DREB/CBF expression in wheat and barley using the stress-inducible promoters of HD-Zip I genes: impact on plant development, stress tolerance and yield

Genome-wide investigation and analysis of NAC transcription factor family in Populus tomentosa and expression analysis under salt stress

The NAC transcription factor family is one of the largest families of TFs in plants, and members of NAC gene family play important roles in plant growth and stress response. Recent release of the haplotype-resolved genome assembly of P. tomentosa provide a platform for NAC protein genome-wide analysis. A total of 270 NAC genes were identified and a comprehensive overview of the PtoNAC gene family is presented, including gene promoter, structure and conserved motif analyses, chromosome localization and collinearity analysis, protein phylogeny, expression pattern, and interaction analysis. The results indicate that protein length, molecular weight, and theoretical isoelectric points of the NAC TF family vary, while gene structure and motif are relatively conserved. Chromosome mapping analysis showed that the P. tomentosa NAC genes are unevenly distributed on 19 chromosomes. The interchromosomal evolutionary results indicate 12 pairs of tandem and 280 segmental duplications. Segmental duplication is possibly related to amplification of P. tomentosa NAC gene family. Expression patterns of 35 PtoNAC genes from P. tomentosa subgroup were analysed under high salinity, and seven NAC genes were induced by this treatment. Promoter and protein interaction network analyses showed that PtoNAC genes are closely associated with growth, development, and abiotic and biotic stress, especially salt stress. These results provide a meaningful reference for follow-up studies of the functional characteristics of NAC genes in the mechanism of stress response and their potential roles in development of P. tomentosa.

Functional and regulatory diversity of homeobox-leucine zipper transcription factors BnaHB6 under dehydration and salt stress in Brassica napus L

The plant-specific homeodomain-leucine zipper I subfamily is involved in the regulation of various biological processes, particularly growth, development and stress response. In the present study, we characterized four BnaHB6 homologues from Brassica napus. All BnaHB6 proteins have transcriptional activation activity. Structural and functional data indicate the complex role of BnaHB6 genes in regulating biological processes, with some functions conserved and others diverged. Transcriptional analyzes revealed that they are induced in a similar manner in different tissues but show different expression patterns in response to stress and circadian rhythm. Only the BnaA09HB6 and BnaC08HB6 genes are expressed under dehydration and salt stress, and in darkness. The partial transcriptional overlap of BnaHB6s with the evolutionarily related genes BnaHB5 and BnaHB16 was also observed. Transgenic Arabidopsis thaliana plants expressing a single proBnaHB6::GUS partially confirmed the expression results. Bioinformatic analysis allowed the identification of TF-binding sites in the BnaHB6 promoters that may control their expression under stress and circadian rhythm. ChIP-qPCR analysis revealed that BnaA09HB6 and BnaC08HB6 bind directly to the promoters of the target genes BnaABF4 and BnaDREB2A. Comparison of their expression patterns in the WT plants and the bnac08hb6 mutant showed that BnaC08HB6 positively regulates the expression of the BnaABF4 and BnaDREB2A genes under dehydration and salt stress. We conclude that four BnaHB6 homologues have distinct functions in response to stress despite high sequence similarity, possibly indicating different binding preferences with BnaABF4 and BnaDREB2A. We hypothesize that BnaC08HB6 and BnaA09HB6 function in a complex regulatory network under stress.

Overexpression of MsDREB1C Modulates Growth and Improves Forage Quality in Tetraploid Alfalfa (Medicago sativa L.)

DREB has been reported to be involved in plant growth and response to environmental factors. However, the function of DREB in growth and development has not been elucidated in alfalfa (Medicago sativa L.), a perennial tetraploid forage cultivated worldwide. In this study, an ortholog of MtDREB1C was characterized from alfalfa and named MsDREB1C accordingly. MsDREB1C was significantly induced by abiotic stress. The transcription factor MsDREB1C resided in the nucleus and had self-transactivation activity. The MsDREB1C overexpression (OE) alfalfa displayed growth retardation under both long-day and short-day conditions, which was supported by decreased MsGA20ox and upregulated MsGA2ox in the OE lines. Consistently, a decrease in active gibberellin (GA) was detected, suggesting a negative effect of MsDREB1C on GA accumulation in alfalfa. Interestingly, the forage quality of the OE lines was better than that of WT lines, with higher crude protein and lower lignin content, which was supported by an increase in the leaf-stem ratio (LSR) and repression of several lignin-synthesis genes (MsNST, MsPAL1, MsC4H, and Ms4CL). Therefore, this study revealed the effects of MsDREB1C overexpression on growth and forage quality via modifying GA accumulation and lignin synthesis, respectively. Our findings provide a valuable candidate for improving the critical agronomic traits of alfalfa, such as overwintering and feeding value of the forage.

Gene pyramiding for boosted plant growth and broad abiotic stress tolerance

Abiotic stresses such as salinity, heat and drought seriously impair plant growth and development, causing a significant loss in crop yield and ornamental value. Biotechnology approaches manipulating specific genes prove to be effective strategies in crop trait modification. The Arabidopsis vacuolar pyrophosphatase gene AVP1, the rice SUMO E3 ligase gene OsSIZ1 and the cyanobacterium flavodoxin gene Fld have previously been implicated in regulating plant stress responses and conferring enhanced tolerance to different abiotic stresses when individually overexpressed in various plant species. We have explored the feasibility of combining multiple favourable traits brought by individual genes to acquire superior plant performance. To this end, we have simultaneously introduced AVP1, OsSIZ1 and Fld in creeping bentgrass. Transgenic (TG) plants overexpressing these three genes performed significantly better than wild type controls and the TGs expressing individual genes under both normal and various abiotic stress conditions, exhibited significantly enhanced plant growth and tolerance to drought, salinity and heat stresses as well as nitrogen and phosphate starvation, which were associated with altered physiological and biochemical characteristics and delicately fine-tuned expression of genes involved in plant stress responses. Our results suggest that AVP1, OsSIZ1 and Fld function synergistically to regulate plant development and plant stress response, leading to superior overall performance under both normal and adverse environments. The information obtained provides new insights into gene stacking as an effective approach for plant genetic engineering. A similar strategy can be extended for the use of other beneficial genes in various crop species for trait modifications, enhancing agricultural production.

The Triticeae CBF Gene Cluster-To Frost Resistance and Beyond

The pivotal role of CBF/DREB1 transcriptional factors in Triticeae crops involved in the abiotic stress response has been highlighted. The CBFs represent an important hub in the ICE-CBF-COR pathway, which is one of the most relevant mechanisms capable of activating the adaptive response to cold and drought in wheat, barley, and rye. Understanding the intricate mechanisms and regulation of the cluster of CBF genes harbored by the homoeologous chromosome group 5 entails significant potential for the genetic improvement of small grain cereals. Triticeae crops seem to share common mechanisms characterized, however, by some peculiar aspects of the response to stress, highlighting a combined landscape of single-nucleotide variants and copy number variation involving CBF members of subgroup IV. Moreover, while chromosome 5 ploidy appears to confer species-specific levels of resistance, an important involvement of the ICE factor might explain the greater tolerance of rye. By unraveling the genetic basis of abiotic stress tolerance, researchers can develop resilient varieties better equipped to withstand extreme environmental conditions. Hence, advancing our knowledge of CBFs and their interactions represents a promising avenue for improving crop resilience and food security.

Wheat adaptation to environmental stresses under climate change: Molecular basis and genetic improvement

Wheat (Triticum aestivum) is a staple food for about 40% of the world's population. As the global population has grown and living standards improved, high yield and improved nutritional quality have become the main targets for wheat breeding. However, wheat production has been compromised by global warming through the more frequent occurrence of extreme temperature events, which have increased water scarcity, aggravated soil salinization, caused plants to be more vulnerable to diseases, and directly reduced plant fertility and suppressed yield. One promising option to address these challenges is the genetic improvement of wheat for enhanced resistance to environmental stress. Several decades of progress in genomics and genetic engineering has tremendously advanced our understanding of the molecular and genetic mechanisms underlying abiotic and biotic stress responses in wheat. These advances have heralded what might be considered a "golden age" of functional genomics for the genetic improvement of wheat. Here, we summarize the current knowledge on the molecular and genetic basis of wheat resistance to abiotic and biotic stresses, including the QTLs/genes involved, their functional and regulatory mechanisms, and strategies for genetic modification of wheat for improved stress resistance. In addition, we also provide perspectives on some key challenges that need to be addressed.

Evolutionary Consequences of Functional and Regulatory Divergence of HD-Zip I Transcription Factors as a Source of Diversity in Protein Interaction Networks in Plants

The HD superfamily has been studied in detail for several decades. The plant-specific HD-Zip I subfamily attracts the most attention because of its involvement in plant development and stress responses. In this review, we provide a comprehensive insight into the evolutionary events responsible for the functional redundancy and diversification of the HD-Zip I genes in regulating various biological processes. We summarized the evolutionary history of the HD-Zip family, highlighting the important role of WGDs in its expansion and divergence of retained duplicates in the genome. To determine the relationship between the evolutionary origin and functional conservation of HD-Zip I in different species, we performed a phylogenetic analysis, compared their expression profiles in different tissues and under stress and traced the role of orthologs and paralogs in regulating developmental processes. We found that HD-Zip I from different species have similar gene structures with a highly conserved HD and Zip, bind to the same DNA sequences and are involved in similar biological processes. However, they exhibit a functional diversity, which is manifested in altered expression patterns. Some of them are involved in the regulation of species-specific leaf morphology and phenotypes. Here, we discuss the role of changes in functional domains involved in DNA binding and protein interaction of HD-Zip I and in cis-regulated regions of its target genes in promoting adaptive innovations through the formation of de novo regulatory systems. Understanding the role of the HD-Zip I subfamily in organism-environment interactions remains a challenge for evolutionary developmental biology (evo-devo).

DIW1 encoding a clade I PP2C phosphatase negatively regulates drought tolerance by de-phosphorylating TaSnRK1.1 in wheat

Drought seriously impacts wheat production (Triticum aestivum L.), while the exploitation and utilization of genes for drought tolerance are insufficient. Leaf wilting is a direct reflection of drought tolerance in plants. Clade A PP2Cs are abscisic acid (ABA) co-receptors playing vital roles in the ABA signaling pathway, regulating drought response. However, the roles of other clade PP2Cs in drought tolerance, especially in wheat, remain largely unknown. Here, we identified a gain-of-function drought-induced wilting 1 (DIW1) gene from the wheat Aikang 58 mutant library by map-based cloning, which encodes a clade I protein phosphatase 2C (TaPP2C158) with enhanced protein phosphatase activity. Phenotypic analysis of overexpression and CRISPR/Cas9 mutant lines demonstrated that DIW1/TaPP2C158 is a negative regulator responsible for drought resistance. We found that TaPP2C158 directly interacts with TaSnRK1.1 and de-phosphorylates it, thus inactivating the TaSnRK1.1-TaAREB3 pathway. TaPP2C158 protein phosphatase activity is negatively correlated with ABA signaling. Association analysis suggested that C-terminal variation of TaPP2C158 changing protein phosphatase activity is highly correlated with the canopy temperature, and seedling survival rate under drought stress. Our data suggest that the favorable allele with lower phosphatase activity of TaPP2C158 has been positively selected in Chinese breeding history. This work benefits us in understanding the molecular mechanism of wheat drought tolerance, and provides elite genetic resources and molecular markers for improving wheat drought tolerance.

Genome-Wide Identification and Expression Profiles of C-Repeat Binding Factor Transcription Factors in Betula platyphylla under Abiotic Stress

CBF (C-repeat binding factor) transcription factor subfamily belongs to AP2/ERF (Apetala 2/ethylene-responsive factor) transcription factor family, known for playing a vital role in plant abiotic stress response. Although some CBF transcription factors have been identified in several species, such as Arabidopsis, tobacco, tomato and poplar, research of CBF focus mainly on model plant Arabidopsis and have not been reported in Betula platyphylla yet. In this study, a total of 20 BpCBF subfamily members were identified. The conserved domains, physicochemical properties, exon-intron gene structure and the structure of conserved protein motifs of BpCBFs were analyzed via bioinformatic tools. The collinearity analysis of CBF genes was performed between Betula platyphylla and Arabidopsis thaliana, Betula platyphylla, and Populus trichocarpa. The cis-acting elements in the promoter region of BpCBFs were identified, which were mainly environmental stress-related and hormone-related element components. In this case, the expression patterns of the 20 BpCBFs upon ABA or salt treatment were investigated. Most of these transcription factors were responsive to ABA or salt stress in different plant tissues. The up-regulation trend upon cold treatment of the six cold-responsive genes validated by qRT-PCR was consistent with the result of RNA-seq. BpCBF7 showed transcription activating activity. This study sheds light on the responses of BpCBFs to abiotic stress and provides a reference for further study of CBF transcription factors in woody plants.

Exploration of the Regulatory Pathways and Key Genes Involved in the Response to Saline-Alkali Stress in Betula platyphylla via RNA-Seq Analysis

The pH of saline-alkali soil is high because of carbonate salts, and the deleterious effects of saline-alkali soil on the growth of plants are greater than those of saline soil. Few studies have examined the saline-alkali tolerance of Betula platyphylla at the molecular level. To clarify the regulatory mechanism underlying saline-alkali tolerance in B. platyphylla, RNA sequencing analysis of B. platyphylla seedlings treated with NaHCO₃ was conducted. Differences in gene expression in the roots of B. platyphylla seedlings under saline-alkali stress (induced via NaHCO₃) for 3 h and 6 h were characterized, and a total of 595 and 607 alkali stress-responsive genes were identified, respectively. Most differentially expressed genes were involved in stress, signal transduction, secondary metabolic process, regulation of jasmonic acid, and the abiotic stimulus signaling pathway. The single nucleotide polymorphism loci in the differentially expressed genes were associated with the alkaline-salt tolerance in birch germplasm. In addition, birch plants overexpressing WRKY70 and NAC9 were obtained using the A. tumefaciens-mediated transient transformation method, and these two genes were found to play key roles in saline-alkali tolerance. Additional study revealed that WRKY70 and NAC9 can increase resistance to saline-alkali stress by enhancing reactive oxygen species scavenging and inhibiting cell death in birch plants. The results of this study enhance our understanding of the saline-alkali stress tolerance of B. platyphylla at the molecular level, and provide several key genes that could be used in the breeding of birch plants in the future.

The DREB transcription factor, a biomacromolecule, responds to abiotic stress by regulating the expression of stress-related genes

Abiotic stress is a crucial factor that affects plant survival and growth and even leads to plant death in severe cases. Transcription factors can enhance the ability of plants to fight against various stresses by controlling the expression of downstream genes. The dehydration response element binding protein (DREB) is the most extensive subfamily of AP2/ERF transcription factors involved in abiotic stress. However, insufficient research on the signal network of DREB transcription factors has limited plant growth and reproduction. Furthermore, field planting of DREB transcription factors and their roles under multiple stress also require extensive research. Previous reports on DREB transcription factors have focused on the regulation of DREB expression and its roles in plant abiotic stress. In recent years, there has been new progress in DREB transcription factors. Here, the structure and classification, evolution and regulation, role in abiotic stress, and application in crops of DREB transcription factors were reviewed. And this paper highlighted the evolution of DREB1/CBF, as well as the regulation of DREB transcription factors under the participation of plant hormone signals and the roles of subgroups in abiotic stress. In the future, it will lay a solid foundation for further study of DREB transcription factors and pave the way for the cultivation of resistant plants.

Global crotonylatome and GWAS revealed a TaSRT1-TaPGK model regulating wheat cold tolerance through mediating pyruvate

Here, we reported the complete profiling of the crotonylation proteome in common wheat. Through a combination of crotonylation and multi-omics analysis, we identified a TaPGK associated with wheat cold stress. Then, we confirmed the positive role of TaPGK-modulating wheat cold tolerance. Meanwhile, we found that cold stress induced lysine crotonylation of TaPGK. Moreover, we screened a lysine decrotonylase TaSRT1 interacting with TaPGK and found that TaSRT1 negatively regulated wheat cold tolerance. We subsequently demonstrated TaSRT1 inhibiting the accumulation of TaPGK protein, and this inhibition was possibly resulted from decrotonylation of TaPGK by TaSRT1. Transcriptome sequencing indicated that overexpression of TaPGK activated glycolytic key genes and thereby increased pyruvate content. Moreover, we found that exogenous application of pyruvate sharply enhanced wheat cold tolerance. These findings suggest that the TaSRT1-TaPGK model regulating wheat cold tolerance is possibly through mediating pyruvate. This study provided two valuable cold tolerance genes and dissected diverse mechanism of glycolytic pathway involving in wheat cold stress.

Identification and functional analysis of calcium sensor calmodulins from heavy metal hyperaccumulator Noccaea caerulescens

Noccaea caerulescens (J. Presl & C. Presl) F. K. Mey. is a heavy metal hyperaccumulator exhibiting extreme tolerance to various environmental stresses. To date, the functional role of Ca2+ -binding protein in this plant is largely unknown. To investigate the function of calmodulins (CaMs) in N. caerulescens , CaM2 , a Ca2+ sensor encoding gene, was identified and functionally characterised. Protein structure analysis showed that NcCaM2 contains four classic exchange factor (EF)-hand motifs with high sequence similarity to the CaM proteins from model plant Arabidopsis thaliana L. Tissue specific expression analysis showed that NcCaM2 is constitutively expressed in stems, leaves, and roots. Expression level of NcCaM2 was significantly upregulated under various environmental stimulus, indicating a potential involvement of NcCaM2 in the tolerance to abiotic stresses. The heterologous expression of NcCaM2 in a yeast mutant strain increased the heavy metal tolerance in yeast cells. Furthermore, the constitutive expression of NcCaM2 enhanced the heavy metal tolerance capability of transgenic tobacco (Nicotiana tabacum L.) plants. Our data suggested an important role of NcCaM2 in the responses to environmental stresses and provided a potential target gene to enhance of the ability to hyperaccumulate metals.

Genome-wide identification and expression analysis of DREB family genes in cotton

BACKGROUND

Dehydration responsive element-binding (DREB) transcription factors are widely present in plants, and involve in signalling transduction, plant growth and development, and stress response. DREB genes have been characterized in multiple species. However, only a few DREB genes have been studied in cotton, one of the most important fibre crops. Herein, the genome‑wide identification, phylogeny, and expression analysis of DREB family genes are performed in diploid and tetraploid cotton species.

RESULTS

In total, 193, 183, 80, and 79 putative genes containing the AP2 domain were identified using bioinformatics approaches in G. barbadense, G. hirsutum, G. arboretum, and G. raimondii, respectively. Phylogenetic analysis showed that based on the categorization of Arabidopsis DREB genes, 535 DREB genes were divided into six subgroups (A1-A6) by using MEGA 7.0. The identified DREB genes were distributed unevenly across 13/26 chromosomes of A and/or D genomes. Synteny and collinearity analysis confirmed that during the evolution, the whole genome duplications, segmental duplications, and/or tandem duplications occurred in cotton DREB genes, and then DREB gene family was further expanded. Further, the evolutionary trees with conserved motifs, cis-acting elements, and gene structure of cotton DREB gene family were predicted, and these results suggested that DREB genes might be involved in the hormone and abiotic stresses responses. The subcellular localization showed that in four cotton species, DREB proteins were predominantly located in the nucleus. Further, the analysis of DREB gene expression was carried out by real-time quantitative PCR, confirming that the identified DREB genes of cotton were involved in response to early salinity and osmotic stress.

CONCLUSIONS

Collectively, our results presented a comprehensive and systematic understanding in the evolution of cotton DREB genes, and demonstrated the potential roles of DREB family genes in stress and hormone response.

Developing drought-smart, ready-to-grow future crops

Breeding crop plants with increased yield potential and improved tolerance to stressful environments is critical for global food security. Drought stress (DS) adversely affects agricultural productivity worldwide and is expected to rise in the coming years. Therefore, it is vital to understand the physiological, biochemical, molecular, and ecological mechanisms associated with DS. This review examines recent advances in plant responses to DS to expand our understanding of DS-associated mechanisms. Suboptimal water sources adversely affect crop growth and yields through physical impairments, physiological disturbances, biochemical modifications, and molecular adjustments. To control the devastating effect of DS in crop plants, it is important to understand its consequences, mechanisms, and the agronomic and genetic basis of DS for sustainable production. In addition to plant responses, we highlight several mitigation options such as omics approaches, transgenics breeding, genome editing, and biochemical to mechanical methods (foliar treatments, seed priming, and conventional agronomic practices). Further, we have also presented the scope of conventional and speed breeding platforms in helping to develop the drought-smart future crops. In short, we recommend incorporating several approaches, such as multi-omics, genome editing, speed breeding, and traditional mechanical strategies, to develop drought-smart cultivars to achieve the 'zero hunger' goal.

Screening Spring Wheat Genotypes for TaDreb-B1 and Fehw3 Genes under Severe Drought Stress at the Germination Stage Using KASP Technology

Drought stress is a major yield-limiting factor throughout the world in wheat (Triticum aestivum L.), causing losses of up to 80% of the total yield. The identification of factors affecting drought stress tolerance in the seedling stage is especially important to increase adaptation and accelerate the grain yield potential. In the current study, 41 spring wheat genotypes were tested for their tolerance to drought at the germination stage under two different polyethylene glycol concentrations (PEG) of 25% and 30%. For this purpose, twenty seedlings from each genotype were evaluated in triplicate with a randomized complete block design (RCBD) in a controlled growth chamber. The following nine parameters were recorded: germination pace (GP), germination percentage (G%), number of roots (NR), shoot length (SL), root length (RL), shoot-root length ratio (SRR), fresh biomass weight (FBW), dry biomass weight (DBW), and water content (WC). An analysis of variance (ANOVA) revealed highly significant differences (p < 0.01) among the genotypes, treatments (PEG25%, PEG30%) and genotypes × treatment interaction, for all traits. The broad-sense heritability (H2) estimates were very high in both concentrations. They ranged from 89.4 to 98.9% under PEG25% and from 70.8 to 98.7% under PEG30%. Citr15314 (Afghanistan) was among the best performing genotypes under both concentrations for most of the germination traits. Two KASP markers for TaDreb-B1 and Fehw3 genes were used to screen all genotypes and to study the effect of these on drought tolerance at the germination stage. All genotypes with Fehw3 (only) showed a better performance for most traits under both concentrations compared to other genotypes having TaDreb-B1 or having both genes. To our knowledge, this work is the first report showing the effect of the two genes on germination traits under severe drought stress conditions.

Genome-wide identification and expression analysis of DREB genes in alfalfa (Medicago sativa) in response to cold stress

Dehydration-responsive element-binding proteins (DREBs) belong to members of the AP2/ERF transcription factor superfamily, which has been reported to involve various abiotic-stress responses and tolerance in plants. However, research on the DREB-family is still limited in alfalfa (Medicago sativa L.), a forage legume cultivated worldwide. The recent genome-sequence release of the alfalfa cultivar "XinJiangDaYe" allowed us to identify 172 DREBs by a multi-step homolog search. The phylogenetic analysis indicated that such MsDREBs could be classified into 5 groups, namely A-1 (56 members), A-2 (39), A-3 (3), A-4 (61) and 13 (A-5 (13), thus adding substantial new members to the DREB-family in alfalfa. Furthermore, a comprehensive survey in silico of conserved motif, gene structure, molecular weight, and isoelectric point (pI) as well as gene expression was conducted. The resulting data showed that, for cold-stress response, 33 differentially expressed MsDREBs were identified with a threshold of Log2-fold > 1, and most of which were transcriptionally upregulated within 48 h during a cold treatment(s). Moreover, the expression profiling of MsDREBs from two ecotypes of alfalfa subspecies i.e. M. sativa ssp. falcata (F56, from a colder region of Central Asia) and M. sativa ssp. sativa (B47, from Near East) revealed that most of the cold-stress responsive MsDREBs exhibited a significantly lower expression in F56, leading to a proposal of the existence of a distinct mechanism(s) for cold tolerance regulated by DREB-related action, which would have been evolved in alfalfa with a genotypic specificity. Additionally, by examining the transcriptome of a freezing-tolerance species (M. sativa cv. Zhaodong), eight DREBs were found to be implicated in a long-term freezing-stress adaptation with a great potential. Taken together, the current genome-wide identification in alfalfa points to the importance of some MsDREBs in the cold-stress response, providing some promising molecular targets to be functionally characterized for the improvement of cold tolerance in crops including alfalfa.

Candidate Genes Associated with Abiotic Stress Response in Plants as Tools to Engineer Tolerance to Drought, Salinity and Extreme Temperatures in Wheat: An Overview

Wheat represents one of the most important staple food crops worldwide and its genetic improvement is fundamental to meeting the global demand of the growing population. However, the environmental stresses, worsened by climate change, and the increasing deterioration of arable land make it very difficult to fulfil this demand. In light of this, the tolerance of wheat to abiotic stresses has become a key objective of genetic improvement, as an effective strategy to ensure high yields without increasing the cultivated land. Genetic erosion related to modern agriculture, whereby elite, high-yielding wheat varieties are the product of high selection pressure, has reduced the overall genetic diversity, including the allelic diversity of genes that could be advantageous for adaptation to adverse environmental conditions. This makes traditional breeding a less effective or slower approach to generating new stress-tolerant wheat varieties. Either mining for the diversity of not-adapted large germplasm pools, or generating new diversity, are the mainstream approaches to be pursued. The advent of genetic engineering has opened the possibility to create new plant variability and its application has provided a strong complement to traditional breeding. Genetic engineering strategies such as transgenesis and genome editing have then provided the opportunity to improve environmental tolerance traits of agronomic importance in cultivated species. As for wheat, several laboratories worldwide have successfully produced transgenic wheat lines with enhanced tolerance to abiotic stresses, and, more recently, significant improvements in the CRISPR/Cas9 tools available for targeted variations within the wheat genome have been achieved. In light of this, the present review aims to provide successful examples of genetic engineering applications for the improvement of wheat adaptation to drought, salinity and extreme temperatures, which represent the most frequent and most severe events causing the greatest losses in wheat production worldwide.

Genome-Wide Identification and Expression Profile of the HD-Zip Transcription Factor Family Associated with Seed Germination and Abiotic Stress Response in Miscanthus sinensis

Miscanthus sinensis is an ornamental grass, non-food bioenergy crop, and forage with high feeding value. It can adapt to many kinds of soil conditions due to its high level of resistance to various abiotic stresses. However, a low level of seed germination restricts the utilization and application of M. sinensis. It is reported that the Homeodomain-leucine zipper (HD-Zip) gene family participates in plant growth and development and ability to cope with outside environment stresses, which may potentially regulate seed germination and stress resistance in M. sinensis. In this study, a complete overview of M. sinensis HD-Zip genes was conducted, including gene structure, conserved motifs, chromosomal distribution, and gene duplication patterns. A total of 169 members were identified, and the HD-Zip proteins were divided into four subgroups. Inter-chromosomal evolutionary analysis revealed that four pairs of tandem duplicate genes and 72 segmental duplications were detected, suggesting the possible role of gene replication events in the amplification of the M. sinensis HD-Zip gene family. There was an uneven distribution of HD-Zip genes on 19 chromosomes of M. sinensis. Also, evolutionary analysis showed that M. sinensis HD-Zip gene family members had more collinearity with monocotyledons and less with dicotyledons. The gene structure analysis showed that there were 93.5% of proteins with motif 1 and motif 4, while motif 10 was only found in group IV. Based on the cis-elements analysis, it appeared that most of the genes were related to plant growth and development, various hormones, and abiotic stress. Furthermore, qRT-PCR analysis showed that Misin06G303300.1 was significantly expressed in seed germination and Misin05G030000.1 and Misin06G303300.1 were highly expressed under chromium, salt, and drought stress. Results in this study will provide a basis for further exploring the potential role of HD-Zip genes in stress responses and genetic improvement of M. sinensis seed germination.

Field evaluation of TaDREB2B-ectopic expression sugarcane (Saccharum spp. hybrid) for drought tolerance

Sugarcane is one of the most crucial sugar crops globally that supplies the main raw material for sugar and ethanol production, but drought stress causes a severe decline in sugarcane yield worldwide. Enhancing sugarcane drought resistance and reducing yield and quality losses is an ongoing challenge in sugarcane genetic improvement. Here, we introduced a Tripidium arundinaceum dehydration-responsive element-binding transcription factor (TaDREB2B) behind the drought-responsible RD29A promoter into a commercial sugarcane cultivar FN95-1702 and subsequently conducted a series of drought tolerance experiments and investigation of agronomic and quality traits. Physiological analysis indicated that Prd29A: TaDREB2B transgenic sugarcane significantly confers drought tolerance in both the greenhouses and the field by enhancing water retention capacity and reducing membrane damage without compromising growth. These transgenic plants exhibit obvious improvements in yield performance and various physiological traits under the limited-irrigation condition in the field, such as increasing 41.9% yield and 44.4% the number of ratooning sugarcane seedlings. Moreover, Prd29A: TaDREB2B transgenic plants do not penalize major quality traits, including sucrose content, gravity purity, Brix, etc. Collectively, our results demonstrated that the Prd29A-TaDREB2B promoter-transgene combination will be a useful biotechnological tool for the increase of drought tolerance and the minimum of yield losses in sugarcane.

A gain-of-function allele of a DREB transcription factor gene ameliorates drought tolerance in wheat

Drought is a major environmental factor limiting wheat production worldwide. However, the genetic components underlying wheat drought tolerance are largely unknown. Here, we identify a DREB transcription factor gene (TaDTG6-B) by genome-wide association study that is tightly associated with drought tolerance in wheat. Candidate gene association analysis revealed that a 26-bp deletion in the TaDTG6-B coding region induces a gain-of-function for TaDTG6-BDel574, which exhibits stronger transcriptional activation, protein interactions, and binding activity to dehydration-responsive elements (DRE)/CRT cis-elements than the TaDTG6-BIn574 encoded by the allele lacking the deletion, thus conferring greater drought tolerance in wheat seedlings harboring this variant. Knockdown of TaDTG6-BDel574 transcripts attenuated drought tolerance in transgenic wheat, whereas its overexpression resulted in enhanced drought tolerance without accompanying phenotypic abnormalities. Furthermore, the introgression of the TaDTG6-BDel574 elite allele into drought-sensitive cultivars improved their drought tolerance, thus providing a valuable genetic resource for wheat breeding. We also identified 268 putative target genes that are directly bound and transcriptionally regulated by TaDTG6-BDel574. Further analysis showed that TaDTG6-BDel574 positively regulates TaPIF1 transcription to enhance wheat drought tolerance. These results describe the genetic basis and accompanying mechanism driving phenotypic variation in wheat drought tolerance, and provide a novel genetic resource for crop breeding programs.

Transcriptional regulatory network of plant cold-stress responses

Recent studies have revealed the complex and flexible transcriptional regulatory network involved in cold-stress responses. Focusing on two major signaling pathways that respond to cold stress, we outline current knowledge of the transcriptional regulatory network and the post-translational regulation of transcription factors in the network. Cold-stress signaling pathways are closely associated with other signaling pathways such as those related to the circadian clock, and large amounts of data on their crosstalk and tradeoffs are available. However, it remains unknown how plants sense and transmit cold-stress signals to regulate gene expression. We discuss recent reports on cold-stress sensing and associated signaling pathways that regulate the network. We also emphasize future directions for developing abiotic stress-tolerant crop plants.

Overexpression of cowpea NAC transcription factors promoted growth and stress tolerance by boosting photosynthetic activity in Arabidopsis

ATAF-like NAC transcription factors are bonafide regulators of stress-signaling. However, their overexpression often exerts growth-retardation by activating ABA-hypersensitivity, chloroplast-degradation, or carbon-starvation. To improve tolerance to multiple stress complying with growth sustainability, we examined two ATAF orthologs, VuNAC1 and VuNAC2, isolated from a drought-hardy cowpea genotype, for a harmonized regulation of stress and growth signaling. The genes were induced by dehydration, NaCl, polyethylene glycol, heat, cold, ABA, and light. Analysis of the promoter-elements and regulatory network corroborated the integration of circadian, hormonal, stress, developmental, and nutrition signals, being VuNAC1/2 the central transcriptional-switch interfacing growth and stress responses. The constitutive gene overexpression in Arabidopsis resulted in an improved embryonic, rosette, and inflorescence growth, under optimum as well as limiting nutrition, in association with increased photosynthetic activity and stomatal-density. The transgenic seedlings manifested tolerance to dehydration, salinity, aluminum, cadmium, and H₂O₂ toxicity, in addition to ABA-mediated seed dormancy and hypersensitivity. The soil-grown plants survived severe drought and hypersalinity by maintaining the water-status and membrane integrity through the accumulation of stress protectants, such as proline, glutathione, and ascorbate. Unlike their orthologs from other species, VuNAC1/2 conferred tolerance to multiple abiotic stresses in line with improved growth attributes via regulation of photosynthetic controls and nutritional balance, suggesting growth being a crucial component of stress-tolerance and recovery. Such unique stress-responsive transcription factors, which also confer photosynthetic gain, could be sustainable biotechnological tools for developing stress-tolerant crops and translating the improved growth into yield without unintended trade-offs.

Quercus suber Roots Activate Antioxidant and Membrane Protective Processes in Response to High Salinity

Cork oak (Quercus suber) is a species native to Mediterranean areas and its adaptation to the increasingly prevalent abiotic stresses, such as soil salinization, remain unknown. In sequence with recent studies on salt stress response in the leaf, it is fundamental to uncover the plasticity of roots directly exposed to high salinity to better understand how Q. suber copes with salt stress. In the present study we aimed to unveil the antioxidants and key-genes involved in the stress-responses (early vs. later responses) of Q. suber roots exposed to high salinity. Two-month-old Q. suber plants were watered with 300 mM NaCl solution and enzymatic and non-enzymatic antioxidants, lipid peroxidation and the relative expression of genes related to stress response were analysed 8 h and 6 days after salt treatment. After an 8 h of exposure, roots activated the expression of QsLTI30 and QsFAD7 genes involved in stress membrane protection, and QsRAV1 and QsCZF1 genes involved in tolerance and adaptation. As a result of the continued salinity stress (6 days), lipid peroxidation increased, which was associated with an upregulation of QsLTI30 gene. Moreover, other protective mechanisms were activated, such as the upregulation of genes related to antioxidant status, QsCSD1 and QsAPX2, and the increase of the antioxidant enzyme activities of superoxide dismutase, catalase, and ascorbate peroxidase, concomitantly with total antioxidant activity and phenols. These data suggest a response dependent on the time of salinity exposure, leading Q. suber roots to adopt protective complementary strategies to deal with salt stress.

HD-ZIP Gene Family: Potential Roles in Improving Plant Growth and Regulating Stress-Responsive Mechanisms in Plants

Exploring the molecular foundation of the gene-regulatory systems underlying agronomic parameters or/and plant responses to both abiotic and biotic stresses is crucial for crop improvement. Thus, transcription factors, which alone or in combination directly regulated the targeted gene expression levels, are appropriate players for enlightening agronomic parameters through genetic engineering. In this regard, homeodomain leucine zipper (HD-ZIP) genes family concerned with enlightening plant growth and tolerance to environmental stresses are considered key players for crop improvement. This gene family containing HD and LZ domain belongs to the homeobox superfamily. It is further classified into four subfamilies, namely HD-ZIP I, HD-ZIP II, HD-ZIP III, and HD-ZIP IV. The first HD domain-containing gene was discovered in maize cells almost three decades ago. Since then, with advanced technologies, these genes were functionally characterized for their distinct roles in overall plant growth and development under adverse environmental conditions. This review summarized the different functions of HD-ZIP genes in plant growth and physiological-related activities from germination to fruit development. Additionally, the HD-ZIP genes also respond to various abiotic and biotic environmental stimuli by regulating defense response of plants. This review, therefore, highlighted the various significant aspects of this important gene family based on the recent findings. The practical application of HD-ZIP biomolecules in developing bioengineered plants will not only mitigate the negative effects of environmental stresses but also increase the overall production of crop plants.

Elevation of GhDREB1B transcription by a copy number variant significantly improves chilling tolerance in cotton

The elevation of transcript levels of GhDREB1B causes the accumulation of osmoregulants and mitigation of reactive oxygen species, which contributes to the enhanced resistance to chilling stress in AiSheng98 cotton. Low temperature is one of the key environmental stresses that impairs cotton growth and restricts fiber productivity. Dehydration responsive element binding (DREB) transcription factors play an important role in cold response in plants by modulating the transcription level of cold-responsive genes to protect the plants from low-temperature stress. Here, we showed that GhDREB1B, a copy number variant in the AiSheng98 (AS98) cotton mutant, significantly improved chilling tolerance in cotton seedlings, while silencing of GhDREB1B made transgenic cotton sensitive to chilling stress in AS98 cotton compared with control plants. Elevated GhDREB1B transcript level activated the expression of major cold-responsive genes. Genome-wide expression profiling by RNA sequencing revealed the upregulation of genes related to fatty acids, lipid proteins, osmoprotection, and anti-oxidative enzymes in AiSheng98. Excessive accumulation of malondialdehyde (MDA) and higher ion leakage rates occurred in wild-type LFH10 plants when compared to those of Aisheng98 during chilling stress, signifying lower chilling tolerance in the wild-type than in Aisheng98. Furthermore, the Aisheng98 mutant under chilling stress accumulated higher levels of free proline and soluble sugar than LFH10 accumulated. These results suggest that GhDREB1B is a positive regulator and its variant can alter the expression patterns of major low-temperature stress-related genes and enhance chilling tolerance in cotton.

Identification of a 193 bp promoter region of TaNRX1-D gene from common wheat that contributes to osmotic or ABA stress inducibility in transgenic Arabidopsis

BACKGROUND

Cloning and characterizing the drought-inducible promoters is essential for their use in crop resistance's genetic improvement. Previous studies have shown that the TaNRX1-D gene participates in regulating the response of wheat to drought stress. However, its promoter has not yet been identified.

OBJECTIVE

In this study, we aimed to characterize the promoter of the TaNRX1-D gene.

METHODS

The promoter of TaNRX1-D (named P0, 2081 bp) was isolated from common wheat with several cis-acting elements that regulate in response to abiotic stresses and some core cis-acting elements. Functional verification of the promoter, eight 5'-deletion fragments of TaNRX1-D promoter, was fused to the β-glucuronidase (GUS) gene P0::GUS ~ P7::GUS and transformed into Arabidopsis, respectively. Agrobacterium-mediated GUS transient assay the P6a and P6b promoter regions in tobacco leaves under normal, osmotic or ABA stress.

RESULTS

Activity analysis of the full-length promoter (P0) showed that the intensity of stronger β-glucuronidase (GUS) staining in the roots and leaves was obtained during the growth of transgenic Arabidopsis. P0::GUS displayed the GUS activity was much higher in the roots and leaves than in other parts of the transgenic plant under normal conditions, which was similarly within wheat. Analysis of the 5'-deletion fragments revealed that P0::GUS ~ P6::GUS responded well upon exposure to osmotic (polyethylene glycol-6000, PEG6000) and abscisic acid (ABA) stress treatments and expressed significantly higher GUS activity than the CaMV35S promoter (35S::GUS), while P7::GUS did not. GUS transient assay in tobacco leaves showed that the GUS activities of P6a and P6b were lower than P6 in the PEG6000 and ABA stresses.

CONCLUSION

The 193 bp (P6) segment was considered the core region of TaNRX1-D responding to PEG6000 or ABA treatment. GUS activity assay in transgenic Arabidopsis showed that this segment was sufficient for the PEG6000 or ABA stress response. The identified 193 bp promoter of TaNRX1-D in this study will help breed osmotic or ABA tolerant crops. The 36 bp segment between P6 and P6b (-193 to -157 bp) was considered the critical sequence for the TaNRX1-D gene responding to PEG6000 or ABA treatment.

Integrating transcriptome and metabolome analyses of the response to cold stress in pumpkin (Cucurbita maxima)

Cucurbita maxima belong to the genus Cucurbita and are of nutritional and economic importance. Physiological activity, transcriptome, and metabolome analyses of leaf samples from the C. maxima inbreding line IL7 treated at 5 °C and 25 °C were performed. Cold stress resulted in a significant increase in the malondialdehyde content, relative electrical conductivity, soluble protein, sugar content, and catalase activity. A total of 5,553 differentially expressed genes were identified, of which 2,871 were up-regulated and 2,682 down-regulated. In addition, the transcription of differentially expressed genes in the plant hormone signal transduction pathway and transcription factor families of AP2/ERF, bHLH, WRKY, MYB, and HSF was activated. Moreover, 114 differentially expressed metabolites were identified by gas chromatography time-of-flight mass spectrometry, particularly through the analysis of carboxylic acids and derivatives, and organooxygen compounds. The demonstration of a series of potential metabolites and corresponding genes highlighted a comprehensive regulatory mechanism. These findings will provide novel insights into the molecular mechanisms associated with the response to cold stress in C. maxima.

Three AP2/ERF family members modulate flavonoid synthesis by regulating type IV chalcone isomerase in citrus

Flavanones and flavones are excellent source of bioactive compounds but the molecular basis of their highly efficient production remains elusive. Chalcone isomerase (CHI) family proteins play essential roles in flavonoid biosynthesis but little are known about the transcription factors controlling their gene expression. Here, we identified a type IV CHI (designated as CitCHIL1) from citrus which enhances the accumulation of citrus flavanones and flavones (CFLs). CitCHIL1 participates in a CFL biosynthetic metabolon and assists the cyclization of naringenin chalcone to (2S)-naringenin, which leads to the efficient influx of substrates to chalcone synthase (CHS) and improves the catalytic efficiency of CHS. Overexpressing CitCHIL1 in Citrus and Arabidopsis significantly increased flavonoid content and RNA interference-induced silencing of CitCHIL1 in citrus led to a 43% reduction in CFL content. Three AP2/ERF transcription factors were identified as positive regulators of the CitCHIL1 expression. Of these, two dehydration-responsive element binding (DREB) proteins, CitERF32 and CitERF33, activated the transcription by directly binding to the CGCCGC motif in the promoter, while CitRAV1 (RAV: related to ABI3/VP1) formed a transcription complex with CitERF33 that strongly enhanced the activation efficiency and flavonoid accumulation. These results not only illustrate the specific function that CitCHIL1 executes in CFL biosynthesis but also reveal a new DREB-RAV transcriptional complex regulating flavonoid production.

Calmodulin binding transcription activators: An interplay between calcium signalling and plant stress tolerance

In plants, next to the secondary messengers lies an array of signal relaying molecules among which Calmodulins convey the unequivocal alarms of calcium influxes to Calmodulin-Binding Transcription Activators (CAMTA). Upon reception, CAMTA transcription factors decode the calcium signatures by transcribing the genes corresponding to the specific stimulus, thus have direct/indirect engagement in the complex signalling crosstalk. CAMTA transcription factors make an important contribution to the genome of all eukaryotes, including plants, from Brassica napus (18) to Carica papaya (2), the number of CAMTA genes varies across the plant species, however they exhibit a similar evolutionarily conserved domain organization including a DNA-Binding Domain (CG-1), a Transcription Factor Immunoglobulin Binding Domain (TIG), a Calmodulin-Binding Domain (CaMBD/IQ) and several Ankyrin repeats. The regulatory region of CAMTA genes possess multiple stress-responsive cis motifs including ABRE, SARE, G-box, W-box, AuXRE, DRE and others. CAMTA TFs in Arabidopsis have been studied extensively, however in other plants (with a few exceptions), the evidence merely bases upon expression analyses. CAMTAs are reported to orchestrate biotic as well as abiotic stresses including those occurring due to water and temperature fluctuations as well as heavy metals, light and salinity. Through CG-1 domain, CAMTA TFs bind the CG-box in the promoter of their target genes and modulate their expression under adverse conditions. Here we present a glimpse of how calcium signatures are coded and decoded and translated into necessary responses. In addition, we have emphasized on exploitation of the multiple-stress responsive nature of CAMTAs in engineering plants with desired traits.

Genome-wide characterization and expression profiling of Eucalyptus grandis HD-Zip gene family in response to salt and temperature stress

BACKGROUND

The HD-Zip transcription factors are unique to plants and play an essential role in plant growth, development and stress responses. The HD-Zip transcription factor family consists of a highly conserved homeodomain (HD) and a leucine zipper domain (LZ) domain. Although the HD-Zip gene family has been extensively studied in many plant species, a systematic study of the Eucalyptus HD-Zip family has not been reported until today. Here, we systematically identified 40 HD-Zip genes in Eucalyptus (Eucalyptus grandis). Besides, we comprehensively analyzed the HD-Zips of Eucalyptus by studying the homology, conserved protein regions, gene structure, 3D structure of the protein, location of the genes on the chromosomes and the expression level of the genes in different tissues.

RESULTS

The HD-Zip family in Eucalyptus has four subfamilies, which is consistent with other plants such as Arabidopsis and rice. Moreover, genes that are in the same group tend to have similar exon-intron structures, motifs, and protein structures. Under salt stress and temperature stress, the Eucalyptus HD-Zip transcription factors show a differential expression pattern.

CONCLUSIONS

Our findings reveal the response of HD-Zip transcription factors under salt and temperature stresses, laying a foundation for future analysis of Eucalyptus HD-Zip transcription factors.

Two Alternative Splicing Variants of AtERF73/HRE1, HRE1α and HRE1β, Have Differential Transactivation Activities in Arabidopsis

AtERF73/HRE1 is an AP2/ERF transcription factor in Arabidopsis and has two distinct alternative splicing variants, HRE1α and HRE1β. In this study, we examined the differences between the molecular functions of HRE1α and HRE1β. We found that HRE1α and HRE1β are both involved in hypoxia response and root development and have transactivation activity. Two conserved motifs in the C-terminal region of HRE1α and HRE1β, EELL and LWSY-like, contributed to their transactivation activity, specifically the four E residues in the EELL motif and the MGLWS amino acid sequence at the end of the LWSY-like motif. The N-terminal region of HRE1β also showed transactivation activity, mediated by the VDDG motif, whereas that of HRE1α did not. The transactivation activity of HRE1β was stronger than that of HRE1α in Arabidopsis protoplasts. Both transcription factors transactivated downstream genes via the GCC box. RNA-sequencing analysis further supported that both HRE1α and HRE1β might regulate gene expression associated with the hypoxia stress response, although they may transactivate different subsets of genes in downstream pathways. Our results, together with previous studies, suggested that HRE1α and HRE1β differentially transactivate downstream genes in hypoxia response and root development in Arabidopsis.

Transcriptome Analysis Reveals Potential Roles of Abscisic Acid and Polyphenols in Adaptation of Onobrychis viciifolia to Extreme Environmental Conditions in the Qinghai-Tibetan Plateau

A detailed understanding of the molecular mechanisms of plant stress resistance in the face of ever-changing environmental stimuli will be helpful for promoting the growth and production of crop and forage plants. Investigations of plant responses to various single abiotic or biotic factors, or combined stresses, have been extensively reported. However, the molecular mechanisms of plants in responses to environmental stresses under natural conditions are not clearly understood. In this study, we carried out a transcriptome analysis using RNA-sequencing to decipher the underlying molecular mechanisms of Onobrychis viciifolia responding and adapting to the extreme natural environment in the Qinghai-Tibetan Plateau (QTP). The transcriptome data of plant samples collected from two different altitudes revealed a total of 8212 differentially expressed genes (DEGs), including 5387 up-regulated and 2825 down-regulated genes. Detailed analysis of the identified DEGs uncovered that up-regulation of genes potentially leading to changes in hormone homeostasis and signaling, particularly abscisic acid-related ones, and enhanced biosynthesis of polyphenols play vital roles in the adaptive processes of O. viciifolia. Interestingly, several DEGs encoding uridine diphosphate glycosyltransferases, which putatively regulate phytohormone homeostasis to resist environmental stresses, were also discovered. Furthermore, numerous DEGs encoding transcriptional factors, such as members of the myeloblastosis (MYB), homeodomain-leucine zipper (HD-ZIP), WRKY, and nam-ataf1,2-cuc2 (NAC) families, might be involved in the adaptive responses of O. viciifolia to the extreme natural environmental conditions. The DEGs identified in this study represent candidate targets for improving environmental stress resistance of O. viciifolia grown in higher altitudes of the QTP, and can provide deep insights into the molecular mechanisms underlying the responses of this plant species to the extreme natural environmental conditions of the QTP.

Transcription Factors in Plant Stress Responses: Challenges and Potential for Sugarcane Improvement

Increasing vulnerability of crops to a wide range of abiotic and biotic stresses can have a marked influence on the growth and yield of major crops, especially sugarcane (Saccharum spp.). In response to various stresses, plants have evolved a variety of complex defense systems of signal perception and transduction networks. Transcription factors (TFs) that are activated by different pathways of signal transduction and can directly or indirectly combine with cis-acting elements to modulate the transcription efficiency of target genes, which play key regulators for crop genetic improvement. Over the past decade, significant progresses have been made in deciphering the role of plant TFs as key regulators of environmental responses in particular important cereal crops; however, a limited amount of studies have focused on sugarcane. This review summarizes the potential functions of major TF families, such as WRKY, NAC, MYB and AP2/ERF, in regulating gene expression in the response of plants to abiotic and biotic stresses, which provides important clues for the engineering of stress-tolerant cultivars in sugarcane.

DEAR4, a Member of DREB/CBF Family, Positively Regulates Leaf Senescence and Response to Multiple Stressors in Arabidopsis thaliana

Leaf senescence is a programmed developmental process regulated by various endogenous and exogenous factors. Here we report the characterization of the senescence-regulating role of DEAR4 (AT4G36900) from the DREB1/CBF (dehydration-responsive element binding protein 1/C-repeat binding factor) family in Arabidopsis. The expression of DEAR4 is associated with leaf senescence and can be induced by ABA, JA, darkness, drought and salt stress. Transgenic plants over-expressing DEAR4 showed a dramatically enhanced leaf senescence phenotype under normal and dark conditions while the dear4 knock-down mutant displayed delayed senescence. DEAR4 over-expressing plants showed decreased seed germination rate under ABA and salt stress conditions as well as decreased drought tolerance, indicating that DEAR4 was involved in both senescence and stress response processes. Furthermore, we found that DEAR4 protein displayed transcriptional repressor activities in yeast cells. DEAR4 could directly repress the expression of a subset of COLD-REGULATED (COR) and RESPONSIVE TO DEHYDRATION (RD) genes which have been shown to be involved in leaf longevity and stress response. Also we found that DERA4 could induce the production of Reactive oxygen species (ROS), the common signal of senescence and stress responses, which gives us the clue that DEAR4 may play an integrative role in senescence and stress response via regulating ROS production.

Transcription Factors Associated with Abiotic and Biotic Stress Tolerance and Their Potential for Crops Improvement

In field conditions, crops are adversely affected by a wide range of abiotic stresses including drought, cold, salt, and heat, as well as biotic stresses including pests and pathogens. These stresses can have a marked effect on crop yield. The present and future effects of climate change necessitate the improvement of crop stress tolerance. Plants have evolved sophisticated stress response strategies, and genes that encode transcription factors (TFs) that are master regulators of stress-responsive genes are excellent candidates for crop improvement. Related examples in recent studies include TF gene modulation and overexpression approaches in crop species to enhance stress tolerance. However, much remains to be discovered about the diverse plant TFs. Of the >80 TF families, only a few, such as NAC, MYB, WRKY, bZIP, and ERF/DREB, with vital roles in abiotic and biotic stress responses have been intensively studied. Moreover, although significant progress has been made in deciphering the roles of TFs in important cereal crops, fewer TF genes have been elucidated in sorghum. As a model drought-tolerant crop, sorghum research warrants further focus. This review summarizes recent progress on major TF families associated with abiotic and biotic stress tolerance and their potential for crop improvement, particularly in sorghum. Other TF families and non-coding RNAs that regulate gene expression are discussed briefly. Despite the emphasis on sorghum, numerous examples from wheat, rice, maize, and barley are included. Collectively, the aim of this review is to illustrate the potential application of TF genes for stress tolerance improvement and the engineering of resistant crops, with an emphasis on sorghum.