OsFBX322 fusion protein in tobacco leaf epidermis indicated that OsFBX322 is localized to the nucleus. To determine the effect of OsFBX322 expression on radiation response, OsFBX322 was overexpressed in Arabidopsis. Transgenic overexpression lines were more sensitive to gamma irradiation than control plants. These results suggest that OsFBX322 plays a negative role in the defense response to radiation in plants. In addition, we obtained four co-expression genes of OsFBX322 by specific co-expression networks using the ARANCE. Quantitative RT-PCR showed that the four genes were also downregulated after exposure to the three types of radiation. These results imply that the co-expressed genes may serve as key regulators in the radiation response pathway in plants.

The barley transcription factor HvMYB1 is a positive regulator of drought tolerance

Transcription factors such as MYB have previously been associated with the plant response to drought. In this work, studies on the function of the barley (Hordeum vulgare L.) transcription factor HvMYB1 show that gene expression is upregulated in wildtype barley roots and leaves under drought and osmotic stress. Transgenic barley plants that overexpress HvMYB1 were found to be more resistant to drought, showing enhanced relative water content and reduced water loss rate and stomatal conductance as compared to control plants. Levels of the osmolyte proline were enhanced as was expression of dehydrin HvDNH6 in the transgenic lines under drought conditions. The levels of the reactive oxygen species H₂O₂ were enhanced in wildtype roots and leaves by drought, but less so in the HvMYB1 overexpressing lines. Enzyme activity of the low affinity H₂O₂ degrading enzyme catalase (EC 1.11.1.6) was also lower in droughted HvMYB1 overexpressing lines. Gene expression of the high affinity ROS scavengers ASCORBATE PEROXIDASE and GLUTATHIONE PEROXIDASE was found to be constitutively high in the overexpressing lines, whereas CATALASE gene expression was similar to the control plants. These results suggest a role for HvMYB1 in protecting plants against drought in the vegetative plant by acting as a mediator of abscisic acid action.

A WRKY transcription factor PbrWRKY53 from Pyrus betulaefolia is involved in drought tolerance and AsA accumulation

WRKY comprises a large family of transcription factors in plants, but most WRKY members are still poorly understood. In this study, we report the identification and functional characterization of PbrWRKY53 isolated from Pyrus betulaefolia. PbrWRKY53 was greatly up-regulated by drought and abscisic acid, but slightly induced by salt and cold. Subcellar localization analyses showed that PbrWRKY53 was located in the nucleus. Ectopic expression of PbrWRKY53 in tobacco and Pyrus ussuriensis conferred enhanced tolerance to drought stress. The transgenic plants exhibited better water status, less reactive oxygen species generation and higher levels of antioxidant enzyme activities and metabolites than the wild type. In addition, overexpression of PbrWRKY53 in transgenic tobacco resulted in enhanced expression level of PbrNCED1, and led to the increase in larger amount of vitamin C accumulation in comparison to WT. Knock-down of PbrWRKY53 in P. ussuriensis down-regulated PbrNCED1 abundance, accompanied by compromised drought tolerance. Yeast one-hybrid assay, EMSA and transient expression analysis demonstrated that PbrWRKY53 could bind to the W-box element in the promoter region of PbrNCED1. Taken together, these results demonstrated that PbrWRKY53 plays a positive role in drought tolerance, which might be, at least in part, promoting production of vitamin C via regulating PbrNCED1 expression.

Arabidopsis species deploy distinct strategies to cope with drought stress

BACKGROUND AND AIMS

Water limitation is an important determinant of the distribution, abundance and diversity of plant species. Yet, little is known about how the response to limiting water supply changes among closely related plant species with distinct ecological preferences. Comparison of the model annual species Arabidopsis thaliana with its close perennial relatives A. lyrata and A. halleri, can help disentangle the molecular and physiological changes contributing to tolerance and avoidance mechanisms, because these species must maintain tolerance and avoidance mechanisms to increase long-term survival, but they are exposed to different levels of water stress and competition in their natural habitat.

METHODS

A dry-down experiment was conducted to mimic a period of missing precipitation. The covariation of a progressive decrease in soil water content (SWC) with various physiological and morphological plant traits across a set of representative genotypes in A. thaliana, A. lyrata and A. halleri was quantified. Transcriptome changes to soil dry-down were further monitored.

KEY RESULTS

The analysis of trait covariation demonstrates that the three species differ in the strategies they deploy to respond to drought stress. Arabidopsis thaliana showed a drought avoidance reaction but failed to survive wilting. Arabidopsis lyrata efficiently combined avoidance and tolerance mechanisms. In contrast, A. halleri showed some degree of tolerance to wilting but it did not seem to protect itself from the stress imposed by drought. Transcriptome data collected just before plant wilting and after recovery corroborated the phenotypic analysis, with A. lyrata and A. halleri showing a stronger activation of recovery- and stress-related genes, respectively.

CONCLUSIONS

The response of the three Arabidopsis species to soil dry-down reveals that they have evolved distinct strategies to face drought stress. These strategic differences are in agreement with the distinct ecological priorities of the stress-tolerant A. lyrata, the competitive A. halleri and the ruderal A. thaliana.

Transgenic tomatoes for abiotic stress tolerance: status and way ahead

Tomato (Solanum lycopersicum) is one of the most important vegetable crops; its production, productivity and quality are adversely affected by abiotic stresses. Abiotic stresses such as drought, extreme temperature and high salinity affect almost every stage of tomato life cycle. Depending upon the plant stage and duration of the stress, abiotic stress causes about 70% yield loss. Several wild tomato species have the stress tolerance genes; however, it is very difficult to transfer them into cultivars due to high genetic distance and crossing barriers. Transgenic technology is an alternative potential tool for the improvement of tomato crop to cope with abiotic stress, as it allows gene transfer across species. In recent decades, many transgenic tomatoes have been developed, and many more are under progress against abiotic stress using transgenes such as DREBs, Osmotin, ZAT12 and BADH2. The altered expression of these transgenes under abiotic stresses are involved in every step of stress responses, such as signaling, control of transcription, proteins and membrane protection, compatible solute (betaines, sugars, polyols, and amino acids) synthesis, and free-radical and toxic-compound scavenging. The stress-tolerant transgenic tomato development is based on introgression of a gene with known function in stress response and putative tolerance. Transgenic tomato plants have been developed against drought, heat and salt stress with the help of various transgenes, expression of which manages the stress at the cellular level by modulating the expression of downstream genes to ultimately improve growth and yield of tomato plants and help in sustainable agricultural production. The transgenic technology could be a faster way towards tomato improvement against abiotic stress. This review provides comprehensive information about transgenic tomato development against abiotic stress such as drought, heat and salinity for researcher attention and a better understanding of transgenic technology used in tomato improvement and sustainable agricultural production.

Dynamic changes in the starch-sugar interconversion within plant source and sink tissues promote a better abiotic stress response

Starch is a significant store of sugars, and the starch-sugar interconversion in source and sink tissues plays a profound physiological role in all plants. In this review, we discuss how changes in starch metabolism can facilitate adaptive changes in source-sink carbon allocation for protection against environmental stresses. The stress-related roles of starch are described, and published mechanisms by which starch metabolism responds to short- or long-term water deficit, salinity, or extreme temperatures are discussed. Numerous examples of starch metabolism as a stress response are also provided, focusing on studies where carbohydrates and cognate enzymes were assayed in source, sink, or both. We develop a model that integrates these findings with the theoretical and known roles of sugars and starch in various species, tissues, and developmental stages. In this model, localized starch degradation into sugars is vital to the plant cold stress response, with the sugars produced providing osmoprotection. In contrast, high starch accumulation is prominent under salinity stress, and is associated with higher assimilate allocation from source to sink. Our model explains how starch-sugar interconversion can be a convergent point for regulating carbon use in stress tolerance at the whole-plant level.

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.

Low-temperature tolerance in land plants: Are transcript and membrane responses conserved?

Plants' tolerance of low temperatures is an economically and ecologically important limitation on geographic distributions and growing seasons. Tolerance for low temperatures varies significantly across different plant species, and different mechanisms likely act in different species. In order to survive low-temperature stress, plant membranes must maintain their fluidity in increasingly cold and oxidative cellular environments. The responses of different species to low-temperature stress include changes to the types and desaturation levels of membrane lipids, though the precise lipids affected tend to vary by species. Regulation of membrane dynamics and other low-temperature tolerance factors are controlled by both transcriptional and post-transcriptional mechanisms. Here, we review low-temperature induced changes in both membrane lipid composition and gene transcription across multiple related plant species with differing degrees of low-temperature tolerance. We attempt to define a core set of changes for transcripts and lipids across species and treatment variations. Some responses appear to be consistent across all species for which data are available, while many others appear likely to be species or family-specific. Potential rationales are presented, including variance in testing, reporting and the importance of considering the level of stress perceived by the plant.

PtDRG1, a Desiccation Response Gene from Pyropia tenera (Rhodophyta), Exhibits Chaperone Function and Enhances Abiotic Stress Tolerance

Pyropia are commercially valuable marine red algae that grow in the intertidal zone. They are extremely tolerant to desiccation stress. We have previously identified and reported desiccation response genes (DRGs) based on transcriptome analysis of P. tenera. Among them, PtDRG1 encodes a polypeptide of 22.6 kDa that is located in the chloroplast. PtDRG1 does not share sequence homology with any known gene deposited in public database. Transcription of PtDRG1 gene was upregulated by osmotic stress induced by mannitol or H₂O₂ as well as desiccation stress, but not by heat. When PtDRG1 was overexpressed in Escherichia coli or Chlamydomonas, transformed cells grew much better than control cells under high temperature as well as osmotic stress induced by mannitol and NaCl. In addition, PtDRG1 significantly reduced thermal aggregation of substrate protein under heat stress condition. These results demonstrate that PtDRG1 has a chaperone function and plays a role in tolerance mechanism for abiotic stress. This study shows that red algae have unknown stress proteins such as PtDRG1 that contributes to stress tolerance.