Transcription factors as tools to engineer enhanced drought stress tolerance in plants

Transcriptome and network analysis pinpoint ABA and plastid ribosomal proteins as main contributors to salinity tolerance in the rice variety, CSR28

Salinity stress is a major challenge for rice production, especially at seedling stage. To gain comprehensive insight into the molecular mechanisms and potential candidate genes involved in rice salinity stress response, we integrated physiological, transcriptome and network analysis to investigate salinity tolerance in two contrasting rice genotypes. The root and shoot samples were collected at two timepoints (6 hours and 54 hours) of high salt treatment. Element assay showed that the tolerant genotype CSR28 had lower Na+/K+ ratio in both organs than in those of the sensitive genotype IR28 under salinity stress. A total of 15,483 differentially expressed genes (DEGs) were identified from the RNA-Seq analysis. The salt-specific genes were mainly involved in metabolic processes, response to stimulus, and transporter activity, and were enriched in key metabolic pathways such as, biosynthesis of secondary metabolites, plant hormone signal transduction, and carotenoid biosynthesis. Furthermore, the results showed that the differential genes involved in abscisic acid (ABA) biosynthesis were specifically up-regulated in the tolerant genotype. Network analysis revealed 50 hub genes for the salt-specific genes in the roots of CSR28 which mainly encodes ribosomal proteins (RPs). Functional validation of the nine hub genes revealed three plastid RPs (PRPs), including OsPRPL17, OsPRPS9 and OsPRPL11, which contributes to protein synthesis, chloroplast development and stress signaling. Our findings suggested that ABA and PRPs play key roles to enhance of salinity tolerance in CSR28. Our study provides valuable information for further investigations of the candidate genes associated with salt tolerance and the development of salt-tolerant rice varieties.

Genome-wide identification of 1R-MYB transcription factors family and functional characterization of TrMYB130 under drought stresses in Trifolium repens (L.)

White clover (Trifolium repens L.) is a high-quality leguminous forage, but its short rooting habit, poor transpiration tolerance, and drought tolerance, have become a key factor restricting its growth and cultivation. 1R-MYB transcription factors (TFs) are a significant subfamily of TFs in plants, playing a vital role in regulating plant responses to drought stress, however, knowledge about the role of 1R-MYB transcription factors in white clover is still limited. We identified 134 1R-MYB members, which were unevenly designated onto 16 chromosomes and divided phylogenetically into five subgroups. The members of the same subgroup had conserved motifs. Collinearity analysis revealed that segmental and tandem duplications significantly contributed to the expansion of the Tr1R-MYBs. Tr1R-MYBs promoter region enriched with potential drought cis-acting regulatory elements. The RT-qPCR results show that the five Tr1R-MYB genes (TrMYB41, TrMYB49, TrMYB94, TrMYB125, TrMYB130) have a certain degree of response under drought stress conditions but exhibited different expression profiles. Furthermore, subcellular localization analysis showed that the TrMYB130 protein is primarily located in the nucleus. Overexpression of this protein in transgenic Arabidopsis (Arabidopsis thaliana L.) was found to impair drought tolerance. Our findings will establish a basis for deeper investigation into the characteristics and functions of 1R-MYB TFs, as well as for employing genetic engineering techniques to improve white clover.

Comparative transcriptomics reveals potential regulators of climate adaptation in Santalum album L. (Indian Sandalwood)

Santalum album L. (Indian Sandalwood), a valued tree species known for its fragrant heartwood and essential oil is facing increasing threat due to severe anthropogenic pressures compounded by climate change which has resulted in depletion of its adaptive gene pool. The present study investigates the transcriptome-level responses of nine sandalwood genotypes sourced from diverse climatic zones to identify adaptive genes in the species. Comparative transcriptomics predicted 727, 1141 and 479 differentially expressed transcripts (DETs) across wet vs. dry; monsoon vs. dry and wet vs. monsoon conditions, respectively, and majority of DETs were up-regulated in samples sourced from high rainfall areas. Transcripts including heat shock proteins, Zinc finger binding protein, ribosomal proteins, transcription factors and protein kinase were identified as probable regulators of climate adaptation in S. album. The expression changes of eight selected transcripts were further validated by real-time quantitative PCR. Protein-protein interaction analysis revealed key hub transcripts involved in climate response, while alternative splicing events in transcripts such as SURP and G-patch domain-containing protein 1-like protein, G-type lectin S-receptor-like serine/threonine protein kinase B120, Tetraspanin-3 and ARM repeat superfamily protein indicated the probable role of alternate splicing in increasing the transcript diversity during adaptation. This study presents the first insight into the molecular mechanisms of climate adaptation in the species and can form the basis for specific interventions such as selective breeding, genetic manipulation, and habitat management for conservation and long-term survival of sandalwood.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-025-04218-4.

Epibrassinolide Regulates Lhcb5 Expression Though the Transcription Factor of MYBR17 in Maize

Photosynthesis, which is the foundation of crop growth and development, is accompanied by complex transcriptional regulatory mechanisms. Research has established that brassinosteroids (BRs) play a role in regulating plant photosynthesis, with the majority of research focusing on the physiological level and regulation of rate-limiting enzymes in the dark reactions of photosynthesis. However, studies on their effects on maize photosynthesis, specifically on light-harvesting antenna proteins, have yet to be conducted. The peripheral light-harvesting antenna protein Lhcb5 is crucial for capturing and dissipating light energy. Herein, by analyzing the transcriptomic data of maize seedling leaves treated with 24-epibrassinolide (EBR) and verifying them using qPCR experiments, we found that the MYBR17 transcription factor may regulate the expression of the photosynthetic light-harvesting antenna protein gene. Further experiments using protoplast transient expression and yeast one-hybrid tests showed that the maize transcription factor MYBR17 responds to EBR signals and binds to the promoter of the light-harvesting antenna protein Lhcb5, thereby upregulating its expression. These results were validated using an Arabidopsis mybr17 mutant. Our results offer a theoretical foundation for the application of BRs to enhance the photosynthetic efficiency of maize.

Transcriptome Profiles Reveals ScDREB10 from Syntrichia caninervis Regulated Phenylpropanoid Biosynthesis and Starch/Sucrose Metabolism to Enhance Plant Stress Tolerance

Desiccation is a kind of extreme form of drought stress and desiccation tolerance (DT) is an ancient trait of plants that allows them to survive tissue water potentials reaching -100 MPa or lower. ScDREB10 is a DREB A-5 transcription factor gene from a DT moss named Syntrichia caninervis, which has strong comprehensive tolerance to osmotic and salt stresses. This study delves further into the molecular mechanism of ScDREB10 stress tolerance based on the transcriptome data of the overexpression of ScDREB10 in Arabidopsis under control, osmotic and salt treatments. The transcriptional analysis of weight gene co-expression network analysis (WGCNA) showed that "phenylpropanoid biosynthesis" and "starch and sucrose metabolism" were key pathways in the network of cyan and yellow modules. Meanwhile, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis of differentially expressed genes (DEGs) also showed that "phenylpropanoid biosynthesis" and "starch and sucrose metabolism" pathways demonstrate the highest enrichment in response to osmotic and salt stress, respectively. Quantitative real-time PCR (qRT-PCR) results confirmed that most genes related to phenylpropanoid biosynthesis" and "starch and sucrose metabolism" pathways in overexpressing ScDREB10 Arabidopsis were up-regulated in response to osmotic and salt stresses, respectively. In line with the results, the corresponding lignin, sucrose, and trehalose contents and sucrose phosphate synthase activities were also increased in overexpressing ScDREB10 Arabidopsis under osmotic and salt stress treatments. Additionally, cis-acting promoter element analyses and yeast one-hybrid experiments showed that ScDREB10 was not only able to bind with classical cis-elements, such as DRE and TATCCC (MYBST1), but also bind with unknown element CGTCCA. All of these findings suggest that ScDREB10 may regulate plant stress tolerance by effecting phenylpropanoid biosynthesis, and starch and sucrose metabolism pathways. This research provides insights into the molecular mechanisms underpinning ScDREB10-mediated stress tolerance and contributes to deeply understanding the A-5 DREB regulatory mechanism.

ROS scavenging enzyme-encoding genes play important roles in the desert moss Syntrichia caninervis response to extreme cold and desiccation stresses

Abiotic stress is one of the major environmental constraints limiting plant growth. Syntrichia caninervis is one of the unique plant models that can cope with harsh environments. Reactive oxygen species (ROS) are a vital signaling molecule for protecting plants from oxidative stress, but research on ROS in S. caninervis is limited. Here, we identified 112 ROS genes in S. caninervis, including 40 GSTs, 51 PODs, 9 SODs, 6 CATs, 3 GPXs and 3 APXs families. GO and KEGG analyses showed that ROS genes are involved in responses to various stimuli and phenylpropanoid biosynthesis. ROS genes contain many stress-responsive and hormonal cis-elements in their promoter regions. More ROS genes were induced by cold stress than desiccation stress, and both conditions changed the transcript abundances of several ROS genes. CAT and POD, H2O2, MDA, and GSH were also induced under biotic stress, specifically CAT activity. The results indicated that the ScCAT genes and their activities could be strongly associated with the regulation of ROS production. This is the first systematic identification of ROS genes in S. caninervis and our findings contribute to further research into the roles of ScROS adjustment under abiotic stress while also providing excellent genetic resources for plant breeding.

The Classification, Molecular Structure and Biological Biosynthesis of Flavonoids, and Their Roles in Biotic and Abiotic Stresses

With the climate constantly changing, plants suffer more frequently from various abiotic and biotic stresses. However, they have evolved biosynthetic machinery to survive in stressful environmental conditions. Flavonoids are involved in a variety of biological activities in plants, which can protect plants from different biotic (plant-parasitic nematodes, fungi and bacteria) and abiotic stresses (salt stress, drought stress, UV, higher and lower temperatures). Flavonoids contain several subgroups, including anthocyanidins, flavonols, flavones, flavanols, flavanones, chalcones, dihydrochalcones and dihydroflavonols, which are widely distributed in various plants. As the pathway of flavonoid biosynthesis has been well studied, many researchers have applied transgenic technologies in order to explore the molecular mechanism of genes associated with flavonoid biosynthesis; as such, many transgenic plants have shown a higher stress tolerance through the regulation of flavonoid content. In the present review, the classification, molecular structure and biological biosynthesis of flavonoids were summarized, and the roles of flavonoids under various forms of biotic and abiotic stress in plants were also included. In addition, the effect of applying genes associated with flavonoid biosynthesis on the enhancement of plant tolerance under various biotic and abiotic stresses was also discussed.

Genome-Wide Characterization and Expression Analysis of Transcription Factor Families in Desert Moss Syntrichia caninervis under Abiotic Stresses

Transcription factor (TF) families play important roles in plant stress responses. S. caninervis is a new model moss for plant desiccation tolerance studies. Here, we report a high-confidence identification and characterization of 591 TFs representing 52 families that covered all chromosomes in S. caninervis. GO term and KEGG pathway analysis showed that TFs were involved in the regulation of transcription, DNA-templated, gene expression, binding activities, plant hormone signal transduction, and circadian rhythm. A number of TF promoter regions have a mixture of various hormones-related cis-regulatory elements. AP2/ERF, bHLH, MYB, and C2H2-zinc finger TFs were the overrepresented TF families in S. caninervis, and the detailed classification of each family is performed based on structural features. Transcriptome analysis revealed the transcript abundances of some ScAP2/ERF, bHLH, MYB, and C2H2 genes were accumulated in the treated S. caninervis under cold, dehydration, and rehydration stresses. The RT-qPCR results strongly agreed with RNA-seq analysis, indicating these TFs might play a key role in S. caninervis response to abiotic stress. Our comparative TF characterization and classification provide the foundations for functional investigations of the dominant TF genes involved in S. caninervis stress response, as well as excellent stress tolerance gene resources for plant stress resistance breeding.

Genome-Wide Identification and Analysis of MYB Transcription Factor Family in Hibiscus hamabo

MYB transcription factors constitute one of the largest gene families in plants and play essential roles in the regulation of plant growth, responses to stress, and a wide variety of physiological and biochemical processes. In this study, 204 MYB proteins (HhMYBs) were identified in the Hibiscus hamabo Sieb. et Zucc (H. hamabo) genome and systematically analyzed based on their genomic sequence and transcriptomic data. The candidate HhMYB proteins and MYBs of Arabidopsis thaliana were divided into 28 subfamilies based on the analysis of their phylogenetic relationships and their motif patterns. Expression analysis using RNA-seq and quantitative real-time PCR (qRT-PCR) indicated that most HhMYBs are differentially regulated under drought and salt stresses. qRT-PCR analysis of seven selected HhMYBs suggested that the HhMYB family may have regulatory roles in the responses to stress and hormones. This study provides a framework for a more comprehensive analysis of the role of MYBs in the response to abiotic stress in H. hamabo.

IPA1 improves drought tolerance by activating SNAC1 in rice

Drought is a major abiotic stress to rice (Oryza sativa) during growth. Ideal Plant Architecture (IPA1), the first cloned gene controlling the ideal plant type in rice, has been reported to function in both ideal rice plant architecture and biotic resistance. Here, we report that the IPA1/OsSPL14, encoding a transcriptional factor, positively regulates drought tolerance in rice. The IPA1 is constitutively expressed and regulated by H₂O₂, abscisic acid, NaCl and polyethylene glycol 6000 treatments in rice. Furthermore, the IPA1-knockout plants showed much greater accumulation of H₂O₂ as measured by 3,3'-diaminobenzidine staining in leaves compared with WT plants. Yeast one-hybrid, dual-luciferase and electrophoretic mobility shift assays indicated that the IPA1 directly activates the promoter of SNAC1. Expression of SNAC1 is significantly down-regulated in IPA1 knockout plants. Further investigation indicated that the IPA1 plays a positive role in drought-stress tolerance by inducing reactive oxygen species scavenging in rice. Together, these findings indicated that the IPA1 played important roles in drought tolerance by regulating SNAC1, thus activating the antioxidant system in rice.

The ScAPD1-like gene from the desert moss Syntrichia caninervis enhances resistance to Verticillium dahliae via phenylpropanoid gene regulation

Soloist is a member of a distinct and small subfamily within the AP2/ERF transcriptional factor family that play important roles in plant biotic and abiotic stress responses. There are limited studies of Soloist genes and their functions are poorly understood. We characterized the abiotic and biotic stress tolerance function of the ScSoloist gene (designated as ScAPD1-like) from the desert moss Syntrichia caninervis. ScAPD1-like responded to multiple abiotic, biotic stresses and plant hormone treatments. ScAPD1-like protein located to the nucleus and bound to several DNA elements. Overexpression of ScAPD1-like in Arabidopsis did not alter abiotic stress resistance or inhibit Pseudomonas syringae pv. tomato (Pst) DC3000 infection. However, overexpression of ScAPD1-like significantly increased the resistance of transgenic Arabidopsis and S. caninervis to Verticillium dahliae infection, decreased reactive oxygen species accumulation and improved reactive oxygen species scavenging activity. ScAPD1-like overexpression plants altered the abundance of transcripts for lignin synthesis and promoted lignin accumulation in Arabidopsis. ScAPD1-like directly bind to RAV1, AC elements, and TATA-box in the promoters of AtPAL1 and AtC4H genes, respectively, in vitro. Chromatin immunoprecipitation-quantitative polymerase chain reaction assays demonstrated ScAPD1-like directly bound to PAL and C4H genes promoters in Arabidopsis and their homologs in S. caninervis. In S. caninervis, ScAPD1-like overexpression and RNAi directly regulated the abundance of ScPAL and ScC4H transcripts and modified the metabolites of phenylpropanoid pathway. We provide insight into the function of Soloist in plant defense mechanisms that likely occurs through activation of the phenylpropanoid biosynthesis pathway. ScAPD1-like is a promising candidate gene for breeding strategies to improve resistance to Verticillium wilt.

Biotechnological Interventions in Tomato (Solanum lycopersicum) for Drought Stress Tolerance: Achievements and Future Prospects

Tomato production is severely affected by abiotic stresses (drought, flood, heat, and salt) and causes approximately 70% loss in yield depending on severity and duration of the stress. Drought is the most destructive abiotic stress and tomato is very sensitive to the drought stress, as cultivated tomato lack novel gene(s) for drought stress tolerance. Only 20% of agricultural land worldwide is irrigated, and only 14.51% of that is well-irrigated, while the rest is rain fed. This scenario makes drought very frequent, which restricts the genetically predetermined yield. Primarily, drought disturbs tomato plant physiology by altering plant–water relation and reactive oxygen species (ROS) generation. Many wild tomato species have drought tolerance gene(s); however, their exploitation is very difficult because of high genetic distance and pre- and post-transcriptional barriers for embryo development. To overcome these issues, biotechnological methods, including transgenic technology and CRISPR-Cas, are used to enhance drought tolerance in tomato. Transgenic technology permitted the exploitation of non-host gene/s. On the other hand, CRISPR-Cas9 technology facilitated the editing of host tomato gene(s) for drought stress tolerance. The present review provides updated information on biotechnological intervention in tomato for drought stress management and sustainable agriculture.

Molecular mechanisms associated with microbial biostimulant-mediated growth enhancement, priming and drought stress tolerance in maize plants

Microbial-based biostimulants are emerging as effective strategies to improve agricultural productivity; however, the modes of action of such formulations are still largely unknown. Thus, herein we report elucidated metabolic reconfigurations in maize (Zea mays) leaves associated with growth promotion and drought stress tolerance induced by a microbial-based biostimulant, a Bacillus consortium. Morphophysiological measurements revealed that the biostimulant induced a significant increase in biomass and enzymatic regulators of oxidative stress. Furthermore, the targeted metabolomics approach revealed differential quantitative profiles in amino acid-, phytohormone-, flavonoid- and phenolic acid levels in plants treated with the biostimulant under well-watered, mild, and severe drought stress conditions. These metabolic alterations were complemented with gene expression and global DNA methylation profiles. Thus, the postulated framework, describing biostimulant-induced metabolic events in maize plants, provides actionable knowledge necessary for industries and farmers to confidently and innovatively explore, design and fully implement microbial-based formulations and strategies into agronomic practices for sustainable agriculture and food production.

Biocontrol Methods in Avoidance and Downsizing of Mycotoxin Contamination of Food Crops

By increasing the resistance of seeds against abiotic and biotic stress, the possibility of cereal mold contamination and hence the occurrence of secondary mold metabolites mycotoxins decreases. The use of biological methods of seed treatment represents a complementary strategy, which can be implemented as an environmental-friendlier approach to increase the agricultural sustainability. Whereas the use of resistant cultivars helps to reduce mold growth and mycotoxin contamination at the very beginning of the production chain, biological detoxification of cereals provides additional weapons against fungal pathogens in the later stage. Most efficient techniques can be selected and combined on an industrial scale to reduce losses and boost crop yields and agriculture sustainability, increasing at the same time food and feed safety. This paper strives to emphasize the possibility of implementation of biocontrol methods in the production of resistant seeds and the prevention and reduction in cereal mycotoxin contamination.

Ingeniería genética contra estrés abiótico en cultivos neotropicales: osmolitos, factores de transcripción y CRISPR/Cas9

El neotrópico es sitio de origen de gran variedad de plantas que actualmente son cultivadas con éxito en diferentes regiones del mundo. Sin embargo, condiciones climáticas adversas, que se pueden ver acrecentadas por efectos del cambio climático antropogénico, pueden afectar su rendimiento y productividad debido a las situaciones de estrés abiótico que se pueden generar. Como alternativa para contrarrestar estos efectos, se ha experimentado con modificaciones genéticas, particularmente en genes relacionados con la producción de osmolitos y factores de transcripción que han llevado a que estas plantas, a nivel experimental, tengan mayor tolerancia a estrés oxidativo, altas y bajas temperaturas y fotoinhibición, sequía y salinidad, mediante la acumulación de osmoprotectores, la regulación en la expresión de genes y cambios en el fenotipo. En este trabajo se presentan y describen las estrategias metodológicas planteadas con estos fines y se complementan con ejemplos de trabajos realizados en cultivos de origen neotropical de importancia económica, como maíz, algodón, papa y tomate. Además, y debido a la novedad y potencial que ofrece la edición génica por medio del sistema CRISPR/Cas9, también se mencionan trabajos realizados en plantas con origen neotropical, enfocados en comprender e implementar mecanismos de tolerancia a sequía. Las metodologías aquí descritas podrían constituirse en opciones prácticas para mejorar la seguridad alimentaria con miras a contrarrestar las consecuencias negativas del cambio climático antropogénico.

Functions of silicon in plant drought stress responses

Silicon (Si), the second most abundant element in Earth's crust, exerts beneficial effects on the growth and productivity of a variety of plant species under various environmental conditions. However, the benefits of Si and its importance to plants are controversial due to differences among the species, genotypes, and the environmental conditions. Although Si has been widely reported to alleviate plant drought stress in both the Si-accumulating and nonaccumulating plants, the underlying mechanisms through which Si improves plant water status and maintains water balance remain unclear. The aim of this review is to summarize the morphoanatomical, physiological, biochemical, and molecular processes that are involved in plant water status that are regulated by Si in response to drought stress, especially the integrated modulation of Si-triggered drought stress responses in Si accumulators and intermediate- and excluder-type plants. The key mechanisms influencing the ability of Si to mitigate the effects of drought stress include enhancing water uptake and transport, regulating stomatal behavior and transpirational water loss, accumulating solutes and osmoregulatory substances, and inducing plant defense- associated with signaling events, consequently maintaining whole-plant water balance. This study evaluates the ability of Si to maintain water balance under drought stress conditions and suggests future research that is needed to implement the use of Si in agriculture. Considering the complex relationships between Si and different plant species, genotypes, and the environment, detailed studies are needed to understand the interactions between Si and plant responses under stress conditions.

Transcriptomic responses to drought stress in Polygonatum kingianum tuber

BACKGROUND

Polygonatum kingianum Coll. et Hemsl. is an important plant in Traditional Chinese Medicine. The extracts from its tubers are rich in polysaccharides and other metabolites such as saponins. It is a well-known concept that growing medicinal plants in semi-arid (or drought stress) increases their natural compounds concentrations. This study was conducted to explore the morpho-physiological responses of P. kingianum plants and transcriptomic signatures of P. kingianum tubers exposed to mild, moderate, and severe drought and rewatering.

RESULTS

The stress effects on the morpho-physiological parameters were dependent on the intensity of the drought stress. The leaf area, relative water content, chlorophyll content, and shoot fresh weight decreased whereas electrolyte leakage increased with increase in drought stress intensity. A total of 53,081 unigenes were obtained; 59% of which were annotated. We observed that 1352 and 350 core genes were differentially expressed in drought and rewatering, respectively. Drought stress driven differentially expressed genes (DEGs) were enriched in phenylpropanoid biosynthesis, flavonoid biosynthesis, starch and sucrose metabolism, and stilbenoid diarylheptanoid and gingerol biosynthesis, and carotenoid biosynthesis pathways. Pathways such as plant-pathogen interaction and galactose metabolism were differentially regulated between severe drought and rewatering. Drought reduced the expression of lignin, gingerol, and flavonoid biosynthesis related genes and rewatering recovered the tubers from stress by increasing the expression of the genes. Increased expression of carotenoid biosynthesis pathway related genes under drought suggested their important role in stress endurance. An increase in starch and sucrose biosynthesis was evident from transcriptomic changes under drought stress. Rewatering recovered the drought affected tubers as evident from the contrasting expression profiles of genes related to these pathways. P. kingianum tuber experiences an increased biosynthesis of sucrose, starch, and carotenoid under drought stress. Drought decreases the flavonoids, phenylpropanoids, gingerol, and lignin biosynthesis. These changes can be reversed by rewatering the P. kingianum plants.

CONCLUSIONS

These results provide a transcriptome resource for P. kingianum and expands the knowledge on the effect of drought and rewatering on important pathways. This study also provides a large number of candidate genes that could be manipulated for drought stress tolerance and managing the polysaccharide and secondary metabolites' contents in P. kingianum.

Identification of Differential Drought Response Mechanisms in Medicago sativa subsp. sativa and falcata through Comparative Assessments at the Physiological, Biochemical, and Transcriptional Levels

Alfalfa (Medicago sativa L.) is an extensively grown perennial forage legume, and although it is relatively drought tolerant, it consumes high amounts of water and depends upon irrigation in many regions. Given the progressive decline in water available for irrigation, as well as an escalation in climate change-related droughts, there is a critical need to develop alfalfa cultivars with improved drought resilience. M. sativa subsp. falcata is a close relative of the predominantly cultivated M. sativa subsp. sativa, and certain accessions have been demonstrated to exhibit superior performance under drought. As such, we endeavoured to carry out comparative physiological, biochemical, and transcriptomic evaluations of an as of yet unstudied drought-tolerant M. sativa subsp. falcata accession (PI 641381) and a relatively drought-susceptible M. sativa subsp. sativa cultivar (Beaver) to increase our understanding of the molecular mechanisms behind the enhanced ability of falcata to withstand water deficiency. Our findings indicate that unlike the small number of falcata genotypes assessed previously, falcata PI 641381 may exploit smaller, thicker leaves, as well as an increase in the baseline transcriptional levels of genes encoding particular transcription factors, protective proteins, and enzymes involved in the biosynthesis of stress-related compounds. These findings imply that different falcata accessions/genotypes may employ distinct drought response mechanisms, and the study provides a suite of candidate genes to facilitate the breeding of alfalfa with enhanced drought resilience in the future.

Silicon mediated abiotic stress tolerance in plants using physio-biochemical, omic approach and cross-talk with phytohormones

Silicon (Si) is the second most abundant element present on the lithosphere and a quasi-essential element for plants' cellular and developmental processes. Si is associated with augmented germination, growth, photosynthesis, gas exchange, photosystem efficiency, and yield attributes in unstressed and stressed plants. The exogenous application of Si facilitates morpho-physiological and biochemical traits. It triggers the content of compatible osmolyte and enzymatic and non-enzymatic antioxidants, which decreases reactive oxygen species like hydrogen peroxide and superoxide. Uptake and transport of Si in plants are discussed in this review. Furthermore, the potent roles of Si in plants are emphasized. The cross-talk of Si with phytohormones such as auxins, cytokinins, gibberellins, abscisic acid, brassinosteroids, salicylic acid, nitric oxide, jasmonic acid, and ethylene is also presented. Moreover, attempts have been made to cover the contribution of Si mediated enhancement in 'omics' (genomic, transcriptomic, proteomic, metabolomic, and ionomic) approach that is useful in diminishing stress. This review aims to provide Si integration with phytohormone and utilization of 'omic approaches' to understand the role of Si in plants. This review also underlines the need for future research to evaluate the role of Si during abiotic stress in plants and the identification of gaps in understanding this process as a whole at a broader level.

Two generation reproduction toxicity study of GmDREB3 gene modified wheat in Wistar rats

To study reproductive toxicity of gene modified wheat generated by introducing DREB3 (drought response element binding protein 3) gene, Wistar rats of were allocated into 3 groups and fed with DREB3 gene modified wheat mixture diet (GM group), non-gene modified wheat mixture diet (Non-GM group) and AIN-93 diet (Control group) from parental generation (F0) to the second offspring (F2). GM wheat and Non-GM wheat, Jimai22, were both formulated into diets at a ratio of 69.55% according to AIN93 diet for rodent animals. Compared with non-GM group, no biologically related differences were observed in GM group rats with respect to reproductive performance such as fertility rate, gestation rate, mean duration, hormone level, reproductive organ pathology and developmental parameters such as body weight, body length, food consumption, neuropathy, behavior, immunotoxicity, hematology and serum chemistry. In conclusion, no adverse effect were found relevant to GM wheat in the two generation reproduction toxicity study, indicating the GM wheat is a safe alternative for its counterpart wheat regarding to reproduction toxicity.

Plant Transcription Factors Involved in Drought and Associated Stresses

Transcription factors (TFs) play a significant role in signal transduction networks spanning the perception of a stress signal and the expression of corresponding stress-responsive genes. TFs are multi-functional proteins that may simultaneously control numerous pathways during stresses in plants-this makes them powerful tools for the manipulation of regulatory and stress-responsive pathways. In recent years, the structure-function relationships of numerous plant TFs involved in drought and associated stresses have been defined, which prompted devising practical strategies for engineering plants with enhanced stress tolerance. Vast data have emerged on purposely basic leucine zipper (bZIP), WRKY, homeodomain-leucine zipper (HD-Zip), myeloblastoma (MYB), drought-response elements binding proteins/C-repeat binding factor (DREB/CBF), shine (SHN), and wax production-like (WXPL) TFs that reflect the understanding of their 3D structure and how the structure relates to function. Consequently, this information is useful in the tailored design of variant TFs that enhances our understanding of their functional states, such as oligomerization, post-translational modification patterns, protein-protein interactions, and their abilities to recognize downstream target DNA sequences. Here, we report on the progress of TFs based on their interaction pathway participation in stress-responsive networks, and pinpoint strategies and applications for crops and the impact of these strategies for improving plant stress tolerance.

Silicon biology in crops under abiotic stress: A paradigm shift and cross-talk between genomics and proteomics

Silicon is a beneficial element to improve the biological process, growth, development, and crop productivity. The review mainly focuses on the advantage of crops supplemented with silicon, how Si alleviate abiotic stress as well as regulate the genes and proteins involved in metabolic and biological functions in plants. Abiotic stress causes damage to the proteins, nucleic acids, affect transpiration rate, stomatal conductance, alter the nutrient balance, and cell desiccation which could reduce the growth and development of the plants. To overcome from this problem researchers, focus on beneficial element like silicon to protect the plants against various abiotic stresses. The previous review reports are based on the application of silicon on salinity and drought stress, plant defense mechanism, the elevation of plant metabolism, enhancement of the biochemical and physiological properties, regulation of secondary metabolites and plant hormone. Here, we discuss about the silicon uptake and accumulation in plants, and silicon regulates the reactive oxygen species under abiotic stress, further we mainly focus on the genes and proteins which play a vital role in plants with silicon supplementation. The study can help the researchers to focus further on plants to improve the advancement in them under abiotic stress.

A Comparison of the Transcriptomes of Cowpeas in Response to Two Different Ionizing Radiations

In this study, gene expression changes in cowpea plants irradiated by two different types of radiation: proton-beams and gamma-rays were investigated. Seeds of the Okdang cultivar were exposed to 100, 200, and 300 Gy of gamma-rays and proton-beams. In transcriptome analysis, the 32, 75, and 69 differentially expressed genes (DEGs) at each dose of gamma-ray irradiation compared with that of the control were identified. A total of eight genes were commonly up-regulated for all gamma-ray doses. However, there were no down-regulated genes. In contrast, 168, 434, and 387 DEGs were identified for each dose of proton-beam irradiation compared with that of the control. A total of 61 DEGs were commonly up-regulated for all proton-beam doses. As a result of GO and KEGG analysis, the ranks of functional categories according to the number of DEGs were not the same in both treatments and were more diverse in terms of pathways in the proton-beam treatments than gamma-ray treatments. The number of genes related to defense, photosynthesis, reactive oxygen species (ROS), plant hormones, and transcription factors (TF) that were up-/down-regulated was higher in the proton beam treatment than that in gamma ray treatment. Proton-beam treatment had a distinct mutation spectrum and gene expression pattern compared to that of gamma-ray treatment. These results provide important information on the mechanism for gene regulation in response to two ionizing radiations in cowpeas.

Impact of the overexpression of the StDREB1 transcription factor on growth parameters, yields, and chemical composition of tubers from greenhouse and field grown potato plants

Potato plants are often exposed to biotic and abiotic stresses that negatively impact their growth, development, and yield. Plants respond to different stresses by inducing large numbers of stress-responsive genes, which can be either functional or regulatory genes. Among regulatory genes, Dehydration Responsive Element Binding (DREB) genes are considered as one of the main groups of transcriptional regulators. The overexpression of these factors in several transgenic plants leads to enhancement of abiotic stress tolerance. However, a number of reports showed that the overexpression of DREB factors under control of constitutive promoter, affects their morphology and production. Therefore, it becomes interesting to evaluate the effect of the overexpression of this StDREB1 transcription factor on plant growth, morphology, yield and tuber composition under both greenhouse and field culture conditions. To our knowledge, there is no available data on the effect of DREBA-4 overexpression on potato plants morphology and yield. Indeed, most studies focused on DREB genes from A-1 and A-2 groups for other plant species. Our results showed that StDREB1, a A-4 group of DREB gene from potato (Solanum tuberosum L.), overexpressing plants did not show any growth retardation. On the contrary, they seem to be more vigorous, and produced higher tuber weight in greenhouse and field culture than the wild type (WT) plants. Moreover, the overexpression of StDREB1 transcription factor seemed to have an effect on tuber quality in terms of dry matter, starch contents and reducing sugars in comparison to the WT tubers. These data suggest that the StDREB1 gene from A-4 group of DREB subfamily can be a good candidate in potato breeding for stress tolerance.

Transcriptome analysis uncovers the gene expression profile of salt-stressed potato (Solanum tuberosum L.)

Potato (Solanum tuberosum L.) is an important staple food worldwide. However, its growth has been heavily suppressed by salt stress. The molecular mechanisms of salt tolerance in potato remain unclear. It has been shown that the tetraploid potato Longshu No. 5 is a salt-tolerant genotype. Therefore, in this study we conducted research to identify salt stress response genes in Longshu No. 5 using a NaCl treatment and time-course RNA sequencing. The total number of differentially expressed genes (DEGs) in response to salt stress was 5508. Based on Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, it was found that DEGs were significantly enriched in the categories of nucleic acid binding, transporter activity, ion or molecule transport, ion binding, kinase activity and oxidative phosphorylation. Particularly, the significant differential expression of encoding ion transport signaling genes suggests that this signaling pathway plays a vital role in salt stress response in potato. Finally, the DEGs in the salt response pathway were verified by Quantitative real-time PCR (qRT-PCR). These results provide valuable information on the salt tolerance of molecular mechanisms in potatoes, and establish a basis for breeding salt-tolerant cultivars.

Transcriptome Response to Drought, Rehydration and Re-Dehydration in Potato

Potato is an important food crop and its production is susceptible to drought. Drought stress in crop growth is usually multiple- or long-term. In this study, the drought tolerant potato landrace Jancko Sisu Yari was treated with drought stress, rehydration and re-dehydration, and RNA-seq was applied to analyze the characteristics of gene regulation during these treatments. The results showed that drought-responsive genes mainly involved photosynthesis, signal transduction, lipid metabolism, sugar metabolism, wax synthesis, cell wall regulation, osmotic adjustment. Potato also can be recovered well in the re-emergence of water through gene regulation. The recovery of rehydration mainly related to patatin, lipid metabolism, sugar metabolism, flavonoids metabolism and detoxification besides the reverse expression of the most of drought-responsive genes. The previous drought stress can produce a positive responsive ability to the subsequent drought by drought hardening. Drought hardening was not only reflected in the drought-responsive genes related to the modified structure and cell components, but also in the hardening of gene expression or the "memory" of drought-responsive genes. Abundant genes involved photosynthesis, signal transduction, sugar metabolism, protease and protease inhibitors, flavonoids metabolism, transporters and transcription factors were subject to drought hardening or memorized drought in potato.

Physiology and transcriptome analyses reveal a protective effect of the radical scavenger melatonin in aging maize seeds

To determine the role of melatonin in aging maize seeds (Zea mays L.), we investigated the physiological characteristics and performance analysis of the transcriptome after applying melatonin to maize seeds as a response to aging. In this study, we demonstrated that applying exogenous melatonin alleviated aging-induced oxidative damage, improved the activity of aging seeds, promoted growth of the germ and radicle, enhanced antioxidant enzyme activity, and reduced membrane lipid peroxidation. In addition, transcriptome sequencing revealed that various metabolic processes were induced by exogenous melatonin application in aging maize seeds, including hormone signal transduction, cellular processes, carbohydrate metabolism, secondary metabolites, and amino acid metabolism. In summary, the findings provide a more comprehensive understanding for analysing the protective effect of melatonin in aging maize seeds.

Temporal restriction of salt inducibility in expression of salinity-stress related gene by the circadian clock in Solanum lycopersicum

Exposure to salinity causes plants to trigger transcriptional induction of a particular set of genes for initiating salinity-stress responses. Recent transcriptome analyses reveal that expression of a population of salinity-inducible genes also exhibits circadian rhythms. However, since the analyses were performed independently from those with salinity stress, it is unclear whether the observed circadian rhythms simply represent their basal expression levels independently from their induction by salinity, or these rhythms demonstrate the function of the circadian clock to actively limit the timing of occurrence of the salinity induction to particular times in the day. Here, by using tomato, we demonstrate that salt inducibility in expression of particular salinity-stress related genes is temporally controlled in the day. Occurrence of salinity induction in expression of SlSOS2 and P5CS, encoding a sodium/hydrogen antiporter and an enzyme for proline biosynthesis, is limited specifically to the morning, whereas that of SlDREB2, which encodes a transcription factor involved in tomato responses to several abiotic stresses such as salinity and drought, is restricted specifically to the evening. Our findings not only demonstrate potential importance in further investigating the basis and significance of circadian gated salinity stress responses under fluctuating day/night conditions, but also provide the potential to exploit an effective way for improving performance of salinity resistance in tomato.

Transcription factors involved in abiotic stress responses in Maize (Zea mays L.) and their roles in enhanced productivity in the post genomics era

BACKGROUND

Maize (Zea mays L.) is a principal cereal crop cultivated worldwide for human food, animal feed, and more recently as a source of biofuel. However, as a direct consequence of water insufficiency and climate change, frequent occurrences of both biotic and abiotic stresses have been reported in various regions around the world, and recently, this has become a constant threat in increasing global maize yields. Plants respond to abiotic stresses by utilizing the activities of transcription factors (TFs), which are families of genes coding for specific TF proteins. TF target genes form a regulon that is involved in the repression/activation of genes associated with abiotic stress responses. Therefore, it is of utmost importance to have a systematic study on each TF family, the downstream target genes they regulate, and the specific TF genes involved in multiple abiotic stress responses in maize and other staple crops.

METHOD

In this review, the main TF families, the specific TF genes and their regulons that are involved in abiotic stress regulation will be briefly discussed. Great emphasis will be given on maize abiotic stress improvement throughout this review, although other examples from different plants like rice, Arabidopsis, wheat, and barley will be used.

RESULTS

We have described in detail the main TF families in maize that take part in abiotic stress responses together with their regulons. Furthermore, we have also briefly described the utilization of high-efficiency technologies in the study and characterization of TFs involved in the abiotic stress regulatory networks in plants with an emphasis on increasing maize production. Examples of these technologies include next-generation sequencing, microarray analysis, machine learning, and RNA-Seq.

CONCLUSION

In conclusion, it is expected that all the information provided in this review will in time contribute to the use of TF genes in the research, breeding, and development of new abiotic stress tolerant maize cultivars.

Ammopiptanthus mongolicus stress-responsive NAC gene enhances the tolerance of transgenic Arabidopsis thaliana to drought and cold stresses

Drought and cold are the primary factors limiting plant growth worldwide. The Ammopiptanthus mongolicus NAC11 (AmNAC11) gene encodes a stress-responsive transcription factor. Expression of the AmNAC11 gene was induced by drought, cold and high salinity. The AmNAC11 protein was localized in the nucleus and plays an important role in tolerance to drought, cold and salt stresses. We also found that differential expression of AmNAC11 was induced in the early stages of seed germination and was related to root growth. When the AmNAC11 gene was introduced into Arabidopsis thaliana by an Agrobacterium-mediated method, the transgenic lines expressing AmNAC11 displayed significantly enhanced tolerance to drought and freezing stresses compared to wild-type Arabidopsis thaliana plants. These results indicated that over-expression of the AmNAC11 gene in Arabidopsis could significantly enhance its tolerance to drought and freezing stresses. Our study provides a promising approach to improve the tolerance of crop cultivars to abiotic stresses through genetic engineering.

MYB-CC transcription factor, TaMYBsm3, cloned from wheat is involved in drought tolerance

BACKGROUND

MYB-CC transcription factors (TFs) genes have been demonstrated to be involved in the response to inorganic phosphate (Pi) starvation and regulate some Pi-starvation-inducible genes. However, their role in drought stress has not been investigated in bread wheat. In this study, the TaMYBsm3 genes, including TaMYBsm3-A, TaMYBsm3-B, and TaMYBsm3-D, encoding MYB-CC TF proteins in bread wheat, were isolated to investigate the possible molecular mechanisms related to drought-tolerance in plants.

RESULTS

TaMYBsm3-A, TaMYBsm3-B, and TaMYBsm3-D were mapped on chromosomes 6A, 6B, and 6D in wheat, respectively. TaMYBsm3 genes belonged to MYB-CC TFs, containing a conserved MYB DNA-binding domain and a conserved coiled-coil domain. TaMYBsm3-D was localized in the nucleus, and the N-terminal region was a transcriptional activation domain. TaMYBsm3 genes were ubiquitously expressed in different tissues of wheat, and especially highly expressed in the stamen and pistil. Under drought stress, transgenic plants exhibited milder wilting symptoms, higher germination rates, higher proline content, and lower MDA content comparing with the wild type plants. P5CS1, DREB2A, and RD29A had significantly higher expression in transgenic plants than in wild type plants.

CONCLUSION

TaMYBsm3-A, TaMYBsm3-B, and TaMYBsm3-D were associated with enhanced drought tolerance in bread wheat. Overexpression of TaMYBsm3-D increases the drought tolerance of transgenic Arabidopsis through up-regulating P5CS1, DREB2A, and RD29A.

Crassulacean Acid Metabolism Abiotic Stress-Responsive Transcription Factors: a Potential Genetic Engineering Approach for Improving Crop Tolerance to Abiotic Stress

This perspective paper explores the utilization of abiotic stress-responsive transcription factors (TFs) from crassulacean acid metabolism (CAM) plants to improve abiotic stress tolerance in crop plants. CAM is a specialized type of photosynthetic adaptation that enhances water-use efficiency (WUE) by shifting CO2 uptake to all or part of the nighttime when evaporative water losses are minimal. Recent studies have shown that TF-based genetic engineering could be a useful approach for improving plant abiotic stress tolerance because of the role of TFs as master regulators of clusters of stress-responsive genes. Here, we explore the use of abiotic stress-responsive TFs from CAM plants to improve abiotic stress tolerance and WUE in crops by controlling the expression of gene cohorts that mediate drought-responsive adaptations. Recent research has revealed several TF families including AP2/ERF, MYB, WRKY, NAC, NF-Y, and bZIP that might regulate water-deficit stress responses and CAM in the inducible CAM plant Mesembryanthemum crystallinum under water-deficit stress-induced CAM and in the obligate CAM plant Kalanchoe fedtschenkoi. Overexpression of genes from these families in Arabidopsis thaliana can improve abiotic stress tolerance in A. thaliana in some instances. Therefore, we propose that TF-based genetic engineering with a small number of CAM abiotic stress-responsive TFs will be a promising strategy for improving abiotic stress tolerance and WUE in crop plants in a projected hotter and drier landscape in the 21st-century and beyond.

Transcriptome Profiling Reveals Effects of Drought Stress on Gene Expression in Diploid Potato Genotype P3-198

Potato (Solanum tuberosum L.) is one of the three most important food crops worldwide; however, it is strongly affected by drought stress. The precise molecular mechanisms of drought stress response in potato are not very well understood. The diploid potato genotype P3-198 has been verified to be highly resistant to drought stress. Here, a time-course experiment was performed to identify drought resistance response genes in P3-198 under polyethylene glycol (PEG)-induced stress using RNA-sequencing. A total of 1665 differentially expressed genes (DEGs) were specifically identified, and based on gene ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, the transcription factor activity, protein kinase activity, and the plant hormone signal transduction process were significantly enriched. Annotation revealed that these DEGs mainly encode transcription factors, protein kinases, and proteins related to redox regulation, carbohydrate metabolism, and osmotic adjustment. In particular, genes encoding abscisic acid (ABA)-dependent signaling molecules were significantly differentially expressed, which revealed the important roles of the ABA-dependent signaling pathway in the early response of P3-198 to drought stress. Quantitative real-time PCR experimental verification confirmed the differential expression of genes in the drought resistance signaling pathway. Our results provide valuable information for understanding potato drought-resistance mechanisms, and also enrich the gene resources available for drought-resistant potato breeding.

An apple transcription factor, MdDREB76, confers salt and drought tolerance in transgenic tobacco by activating the expression of stress-responsive genes

KEY MESSAGE

An apple gene, MdDREB76 encodes a functional transcription factor and imparts salinity and drought stress endurance to transgenic tobacco by activating expression of stress-responsive genes. The dehydration-responsive element (DRE)-binding protein (DREB) transcription factors are well known to be involved in regulating abiotic stress-mediated gene expression in plants. In this study, MdDREB76 gene was isolated from apple (Malus x domestica), which encodes a functional transcription factor protein. Overexpression of MdDREB76 in tobacco conferred salt and drought stress tolerance to transgenic lines by inducing antioxidant enzymes, such as superoxide dismutase, ascorbate peroxidase and catalase. The higher membrane stability index, relative water content, proline, total soluble sugar content and lesser H2O2content, electrolyte leakage and lipid peroxidation in transgenics support the improved physiological status of transgenic plants as compared to WT plants under salinity and drought stresses. The MdDREB76 overexpression upregulated the expression of stress-responsive genes that provide salinity and drought stress endurance to the plants. Compared to WT plants, transgenic lines exhibited healthy growth and higher yield under stress conditions. The present study reports MdDREB76 as a key regulator that switches on the battery of downstream genes which impart salt and osmotic stress endurance to the transgenic plants and can be used for genetic engineering of crop plants to combat salinity and drought stresses.

Ectopic Expression of OsDREB1G, a Member of the OsDREB1 Subfamily, Confers Cold Stress Tolerance in Rice

Plants adapt to adverse environmental conditions through physiological responses, such as induction of the abscisic acid signaling pathway, stomatal regulation, and root elongation. Altered gene expression is a major molecular response to adverse environmental conditions in plants. Several transcription factors function as master switches to induce the expression of stress-tolerance genes. To find out a master regulator for the cold stress tolerance in rice, we focused on functionally identifying DREB subfamily which plays important roles in cold stress tolerance of plants. Here, we characterized OsDREB1G (LOC_Os02g45450), a functionally unidentified member of the DREB1 subgroup. OsDREB1G is specifically induced under cold stress conditions among several abiotic stresses examined. This gene is dominantly expressed in leaf sheath, blade, node, and root. Transgenic rice overexpressing this gene exhibited strong cold tolerance and growth retardation, like transgenic rice overexpressing other OsDREB1 genes. However, unlike these rice lines, transgenic rice overexpressing OsDREB1G did not exhibit significant increases in drought or salt tolerance. Cold-responsive genes were highly induced in transgenic rice overexpressing DREB1G compared to wild type. In addition, OsDREB1G overexpression directly induced the expression of a reporter gene fused to the promoters of cold-induced genes in rice protoplasts. Therefore, OsDREB1G is a typical CBF/DREB1 transcription factor that specifically functions in the cold stress response. Therefore, OsDREB1G could be useful for developing transgenic rice with enhanced cold-stress tolerance.

Basic transcription factor 3 expression silencing attenuates colon cancer cell proliferation and migration in vitro

Basic transcription factor 3 (BTF3) is an RNA polymerase II transcription factor that also regulates apoptosis. Numerous studies have identified that BTF3 is aberrantly expressed in several types of tumor. However, the function of BTF3 in colorectal cancer remains unknown. The aim of the present study was to assess the function of BTF3 during colon cancer tumorigenesis. Applying a lentivirus-transfected short hairpin RNA approach, expression of BTF3 was dysregulated in the colon cancer HCT116 and HT-29 cell lines; knockdown efficiency was verified using the quantitative polymerase chain reaction and western blotting. To determine the function of BTF3 in colon cancer, cell proliferation was assessed using an MTT assay, cell apoptosis and the cell cycle were assessed using flow cytometry, and cell migration was assessed using a Transwell assay. Knockdown of BTF3 inhibited cell proliferation, possibly because BTF3 knockdown induced cell early apoptosis and arrested cells in G₀-G₁ phase. BTF3 knockdown also inhibited cell migration. The results of the present study identified that BTF3 expression is associated with colon cancer progress, and BTF3 may therefore be a molecular marker for diagnosis and treatment outcomes of human colon cancer.

Structural, Functional, and Evolutionary Characterization of Major Drought Transcription Factors Families in Maize

Drought is one of the major threats to the maize yield especially in subtropical production systems. Understanding the genes and regulatory mechanisms of drought tolerance is important to sustain the yield. Transcription factors (TFs) play a major role in gene regulation under drought stress. In the present study, a set of 15 major TF families comprising 1,436 genes was structurally and functionally characterized. The functional annotation indicated that the genes were involved in ABA signaling, ROS scavenging, photosynthesis, stomatal regulation, and sucrose metabolism. Duplication was identified as the primary force in divergence and expansion of TF families. Phylogenetic relationship was developed for individual TF and combined TF families. Phylogenetic analysis clustered the genes into specific and mixed groups. Gene structure analysis revealed that more number of genes were intron-rich as compared to intron-less. Drought-responsive cis-regulatory elements such as ABREA, ABREB, DRE1, and DRECRTCOREAT have been identified. Expression and interaction analyses identified leaf-specific bZIP TF, GRMZM2G140355, as a potential contributor toward drought tolerance in maize. Protein-protein interaction network of 269 drought-responsive genes belonging to different TFs has been provided. The information generated on structural and functional characteristics, expression, and interaction of the drought-related TF families will be useful to decipher the drought tolerance mechanisms and to breed drought-tolerant genotypes in maize.

Molecular cloning and expression analysis of three ThERFs involved in the response to waterlogging stress of Taxodium 'Zhongshanshan406', and subcellular localization of the gene products

As a subfamily of the APETALA 2/ethylene response element binding protein (AP2/EREBP) transcription factor superfamily, the ethylene response factor (ERF) is widely involved in the regulation of growth and response to various abiotic stresses in plants, and has been shown to be the main transcription factor regulating transcription of the genes related to hypoxia and waterlogging stress. In this study, three ThERF genes, with significant differences in expression profile in response to flooding stress, were identified from the transcriptomics data acquired from Taxodium hybrid ‘Zhongshanshan 406’ (T. mucronatum Tenore × T. distichum (L.) Rich) under waterlogging stress: ThERF15, ThERF39 and ThRAP2.3 (GenBank ID: KY463467, KY463468 and KY463470, respectively).The full-length cDNA of each of the three ERFs was obtained using the RACE (rapid amplification cDNA ends) method, and all three were intron-free. Multiple protein sequence alignments indicated that ThERF15, ThERF39 and ThRAP2.3 proteins all had only one AP2-ERF domain and belonged to the ERF subfamily. A transient gene expression assay demonstrated that ThERF15, ThERF39 and ThRAP2.3 were all localized to the nucleus. Real-time quantitative PCR (qPCR) revealed that the expression of ThERF15, ThERF39 and ThRAP2.3 exhibited significant differences, compared with the control, in response to two levels of flooding treatment (half-flooding or total-submergence) of ‘Zhongshanshan 406’. Quantification of ethylene concentration revealed that ethylene was more relevant to the level of expression than the period of flooding treatment. Based on the experimental results above, ThERF15, ThERF39 and ThRAP2.3 were identified as being related to the regulation of downstream flooding- responsive gene expression in ‘Zhongshanshan 406’. ThRAP2.3 is most likely to be a key downstream-response ERF gene to respond to the output of the ethylene signal generated by flooding stress.

Transcription Factors and Their Roles in Signal Transduction in Plants under Abiotic Stresses

In agricultural production, abiotic stresses are known as the main disturbance leading to negative impacts on crop performance. Research on elucidating plant defense mechanisms against the stresses at molecular level has been addressed for years in order to identify the major contributors in boosting the plant tolerance ability. From literature, numerous genes from different species, and from both functional and regulatory gene categories, have been suggested to be on the list of potential candidates for genetic engineering. Noticeably, enhancement of plant stress tolerance by manipulating expression of Transcription Factors (TFs) encoding genes has emerged as a popular approach since most of them are early stress-responsive genes and control the expression of a set of downstream target genes. Consequently, there is a higher chance to generate novel cultivars with better tolerance to either single or multiple stresses. Perhaps, the difficult task when deploying this approach is selecting appropriate gene(s) for manipulation. In this review, on the basis of the current findings from molecular and post-genomic studies, our interest is to highlight the current understanding of the roles of TFs in signal transduction and mediating plant responses towards abiotic stressors. Furthermore, interactions among TFs within the stress-responsive network will be discussed. The last section will be reserved for discussing the potential applications of TFs for stress tolerance improvement in plants.

Improved short-term drought response of transgenic rice over-expressing maize C4 phosphoenolpyruvate carboxylase via calcium signal cascade

To understand the link between long-term drought tolerance and short-term drought responses in plants, transgenic rice (Oryza sativa L.) plants over-expressing the maize C_4-pepc gene encoding phosphoenolpyruvate carboxylase (PC) and wild-type (WT) rice plants were subjected to PEG 6000 treatments to simulate drought stress. Compared with WT, PC had the higher survival rate and net photosynthetic rate after 16days of drought treatment, and had higher relative water content in leaves after 2h of drought treatment as well, conferring drought tolerance. WT accumulated higher amounts of malondialdehyde, superoxide radicals, and H₂O₂ than PC under the 2-h PEG 6000 treatment, indicating greater damages in WT. Results from pretreatments with a Ca²⁺ chelator and/or antagonist showed that the regulation of the early drought response in PC was Ca²⁺-dependent. The NO and H₂O₂ levels in PC lines were also up-regulated via Ca²⁺ signals, indicating that Ca²⁺ in PC lines also reacted upstream of NO and H₂O₂. 2-h drought treatment increased the transcripts of CPK9 and CPK4 in PC via positive up-regulation of Ca²⁺. The transcripts of NAC6 [NACs (NAM, ATAF1, ATAF2, and CUC2)] and bZIP60 (basic leucine zipper, bZIP) were up-regulated, but those of DREB2B (dehydration-responsive element-binding protein, DREB) were down-regulated, both via Ca²⁺ signals in PC. PEPC activity, expressions of C₄-pepc, and the antioxidant enzyme activities in PC lines were up-regulated via Ca²⁺. These results indicated that Ca²⁺ signals in PC lines can up-regulate the NAC6 and bZIP60 and the downstream targets for early drought responses, conferring drought tolerance for the long term.

Chickpea WRKY70 Regulates the Expression of a Homeodomain-Leucine Zipper (HD-Zip) I Transcription Factor CaHDZ12, which Confers Abiotic Stress Tolerance in Transgenic Tobacco and Chickpea

Drought and salinity are the two major environmental constraints that severely affect global agricultural productivity. Plant-specific HD-Zip transcription factors are involved in plant growth, development and stress responses. In the present study, we explored the functional characteristics and regulation of a novel HD-Zip (I) gene from chickpea, CaHDZ12, in response to water-deficit and salt-stress conditions. Transgenic tobacco lines over-expressing CaHDZ12 exhibited improved tolerance to osmotic stresses and increased sensitivity to abscisic acid (ABA). Physiological compatibility of transgenic lines was found to be more robust compared to the wild-type plants under drought and salinity stress. Additionally, expression of several stress-responsive genes was significantly induced in CaHDZ12 transgenic plants. On the other hand, silencing of CaHDZ12 in chickpea resulted in increased sensitivity to salt and drought stresses. Analysis of different promoter deletion mutants identified CaWRKY70 transcription factor as a transcriptional regulator of CaHDZ12 expression. In vivo and in vitro interaction studies detected an association between CaWRKY70 and CaHDZ12 promoter during stress responses. Epigenetic modifications underlying histone acetylation at the CaHDZ12 promoter region play a significant role in stress-induced activation of this gene. Collectively, our study describes a crucial and unique mechanistic link between two distinct transcription factors in regulating plant adaptive stress response.

Overexpression of GhDof1 improved salt and cold tolerance and seed oil content in Gossypium hirsutum

A homologous GhDof1, which belongs to a large family of plant-specific transcription factor DOF, was isolated from Upland cotton (Gossypium hirsutum L.). GhDof1 protein was located in the nucleus of onion epidermal cells, the core domain of transcriptional activity existed in the C-terminal, and the activity elements of GhDof1 promoter existed in the regions of -645∼ -469bp and -286∼ -132bp of transcriptional start codon. GhDof1 constitutively expressed in leaves, roots and stems, accumulated highest in leaves. The salinity and cold treatments induced GhDof1 transcript accumulation. The GhDof1-overexpressed cotton showed significantly higher salt and cold tolerance over the wild-type plants. Under salt stress, the root growth of overexpressed GhDof1 lines was promoted. The expression levels of stress-responsive genes, GhP5CS, GhSOD and GhMYB, were differently up-regulated in transgenic lines. Oil contents increased in some transgenic plants, and protein contents reduced compared with transformed receptor. These results suggested that GhDof1 was a functional transcription factor for improving the abiotic tolerance and seed oil content in Upland cotton.

Multifaceted role of cycling DOF factor 3 (CDF3) in the regulation of flowering time and abiotic stress responses in Arabidopsis

DNA-binding with one finger (DOF)-type transcription factors are involved in many fundamental processes in higher plants, from responses to light and phytohormones to flowering time and seed maturation, but their relation with abiotic stress tolerance is largely unknown. Here, we identify the roles of CDF3, an Arabidopsis DOF gene in abiotic stress responses and developmental processes like flowering time. CDF3 is highly induced by drought, extreme temperatures and abscisic acid treatment. The CDF3 T-DNA insertion mutant cdf3-1 is much more sensitive to drought and low temperature stress, whereas CDF3 overexpression enhances the tolerance of transgenic plants to drought, cold and osmotic stress and promotes late flowering. Transcriptome analysis revealed that CDF3 regulates a set of genes involved in cellular osmoprotection and oxidative stress, including the stress tolerance transcription factors CBFs, DREB2A and ZAT12, which involve both gigantea-dependent and independent pathways. Consistently, metabolite profiling disclosed that the total amount of some protective metabolites including γ-aminobutyric acid, proline, glutamine and sucrose were higher in CDF3-overexpressing plants. Taken together, these results indicate that CDF3 plays a multifaceted role acting on both flowering time and abiotic stress tolerance, in part by controlling the CBF/DREB2A-CRT/DRE and ZAT10/12 modules.

Silicon Regulates Potential Genes Involved in Major Physiological Processes in Plants to Combat Stress

Silicon (Si), the quasi-essential element occurs as the second most abundant element in the earth's crust. Biological importance of Si in plant kingdom has become inevitable particularly under stressed environment. In general, plants are classified as high, medium, and low silicon accumulators based on the ability of roots to absorb Si. The uptake of Si directly influence the positive effects attributed to the plant but Si supplementation proves to mitigate stress and recover plant growth even in low accumulating plants like tomato. The application of Si in soil as well as soil-less cultivation systems have resulted in the enhancement of quantitative and qualitative traits of plants even under stressed environment. Silicon possesses several mechanisms to regulate the physiological, biochemical, and antioxidant metabolism in plants to combat abiotic and biotic stresses. Nevertheless, very few reports are available on the aspect of Si-mediated molecular regulation of genes with potential role in stress tolerance. The recent advancements in the era of genomics and transcriptomics have opened an avenue for the determination of molecular rationale associated with the Si amendment to the stress alleviation in plants. Therefore, the present endeavor has attempted to describe the recent discoveries related to the regulation of vital genes involved in photosynthesis, transcription regulation, defense, water transport, polyamine synthesis, and housekeeping genes during abiotic and biotic stress alleviation by Si. Furthermore, an overview of Si-mediated modulation of multiple genes involved in stress response pathways such as phenylpropanoid pathway, jasmonic acid pathway, ABA-dependent or independent regulatory pathway have been discussed in this review.

Directed Evolution of Dunaliella salina Ds-26-16 and Salt-Tolerant Response in Escherichia coli

Identification and evolution of salt tolerant genes are crucial steps in developing salt tolerant crops or microorganisms using biotechnology. Ds-26-16, a salt tolerant gene that was isolated from Dunaliella salina, encodes a transcription factor that can confer salt tolerance to a number of organisms including Escherichia coli (E. coli), Haematococcus pluvialis and tobacco. To further improve its salt tolerance, a random mutagenesis library was constructed using deoxyinosine triphosphate-mediated error-prone PCR technology, and then screened using an E. coli expression system that is based on its broad-spectrum salt tolerance. Seven variants with enhanced salt tolerance were obtained. Variant EP-5 that contained mutation S32P showed the most improvement with the E. coli transformant enduring salt concentrations up to 1.54 M, in comparison with 1.03 M for the wild type gene. Besides, Ds-26-16 and EP-5 also conferred E. coli transformant tolerance to freezing, cold, heat, Cu²⁺ and alkaline. Homology modeling revealed that mutation S32P in EP-5 caused the conformational change of N- and C-terminal α-helixes. Expression of Ds-26-16 and EP-5 maintained normal cellular morphology, increased the intracellular antioxidant enzymatic activity, reduced malondialdehyde content, and stimulated Nitric Oxide synthesis, thus enhancing salt tolerance to E. coli transformants.