Characterization of the stress-inducible OsNCED3 promoter in different transgenic rice organs and over three homozygous generations

An ABA biosynthesis enzyme gene OsNCED4 regulates NaCl and cold stress tolerance in rice

Rice (Oryza sativa L.) is susceptible to various abiotic stresses, such as salt, cold, and drought. Therefore, there is an urgent need to explore the relevant genes that enhance tolerance to these stresses. In this study, we identified a gene, OsNCED4 (9-cis-epoxycarotenoid dioxygenase 4), which regulates tolerance to multiple abiotic stresses. OsNCED4 encodes a chloroplast-localized abscisic acid (ABA) biosynthetic enzyme. The expression of OsNCED4 gene was significantly induced by 150 mM NaCl and cold stress. Disruption of OsNCED4 by CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats)/Cas9-mediated mutagenesis resulted in significant sensitivity to NaCl and cold stress. The salt and cold sensitivity of osnced4 mutant was due to the reduction of ABA content and the excessive accumulation of reactive oxygen species (ROS) under stress. Moreover, OsNCED4 also regulates drought stress tolerance of rice seedlings. Taken together, these results indicate that OsNCED4 is a new regulator for multiple abiotic stress tolerance in rice, and provided a potential target gene for enhancing multiple stress tolerance in the future.

Overexpression of Abscisic Acid Biosynthesis Gene OsNCED3 Enhances Survival Rate and Tolerance to Alkaline Stress in Rice Seedlings

Alkaline stress with high pH levels could significantly influence plant growth and survival. The enzyme 9-cis-epoxycarotenoid dioxygenase (NCED) serves as a critical bottleneck in the biosynthesis of abscisic acid (ABA), making it essential for regulating stress tolerance. Here, we show that OsNCED3-overexpressing rice lines have increased ABA content by up to 50.90% and improved transcription levels of numerous genes involved in stress responses that significantly enhance seedling survival rates. Overexpression of OsNCED3 increased the dry weight contents of the total chlorophyll, proline, soluble sugar, starch, and the activities of antioxidant enzymes of rice seedlings, while reducing the contents of O2·-, H2O2, and malondialdehyde under hydroponic alkaline stress conditions simulated by 10, 15, and 20 mmol L-1 of Na2CO3. Additionally, the OsNCED3-overexpressing rice lines exhibited a notable increase in the expression of OsNCED3; ABA response-related genes OsSalT and OsWsi18; ion homeostasis-related genes OsAKT1, OsHKT1;5, OsSOS1, and OsNHX5; and ROS scavenging-related genes OsCu/Zn-SOD, OsFe-SOD, OsPOX1, OsCATA, OsCATB, and OsAPX1 in rice seedling leaves. The results of these findings suggest that overexpression of OsNCED3 upregulates endogenous ABA levels and the expression of stress response genes, which represents an innovative molecular approach for enhancing the alkaline tolerance of rice seedlings.

Strigolactone and abscisic acid synthesis and signaling pathways are enhanced in the wheat oligo-tillering mutant ot1

Tiller number greatly contributes to grain yield in wheat. Using ethylmethanesulfonate mutagenesis, we previously discovered the oligo-tillering mutant ot1. The tiller number was significantly lower in ot1 than in the corresponding wild type from the early tillering stage until the heading stage. Compared to the wild type, the thousand-grain weight and grain length were increased by 15.41% and 31.44%, respectively, whereas the plant height and spike length were decreased by 26.13% and 37.25%, respectively. Transcriptomic analysis was conducted at the regreening and jointing stages to identify differential expressed genes (DEGs). Functional enrichment analysis with the Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) databases showed differential expression of genes associated with ADP binding, transmembrane transport, and transcriptional regulation during tiller development. Differences in tiller number in ot1 led to the upregulation of genes in the strigolactone (SL) and abscisic acid (ABA) pathways. Specifically, the SL biosynthesis genes DWARF (D27), D17, D10, and MORE AXILLARY GROWTH 1 (MAX1) were upregulated by 3.37- to 8.23-fold; the SL signal transduction genes D14 and D53 were upregulated by 1.81- and 1.32-fold, respectively; the ABA biosynthesis genes 9-CIS-EPOXICAROTENOID DIOXIGENASE 3 (NCED3) and NCED5 were upregulated by 1.66- and 3.4-fold, respectively; and SNF1-REGULATED PROTEIN KINASE2 (SnRK2) and PROTEIN PHOSPHATASE 2C (PP2C) genes were upregulated by 1.30- to 4.79-fold. This suggested that the tiller number reduction in ot1 was due to alterations in plant hormone pathways. Genes known to promote tillering growth were upregulated, whereas those known to inhibit tillering growth were downregulated. For example, PIN-FORMED 9 (PIN9), which promotes tiller development, was upregulated by 8.23-fold in ot1; Ideal Plant Architecture 1 (IPA1), which inhibits tiller development, was downregulated by 1.74-fold. There were no significant differences in the expression levels of TILLER NUMBER 1 (TN1) or TEOSINTE BRANCHED 1 (TB1), indicating that the tiller reduction in ot1 was not controlled by known genes. Our findings provide valuable data for subsequent research into the genetic bases and regulatory mechanisms of wheat tillering.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-024-01450-3.

Characterization of the 1-Deoxy-D-xylulose 5-Phosphate synthase Genes in Toona ciliata Suggests Their Role in Insect Defense

The first enzyme, 1-Deoxy-D-xylulose-5-phosphate synthase (DXS), in the 2-C-methyl-D-erythritol-4-phosphate (MEP) pathway for isoprenoid precursor biosynthesis has been reported to function differently according to species. However, the current state of knowledge about this gene family in Toona ciliata is limited. The TcDXS gene family was identified from the whole genome of T. ciliata by firstly using bioinformatics analysis. Then, the phylogenetic tree was built and the promoter cis-elements were predicted. Six DXS genes were identified and divided into three groups, which had similar domains and gene structure. They are located on five different chromosomes and encode products that do not vary much in size. An analysis of the cis-acting elements revealed that TcDXS genes possessed light, abiotic stress, and hormone responsive elements. Ultimately, TcDXS1/2/5 was cloned for an in-depth analysis of their subcellular localization and expression patterns. The subcellular localization results of TcDXS1/2/5 showed that they were located in the chloroplast envelope membranes. Based on tissue-specific analyses, TcDXS1/2/5 had the highest expression in mature leaves. Under Hypsipyla robusta stress, their different expressions indicated that these genes may have insect-resistance functions. This research provides a theoretical basis for further functional verification of TcDXSs in the future, and a new concept for breeding pest-resistant T. ciliata.

Uncovering the role of wheat magnesium transporter family genes in abiotic responses

BACKGROUND

The CorA / MGT / MRS2 family proteins are an important group of magnesium transporter proteins that maintain magnesium ion homeostasis in plant cells. However, little is known about the MGT functions in wheat.

METHODS

The known MGT sequences were used as queries to BlastP against wheat genome IWGSC RefSeq v2.1 assembly (E-value <10-5). Chromosome localization information for each TaMGT gene was obtained from the GFF3 file of the wheat genome data (IWGSCv2.1).The sequence of 1500 bp upstream of the TaMGT genes was extracted from the wheat genome data. The cis-elements were analyzed using PlantCARE online tool.

RESULT

A total of 24 MGT genes were identified on 18 chromosomes of wheat. After functional domain analysis, only TaMGT1A, TaMGT1B, and TaMGT1D had GMN mutations to AMN, while all the other genes had conserved GMN tripeptide motifs. Expression profiling showed that the TaMGT genes were differentially expressed under different stresses and at different growth and development stages. The expression levels of TaMGT4B and TaMGT4A were significantly up-regulated in cold damage. In addition, qRT-PCR results also confirmed that these TaMGT genes are involved in the wheat abiotic stress responses.

CONCLUSION

In conclusion, The results of our research provide a theoretical basis for further research on the function of TaMGT gene family in wheat.

9-cis-epoxycarotenoid dioxygenase 1 confers heat stress tolerance in rice seedling plants

High temperature is one of the main constraints affecting plant growth and development. It has been reported that abscisic acid (ABA) synthesis gene 9-cis-epoxycarotenoid dioxygenase (NCED) positively regulates plant resistance to salt, cold, and drought stresses. However, little is known about the function of the NCED gene in heat tolerance of rice. Here, we found that OsNCED1 was a heat stress inducible gene. Rice seedlings overexpressing OsNCED1 showed enhanced heat tolerance with more abundant ABA content, whereas the knockout mutant osnced1 accumulated less ABA and showed more sensitive to heat stress. Under heat stress, increased expression of OsNCED1 could reduce membrane damage and reactive oxygen species (ROS) level of plants, and elevate the activity of antioxidant enzymes. Moreover, real time-quantitative PCR (RT-qPCR) analysis showed that overexpression of OsNCED1 significantly activated the expression of genes involved in antioxidant enzymes, ABA signaling pathway, heat response, and defense. Together, our results indicate that OsNCED1 positively regulates heat tolerance of rice seedling by raising endogenous ABA contents, which leads to the improved antioxidant capacity and activated expression of heat and ABA related genes.

The root-specific NtR12 promoter-based expression of RIP increased the resistance against bacterial wilt disease in tobacco

BACKGROUND

Tobacco is an important economic crop, but the quality and yield have been severely impaired by bacterial wilt disease (BWD) caused by Ralstonia solanacearum.

METHODS AND RESULTS

Here, we describe a transgenic approach to prevent BWD in tobacco plants. A new root-specific promoter of an NtR12 gene was successfully cloned. The NtR12 promoter drove GUS reporter gene expression to a high level in roots but to less extent in stems, and no significant expression was detected in leaves. The Ribosome-inactivating proteins (RIP) gene from Momordica charantia was also cloned, and its ability to inhibit Ralstonia solanacearum was evaluated using RIP protein produced by the prokaryotic expression system. The RIP gene was constructed downstream of the NtR12 promoter and transformed into the tobacco cultivar "Cuibi No. 1" (CB-1), resulting in many descendants. The resistance against BWD was significantly improved in transgenic tobacco lines expressing NtR12::RIP.

CONCLUSION

This study confirms that the RIP gene confers resistance to BWD and the NtR12 as a new promoter for its specific expression in root and stem. Our findings pave a novel avenue for transgenic engineering to prevent the harmful impact of diseases and pests in roots and stems.

The miR528-D3 Module Regulates Plant Height in Rice by Modulating the Gibberellin and Abscisic Acid Metabolisms

Plant height, as one of the important agronomic traits of rice, is closely related to yield. In recent years, plant height-related genes have been characterized and identified, among which the DWARF3 (D3) gene is one of the target genes of miR528, and regulates rice plant height and tillering mainly by affecting strigolactone (SL) signal transduction. However, it remains unknown whether the miR528 and D3 interaction functions in controlling plant height, and the underlying regulatory mechanism in rice. In this study, we found that the plant height, internode length, and cell length of internodes of d3 mutants and miR528-overexpressing (OE-miR528) lines were greatly shorter than WT, D3-overexpressing (OE-D3), and miR528 target mimicry (OE-MIM528) transgenic plants. Knockout of D3 gene (d3 mutants) or miR528-overexpressing (OE-miR528) triggers a substantial reduction of gibberellin (GA) content, but a significant increase of abscisic acid (ABA) accumulation than in WT. The d3 and OE-miR528 transgenic plants were much more sensitive to GA, but less sensitive to ABA than WT. Moreover, the expression level of GA biosynthesis-related key genes, including OsCPS1, OsCPS2, OsKO2 and OsKAO was remarkably higher in OE-D3 plants, while the NECD2 expression, a key gene involved in ABA biosynthesis, was significantly higher in d3 mutants than in WT and OE-D3 plants. The results indicate that the miR528-D3 module negatively regulates plant height in rice by modulating the GA and ABA homeostasis, thereby further affecting the elongation of internodes, and resulting in lower plant height, which adds a new regulatory role to the D3-mediated plant height controlling in rice.

TaASR1-D confers abiotic stress resistance by affecting ROS accumulation and ABA signalling in transgenic wheat

Cultivating new crop cultivars with multiple abiotic stress tolerances is important for crop production. The abscisic acid-stress-ripening (ASR) protein has been shown to confer abiotic stress tolerance in plants. However, the mechanisms of ASR function under stress condition remain largely unclear. In this study, we characterized all ASR family members in common wheat and constitutively overexpressed TaASR1-D in a commercial hexaploid wheat cultivar Zhengmai 9023. The transgenic wheat plants exhibited increased tolerance to multiple abiotic stresses and increased grain yields under salt stress condition. Overexpression of TaASR1-D conferred enhanced antioxidant capacity and ABA sensitivity in transgenic wheat plants. Further, RNA in situ hybridization results showed that TaASR1-D had higher expression levels in the vascular tissues of leaves and the parenchyma cells around the vascular tissues of roots and stems. Yeast one-hybrid and electrophoretic mobility shift assays revealed that TaASR1-D could directly bind the specific cis-elements in the promoters of TaNCED1 and TaGPx1-D. In conclusion, our findings suggest that TaASR1-D can be used to breed new wheat cultivars with increased multiple abiotic stress tolerances, and TaASR1-D enhances abiotic stress tolerances by reinforcing antioxidant capacity and ABA signalling.

Molecular cloning and characterization of high-affinity potassium transporter (AlHKT2;1) gene promoter from halophyte Aeluropus lagopoides

HKT subfamily II functions as Na⁺- K⁺ co-transporter and prevents plants from salinity stress. A 760 bp promoter region of AlHKT2;1 was isolated, sequenced and cloned. The full length promoter D1, has many cis-regulatory elements like MYB, MBS, W box, ABRE etc. involved in abiotic stress responses. D1 and subsequent 5' deletions were cloned into pCAMBIA1301 and studied for its efficacy in stress conditions in heterologous system. Blue colour staining was observed in flower petals, anther lobe, and dehiscence slit of anther in T₀ plants. The T₁ seedlings showed staining in leaf veins, shoot vasculature and root except root tip. T₁ seedlings were subjected to NaCl, KCl, NaCl + KCl and ABA stresses. GUS activity was quantified by 4-methylumbelliferyl glucuronide (4-MUG) assay under control and stress conditions. The smallest deletion- D4 also showed GUS expression but highest activity was observed in D2 as compared to full length promoter and other deletions. The electrophoretic mobility shift assay using stress-induced protein with different promoter deletions revealed more prominent binding in D2. These results suggest that AlHKT2;1 promoter is involved in abiotic stress response and deletion D2 might be sufficient to drive the stress-inducible expression of various genes involved in providing stress tolerance in plants.

Expression Analyses of Soybean VOZ Transcription Factors and the Role of GmVOZ1G in Drought and Salt Stress Tolerance

Vascular plant one-zinc-finger (VOZ) transcription factor, a plant specific one-zinc-finger-type transcriptional activator, is involved in regulating numerous biological processes such as floral induction and development, defense against pathogens, and response to multiple types of abiotic stress. Six VOZ transcription factor-encoding genes (GmVOZs) have been reported to exist in the soybean (Glycine max) genome. In spite of this, little information is currently available regarding GmVOZs. In this study, GmVOZs were cloned and characterized. GmVOZ genes encode proteins possessing transcriptional activation activity in yeast cells. GmVOZ1E, GmVOZ2B, and GmVOZ2D gene products were widely dispersed in the cytosol, while GmVOZ1G was primarily located in the nucleus. GmVOZs displayed a differential expression profile under dehydration, salt, and salicylic acid (SA) stress conditions. Among them, GmVOZ1G showed a significantly induced expression in response to all stress treatments. Overexpression of GmVOZ1G in soybean hairy roots resulted in a greater tolerance to drought and salt stress. In contrast, RNA interference (RNAi) soybean hairy roots suppressing GmVOZ1G were more sensitive to both of these stresses. Under drought treatment, soybean composite plants with an overexpression of hairy roots had higher relative water content (RWC). In response to drought and salt stress, lower malondialdehyde (MDA) accumulation and higher peroxidase (POD) and superoxide dismutase (SOD) activities were observed in soybean composite seedlings with an overexpression of hairy roots. The opposite results for each physiological parameter were obtained in RNAi lines. In conclusion, GmVOZ1G positively regulates drought and salt stress tolerance in soybean hairy roots. Our results will be valuable for the functional characterization of soybean VOZ transcription factors under abiotic stress.

Genome-Wide Identification of SNAC1-Targeted Genes Involved in Drought Response in Rice

Drought stress can cause huge crop production losses. Drought resistance consists of complex traits, and is regulated by arrays of unclear networks at the molecular level. A stress-responsive NAC transcription factor gene SNAC1 has been reported for its function in the positive regulation of drought resistance in rice, and several downstream SNAC1 targets have been identified. However, a complete regulatory network mediated by SNAC1 in drought response remains unknown. In this study, we performed Chromatin immunoprecipitation sequencing (ChIP-Seq) and RNA-Seq of SNAC1-overexpression transgenic rice (SNAC1-OE) lines and wild-type under normal and moderate drought stress conditions, to identify all SNAC1 target genes at a genome-wide scale by RNA-Seq analyses. We detected 980 differentially expressed genes (DEGs) in the SNAC1-OE lines compared to the wild-type control under drought stress conditions. By ChIP-Seq analyses, we identified 4,339 SNAC1-binding genes under drought stress conditions (SNAC1BGDs). By combining the DEGs and SNAC1BGDs, we identified 93 SNAC1-targeted genes involved in drought responses (SNAC1TGDs). Most SNAC1TGDs are involved in transcriptional regulation, response to water loss, and other processes related to stress responses. Moreover, the major motifs in the SNAC1BGDs promoters include a NAC recognition sequence (NACRS) and an ABA responsive element (ABRE). SNAC1-OE lines are more sensitive to ABA than wild-type. SNAC1 can bind to the OsbZIP23 promoter, an important ABA signaling regulator, and positively regulate the expression of several ABA signaling genes.

Synthetic Promoters: Designing the cis Regulatory Modules for Controlled Gene Expression

Designing the expression cassettes with desired properties remains the most important consideration of gene engineering technology. One of the challenges for predictive gene expression is the modeling of synthetic gene switches to regulate one or more target genes which would directly respond to specific chemical, environmental, and physiological stimuli. Assessment of natural promoter, high-throughput sequencing, and modern biotech inventory aided in deciphering the structure of cis elements and molding the native cis elements into desired synthetic promoter. Synthetic promoters which are molded by rearrangement of cis motifs can greatly benefit plant biotechnology applications. This review gives a glimpse of the manual in vivo gene regulation through synthetic promoters. It summarizes the integrative design strategy of synthetic promoters and enumerates five approaches for constructing synthetic promoters. Insights into the pattern of cis regulatory elements in the pursuit of desirable "gene switches" to date has also been reevaluated. Joint strategies of bioinformatics modeling and randomized biochemical synthesis are addressed in an effort to construct synthetic promoters for intricate gene regulation.

Heterologous expression of rice 9-cis-epoxycarotenoid dioxygenase 4 (OsNCED4) in Arabidopsis confers sugar oversensitivity and drought tolerance

BACKGROUND

The 9-cis-epoxycarotenoid dioxygenases OsNCED4 was cloned from rice in conjunction with OsNCED 1-3 and 5, of which 3 has been shown to function in ABA biosynthesis and alteration of leaf morphology. In higher plants, NCEDs have been shown to be key enzymes controlling ABA biosynthesis and belong to a differentially expressed gene family. Aside from OsNCED3, it remains largely unknown if other OsNCED genes are involved in ABA biosynthesis in rice. Thus, transgenic Arabidopsis plants overexpressing OsNCED4 were generated in the 129B08/nced3 mutant background to explore OsNCED4 function in ABA biosynthesis.

RESULTS

Heterologous expression of OsNCED4 in Arabidopsis increased ABA levels and altered plant size and leaf shape, delayed seed germination, caused sugar oversensitivity in post-germination growth, and enhanced tolerance to drought. The native OsNCED3 and OsNCED4 promoters were expressed in an overlapping pattern in rice seeds and young seedlings, suggesting possible functional redundancy between OsNCED3 and OsNCED4. At the one-leaf stage, similar regulation of OsNCED3 and OsNCED4 gene expression in roots or leaves in response to moderate salt stress (150 mM NaCl) was observed.

CONCLUSION

Like OsNCED3, OsNCED4 is functionally active in ABA biosynthesis in rice. OsNCED3 and OsNCED4 might play redundant roles in controlling ABA biosynthesis in rice, as suggested by GUS staining assay, but this should be further analyzed through complementation of rice NCED knockout mutants.

9-cis-Epoxycarotenoid Dioxygenase 3 Regulates Plant Growth and Enhances Multi-Abiotic Stress Tolerance in Rice

Although abscisic acid (ABA) is an important hormone that regulates seed dormancy, stomatal closure, plant development, as well as responses to environmental stimuli, the physiological mechanisms of ABA response to multiple stress in rice remain poorly understood. In the ABA biosynthetic pathway, 9-cis-epoxycarotenoid dioxygenase (NCED) is the key rate-limiting enzyme. Here, we report important functions of OsNCED3 in multi-abiotic stress tolerance in rice. The OsNCED3 is constitutively expressed in various tissues under normal condition, Its expression is highly induced by NaCl, PEG, and H₂O₂ stress, suggesting the roles for OsNCED3 in response to the multi-abiotic stress tolerance in rice. Compared with wild-type plants, nced3 mutants had earlier seed germination, longer post-germination seedling growth, increased sensitivity to water stress and H₂O₂ stress and increased stomata aperture under water stress and delayed leaf senescence. Further analysis found that nced3 mutants contained lower ABA content compared with wild-type plants, overexpression of OsNCED3 in transgenic plants could enhance water stress tolerance, promote leaf senescence and increase ABA content. We conclude that OsNCED3 mediates seed dormancy, plant growth, abiotic stress tolerance, and leaf senescence by regulating ABA biosynthesis in rice; and may provide a new strategy for improving the quality of crop.

Surviving a Dry Future: Abscisic Acid (ABA)-Mediated Plant Mechanisms for Conserving Water under Low Humidity

Angiosperms are able to respond rapidly to the first sign of dry conditions, a decrease in air humidity, more accurately described as an increase in the vapor pressure deficit between the leaf and the atmosphere (VPD), by abscisic acid (ABA)-mediated stomatal closure. The genes underlying this response offer valuable candidates for targeted selection of crop varieties with improved drought tolerance, a critical goal for current plant breeding programs, to maximize crop production in drier and increasingly marginalized environments, and meet the demands of a growing population in the face of a changing climate. Here, we review current understanding of the genetic mechanisms underpinning ABA-mediated stomatal closure, a key means for conserving water under dry conditions, examine how these mechanisms evolved, and discuss what remains to be investigated.

Isolation and Functional Validation of Salinity and Osmotic Stress Inducible Promoter from the Maize Type-II H+-Pyrophosphatase Gene by Deletion Analysis in Transgenic Tobacco Plants

Salinity and drought severely affect both plant growth and productivity, making the isolation and characterization of salinity- or drought-inducible promoters suitable for genetic improvement of crop resistance highly desirable. In this study, a 1468-bp sequence upstream of the translation initiation codon ATG of the promoter for ZmGAPP (maize Type-II H+-pyrophosphatase gene) was cloned. Nine 5´ deletion fragments (D1-D9) of different lengths of the ZmGAPP promoter were fused with the GUS reporter and translocated into tobacco. The deletion analysis showed that fragments D1-D8 responded well to NaCl and PEG stresses, whereas fragment D9 and CaMV 35S did not. The D8 segment (219 bp; -219 to -1 bp) exhibited the highest promoter activity of all tissues, with the exception of petals among the D1-D9 transgenic tobacco, which corresponds to about 10% and 25% of CaMV 35S under normal and NaCl or PEG stress conditions, respectively. As such, the D8 segment may confer strong gene expression in a salinity and osmotic stress inducible manner. A 71-bp segment (-219 to -148 bp) was considered as the key region regulating ZmGAPP response to NaCl or PEG stress, as transient transformation assays demonstrated that the 71-bp sequence was sufficient for the salinity or osmotic stress response. These results enhance our understanding of the molecular mechanisms regulating ZmGAPP expression, and that the D8 promoter would be an ideal candidate for moderating expression of drought and salinity response genes in transgenic plants.

Transcription Factors and Plants Response to Drought Stress: Current Understanding and Future Directions

Increasing vulnerability of plants to a variety of stresses such as drought, salt and extreme temperatures poses a global threat to sustained growth and productivity of major crops. Of these stresses, drought represents a considerable threat to plant growth and development. In view of this, developing staple food cultivars with improved drought tolerance emerges as the most sustainable solution toward improving crop productivity in a scenario of climate change. In parallel, unraveling the genetic architecture and the targeted identification of molecular networks using modern "OMICS" analyses, that can underpin drought tolerance mechanisms, is urgently required. Importantly, integrated studies intending to elucidate complex mechanisms can bridge the gap existing in our current knowledge about drought stress tolerance in plants. It is now well established that drought tolerance is regulated by several genes, including transcription factors (TFs) that enable plants to withstand unfavorable conditions, and these remain potential genomic candidates for their wide application in crop breeding. These TFs represent the key molecular switches orchestrating the regulation of plant developmental processes in response to a variety of stresses. The current review aims to offer a deeper understanding of TFs engaged in regulating plant's response under drought stress and to devise potential strategies to improve plant tolerance against drought.

The activities of four constitutively expressed promoters in single-copy transgenic rice plants for two homozygous generations

We have characterized four novel constitutive promoters ARP1, H3F3, HSP and H2BF3 that are active in all tissues/stages of transgenic plants and stable over two homozygous generations. Gene promoters that are active and stable over several generations in transgenic plants are valuable tools for plant research and biotechnology. In this study, we characterized four putative constitutive promoters (ARP1, H3F3, HSP and H2BF3) in transgenic rice plants. Promoter regions were fused to the green fluorescence protein (GFP) reporter gene and transformed into rice. Single-copy transgenic lines were then selected and promoter activity was analyzed in various organs and tissues of two successive homozygous generations. All four promoters showed a broad expression profile in most tissues and developmental stages, and indeed the expression of the ARP1 and H3F3 promoters was even greater than that of the PGD1 promoter, a previously described constitutive promoter that has been used in transgenic rice. This observation was based on expression levels in leaves, roots, dry seeds and flowers in both the T2 and T3 generations. Each promoter exhibited comparable levels of activity over two homozygous generations with no sign of transgene silencing, which is an important characteristic of promoters to be used in crop biotechnology applications. These promoters therefore have considerable potential value for the stable and constitutive expression of transgenes in monocotyledonous crops.

Identification and validation of promoters and cis-acting regulatory elements

Studies of promoters that largely regulate gene expression at the transcriptional level are crucial for improving our basic understanding of gene regulation and will expand the toolbox of available promoters for use in plant biotechnology. In this review, we present a comprehensive analysis of promoters and their underlying mechanisms in transcriptional regulation, including epigenetic marks and chromatin-based regulation. Large-scale prediction of promoter sequences and their contributing cis-acting elements has become routine due to recent advances in transcriptomic technologies and genome sequencing of several plants. However, predicted regulatory sequences may or may not be functional and demonstration of the contribution of the element to promoter activity is essential for confirmation of regulatory sequences. Synthetic promoters and introns provide useful approaches for functional validation of promoter sequences. The development and improvement of gene expression tools for rapid, efficient, predictable, and high-throughput analysis of promoter components will be critical for confirmation of the functional regulatory element sequences identified through transcriptomic and genomic analyses.

A distal ABA responsive element in AtNCED3 promoter is required for positive feedback regulation of ABA biosynthesis in Arabidopsis

The plant hormone abscisic acid (ABA) plays a crucial role in plant development and responses to abiotic stresses. Recent studies indicate that a positive feedback regulation by ABA exists in ABA biosynthesis in plants under dehydration stress. To understand the molecular basis of this regulation, we analyzed the cis-elements of the AtNCED3 promoter in Arabidopsis. AtNCED3 encodes the first committed and highly regulated dioxygenase in the ABA biosynthetic pathway. Through delineated and mutagenesis analyses in stable-transformed Arabidopsis, we revealed that a distal ABA responsive element (ABRE: GGCACGTG, -2372 to -2364 bp) is required for ABA-induced AtNCED3 expression. By analyzing the AtNCED3 expression in ABRE binding protein ABF3 over-expression transgenic plants and knock-out mutants, we provide evidence that the ABA feedback regulation of AtNCED3 expression is not mediated by ABF3.

The transcriptional regulatory network in the drought response and its crosstalk in abiotic stress responses including drought, cold, and heat

Drought negatively impacts plant growth and the productivity of crops around the world. Understanding the molecular mechanisms in the drought response is important for improvement of drought tolerance using molecular techniques. In plants, abscisic acid (ABA) is accumulated under osmotic stress conditions caused by drought, and has a key role in stress responses and tolerance. Comprehensive molecular analyses have shown that ABA regulates the expression of many genes under osmotic stress conditions, and the ABA-responsive element (ABRE) is the major cis-element for ABA-responsive gene expression. Transcription factors (TFs) are master regulators of gene expression. ABRE-binding protein and ABRE-binding factor TFs control gene expression in an ABA-dependent manner. SNF1-related protein kinases 2, group A 2C-type protein phosphatases, and ABA receptors were shown to control the ABA signaling pathway. ABA-independent signaling pathways such as dehydration-responsive element-binding protein TFs and NAC TFs are also involved in stress responses including drought, heat, and cold. Recent studies have suggested that there are interactions between the major ABA signaling pathway and other signaling factors in stress responses. The important roles of these TFs in crosstalk among abiotic stress responses will be discussed. Control of ABA or stress signaling factor expression can improve tolerance to environmental stresses. Recent studies using crops have shown that stress-specific overexpression of TFs improves drought tolerance and grain yield compared with controls in the field.

Comparative functional analysis of six drought-responsive promoters in transgenic rice

Rice production is greatly affected by environmental stresses such as drought and high salinity. Transgenic rice plants tolerant to such stresses are expected to be produced. Stress-responsive promoters with low expression under normal growth conditions are needed to minimize the adverse effects of stress-tolerance genes on rice growth. We performed expression analyses of drought-responsive genes in rice plants using a microarray, and selected LIP9, OsNAC6, OsLEA14a, OsRAB16D, OsLEA3-1, and Oshox24 for promoter analysis. Transient assays using the promoters indicated that AREB/ABF (abscisic acid (ABA)-responsive element-binding protein/ABA-binding factor) transcription factors enhanced expressions of these genes. We generated transgenic rice plants containing each promoter and the β-glucuronidase (GUS) reporter gene. GUS assays revealed that the LIP9 and OsNAC6 promoters were induced by drought, high salinity, and ABA treatment, and both promoters showed strong activity under normal growth conditions in the root. The other promoters were strongly induced by stresses and ABA, but showed low activity under normal growth conditions. In seeds, GUS staining showed that Oshox24 expression was low and expressions of the other genes were high. Transgenic rice plants overexpressing OsNAC6 under the control of the Oshox24 promoter showed increased tolerance to drought and high salinity, and no growth defects. These data suggest that the Oshox24 promoter is useful to overexpress stress-tolerance genes without adversely affecting growth.

Genetic engineering of crops: a ray of hope for enhanced food security

Crop improvement has been a basic and essential chase since organized cultivation of crops began thousands of years ago. Abiotic stresses as a whole are regarded as the crucial factors restricting the plant species to reach their full genetic potential to deliver desired productivity. The changing global climatic conditions are making them worse and pointing toward food insecurity. Agriculture biotechnology or genetic engineering has allowed us to look into and understand the complex nature of abiotic stresses and measures to improve the crop productivity under adverse conditions. Various candidate genes have been identified and transformed in model plants as well as agriculturally important crop plants to develop abiotic stress-tolerant plants for crop improvement. The views presented here are an attempt toward realizing the potential of genetic engineering for improving crops to better tolerate abiotic stresses in the era of climate change, which is now essential for global food security. There is great urgency in speeding up crop improvement programs that can use modern biotechnological tools in addition to current breeding practices for providing enhanced food security.

Functional analysis of the 5' regulatory region of the maize GALACTINOL SYNTHASE2 gene

Maize (Zea mays) GALACTINOL SYNTHASE (GolS) is a key enzyme in the raffinose biosynthetic pathway. We have previously characterized the maize GolS2 (ZmGolS2) gene as heat shock induced in maize germinating seeds and cultured cells. Here we report the identification, isolation and characterization of the 1.5Kb, 5' regulatory region of the ZmGolS2 gene. The 1.5kb fragment and its deletions were tested for promoter activity by their regulation of the Renilla (Renilla reniformis) luciferase reporter gene expression in maize protoplasts cultured at either 25°C or 42°C for 24h. The expression of a constitutively expressed firefly (Photinus ssp.) luciferase gene in the same vector was used as a reference. One heat shock element (HSE) was identified by comparing the promoter activity of each fragment under normal and heat shock conditions. Deletion or triplication of this HSE motif, abolished or enhanced the heat shock response of the ZmGolS2 promoter, respectively. This HSE motif is specifically bound by proteins in the nuclear extracts of heat shock stressed, but not unstressed maize cells as confirmed by DNA-EMSA. This work helps to understand the regulatory mechanism of the ZmGolS2 gene under stress conditions.

Characterization of the promoter region of an Arabidopsis gene for 9-cis-epoxycarotenoid dioxygenase involved in dehydration-inducible transcription

Plants respond to dehydration stress and tolerate water-deficit status through complex physiological and cellular processes. Many genes are induced by water deficit. Abscisic acid (ABA) plays important roles in tolerance to dehydration stress by inducing many stress genes. ABA is synthesized de novo in response to dehydration. Most of the genes involved in ABA biosynthesis have been identified, and they are expressed mainly in leaf vascular tissues. Of the products of such genes, 9-cis-epoxycarotenoid dioxygenase (NCED) is a key enzyme in ABA biosynthesis. One of the five NCED genes in Arabidopsis, AtNCED3, is significantly induced by dehydration. To understand the regulatory mechanism of the early stages of the dehydration stress response, it is important to analyse the transcriptional regulatory systems of AtNCED3. In the present study, we found that an overlapping G-box recognition sequence (5'-CACGTG-3') at -2248 bp from the transcriptional start site of AtNCED3 is an important cis-acting element in the induction of the dehydration response. We discuss the possible transcriptional regulatory system of dehydration-responsive AtNCED3 expression, and how this may control the level of ABA under water-deficit conditions.