Advances in the development and use of DREB for improved abiotic stress tolerance in transgenic crop plants

Brassinosteroids biosynthetic gene MdBR6OX2 regulates salt stress tolerance in both apple and Arabidopsis

Salt stress is a critical limiting factor for fruit yield and quality of apples. Brassinosteroids (BRs) play an important role in response to abiotic stresses. In the present study, application of 2,4- Epicastasterone on seedlings of Malus 'M9T337' and Malus domestica 'Gala3' alleviated the physiological effects, such as growth inhibition and leaf yellowing, induced by salt stress. Further analysis revealed that treatment with NaCl induced expression of genes involved in BR biosynthesis in 'M9T337' and 'Gala3'. Among which, the expression of BR biosynthetic gene MdBR6OX2 showed a three-fold upregulation upon salt treatment, suggesting its potential role in response to salt stress in apple. MdBR6OX2, belonging to the CYP450 family, contains a signal peptide region and a P450 domain. Expression patterns analysis showed that the expression of MdBR6OX2 can be significantly induced by different abiotic stresses. Overexpressing MdBR6OX2 enhanced the tolerance of apple callis to salt stress, and the contents of endogenous BR-related compounds, such as Typhastero (TY), Castasterone (CS) and Brassinolide (BL) were significantly increased in transgenic calli compared with that of wild-type. Extopic expression of MdBR6OX2 enhanced tolerance to salt stress in Arabidopsis. Genes associated with salt stress were significantly up-regulated, and the contents of BR-related compounds were significantly elevated under salt stress. Our data revealed that BR-biosynthetic gene MdBR6OX2 positively regulates salt stress tolerance in both apple calli and Arabidopsis.

Characterization of DREB family genes in Lotus japonicus and LjDREB2B overexpression increased drought tolerance in transgenic Arabidopsis

BACKGROUND

Drought stress affects plant growth and development. DREB proteins play important roles in modulating plant growth, development, and stress responses, particularly under drought stress. To study the function of DREB transcription factors (TFs), we screened key DREB-regulating TFs for drought in Lotus japonicus.

RESULTS

Forty-two DREB TFs were identified, and phylogenetic analysis of proteins from L. japonicus classified them into five subfamilies (A1, A2, A4, A5, A6). The gene motif composition of the proteins is conserved within the same subfamily. Based on the cis-acting regulatory element analysis, we identified many growth-, hormone-, and stress-responsive elements within the promoter regions of DREB. We further analyzed the expression pattern of four genes in the A2 subfamily in response to drought stress. We found that the expression of most of the LjDREB A2 subfamily genes, especially LjDREB2B, was induced by drought stress. We further generated LjDREB2B overexpression transgenic Arabidopsis plants. Under drought stress, the growth of wild-type (WT) and overexpressing LjDREB2B (OE) Arabidopsis lines was inhibited; however, OE plants showed better growth. The malondialdehyde content of LjDREB2B overexpressing lines was lower than that of the WT plants, whereas the proline content and antioxidant enzyme activities in the OE lines were significantly higher than those in the WT plants. Furthermore, after drought stress, the expression levels of AtP5CS1, AtP5CS2, AtRD29A, and AtRD29B in the OE lines were significantly higher than those in the WT plants.

CONCLUSIONS

Our results facilitate further functional analysis of L. japonicus DREB. LjDREB2B overexpression improves drought tolerance in transgenic Arabidopsis. These results indicate that DREB holds great potential for the genetic improvement of drought tolerance in L. japonicus.

The Brachypodium distachyon DREB transcription factor BdDREB-39 confers oxidative stress tolerance in transgenic tobacco

Key message BdDREB-39 is a DREB/CBF transcription factor, localized in the nucleus with transactivation activity, and BdDREB-39-overexpressing transgenic yeasts and tobacco enhanced the tolerance to oxidative stress.Abstract The DREB/CBF transcription factors are generally recognized to play an important factor in plant growth, development and response to various abiotic stresses. However, the mechanism of DREB/CBFs in oxidative stress response is largely unknown. This study isolated a DREB/CBF gene BdDREB-39 from Brachypodium distachyon (B. distachyon). Multiple sequence alignment and phylogenetic analysis showed that BdDREB-39 was closely related to the DREB proteins of oats, barley, wheat and rye and therefore its study can provide a reference for the excavation and genetic improvement of BdDREB-39 or its homologs in its closely related species. The transcript levels of BdDREB-39 were significantly up-regulated under H2O2 stress. BdDREB-39 was localised in the nucleus and functioned as a transcriptional activator. Overexpression of BdDREB-39 enhanced H2O2 tolerance in yeast. Transgenic tobaccos with BdDREB-39 had higher germination rates, longer root, better growth status, lesser reactive oxygen species (ROS) and malondialdehyde (MDA), and higher superoxide dismutase (SOD) and peroxidase (POD) activities than wild type (WT). The expression levels of ROS-related and stress-related genes were improved by BdDREB-39. In summary, these results revealed that BdDREB-39 can improve the viability of tobacco by regulating the expression of ROS and stress-related genes, allowing transgenic tobacco to accumulate lower levels of ROS and reducing the damage caused by ROS to cells. The BdDREB-39 gene has the potential for developing plant varieties tolerant to 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.

Comprehensive genome-wide analysis of the DREB gene family in Moso bamboo (Phyllostachys edulis): evidence for the role of PeDREB28 in plant abiotic stress response

Dehydration response element binding (DREB) proteins are vital for plant abiotic stress responses, but the understanding of DREBs in bamboo, an important sustainable non-timber forest product, is limited. Here we conducted a comprehensive genome-wide analysis of the DREB gene family in Moso bamboo, representing the most important running bamboo species in Asia. In total, 44 PeDREBs were identified, and information on their gene structures, protein motifs, phylogenetic relationships, and stress-related cis-regulatory elements (CREs) was provided. Based on the bioinformatical analysis, we further analyzed PeDREBs from the A5 group and found that four of five PeDREB transcripts were induced by salt, drought, and cold stresses, and their proteins could bind to stress-related CREs. Among these, PeDREB28 was selected as a promising candidate for further functional characterization. PeDREB28 is localized in nucleus, has transcriptional activation activity, and could bind to the DRE- and coupling element 1- (CE1) CREs. Overexpression of PeDREB28 in Arabidopsis and bamboo improved plant abiotic stress tolerance. Transcriptomic analysis showed that broad changes due to the overexpression of PeDREB28. Furthermore, 628 genes that may act as the direct PeDREB28 downstream genes were identified by combining DAP-seq and RNA-seq analysis. Moreover, we confirmed that PeDREB28 could bind to the promoter of pyrabactin-resistance-like gene (DlaPYL3), which is a homolog of abscisic acid receptor in Arabidopsis, and activates its expression. In summary, our study provides important insights into the DREB gene family in Moso bamboo, and contributes to their functional verification and genetic engineering applications in the future.

Functional Characterization of AP2/ERF Transcription Factors during Flower Development and Anthocyanin Biosynthesis Related Candidate Genes in Lycoris

The APETALA2/ethylene-responsive transcription factor (AP2/ERF) family has been extensively investigated because of its significant involvement in plant development, growth, fruit ripening, metabolism, and plant stress responses. To date, there has been little investigation into how the AP2/ERF genes influence flower formation and anthocyanin biosynthesis in Lycoris. Herein, 80 putative LrAP2/ERF transcription factors (TFs) with complete open reading frames (ORFs) were retrieved from the Lycoris transcriptome sequence data, which could be divided into five subfamilies dependent on their complete protein sequences. Furthermore, our findings demonstrated that genes belonging to the same subfamily had structural similarities and conserved motifs. LrAP2/ERF genes were analyzed for playing an important role in plant growth, water deprivation, and flower formation by means of gene ontology (GO) enrichment analysis. The expression pattern of the LrAP2/ERF genes differed across tissues and might be important for Lycoris growth and flower development. In response to methyl jasmonate (MeJA) exposure and drought stress, the expression of each LrAP2/ERF gene varied across tissues and time. Moreover, a total of 20 anthocyanin components were characterized using ultra-performance liquid chromatography-electrospray ionization tandem mass spectrometry (UPLC-ESI-MS/MS) analysis, and pelargonidin-3-O-glucoside-5-O-arabinoside was identified as the major anthocyanin aglycone responsible for the coloration of the red petals in Lycoris. In addition, we mapped the relationships between genes and metabolites and found that LrAP2/ERF16 is strongly linked to pelargonidin accumulation in Lycoris petals. These findings provide the basic conceptual groundwork for future research into the molecular underpinnings and regulation mechanisms of AP2/ERF TFs in anthocyanin accumulation and Lycoris floral development.

Genome-Wide Identification, Evolution, and Expression Analyses of AP2/ERF Family Transcription Factors in Erianthus fulvus

The AP2/ERF transcription factor family is one of the most important gene families in plants and plays a vital role in plant abiotic stress responses. Although Erianthus fulvus is very important in the genetic improvement of sugarcane, there are few studies concerning AP2/ERF genes in E. fulvus. Here, we identified 145 AP2/ERF genes in the E. fulvus genome. Phylogenetic analysis classified them into five subfamilies. Evolutionary analysis showed that tandem and segmental duplication contributed to the expansion of the EfAP2/ERF family. Protein interaction analysis showed that twenty-eight EfAP2/ERF proteins and five other proteins had potential interaction relationships. Multiple cis-acting elements present in the EfAP2/ERF promoter were related to abiotic stress response, suggesting that EfAP2/ERF may contribute to adaptation to environmental changes. Transcriptomic and RT-qPCR analyses revealed that EfDREB10, EfDREB11, EfDREB39, EfDREB42, EfDREB44, EfERF43, and EfAP2-13 responded to cold stress, EfDREB5 and EfDREB42 responded to drought stress, and EfDREB5, EfDREB11, EfDREB39, EfERF43, and EfAP2-13 responded to ABA treatment. These results will be helpful for better understanding the molecular features and biological role of the E. fulvus AP2/ERF genes and lay a foundation for further research on the function of EfAP2/ERF genes and the regulatory mechanism of the abiotic stress response.

Comparative Analysis of the Response to Polyethylene Glycol-Simulated Drought Stress in Roots from Seedlings of "Modern" and "Ancient" Wheat Varieties

Durum wheat is widely cultivated in the Mediterranean, where it is the basis for the production of high added-value food derivatives such as pasta. In the next few years, the detrimental effects of global climate change will represent a serious challenge to crop yields. For durum wheat, the threat of climate change is worsened by the fact that cultivation relies on a few genetically uniform, elite varieties, better suited to intensive cultivation than "traditional" ones but less resistant to environmental stress. Hence, the renewed interest in "ancient" traditional varieties are expected to be more tolerant to environmental stress as a source of genetic resources to be exploited for the selection of useful agronomic traits such as drought tolerance. The aim of this study was to perform a comparative analysis of the effect and response of roots from the seedlings of two durum wheat cultivars: Svevo, a widely cultivated elite variety, and Saragolla, a traditional variety appreciated for its organoleptic characteristics, to Polyethylene glycol-simulated drought stress. The effect of water stress on root growth was analyzed and related to biochemical data such as hydrogen peroxide production, electrolyte leakage, membrane lipid peroxidation, proline synthesis, as well as to molecular data such as qRT-PCR analysis of drought responsive genes and proteomic analysis of changes in the protein repertoire of roots from the two cultivars.

ScCBF1 plays a stronger role in cold, salt and drought tolerance than StCBF1 in potato (Solanum tuberosum)

Solanum tuberosum (St) and Solanum commersonii (Sc) are two potato varieties with different freezing tolerance. Among them, St is a freezing-sensitive variety and. Sc is a cold-resistant wild potato. CBF/DREB family members mainly function in response to freezing stress. In order to explore the different roles of St C-Repeat Binding Factor1 (StCBF1) and Sc C-Repeat Binding Factor1 (ScCBF1) in potato plants (Solanum tuberosum) under stress conditions, two kinds of potato lines were obtained with ScCBF1 and StCBF1 overexpressing respectively. Phenotypes analysis showed that both overexpressing ScCBF1 and StCBF1 caused smaller leaves, and reduced tuber yield. While the limited phenotypes of StCBF1 lines were more severe than that of ScCBF lines. After freezing treatment, StCBF1 over expression plants grown better than WT plants and worse than ScCBF1 over expression plants. Specifically, compared with wild-type lines, overexpressing ScCBF1 could up-regulate fatty acid desaturase genes, key enzyme of Calvin cycle genes, and antioxidant enzyme genes. Both ScCBF1 and StCBF1 lines showed higher PSII activity, thus maintaining a higher photosynthetic rate under cold stress. In addition, we also found that overexpression ScCBF1 and StCBF1 could also enhance the drought and salt tolerance in potato. In summary, ScCBF1 plays a stronger role in cold, salt, and drought tolerance than StCBF1 in potato (Solanum tuberosum).

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

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

Three strategies of transgenic manipulation for crop improvement

Heterologous expression of exogenous genes, overexpression of endogenous genes, and suppressed expression of undesirable genes are the three strategies of transgenic manipulation for crop improvement. Up to 2020, most (227) of the singular transgenic events (265) of crops approved for commercial release worldwide have been developed by the first strategy. Thirty-eight of them have been transformed by synthetic sequences transcribing antisense or double-stranded RNAs and three by mutated copies for suppressed expression of undesirable genes (the third strategy). By the first and the third strategies, hundreds of transgenic events and thousands of varieties with significant improvement of resistance to herbicides and pesticides, as well as nutritional quality, have been developed and approved for commercial release. Their application has significantly decreased the use of synthetic pesticides and the cost of crop production and increased the yield of crops and the benefits to farmers. However, almost all the events overexpressing endogenous genes remain at the testing stage, except one for fertility restoration and another for pyramiding herbicide tolerance. The novel functions conferred by the heterologously expressing exogenous genes under the control of constitutive promoters are usually absent in the recipient crops themselves or perform in different pathways. However, the endogenous proteins encoded by the overexpressing endogenous genes are regulated in complex networks with functionally redundant and replaceable pathways and are difficult to confer the desirable phenotypes significantly. It is concluded that heterologous expression of exogenous genes and suppressed expression by RNA interference and clustered regularly interspaced short palindromic repeats-cas (CRISPR/Cas) of undesirable genes are superior to the overexpression of endogenous genes for transgenic improvement of crops.

Comprehensive Profiling of Tubby-Like Proteins in Soybean and Roles of the GmTLP8 Gene in Abiotic Stress Responses

Tubby-like proteins (TLPs) are transcription factors that are widely present in eukaryotes and generally participate in growth and developmental processes. Using genome databases, a total of 22 putative TLP genes were identified in the soybean genome, and unevenly distributed across 13 chromosomes. Phylogenetic analysis demonstrated that the predicted GmTLP proteins were divided into five groups (I-V). Gene structure, protein motifs, and conserved domains were analyzed to identify differences and common features among the GmTLPs. A three-dimensional protein model was built to show the typical structure of TLPs. Analysis of publicly available gene expression data showed that GmTLP genes were differentially expressed in response to abiotic stresses. Based on those data, GmTLP8 was selected to further explore the role of TLPs in soybean drought and salt stress responses. GmTLP8 overexpressors had improved tolerance to drought and salt stresses, whereas the opposite was true of GmTLP8-RNAi lines. 3,3-diaminobenzidine and nitro blue tetrazolium staining and physiological indexes also showed that overexpression of GmTLP8 enhanced the tolerance of soybean to drought and salt stresses; in addition, downstream stress-responsive genes were upregulated in response to drought and salt stresses. This study provides new insights into the function of GmTLPs in response to abiotic stresses.

Cross-species transcriptomic analyses reveals common and opposite responses in Arabidopsis, rice and barley following oxidative stress and hormone treatment

BACKGROUND

For translational genomics, a roadmap is needed to know the molecular similarities or differences between species, such as model species and crop species. This knowledge is invaluable for the selection of target genes and pathways to alter downstream in response to the same stimuli. Here, the transcriptomic responses to six treatments including hormones (abscisic acid - ABA and salicylic acid - SA); treatments that cause oxidative stress (3-amino-1,2,4-triazole - 3AT, methyl viologen - MV); inhibit respiration (antimycin A - AA) or induce genetic damage (ultraviolet radiation -UV) were analysed and compared between Arabidopsis (Arabidopsis thaliana), barley (Hordeum vulgare) and rice (Oryza sativa).

RESULTS

Common and opposite responses were identified between species, with the number of differentially expressed genes (DEGs) varying greatly between treatments and species. At least 70% of DEGs overlapped with at least one other treatment within a species, indicating overlapping response networks. Remarkably, 15 to 34% of orthologous DEGs showed opposite responses between species, indicating diversity in responses, despite orthology. Orthologous DEGs with common responses to multiple treatments across the three species were correlated with experimental data showing the functional importance of these genes in biotic/abiotic stress responses. The mitochondrial dysfunction response was revealed to be highly conserved in all three species in terms of responsive genes and regulation via the mitochondrial dysfunction element.

CONCLUSIONS

The orthologous DEGs that showed a common response between species indicate conserved transcriptomic responses of these pathways between species. However, many genes, including prominent salt-stress responsive genes, were oppositely responsive in multiple-stresses, highlighting fundamental differences in the responses and regulation of these genes between species. This work provides a resource for translation of knowledge or functions between species.

Genome-wide investigation of AP2/ERF gene family in the desert legume Eremosparton songoricum: Identification, classification, evolution, and expression profiling under drought stress

Eremosparton songoricum (Litv.) Vass. is a rare leafless legume shrub endemic to central Asia which grows on bare sand. It shows extreme drought tolerance and is being developed as a model organism for investigating morphological, physiological, and molecular adaptations to harsh desert environments. APETALA2/Ethylene Responsive Factor (AP2/ERF) is a large plant transcription factor family that plays important roles in plant responses to various biotic and abiotic stresses and has been extensively studied in several plants. However, our knowledge on the AP2/ERF family in legume species is limited, and no respective study was conducted so far on the desert shrubby legume E. songoricum. Here, 153 AP2/ERF genes were identified based on the E. songoricum genome data. EsAP2/ERFs covered AP2 (24 genes), DREB (59 genes), ERF (68 genes), and Soloist (2 genes) subfamilies, and lacked canonical RAV subfamily genes based on the widely used classification method. The DREB and ERF subfamilies were further divided into A1-A6 and B1-B6 groups, respectively. Protein motifs and exon-intron structures of EsAP2/ERFs were also examined, which matched the subfamily/group classification. Cis-acting element analysis suggested that EsAP2/ERF genes shared many stress- and hormone-related cis-regulatory elements. Moreover, the gene numbers and the ratio of each subfamily and the intron-exon structures were systematically compared with other model plants ranging from algae to angiosperms, including ten legumes. Our results supported the view that AP2 and ERF evolved early and already existed in algae, whereas RAV and DREB began to appear in moss species. Almost all plant AP2 and Soloist genes contained introns, whereas most DREB and ERF genes did not. The majority of EsAP2/ERFs were induced by drought stress based on RNA-seq data, EsDREBs were highly induced and had the largest number of differentially expressed genes in response to drought. Eight out of twelve representative EsAP2/ERFs were significantly up-regulated as assessed by RT-qPCR. This study provides detailed insights into the classification, gene structure, motifs, chromosome distribution, and gene expression of AP2/ERF genes in E. songoricum and lays a foundation for better understanding of drought stress tolerance mechanisms in legume plants. Moreover, candidate genes for drought-resistant plant breeding are proposed.

Genome-wide identification and expression analysis of ethylene responsive factor family transcription factors in Juglans regia

Background

Walnut is an important economic tree species with prominent economic value and ecological functions. However, in recent years, walnuts have become susceptible to drought stress, resulting in a decline in comprehensive benefits. Therefore, it is necessary to identify the regulatory molecular mechanism associated with walnut response to drought. In many plants, ethylene responsive factor (ERF) gene family plays important roles in response to biotic and abiotic stress, especial drought. Therefore, the identification and characterisation of walnut ERF genes will benefit walnut with regard to the clarification of drought response mechanism as well as the management, production, and quality of plantations.

Methods

‘ERF’ was compared against the walnut transcriptome, and the JrERFs with a complete open reading frame (ORF) were identified by ORF Finder. The molecular weights, amino acid residues, and theoretical isoelectric point (pI) were predicted by ExPASy. The distribution of JrERFs in chromosome locations was determined based on walnut genome data from NCBI. The intron-exon structures and conserved domains were analysed using Gene Structure Display Server 2.0 and CD-Search, accordingly. Multi-sequence alignment and a phylogenetic tree were constructed by ClustalX2.1 and MEGA7, respectively. The conserved motifs were acquired using MEME. Total RNA was isolated using the cetyltrimethylammonium ammonium bromide (CTAB) method (Yang et al., 2018). Gene expression was determined by using real-time quantitative polymerase chain reaction (qRT-PCR) analysis and calculated according to the 2^−ΔΔCT method (Livak & Schmittgen, 2001).

Results

A total of 44 JrERFs were identified from the walnut transcriptome, whose ORFs were 450–1,239 bp in length. The molecular weights of the JrERF proteins (consisting 149–412 amino acids) were 16.81–43.71 kDa, with pI ranging from 4.8 (JrERF11) to 9.89 (JrERF03). The JrERFs can be divided into six groups (B1–B6), and among the groups, B6 contained the most number of members. Each JrERF contained 1–6 motifs and each motif comprised 9–50 amino acids. Among the motifs, motif1, motif2, and motif3 were the most abundant. More than 40% of JrERFs were up-regulated continuously when subjected to ethephon (ETH), PEG₆₀₀₀, and PEG₆₀₀₀+ETH treatments. Of all the JrERFs, JrERF11 showed the highest expression. Therefore, we conclude that walnut ERF genes are highly conserved and involved in the regulation of drought response in the presence of ETH. JrERFs are possibly important candidate genes for molecular breeding; hence, the findings of this study provides the theoretical basis for further investigation of ERF genes in walnut and other species.

A Novel Heat Shock Transcription Factor (ZmHsf08) Negatively Regulates Salt and Drought Stress Responses in Maize

Heat shock transcription factors (HSFs) play important roles in plant growth, development, and stress responses. However, the function of these transcription factors in abiotic stress responses in maize (Zea mays) remains largely unknown. In this study, we characterized a novel HSF transcription factor gene, ZmHsf08, from maize. ZmHsf08 was highly homologous to SbHsfB1, BdHsfB1, and OsHsfB1, and has no transcriptional activation activity. The expression profiles demonstrated that ZmHsf08 was differentially expressed in various organs of maize and was induced by salt, drought, and abscisic acid (ABA) treatment. Moreover, the overexpression of ZmHsf08 in maize resulted in enhanced sensitivity to salt and drought stresses, displaying lower survival rates, higher reactive oxygen species (ROS) levels, and increased malondialdehyde (MDA) contents compared with wild-type (WT) plants. Furthermore, RT-qPCR analyses revealed that ZmHsf08 negatively regulates a number of stress/ABA-responsive genes under salt and drought stress conditions. Collectively, these results indicate that ZmHsf08 plays a negative role in response to salt and drought stresses in maize.

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

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

Physiological and molecular responses for long term salinity stress in common fig (Ficus carica L.)

Salinity stress in increasingly becoming a major challenge in current and expanding agricultural ecosystems. Unlike temporal abiotic stresses, plants are usually exposed to salinity stress for an entire lifespan. Therefore, a long term effect (10 weeks) of continuous salinity exposure was investigated for three common fig landraces (Zraki, Mwazi, and Khdari). Both relative water content and chlorophyll content decreased with elevated salinity stress, while stem length barely changed. The most prominent decline was observed in root biomass. The data would align common fig to moderately tolerant threshold slop with a C₅₀ range of 100 to 150 mM NaCl. A high and significant correlation was evident between root biomass and chlorophyll content (85%). Concurrently, differential expression of putative salinity responsive genes in common fig were determined; signal peptide peptidase-like 2B (FcSPPL2B), dehydration responsive element binding protein (FcDREB), calcineurin B-like protein (CBL)-CBL-interacting serine/threonine-protein kinase 11 (FcCIPK11), sorbitol dehydrogenase (FcSORD) and dehydrin (FcDHN). The data were discussed for each gene in respect of its potential role in salinity stress mitigation. The combined physiological and molecular data would conclude Zraki as the most salinity tolerant genotype. The major implication of the data emphasizes the tremendous genotype by environment (salinity stress) interaction in common fig.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at (10.1007/s12298-020-00921-z).

Genome-Wide Analysis of the Catharanthus roseus RLK1-Like in Soybean and GmCrRLK1L20 Responds to Drought and Salt Stresses

Abiotic stresses, such as drought and salinity, severely affects the growth, development and productivity of the plants. The Catharanthus roseus RLK1-like (CrRLK1L) protein kinase family is involved in several processes in the plant life cycle. However, there have been few studies addressing the functions of CrRLK1L proteins in soybean. In this study, 38 CrRLK1L genes were identified in the soybean genome (Glycine max Wm82.a2.v1). Phylogenetic analysis demonstrated that soybean CrRLK1L genes were grouped into clusters, cluster I, II, III. The chromosomal mapping demonstrated that 38 CrRLK1L genes were located in 14 of 20 soybean chromosomes. None were discovered on chromosomes 1, 4, 6, 7, 11, and 14. Gene structure analysis indicated that 73.6% soybean CrRLK1L genes were characterized by a lack of introns.15.7% soybean CrRLK1L genes only had one intron and 10.5% soybean CrRLK1L genes had more than one intron. Five genes were obtained from soybean drought- and salt-induced transcriptome databases and were found to be highly up-regulated. GmCrRLK1L20 was notably up-regulated under drought and salinity stresses, and was therefore studied further. Subcellular localization analysis revealed that the GmCrRLK1L20 protein was located in the cell membrane. The overexpression of the GmCrRLK1L20 gene in soybean hairy roots improved both drought tolerance and salt stresses and enhanced the expression of the stress-responsive genes GmMYB84, GmWRKY40, GmDREB-like, GmGST15, GmNAC29, and GmbZIP78. These results indicated that GmCrRLK1L20 could play a vital role in defending against drought and salinity stresses in soybean.

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.