Functional Characterization of TaSnRK2.8 Promoter in Response to Abiotic Stresses by Deletion Analysis in Transgenic Arabidopsis

TaCDPK1-5A positively regulates drought response through modulating osmotic stress responsive-associated processes in wheat (Triticum aestivum)

KEY MESSAGE

Wheat TaCDPK1-5A plays critical roles in mediating drought tolerance through regulating osmotic stress-associated physiological processes. Calcium (Ca2+) acts as an essential second messenger in plant signaling pathways and impacts plant abiotic stress responses. This study reported the function of TaCDPK1-5A, a calcium-dependent protein kinase (CDPK) gene in T. aestivum, in mediating drought tolerance. TaCDPK1-5A sensitively responded to drought and exogenous abscisic acid (ABA) signaling, displaying induced transcripts in plants under drought and ABA treatments. Yeast two-hybrid and co-immunoprecipitation assays revealed that TaCDPK1-5A interacts with the mitogen-activated protein kinase TaMAPK4-7D whereas the latter with ABF transcription factor TaABF1-3A, suggesting that TaCDPK1-5A constitutes a signaling module with above partners to transduce signals initiated by drought/ABA stressors. Overexpression of TaCDPK1-5A, TaMAPK4-7D and TaABF1-3A enhanced plant drought adaptation by modulating the osmotic stress-related physiological indices, including increased osmolyte contents, enlarged root morphology, and promoted stomata closure. Yeast one-hybrid assays indicated the binding ability of TaABF1-3A with promoters of TaP5CS1-1B, TaPIN3-5A, and TaSLAC1-3-2A, the genes encoding P5CS enzyme, PIN-FORMED protein, and slow anion channel, respectively. ChIP-PCR and transcriptional activation assays confirmed that TaABF1-3A regulates these genes at transcriptional level. Moreover, transgene analysis indicated that these stress-responsive genes positively regulated proline biosynthesis (TaP5CS1-1B), root morphology (TaPIN3-5A), and stomata closing (TaSLAC1-3-2A) upon drought signaling. Positive correlations were observed between yield and the transcripts of TaCDPK1-5A signaling partners in wheat cultivars under drought condition, with haplotype TaCDPK1-5A-Hap1 contributing to improved drought tolerance. Our study concluded that TaCDPK1-5A positively regulates drought adaptation and is a valuable target for molecular breeding the drought-tolerant cultivars in T. aestivum.

Isolation and Characterization of Erianthus arundinaceus Phosphate Transporter 1 (PHT1) Gene Promoter and 5' Deletion Analysis of Transcriptional Regulation Regions under Phosphate Stress in Transgenic Tobacco

Phosphorus deficiency highly interferes with plant growth and development. Plants respond to persistent P deficiency by coordinating the expression of genes involved in the alleviation of stress. Promoters of phosphate transporter genes are a great choice for the development of genetically modified plants with enhanced phosphate uptake abilities, which improve crop yields in phosphate-deficient soils. In our previous study, the sugarcane phosphate transporter PHT1;2 gene showed a significantly high expression under salinity stress. In this study, the Erianthus arundinaceus EaPHT1;2 gene was isolated and characterized using various in silico tools. The deduced 542 amino acid residues have 10 transmembrane domains, with a molecular weight and isoelectric point of 58.9 kDa and 9.80, respectively. They displayed 71-96% similarity with Arabidopsis thaliana, Zea mays, and the Saccharum hybrid. To elucidate the function of the 5' regulatory region, the 1.1 kb promoter was isolated and validated in tobacco transgenics under Pi stress. The EaPHT1;2 promoter activity was detected using a β-glucuronidase (GUS) assay. The EaPHT1;2 promoter showed 3- to 4.2-fold higher expression than the most widely used CaMV35S promoter. The 5' deletion analysis with and without 5' UTRs revealed a small-sized 374 bp fragment with the highest promoter activity among 5' truncated fragments, which was 2.7 and 4.2 times higher than the well-used CaMV35S promoter under normal and Pi deprivation conditions, respectively. The strong and short promoter of EaPHT1;2 with 374 bp showed significant expression in low-Pi-stress conditions and it could be a valuable source for the development of stress-tolerant transgenic crops.

Isolation and characterization of drought and ABA responsive promoter of a transcription factor encoding gene from rice

Water deficit is a significant impediment to enhancing rice yield. Genetic engineering tools have enabled agriculture researchers to develop drought-tolerant cultivars of rice. A common strategy to achieve this involves expressing drought-tolerant genes driven by constitutive promoters such as CaMV35S. However, the use of constitutive promoters is often limited by the adverse effects it has on the growth and development of the plant. Additionally, it has been observed that monocot-derived promoters are more successful in driving gene expression in monocots than in dicots. Substitution of constitutive promoters with stress-inducible promoters is the currently used strategy to overcome this limitation. In the present study, a 1514 bp AP2/ERF promoter that drives the expression of a transcription factor was cloned and characterized from drought-tolerant Indian rice genotype N22. The AP2/ERF promoter was fused to the GUS gene (uidA) and transformed in Arabidopsis and rice plants. Histochemical GUS staining of transgenic Arabidopsis plants showed AP2/ERF promoter activity in roots, stems, and leaves. Water deficit stress and ABA upregulate promoter activity in transformed Arabidopsis and rice. Quantitative PCR for uidA expression confirmed induced GUS activity in Arabidopsis and rice. This study showed that water deficit inducible Os-AP2/ERF-N22 promoter can be used to overcome the limitations of constitutive promoters. Transformants overexpressing Os-AP2/ERF-N22 showed higher relative water content, membrane stability index, total chlorophyll content, chlorophyll stability index, wax content, osmotic potential, stomatal conductance, transpiration rate, photosynthetic rate and radical scavenging activity. Drought tolerant (N22) showed higher expression of Os-AP2/ERF-N22 than the susceptible (MTU1010) cultivar.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-022-01246-9.

GmPTF1 modifies root architecture responses to phosphate starvation primarily through regulating GmEXPB2 expression in soybean

Though root architecture modifications may be critically important for improving phosphorus (P) efficiency in crops, the regulatory mechanisms triggering these changes remain unclear. In this study, we demonstrate that genotypic variation in GmEXPB2 expression is strongly correlated with root elongation and P acquisition efficiency, and enhancing its transcription significantly improves soybean yield in the field. Promoter deletion analysis was performed using 5' truncation fragments (P1-P6) of GmEXPB2 fused with the GUS gene in soybean transgenic hairy roots, which revealed that the P1 segment containing three E-box elements significantly enhances induction of gene expression in response to phosphate (Pi) starvation. Further experimentation demonstrated that GmPTF1, a basic-helix-loop-helix transcription factor, is the regulatory factor responsible for the induction of GmEXPB2 expression in response to Pi starvation. In short, Pi starvation induced expression of GmPTF1, with the GmPTF1 product directly binding to the E-box motif in the P1 region of the GmEXPB2 promoter. Plus, both GmPTF1 and GmEXPB2 highly expressed in lateral roots, and were significantly enhanced by P deficiency. Further work with soybean stable transgenic plants through RNA sequencing analysis showed that altering GmPTF1 expression significantly impacted the transcription of a series of cell wall genes, including GmEXPB2, and thereby affected root growth, biomass and P uptake. Taken together, this work identifies a novel regulatory factor, GmPTF1, involved in changing soybean root architecture partially through regulation of the expression of GmEXPB2 by binding the E-box motif in its promoter region.

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.

Functional characterization of wheat myo-inositol oxygenase promoter under different abiotic stress conditions in Arabidopsis thaliana

The production of wheat is severely affected by abiotic stresses such as cold, drought, salinity, and high temperature. Although constitutive promoters are frequently used to regulate the expression of alien genes, these may lead to undesirable side-effects in transgenic plants. Therefore, identification and characterization of an inducible promoter that can express transgene only when exposed to stresses are of great importance in the genetic engineering of crop plants. Previous studies have indicated the abiotic stress-responsive behavior of myo-inositol oxygenase (MIOX) gene in different plants. Here, we isolated the MIOX gene promoter from wheat (TaMIOX). The in-silico analysis revealed the presence of various abiotic stress-responsive cis-elements in the promoter region. The TaMIOX promoter was fused with the UidA reporter gene and transformed into Arabidopsis thaliana. The T₃ single-copy homozygous lines were analyzed for GUS activity using histochemical and fluorometric assays. Transcript expression of TaMIOX::UidA was significantly up-regulated by heat (five fold), cold (seven fold), and drought (five fold) stresses as compared to transgenic plants grown without stress-induced conditions. The CaMV35S::UidA plants showed very high GUS activity even in normal conditions. In contrast, the TaMIOX::UidA plants showed prominent GUS activity only in stress treatments (cold, heat, and drought), which suggests the inducible behavior of the TaMIOX promoter. The substrate myo-inositol feeding assay of TaMIOX::UidA plants showed lesser GUS activity as compared to plants treated in abiotic stress conditions. Results support that the TaMIOX promoter could be used as a potential candidate for conditional expression of the transgene in abiotic stress conditions.

Cloning and functional analysis of AmDUF1517 promoter from Ammopiptanthus mongolicus

Domains of unknown function protein family 1517 (DUF1517) in Ammopiptanthus mongolicus, could be induced by abiotic stresses, whose upstream regulatory sequence might be an ideal source of abiotic-induced promoter. In this study, a 1026-bp promoter of AmDUF1517 from A. mongolicus was cloned. Five deletion fragments (Full, Q1-Q4) of different length of the AmDUF1517 promoter were fused with the β-glucuronidase (GUS) reporter and transformed into Arabidopsis thaliana. The deletion analysis showed that sequences Full, Q1 and Q3 responded well to mannitol, NaCl and 4 °C stresses, while Q2 and Q4 segments did not. The Q3 fragment (280 bp; -280 to -1 bp) showed the highest promoter activity under normal and mannitol, NaCl and 4 °C conditions. The result suggested that Q3 in the AmDUF1517 gene promoter could be a new source of induced promoters for abiotic resistance breeding in plant genetic engineering.

Identification of Flower-Specific Promoters through Comparative Transcriptome Analysis in Brassica napus

Brassica napus (oilseed rape) is an economically important oil crop worldwide. Sclerotinia stem rot (SSR) caused by Sclerotinia sclerotiorum is a threat to oilseed rape production. Because the flower petals play pivotal roles in the SSR disease cycle, it is useful to express the resistance-related genes specifically in flowers to hinder further infection with S. sclerotiorum. To screen flower-specific promoters, we first analyzed the transcriptome data from 12 different tissues of the B. napus line ZS11. In total, 249 flower-specific candidate genes with high expression in petals were identified, and the expression patterns of 30 candidate genes were verified by quantitative real-time transcription-PCR (qRT-PCR) analysis. Furthermore, two novel flower-specific promoters (FSP046 and FSP061 promoter) were identified, and the tissue specificity and continuous expression in petals were determined in transgenic Arabidopsis thaliana with fusing the promoters to β-glucuronidase (GUS)-reporter gene. GUS staining, transcript expression pattern, and GUS activity analysis indicated that FSP046 and FSP061 promoter were strictly flower-specific promoters, and FSP046 promoter had a stronger activity. The two promoters were further confirmed to be able to direct GUS expression in B. napus flowers using transient expression system. The transcriptome data and the flower-specific promoters screened in the present study will benefit fundamental research for improving the agronomic traits as well as disease and pest control in a tissue-specific manner.

Investigation of the AQP Family in Soybean and the Promoter Activity of TIP2;6 in Heat Stress and Hormone Responses

Aquaporins (AQPs) are one diverse family of membrane channel proteins that play crucial regulatory roles in plant stress physiology. However, the heat stress responsiveness of AQP genes in soybean remains poorly understood. In this study, 75 non-redundant AQP encoding genes were identified in soybean. Multiple sequence alignments showed that all GmAQP proteins possessed the conserved regions, which contained 6 trans-membrane domains (TM1 to TM6). Different GmAQP members consisted of distinct Asn-Pro-Ala (NPA) motifs, aromatic/arginine (ar/R) selectivity filters and Froger's positions (FPs). Phylogenetic analyses distinguished five sub-families within these GmAQPs: 24 GmPIPs, 24 GmTIPs, 17 GmNIPs, 8 GmSIPs, and 2 GmXIPs. Promoter cis-acting elements analyses revealed that distinct number and composition of heat stress and hormone responsive elements existed in different promoter regions of GmAQPs. QRT-PCR assays demonstrated that 12 candidate GmAQPs with relatively extensive expression in various tissues or high expression levels in root or leaf exhibited different expression changes under heat stress and hormone cues (abscisic acid (ABA), l-aminocyclopropane-l-carboxylic acid (ACC), salicylic acid (SA) and methyl jasmonate (MeJA)). Furthermore, the promoter activity of one previously functionally unknown AQP gene-GmTIP2;6 was investigated in transgenic Arabidopsis plants. The beta-glucuronidase (GUS) activity driven by the promoter of GmTIP2;6 was strongly induced in the heat- and ACC-treated transgenic plants and tended to be accumulated in the hypocotyls, vascular bundles, and leaf trichomes. These results will contribute to uncovering the potential functions and molecular mechanisms of soybean GmAQPs in mediating heat stress and hormone signal responses.

Characterization of wheat TaSnRK2.7 promoter in Arabidopsis

Expression of TaSnRK2.7 promoter is strongly induced under abiotic stress and could be used as a valuable tool for improving plant stress resistance via transgenic techniques. The sucrose non-fermenting 1-related protein kinase 2 (SnRK2) gene family plays pivotal roles in response to abiotic stresses (drought, salinity and cold). Here, we studied the expression of five wheat TaSnRK2.7 promoter-5'-deletion constructs (- 2547, - 1621, - 806, - 599, and - 254) fused to beta-glucuronidase (GUS) in Arabidopsis. Tissue-expression analysis revealed that the - 254 to ATG fragment was sufficient for inducing GUS expression in hypocotyls. Additionally, the - 806 to - 599 and - 2547 to - 1621 fragments contained leaf- and root-specific elements, respectively. Deletion analysis showed that these fragments were unresponsive to ABA treatment, suggesting that TaSnRK2.7 participates in an ABA-independent signaling pathway. Assays examining stress responses of constructs demonstrated that the - 599 to - 254 and - 806 to - 599 fragments contained elements responsive to abiotic and osmotic stress, respectively. The TaSnRK2.7 promoter contained enhancers from - 806 to - 254 and - 2547 to - 1621, while the - 1621 to - 806 fragment contained negative regulatory elements that restrict root and leaf gene expression in response to abiotic stress. Furthermore, under drought and salt stress, the TaSnRK2.7 promoter conferred greater gene expression in leaves than the rd29A promoter, even though both were induced by abiotic stress. These findings enhance our understanding of the molecular mechanisms behind TaSnRK2.7 action, which should prove useful in transgenic studies investigating stress-induced gene expression.

Isolation and Characterization of a Green-Tissue Promoter from Common Wild Rice (Oryza rufipogon Griff.)

Promoters play a very important role in the initiation and regulation of gene transcription. Green-tissue promoter is of great significance to the development of genetically modified crops. Based on RNA-seq data and RT-PCR expression analysis, this study screened a gene, OrGSE (GREEN SPECIAL EXPRESS), which is expressed specifically in green tissues. The study also isolated the promoter of the OrGSE gene (OrGSEp), and predicted many cis-acting elements, such as the CAAT-Box and TATA-Box, and light-responding elements, including circadian, G-BOX and GT1 CONSENSUS. Histochemical analysis and quantification of GUS activity in transgenic Arabidopsis thaliana plants expressing GUS under the control of OrGSEp revealed that this promoter is not only green tissue-specific, but also light-inducible. The ability of a series of 5’-deletion fragments of OrGSEp to drive GUS expression in Arabidopsis was also evaluated. We found that the promoter region from −54 to −114 is critical for the promoter function, and the region from −374 to −114 may contain core cis-elements involved in light response. In transgenic rice expressing GUS under the control of OrGSEp, visualization and quantification of GUS activity showed that GUS was preferentially expressed in green tissues and not in endosperm. OrGSEp is a useful regulatory element for breeding pest-resistant crops.