The Arabidopsis AtbZIP1 transcription factor is a positive regulator of plant tolerance to salt, osmotic and drought stresses

A novel wheat S1-bZIP gene, TabZIP11-D, confers stress resistance in Arabidopsis

Most subgroup S1 basic leucine zipper (bZIP) transcription factors (TFs) play a crucial role in the abiotic stress responses. However, their functions and molecular mechanisms remain poorly characterized in wheat (Triticum aestivum L.). In this study, we identified a novel subgroup S1 bZIP gene, designated TabZIP11-D, which was transcriptionally responsive to abscisic acid (ABA), salt, and cold stresses. TabZIP11-D encodes a nuclear-localized protein that lacks transcriptional activation activity in yeast. The Ca2+ blocker LaCl3 significantly suppressed the salt-induced expression of TabZIP11-D. TabZIP11-D interacted with the Ca2+-dependent protein kinases (TaCDPK1, TaCDPK5, TaCDPK9-1, and TaCDPK30) and the CBL-interacting protein kinase TaCIPK31. Overexpression of TabZIP11-D enhanced salt and freezing tolerance by modulating soluble sugar and proline accumulation, reducing hydrogen peroxide (H2O2) and malondialdehyde (MDA) contents, and regulating the expression levels of stress-responsive genes. Furthermore, TabZIP11-D formed a homodimer with itself and heterodimers with group C bZIP proteins. Modified yeast one-hybrid assays revealed that TabZIP14 and TabZIP36 significantly enhanced TabZIP11-D binding to the G-box cis-element in the promoter region of TaCBF1 gene. These findings demonstrate that TabZIP11-D heterodimerizes with TabZIP14/36 to regulate cold signaling by promoting the TaCBF1 transcription. TabZIP11-D functions as a positive regulator in the salt stress response by interacting with TaCDPK1/5/9-1/30 and TaCIPK31.

Genome-wide identification and characterization of the bZIP family in the Mangrove Plant Kandelia obovata and its role in response to stress

BACKGROUND

The basic leucine zipper (bZIP) transcription factors play crucial roles in plant growth, development, and responses to environmental changes. The mangrove plant Kandelia obovata, native to subtropical and tropical coastal intertidal zones, has evolved various adaptive mechanisms to cope with unstable muddy substrates, tidal fluctuations, saltwater intrusion, and intense ultraviolet radiation. This study aims to provide a comprehensive characterization of the bZIP gene family in K. obovata and investigate its functional roles in response to environmental stresses.

RESULTS

In the K. obovata genome, 66 bZIP genes were identified and named KobZIP1 to KobZIP66, categorized based on their chromosomal locations. These KobZIP genes exhibited diversity in physicochemical properties, such as protein length, molecular weight, and isoelectric point, and were all predicted to localize to the nucleus. Phylogenetic and structural analyses classified the KobZIP genes into 12 subfamilies, with subfamily A containing the majority of members. Gene structure analysis revealed variations in the number and position of exons and introns among subfamilies, reflecting their evolutionary history and potential functional diversity. Conserved motif analysis showed that all bZIP family members contained motifs in the basic and hinge regions, with subfamily D displaying the greatest motif diversity. Promoter region analysis identified various cis-acting elements associated with responses to phytohormones (ABA, GA, ET, IAA, MeJA, SA) and environmental stress. The expression patterns of KobZIP genes across different tissues and under various abiotic stress conditions were analyzed using transcriptomic data and experimental validation.

CONCLUSION

This study provides a comprehensive characterization and functional analysis of the bZIP gene family in K. obovata, offering new insights into their roles in plant development and environmental adaptation. The expression profiles of KobZIP genes during root development and post-embryonic stages, along with their responses to ABA, low temperature, and salt stress, underscore their potential significance in the adaptation of mangrove plants to the intertidal environment.

Genome-Wide Analysis of bZIP Transcription Factors and Expression Patterns in Response to Salt and Drought Stress in Vaccinium corymbosum

The basic leucine zipper (bZIP) transcription factors play essential roles in multiple stress responses and have been identified and functionally characterized in many plant species. However, the bZIP family members in blueberry are unclear. In this study, we identified 102 VcbZIP genes in Vaccinium corymbosum. VcbZIPs were divided into 10 groups based on phylogenetic analysis, and each group shared similar motifs, domains, and gene structures. Predictions of cis-regulatory elements in the upstream sequences of VcbZIP genes indicated that VcbZIP proteins are likely involved in phytohormone signaling pathways and abiotic stress responses. Analyses of RNA deep sequencing data showed that 18, 13, and 7 VcbZIP genes were differentially expressed in response to salt, drought, and ABA stress, respectively, for the blueberry cultivar Northland. Ten VcbZIP genes responded to both salt and drought stress, indicating that salt and drought have unique and overlapping signals. Of these genes, VcbZIP1-3 are responsive to salt, drought, and abscisic acid treatments, and their encoded proteins may integrate salt, drought, and ABA signaling. Furthermore, VcbZIP1-3 from group A and VcbZIP83-84 and VcbZIP75 from group S exhibited high or low expression under salt or drought stress and might be important regulators for improving drought or salt tolerance. Pearson correlation analyses revealed that VcbZIP transcription factors may regulate stress-responsive genes to improve drought or salt tolerance in a functionally redundant manner. Our study provides a useful reference for functional analyses of VcbZIP genes and for improving salt and drought stress tolerance in blueberry.

GmTRAB1, a Basic Leucine Zipper Transcription Factor, Positively Regulates Drought Tolerance in Soybean (Glycine max. L)

The basic leucine zipper (bZIP) transcription factors play crucial roles in plant resistance to environmental challenges, but the biological functions of soybean bZIP members are still unclear. In this study, a drought-related soybean bZIP gene, GmTRAB1, was analyzed. The transcript of GmTRAB1 was upregulated under drought, ABA, and oxidative stresses. Overexpression of GmTRAB1 improved the osmotic stress tolerance of transgenic Arabidopsis and soybean hairy roots associated with increased proline content and activity of antioxidant enzymes and reduced accumulations of malonaldehyde and reactive oxide species. However, RNA interference silencing of GmTRAB1 in the soybean hairy roots improved drought sensitivity. Furthermore, GmTRAB1 increased the sensitivity of transgenic plants to ABA and participated in modulating ABA-regulated stomatal closure upon drought stress. In addition, GmTRAB1 stimulated the transcript accumulation of drought-, ABA-, and antioxidant-related genes to respond to drought. Collectively, this research will contribute to understanding the molecular mechanisms of bZIP transcription factors in soybean's resistance to drought.

Genome-wide analysis and expression profile of the bZIP gene family in Neopyropia yezoensis

The basic leucine zipper (bZIP) family consists of conserved transcription factors which are widely present in eukaryotes and play important regulatory roles in plant growth, development, and stress responses. Neopyropia yezoensis is a red marine macroalga of significant economic importance; however, their bZIP family members and functions have not been systematically identified and analyzed. In the present study, the bZIP gene family in Ny. yezoensis was characterized by investigating gene structures, conserved motifs, phylogenetic relationships, chromosomal localizations, gene duplication events, cis-regulatory elements, and expression profiles. Twenty-three Ny. yezoensis bZIP (NyybZIP) genes were identified and sorted into 13 out of 30 groups, which were classified based on the bZIPs of Ny. yezoensis and 15 other red algae species. Phylogenetic analysis revealed that bZIP genes may have a complex evolutionary pattern in red algae. Cross-species collinearity analysis indicated that the bZIP genes in Ny. yezoensis, Neoporphyra haitanensis, and Porphyra umbilicalis are highly evolutionarily conserved. In addition, we identified four main categories of cis-elements, including development-related, light-responsive, phytohormone-responsive and stress-responsive promoter sequences in NyybZIP genes. Finally, RNA sequencing data and quantitative real-time PCR (qRT-PCR) showed that NyybZIP genes exhibited different expression patterns depending on the life stage. NyybZIP genes were also found to be involved in the nitrogen stress response. We thought that bZIP genes may be involved in Ny. yezoensis growth and development, and play a significant role in nitrogen deficiency response. Taken together, our findings provide new insights into the roles of the bZIP gene family and provide a basis for additional research into its evolutionary history and biological functions.

CmDOF18 positively regulates salinity tolerance in Chrysanthemum morifolium by activating the oxidoreductase system

BACKGROUND

Chrysanthemum, one of the four major cut flowers all over the world, is very sensitive to salinity during cultivation. DNA binding with one finger (DOF) transcription factors play important roles in biological processes in plants. The response mechanism of CmDOF18 from chrysanthemum to salt stress remains unclear.

RESULTS

In this study, CmDOF18 was cloned from Chrysanthemum morifolium, and its expression was induced by salinity stress. The gene encodes a 291-amino acid protein with a typical DOF domain. CmDOF18 was localized to the nucleus in onion epidermal cells and showed transcriptional activation in yeast. CmDOF18 transgenic plants were generated to identify the role of this gene in resistance to salinity treatment. Chrysanthemum plants overexpressing CmDOF18 were more resistant to salinity stress than wild-type plants. Under salinity stress, the malondialdehyde content and leaf electrolyte conductivity in CmDOF18-overexpressing transgenic plants were lower than those in wild-type plants, while the proline content, chlorophyll content, superoxide dismutase activity and peroxidase activity were higher than those in wild-type plants. The opposite findings were observed in gene-silenced plants compared with wild-type plants. The gene expression levels of oxidoreductase increased in CmDOF18-overexpressing transgenic plants but decreased in CmDOF18-SRDX gene-silenced transgenic plants.

CONCLUSION

In summary, we analyzed the function of CmDOF18 from chrysanthemum, which may regulate salinity stress in plants, possibly due to its role in the regulation of oxidoreductase.

Analysis of bZIP gene family in lotus (Nelumbo) and functional study of NnbZIP36 in regulating anthocyanin synthesis

BACKGROUND

The basic leucine zipper (bZIP) family is a predominant group of transcription factors in plants, involved in regulating plant growth, development, and response to stressors. Additionally, the bZIP gene family has a key role in anthocyanin production. Despite the significant role of bZIP genes in plants, their potential contribution in lotus remains understudied.

RESULTS

A total of 124 bZIP genes (59 NnbZIPs and 65 NlbZIPs) were identified from genomes of two lotus species. These genes were classified into 13 groups according to the grouping principle of the Arabidopsis bZIP gene family. Analysis of promoter cis-acting elements indicated that most bZIP gene family members in lotus are associated with response to abiotic stresses. The promoters of some bZIP genes contain MYB binding sites that regulate anthocyanin synthesis. We examined the anthocyanin content of the petals from three different colored lotus, combined with transcriptome data analysis and qRT-PCR results, showing that the expression trends of NnbZIP36 and the homologous gene NlbZIP38 were significantly correlated with the anthocyanin content in lotus petals. Furthermore, we found that overexpression of NnbZIP36 in Arabidopsis promoted anthocyanin accumulation by upregulating the expression of genes (4CL, CHI, CHS, F3H, F3'H, DFR, ANS and UF3GT) related to anthocyanin synthesis.

CONCLUSIONS

Our study enhances the understanding of the bZIP gene family in lotus and provides evidence for the role of NnbZIP36 in regulating anthocyanin synthesis. This study also sets the stage for future investigations into the mechanism by which the bZIP gene family regulates anthocyanin biosynthesis in lotus.

The Potential Role of bZIP55/65 in Nitrogen Uptake and Utilization in Cucumber Is Revealed via bZIP Gene Family Characterization

The bZIP (basic leucine zipper) proteins play crucial roles in various biological functions. Nitrogen (N) is an essential element for plant growth, especially in cucumber (Cucumis sativus) due to its shallow roots. However, the regulation of bZIP genes in cucumber nitrogen metabolism has not been studied yet. In this study, we identified a total of 72 bZIP genes (CsbZIPs) in the cucumber genome that could be classified into 13 groups. These genes were unevenly distributed on seven chromosomes, and synteny analysis showed that the CsbZIP genes were expanded in a segmentally duplicating manner. Furthermore, our genome-wide expression analysis suggested that CsbZIP genes had different patterns and that five CsbZIP genes were regulated by nitrogen treatment in both leaves and roots. Consistent with CsNPF, CsbZIP55 and CsbZIP65 were regulated by nitrogen treatment in leaves and roots. Moreover, the subcellular localization showed that CsbZIP55 and CsbZIP65 were specifically located in the nucleus, and the transcriptional activation assay showed that CsbZIP55 and CsbZIP65 have transcriptional activation activity. Additionally, in the CsbZIP55 and CsbZIP65 overexpression plants, most nitrogen-regulated CsNPF genes were downregulated. Taken together, our comprehensive analysis of the bZIP gene family lays a foundation for understanding the molecular and physiological functions of CsbZIPs.

MdbZIP74 negatively regulates osmotic tolerance and adaptability to moderate drought conditions of apple plants

Drought is the most prominent threat to global agricultural production. The basic leucine zipper (bZIP) family is related to the response to a series of abiotic stress. In this case, apple calli and the seedlings of MdbZIP74-RNAi transgenic lines were obtained. Under osmotic stress and moderate drought conditions, the content of malondialdehyde, relative water content and other stress-related assays were measured. MdbZIP74 was found to negatively regulate the osmotic tolerance of apple callus. The growth of MdbZIP74-RNAi calli enhanced resistance without significant production loss. The silencing of MdbZIP74 contributes to redox balance and the adaptability of apple seedlings to moderate drought conditions. Four related differentially expressed genes in the biosynthesis of cytokinin and catabolic pathway were identified through a transcriptome analysis of MdbZIP74-RNAi seedlings under moderate drought conditions. MdLOG8 was further identified as the target of MdbZIP74 involved in the drought adaptability of apple plants using a dual experiment. Further confirmation showed MdLOG8 was maintained in the MdbZIP74-RNAi seedlings presumably acting as the growth regulator to enhance drought adaptability. It was concluded that the correct regulation of cytokinin level under moderate drought conditions maintains the redox balance and avoids the situation of plants surviving with the minimal resources.

Overexpression of the Brassica rapa bZIP Transcription Factor, BrbZIP-S, Increases the Stress Tolerance in Nicotiana benthamiana

In higher plants, S1-basic region-leucine zipper (S1-bZIP) transcription factors fulfill crucial roles in the physiological homeostasis of carbon and amino acid metabolisms and stress responses. However, very little is known about the physiological role of S1-bZIP in cruciferous vegetables. Here, we analyzed the physiological function of S1-bZIP from Brassica rapa (BrbZIP-S) in modulating proline and sugar metabolism. Overexpression of BrbZIP-S in Nicotiana benthamiana resulted in delayed chlorophyll degradation during the response to dark conditions. Under heat stress or recovery conditions, the transgenic lines exhibited a lower accumulation of H2O2, malondialdehyde, and protein carbonyls compared to the levels in transgenic control plants. These results strongly indicate that BrbZIP-S regulates plant tolerance against dark and heat stress. We propose that BrbZIP-S is a modulator of proline and sugar metabolism, which are required for energy homeostasis in response to environmental stress conditions.

Divergence of functions and expression patterns of soybean bZIP transcription factors

Soybean (Glycine max) is a major protein and oil crop. Soybean basic region/leucine zipper (bZIP) transcription factors are involved in many regulatory pathways, including yield, stress responses, environmental signaling, and carbon-nitrogen balance. Here, we discuss the members of the soybean bZIP family and their classification: 161 members have been identified and clustered into 13 groups. Our review of the transcriptional regulation and functions of soybean bZIP members provides important information for future study of bZIP transcription factors and genetic resources for soybean breeding.

Genome-Wide Identification and Expression Profiles of bZIP Genes in Cannabis sativa L

Background: The bZIP gene family plays roles in biotic and abiotic stress, secondary metabolism, and other aspects in plants. They have been reported in Arabidopsis thaliana, Oryza sativa, Artemisia annua, and other plants, but their roles in Cannabis sativa have not been determined. Materials and Methods: In this study, we analyzed the genome-wide identification and expression profile of the bZIP gene family in C. sativa. Results: A total of 51 members of the bZIP gene family were identified based on the C. sativa genome and numbered in order from CsbZIP1 to CsbZIP51. Their phylogenetic relationships, cis-elements in promoter region, gene structures and motif compositions, physicochemical properties, chromosome locations, and expression profiles, were analyzed. The results showed that the 51 CsbZIPs were unevenly distributed on 10 chromosomes and could be clustered into 11 subfamilies. Furthermore, CsbZIPs located in the same subfamilies presented similar intron/exon organization and motif composition. The expression levels of CsbZIPs in various tissues (flowers, bracts, vegetative leaves, stems, and seeds) were determined using reverse transcription quantitative polymerase chain reaction. The expression levels of CsbZIPs were higher in flowers and bracts. The 51 CsbZIPs were explored, and their structure, evolution, and expression pattern in different tissues of C. sativa were characterized synthetically. The findings indicated that CsbZIPs are essential for the growth and development of C. sativa. Conclusions: These results provide a theoretical basis for subsequent research on hemp bZIP transcription factors and the cultivation of high-cannabidiol and low-tetrahydrocannabinol high-quality cannabis varieties.

AtbZIP62 Acts as a Transcription Repressor to Positively Regulate ABA Responses in Arabidopsis

The basic region/leucine zipper (bZIP) transcription factor AtbZIP62 is involved in the regulation of plant responses to abiotic stresses, including drought and salinity stresses, NO₃ transport, and basal defense in Arabidopsis. It is unclear if it plays a role in regulating plant responses to abscisic acid (ABA), a phytohormone that can regulate plant abiotic stress responses via regulating downstream ABA-responsive genes. Using RT-PCR analysis, we found that the expression level of AtbZIP62 was increased in response to exogenously applied ABA. Protoplast transfection assays show that AtbZIP62 is predominantly localized in the nucleus and functions as a transcription repressor. To examine the roles of AtbZIP62 in regulating ABA responses, we generated transgenic Arabidopsis plants overexpressing AtbZIP62 and created gene-edited atbzip62 mutants using CRISPR/Cas9. We found that in both ABA-regulated seed germination and cotyledon greening assays, the 35S:AtbZIP62 transgenic plants were hypersensitive, whereas atbzip62 mutants were hyposensitive to ABA. To examine the functional mechanisms of AtbZIP62 in regulating ABA responses, we generated Arabidopsis transgenic plants overexpressing 35S:AtbZIP62-GR, and performed transcriptome analysis to identify differentially expressed genes (DEGs) in the presence and absence of DEX, and found that DEGs are highly enriched in processes including response to abiotic stresses and response to ABA. Quantitative RT-PCR results further show that AtbZIP62 may regulate the expression of several ABA-responsive genes, including USP, ABF2, and SnRK2.7. In summary, our results show that AtbZIP62 is an ABA-responsive gene, and AtbZIP62 acts as a transcription repressor to positively regulate ABA responses in Arabidopsis.

Positive selection and heat-response transcriptomes reveal adaptive features of the Brassicaceae desert model, Anastatica hierochuntica

Plant adaptation to a desert environment and its endemic heat stress is poorly understood at the molecular level. The naturally heat-tolerant Brassicaceae species Anastatica hierochuntica is an ideal extremophyte model to identify genetic adaptations that have evolved to allow plants to tolerate heat stress and thrive in deserts. We generated an A. hierochuntica reference transcriptome and identified extremophyte adaptations by comparing Arabidopsis thaliana and A. hierochuntica transcriptome responses to heat, and detecting positively selected genes in A. hierochuntica. The two species exhibit similar transcriptome adjustment in response to heat and the A. hierochuntica transcriptome does not exist in a constitutive heat 'stress-ready' state. Furthermore, the A. hierochuntica global transcriptome as well as heat-responsive orthologs, display a lower basal and higher heat-induced expression than in A. thaliana. Genes positively selected in multiple extremophytes are associated with stomatal opening, nutrient acquisition, and UV-B induced DNA repair while those unique to A. hierochuntica are consistent with its photoperiod-insensitive, early-flowering phenotype. We suggest that evolution of a flexible transcriptome confers the ability to quickly react to extreme diurnal temperature fluctuations characteristic of a desert environment while positive selection of genes involved in stress tolerance and early flowering could facilitate an opportunistic desert lifestyle.

Wheat ocs-Element Binding Factor 1 Enhances Thermotolerance by Modulating the Heat Stress Response Pathway

The basic leucine zipper family (bZIP) represents one of the largest families of transcription factors that play an important role in plant responses to abiotic stresses. However, their role in contributing to thermotolerance in plants is not well explored. In this article, two homoeologs of wheat ocs-element binding factor 1 (TaOBF1-5B and TaOBF1-5D) were found to be heat-responsive TabZIP members. Their expression analysis in Indian wheat cultivars revealed their differential expression pattern and TaOBF1-5B was found to be more receptive to heat stress. Consistent with this, the heterologous overexpression of TaOBF1-5B in Arabidopsis thaliana and Oryza sativa promoted the expression of stress-responsive genes, which contributed to thermotolerance in transgenic plants. TaOBF1-5B was seen to interact with TaHSP90 in the nucleus and TaSTI in the nucleolus and the ER. Thus, the results suggest that TaOBF1-5B might play an important regulatory role in the heat stress response and is a major factor governing thermotolerance in plants.

DgbZIP3 interacts with DgbZIP2 to increase the expression of DgPOD for cold stress tolerance in chrysanthemum

The bZIP transcription factor plays a very important role in abiotic stresses, e.g. drought, salt, and low-temperature stress, but the mechanism of action at low temperature is still unclear. In this study, overexpression of DgbZIP3 led to increased tolerance of chrysanthemum (Chrysanthemum morifolium Ramat.) to cold stress, whereas antisense suppression of DgbZIP3 resulted in decreased tolerance. Electrophoretic mobility shift assay (EMSA), chromatin immunoprecipitation (ChIP), luciferase complementary imaging analysis (LCI), and dual-luciferase reporter gene detection (DLA) experiments indicated that DgbZIP3 directly bound to the promoter of DgPOD and activated its expression. DgbZIP2 was identified as a DgbZIP3-interacting protein using yeast two-hybrid, co-immunoprecipitation, LCI, and bimolecular fluorescence complementation assays. Overexpression of DgbZIP2 led to increased tolerance of chrysanthemum to cold stress, whereas antisense suppression of DgbZIP2 resulted in decreased tolerance. A ChIP-qPCR experiment showed that DgbZIP2 was highly enriched in the promoter of DgPOD, while DLA, EMSA, and LCI experiments further showed that DgbZIP2 could not directly regulate the expression of DgPOD. The above results show that DgbZIP3 interacts with DgbZIP2 to regulate the expression of DgPOD to promote an increase in peroxidase activity, thereby regulating the balance of reactive oxygen species and improving the tolerance of chrysanthemum to low-temperature stress.

Plant Salinity Stress Response and Nano-Enabled Plant Salt Tolerance

The area of salinized land is gradually expanding cross the globe. Salt stress seriously reduces the yield and quality of crops and endangers food supply to meet the demand of the increased population. The mechanisms underlying nano-enabled plant tolerance were discussed, including (1) maintaining ROS homeostasis, (2) improving plant's ability to exclude Na+ and to retain K+, (3) improving the production of nitric oxide, (4) increasing α-amylase activities to increase soluble sugar content, and (5) decreasing lipoxygenase activities to reduce membrane oxidative damage. The possible commonly employed mechanisms such as alleviating oxidative stress damage and maintaining ion homeostasis were highlighted. Further, the possible role of phytohormones and the molecular mechanisms in nano-enabled plant salt tolerance were discussed. Overall, this review paper aims to help the researchers from different field such as plant science and nanoscience to better understand possible new approaches to address salinity issues in agriculture.

Combined Transcriptomics and Metabolomics Analysis Reveals the Molecular Mechanism of Salt Tolerance of Huayouza 62, an Elite Cultivar in Rapeseed (Brassica napus L.)

Soil salinity is one of the most significant abiotic stresses affecting crop yield around the world. To explore the molecular mechanism of salt tolerance in rapeseed (Brassica napus L.), the transcriptome analysis and metabolomics analysis were used to dissect the differentially expressed genes and metabolites in two rapeseed varieties with significant differences in salt tolerance; one is an elite rapeseed cultivar, Huayouza 62. A total of 103 key differentially expressed metabolites (DEMs) and 53 key differentials expressed genes (DEGs) that might be related to salt stress were identified through metabolomics and transcriptomics analysis. GO and KEGG analysis revealed that the DEGs were mainly involved in ion transport, reactive oxygen scavenging, osmotic regulation substance synthesis, and macromolecular protein synthesis. The DEMs were involved in TCA cycle, proline metabolism, inositol metabolism, carbohydrate metabolic processes, and oxidation-reduction processes. In addition, overexpression of BnLTP3, which was one of the key DEGs, could increase tolerance to salt stress in Arabidopsis plants. This study reveals that the regulation mechanism of salt tolerance in rapeseed at the transcriptome and metabolism level and provides abundant data for further in-depth identification of essential salt tolerance genes.

Transcriptome Profiling of the Salt Stress Response in the Leaves and Roots of Halophytic Eutrema salsugineum

Eutrema salsugineum can grow in natural harsh environments; however, the underlying mechanisms for salt tolerance of Eutrema need to be further understood. Herein, the transcriptome profiling of Eutrema leaves and roots exposed to 300 mM NaCl is investigated, and the result emphasized the role of genes involved in lignin biosynthesis, autophagy, peroxisome, and sugar metabolism upon salt stress. Furthermore, the expression of the lignin biosynthesis and autophagy-related genes, as well as 16 random selected genes, was validated by qRT-PCR. Notably, the transcript abundance of a large number of lignin biosynthesis genes such as CCoAOMT, C4H, CCR, CAD, POD, and C3′H in leaves was markedly elevated by salt shock. And the examined lignin content in leaves and roots demonstrated salt stress led to lignin accumulation, which indicated the enhanced lignin level could be an important mechanism for Eutrema responding to salt stress. Additionally, the differentially expressed genes (DEGs) assigned in the autophagy pathway including Vac8, Atg8, and Atg4, as well as DEGs enriched in the peroxisome pathway such as EsPEX7, EsCAT, and EsSOD2, were markedly induced in leaves and/or roots. In sugar metabolism pathways, the transcript levels of most DEGs associated with the synthesis of sucrose, trehalose, raffinose, and xylose were significantly enhanced. Furthermore, the expression of various stress-related transcription factor genes including WRKY, AP2/ERF-ERF, NAC, bZIP, MYB, C2H2, and HSF was strikingly improved. Collectively, the increased expression of biosynthesis genes of lignin and soluble sugars, as well as the genes in the autophagy and peroxisome pathways, suggested that Eutrema encountering salt shock possibly possess a higher capacity to adjust osmotically and facilitate water transport and scavenge reactive oxidative species and oxidative proteins to cope with the salt environment. Thus, this study provides a new insight for exploring the salt tolerance mechanism of halophytic Eutrema and discovering new gene targets for the genetic improvement of crops.

Genome-wide identification and characterization of bZIP transcription factors and their expression profile under abiotic stresses in Chinese pear (Pyrus bretschneideri)

BACKGROUND

In plants, basic leucine zipper transcription factors (TFs) play important roles in multiple biological processes such as anthesis, fruit growth & development and stress responses. However, systematic investigation and characterization of bZIP-TFs remain unclear in Chinese white pear. Chinese white pear is a fruit crop that has important nutritional and medicinal values.

RESULTS

In this study, 62 bZIP genes were comprehensively identified from Chinese Pear, and 54 genes were distributed among 17 chromosomes. Frequent whole-genome duplication (WGD) and dispersed duplication (DSD) were the major driving forces underlying the bZIP gene family in Chinese white pear. bZIP-TFs are classified into 13 subfamilies according to the phylogenetic tree. Subsequently, purifying selection plays an important role in the evolution process of PbbZIPs. Synteny analysis of bZIP genes revealed that 196 orthologous gene pairs were identified between Pyrus bretschneideri, Fragaria vesca, Prunus mume, and Prunus persica. Moreover, cis-elements that respond to various stresses and hormones were found on the promoter regions of PbbZIP, which were induced by stimuli. Gene structure (intron/exon) and different compositions of motifs revealed that functional divergence among subfamilies. Expression pattern of PbbZIP genes differential expressed under hormonal treatment abscisic acid, salicylic acid, and methyl jasmonate  in pear fruits by real-time qRT-PCR.

CONCLUSIONS

Collectively, a systematic analysis of gene structure, motif composition, subcellular localization, synteny analysis, and calculation of synonymous (Ks) and non-synonymous (Ka) was performed in Chinese white pear. Sixty-two bZIP-TFs in Chinese pear were identified, and their expression profiles were comprehensively analyzed under ABA, SA, and MeJa hormones, which respond to multiple abiotic stresses and fruit growth and development. PbbZIP gene occurred through Whole-genome duplication and dispersed duplication events. These results provide a basic framework for further elucidating the biological function characterizations under multiple developmental stages and abiotic stress responses.

Group-C/S1 bZIP heterodimers regulate MdIPT5b to negatively modulate drought tolerance in apple species

Cytokinins play a central role in delaying senescence, reducing oxidative damage and maintaining plant growth during drought. This study showed that the ectopic expression of ProRE-deleted MdIPT5b, a key enzyme involved in cytokinin metabolism, increased the drought tolerance of transgenic Malus domestica (apple) callus and Solanum lycopersicum (tomato) seedlings by maintaining cytokinin homeostasis, and thus maintaining redox balance. Under restricted watering regimes, the yields of transgenic tomato plants were enhanced. Heterodimers of C/S1 bZIP are involved in the cytokinin-mediated drought response. The heterodimers bind the ProRE of MdIPT5b promoter, thus directly suppressing gene transcription. Single C/S1 bZIP members could not independently function as suppressors. However, specific paired members (heterodimers of MdbZIP80 with MdbZIP2 or with MdbZIP39) effectively suppressed transcription. The α-helical structure is essential for the heterodimerization of C/S1 bZIP members and for synergistic transcriptional suppression. As negative regulators of drought tolerance, suppressing either MdbZIP2 or MdbZIP39 alone does not improve the expression of MdIPT5b and did not increase the drought tolerance of transgenic apple callus. However, this could be achieved when they were co-suppressed. The suppression of MdbZIP80 alone could improve MdIPT5b expression and increase the drought tolerance of transgenic apple callus. However, these effects were reversed in response to the cosuppression of MdbZIP80 and MdIPT5b. Similar results were also observed during delayed dark-induced senescence in apple leaves. In conclusion, the apple C/S1 bZIP network (involving MdbZIP2, MdbZIP39 and MdbZIP80) directly suppressed the expression of MdIPT5b, thus negatively modulating drought tolerance and dark-induced senescence in a functionally redundant manner.

Identification and Analysis of bZIP Family Genes in Potato and Their Potential Roles in Stress Responses

The bZIP proteins comprise one of the largest transcription factor families and play important roles in plant growth and development, senescence, metabolic reactions, and stress responses. In this study, 49 bZIP transcription factor-encoding genes (StbZIP genes) on the potato genome were identified and analyzed. The 49 StbZIP genes, which are located on 12 chromosomes of the potato genome, were divided into 11 subgroups together with their Arabidopsis homologs based on the results of phylogenetic analysis. Gene structure and protein motif analysis revealed that members from the same subgroup often possessed similar exon/intron structures and motif organizations, further supporting the results of the phylogenetic analysis. Syntenic analysis indicated the existence of gene duplication events, which might play an important role in the expansion of the bZIP gene family in potato. Expressions of the StbZIP genes were analyzed in a variety of tissues via RNA-Seq data, suggesting functional diversity. Several StbZIP genes were found to be induced by different stress conditions. For example, the expression of StbZIP25, the close homolog of AtbZIP36/ABF2, was significantly upregulated by salt stress treatments. The StbZIP25 protein was found to be located in the nucleus and function as a transcriptional activator. Overexpression of StbZIP25 enhanced salt tolerance in Arabidopsis. The results from this study imply potential roles of the bZIP family genes in the stress response of potato.

Genome-wide characterization of bZIP transcription factors and their expression patterns in response to drought and salinity stress in Jatropha curcas

The basic leucine zipper (bZIP) family is one of the largest families of transcription factors (TFs) in plants and is responsible for various functions, including regulating development and responses to abiotic/biotic stresses. However, the roles of bZIPs in the regulation of responses to drought stress and salinity stress remain poorly understood in Jatropha curcas L., a biodiesel crop. In the present study, 50 JcbZIP genes were identified and classified into ten groups. Cis-element analysis indicated that JcbZIP genes are associated with abiotic stress. Gene expression patterns and quantitative real-time PCR (qRT-PCR) showed that four JcbZIP genes (JcbZIPs 34, 36, 49 and 50) are key resistance-related genes under both drought and salinity stress conditions. On the basis of the results of cis-element and phylogenetic analyses, JcbZIP49 and JcbZIP50 are likely involved in responses to drought and salinity stress; moreover, JcbZIP34 and JcbZIP36 might also play important roles in seed development and response to abiotic stress. These findings advance our understanding of the comprehensive characteristics of JcbZIP genes and provide new insights for functional validation in the further.

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

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

Physiological and transcriptomic analyses reveal the mechanisms underlying the salt tolerance of Zoysia japonica Steud

BACKGROUND

Areas with saline soils are sparsely populated and have fragile ecosystems, which severely restricts the sustainable development of local economies. Zoysia grasses are recognized as excellent warm-season turfgrasses worldwide, with high salt tolerance and superior growth in saline-alkali soils. However, the mechanism underlying the salt tolerance of Zoysia species remains unknown.

RESULTS

The phenotypic and physiological responses of two contrasting materials, Zoysia japonica Steud. Z004 (salt sensitive) and Z011 (salt tolerant) in response to salt stress were studied. The results show that Z011 was more salt tolerant than was Z004, with the former presenting greater K+/Na+ ratios in both its leaves and roots. To study the molecular mechanisms underlying salt tolerance further, we compared the transcriptomes of the two materials at different time points (0 h, 1 h, 24 h, and 72 h) and from different tissues (leaves and roots) under salt treatment. The 24-h time point and the roots might make significant contributions to the salt tolerance. Moreover, GO and KEGG analyses of different comparisons revealed that the key DEGs participating in the salt-stress response belonged to the hormone pathway, various TF families and the DUF family.

CONCLUSIONS

Zoysia salt treatment transcriptome shows the 24-h and roots may make significant contributions to the salt tolerance. The auxin signal transduction family, ABA signal transduction family, WRKY TF family and bHLH TF family may be the most important families in Zoysia salt-stress regulation.

A novel sweetpotato bZIP transcription factor gene, IbbZIP1, is involved in salt and drought tolerance in transgenic Arabidopsis

The overexpression of IbbZIP1 leads to a significant upregulation of abiotic-related genes, suggesting that IbbZIP1 gene confers salt and drought tolerance in transgenic Arabidopsis. Basic region/leucine zipper motif (bZIP) transcription factors regulate flower development, seed maturation, pathogen defense, and stress signaling in plants. Here, we cloned a novel bZIP transcription factor gene, named IbbZIP1, from sweetpotato [Ipomoea batatas (L.) Lam.] line HVB-3. The full length of IbbZIP1 exhibited transactivation activity in yeast. The expression of IbbZIP1 in sweetpotato was strongly induced by NaCl, PEG6000, and abscisic acid (ABA). Its overexpression in Arabidopsis significantly enhanced salt and drought tolerance. Under salt and drought stresses, the transgenic Arabidopsis plants showed significant upregulation of the genes involved in ABA and proline biosynthesis and reactive oxygen species scavenging system, significant increase of ABA and proline contents and superoxide dismutase activity and significant decrease of H₂O₂ content. These results demonstrate that the IbbZIP1 gene confers salt and drought tolerance in transgenic Arabidopsis. This study provides a novel bZIP gene for improving the tolerance of sweetpotato and other plants to abiotic stresses.

Systematic Analysis of Differentially Expressed Maize ZmbZIP Genes between Drought and Rewatering Transcriptome Reveals bZIP Family Members Involved in Abiotic Stress Responses

The basic leucine zipper (bZIP) family of transcription factors (TFs) regulate diverse phenomena during plant growth and development and are involved in stress responses and hormone signaling. However, only a few bZIPs have been functionally characterized. In this paper, 54 maize bZIP genes were screened from previously published drought and rewatering transcriptomes. These genes were divided into nine groups in a phylogenetic analysis, supported by motif and intron/exon analyses. The 54 genes were unevenly distributed on 10 chromosomes and contained 18 segmental duplications, suggesting that segmental duplication events have contributed to the expansion of the maize bZIP family. Spatio-temporal expression analyses showed that bZIP genes are widely expressed during maize development. We identified 10 core ZmbZIPs involved in protein transport, transcriptional regulation, and cellular metabolism by principal component analysis, gene co-expression network analysis, and Gene Ontology enrichment analysis. In addition, 15 potential stress-responsive ZmbZIPs were identified by expression analyses. Localization analyses showed that ZmbZIP17, -33, -42, and -45 are nuclear proteins. These results provide the basis for future functional genomic studies on bZIP TFs in maize and identify candidate genes with potential applications in breeding/genetic engineering for increased stress resistance. These data represent a high-quality molecular resource for selecting resistant breeding materials.

A unique bZIP transcription factor imparting multiple stress tolerance in Rice

BACKGROUND

Rice productivity is adversely affected by environmental stresses. Transcription factors (TFs), as the regulators of gene expression, are the key players contributing to stress tolerance and crop yield. Histone gene binding protein-1b (OsHBP1b) is a TF localized within the Saltol QTL in rice. Recently, we have reported the characterization of OsHBP1b in relation to salinity and drought tolerance in a model system tobacco. In the present study, we over-express the full-length gene encoding OsHBP1b in the homologous system (rice) to assess its contribution towards multiple stress tolerance and grain yield.

RESULTS

We provide evidence to show that transgenic rice plants over-expressing OsHBP1b exhibit better survival and favourable osmotic parameters under salinity stress than the wild type counterparts. These transgenic plants restricted reactive oxygen species accumulation by exhibiting high antioxidant enzyme activity (ascorbate peroxidase and superoxide dismutase), under salinity conditions. Additionally, these transgenic plants maintained the chlorophyll concentration, organellar structure, photosynthesis and expression of photosynthesis and stress-related genes even when subjected to salinity stress. Experiments conducted for other abiotic stresses such as drought and high temperature revealed improved tolerance in these transgenic plants with better root and shoot growth, better photosynthetic parameters, and enhanced antioxidant enzyme activity, in comparison with WT. Further, the roots of transgenic lines showed large cortical cells and accumulated a good amount of callose, unlike the WT roots, thus enabling them to penetrate hard soil and prevent the entry of harmful ions in the cell.

CONCLUSION

Collectively, our results show that rice HBP1b gene contributes to multiple abiotic stress tolerance through several molecular and physiological pathways and hence, may serve as an important gene for providing multiple stress tolerance and improving crop yield in rice.

Genome-wide systematic characterization of bZIP transcription factors and their expression profiles during seed development and in response to salt stress in peanut

BACKGROUND

Plant basic leucine zipper (bZIP) transcription factors play crucial roles in plant growth, development, and abiotic stress responses. However, systematic investigation and analyses of the bZIP gene family in peanut are lacking in spite of the availability of the peanut genome sequence.

RESULTS

In this study, we identified 50 and 45 bZIP genes from Arachis duranensis and A. ipaensis genomes, respectively. Phylogenetic analysis showed that Arachis bZIP genes were classified into nine groups, and these clusters were supported by several group-specific features, including exon/intron structure, intron phases, MEME motifs, and predicted binding site structure. We also identified possible variations in DNA-binding-site specificity and dimerization properties among different Arachis bZIPs by inspecting the amino acid residues at some key sites. Our analysis of the evolutionary history analysis indicated that segmental duplication, rather than tandem duplication, contributed greatly to the expansion of this gene family, and that most Arachis bZIPs underwent strong purifying selection. Through RNA-seq and quantitative real-time PCR (qRT-PCR) analyses, the co-expressed, differentially expressed and several well-studied homologous bZIPs were identified during seed development stages in peanut. We also used qRT-PCR to explore changes in bZIP gene expression in response to salt-treatment, and many candidate bZIPs in groups A, B, and S were proven to be associated with the salt-stress response.

CONCLUSIONS

This study have conducted a genome-wide identification, characterization and expression analysis of bZIP genes in Arachis genomes. Our results provide insights into the evolutionary history of the bZIP gene family in peanut and the funcntion of Arachis bZIP genes during seed development and in response to salt stress.

A Glycine soja group S2 bZIP transcription factor GsbZIP67 conferred bicarbonate alkaline tolerance in Medicago sativa

BACKGROUND

Even though bicarbonate alkaline stress is a serious threat to crop growth and yields, it attracts much fewer researches than high salinity stress. The basic leucine zipper (bZIP) transcription factors have been well demonstrated to function in diverse abiotic stresses; however, their biological role in alkaline tolerance still remains elusive. In this study, we functionally characterized a bZIP gene from Glycine soja GsbZIP67 in bicarbonate alkaline stress responses.

RESULTS

GsbZIP67 was initially identified as a putative bicarbonate responsive gene, on the basis of previous RNA-seq data of 50 mM NaHCO3-treated Glycine soja roots. GsbZIP67 protein possessed a conserved bZIP domain, and belonged to the group S2 bZIP, which is yet less well-studied. Our studies showed that GsbZIP67 targeted to nucleus in Arabidopsis protoplasts, and displayed transcriptional activation activity in yeast cells. The quantitative real-time PCR analyses unraveled the bicarbonate stress responsive expression and tissue specific expression of GsbZIP67 in wild soybean. Further phenotypic analysis illustrated that GsbZIP67 overexpression in alfalfa promoted plant growth under bicarbonate alkaline stress, as evidenced by longer roots and shoots. Furthermore, GsbZIP67 overexpression also modified the physiological indices of transgenic alfalfa under bicarbonate alkaline stress. In addition, the expression levels of several stress responsive genes were also augmented by GsbZIP67 overexpression.

CONCLUSIONS

Collectively, in this study, we demonstrated that GsbZIP67 acted as a positive regulator of plant tolerance to bicarbonate alkaline stress. These results provide direct genetic evidence of group S2 bZIPs in bicarbonate alkaline stress, and will facilitate further studies concerning the cis-elements and/or downstream genes targeted by GsbZIP67 in stress responses.

The Sugar-Signaling Hub: Overview of Regulators and Interaction with the Hormonal and Metabolic Network

Plant growth and development has to be continuously adjusted to the available resources. Their optimization requires the integration of signals conveying the plant metabolic status, its hormonal balance, and its developmental stage. Many investigations have recently been conducted to provide insights into sugar signaling and its interplay with hormones and nitrogen in the fine-tuning of plant growth, development, and survival. The present review emphasizes the diversity of sugar signaling integrators, the main molecular and biochemical mechanisms related to the sugar-signaling dependent regulations, and to the regulatory hubs acting in the interplay of the sugar-hormone and sugar-nitrogen networks. It also contributes to compiling evidence likely to fill a few knowledge gaps, and raises new questions for the future.

The Sugar-Signaling Hub: Overview of Regulators and Interaction with the Hormonal and Metabolic Network

Plant growth and development has to be continuously adjusted to the available resources. Their optimization requires the integration of signals conveying the plant metabolic status, its hormonal balance, and its developmental stage. Many investigations have recently been conducted to provide insights into sugar signaling and its interplay with hormones and nitrogen in the fine-tuning of plant growth, development, and survival. The present review emphasizes the diversity of sugar signaling integrators, the main molecular and biochemical mechanisms related to the sugar-signaling dependent regulations, and to the regulatory hubs acting in the interplay of the sugar-hormone and sugar-nitrogen networks. It also contributes to compiling evidence likely to fill a few knowledge gaps, and raises new questions for the future.

Revisiting the Role of Plant Transcription Factors in the Battle against Abiotic Stress

Owing to diverse abiotic stresses and global climate deterioration, the agricultural production worldwide is suffering serious losses. Breeding stress-resilient crops with higher quality and yield against multiple environmental stresses via application of transgenic technologies is currently the most promising approach. Deciphering molecular principles and mining stress-associate genes that govern plant responses against abiotic stresses is one of the prerequisites to develop stress-resistant crop varieties. As molecular switches in controlling stress-responsive genes expression, transcription factors (TFs) play crucial roles in regulating various abiotic stress responses. Hence, functional analysis of TFs and their interaction partners during abiotic stresses is crucial to perceive their role in diverse signaling cascades that many researchers have continued to undertake. Here, we review current developments in understanding TFs, with particular emphasis on their functions in orchestrating plant abiotic stress responses. Further, we discuss novel molecular mechanisms of their action under abiotic stress conditions. This will provide valuable information for understanding regulatory mechanisms to engineer stress-tolerant crops.

Transcriptome Analysis in Chinese Cabbage (Brassica rapa ssp. pekinensis) Provides the Role of Glucosinolate Metabolism in Response to Drought Stress

Although drought stress is one of the most limiting factors in growth and production of Chinese cabbage (Brassica rapa L. ssp. pekinensis), the underlying biochemical and molecular causes are poorly understood. In the present study, to address the mechanisms underlying the drought responses, we analyzed the transcriptome profile of Chinese cabbage grown under drought conditions. Drought stress transcriptionally activated several transcription factor genes, including AP2/ERFs, bHLHs, NACs and bZIPs, and was found to possibly result in transcriptional variation in genes involved in organic substance metabolic processes. In addition, comparative expression analysis of selected BrbZIPs under different stress conditions suggested that drought-induced BrbZIPs are important for improving drought tolerance. Further, drought stress in Chinese cabbage caused differential acclimation responses in glucosinolate metabolism in leaves and roots. Analysis of stomatal aperture indicated that drought-induced accumulation of glucosinolates in leaves directly or indirectly controlled stomatal closure to prevent water loss, suggesting that organ-specific responses are essential for plant survival under drought stress condition. Taken together, our results provide information important for further studies on molecular mechanisms of drought tolerance in Chinese cabbage.

The C/S1 bZIP Network: A Regulatory Hub Orchestrating Plant Energy Homeostasis

Sustaining energy homeostasis is crucial to every living being. To balance energy supply and demand, plants make use of an evolutionarily conserved management system consisting of two counteracting kinases, TOR (TARGET OF RAPAMYCIN) and SnRK1 (Snf1-RELATED PROTEIN KINASE 1). SnRK1 is involved in reorganizing enzymatic and transcriptional responses to survive energy-limiting conditions. Recently, members of the bZIP (basic leucine zipper) transcription factor family have been established as SnRK1 downstream mediators. We review here current knowledge on the functional impact of these group C and S₁ bZIPs, and analyze their regulation by environmental and endogenous cues. Given their specific homo- and heterodimerization, the so-called C/S₁ bZIP network is proposed to act as a signaling hub that coordinates plant development and stress responses.

Comparative analysis of alfalfa (Medicago sativa L.) leaf transcriptomes reveals genotype-specific salt tolerance mechanisms

BACKGROUND

Soil salinity is an important factor affecting growth, development, and productivity of almost all land plants, including the forage crop alfalfa (Medicago sativa). However, little is known about how alfalfa responds and adapts to salt stress, particularly among different salt-tolerant cultivars.

RESULTS

Among seven alfalfa cultivars, we found that Zhongmu-1 (ZM) is relatively salt-tolerant and Xingjiang Daye (XJ) is salt-sensitive. Compared to XJ, ZM showed slower growth under low-salt conditions, but exhibited stronger tolerance to salt stress. RNA-seq analysis revealed 2237 and 1125 differentially expressed genes (DEGs) between ZM and XJ in the presence and absence of salt stress, among which many genes are involved in stress-related pathways. After salt treatment, compared with the controls, the number of DEGs in XJ (19373) was about four times of that in ZM (4833). We also detected specific differential gene expression patterns: In response to salt stress, compared with XJ, ZM maintained relatively more stable expression levels of genes related to the ROS and Ca²⁺ pathways, phytohormone biosynthesis, and Na⁺/K⁺ transport. Notably, several salt resistance-associated genes always showed greater levels of expression in ZM than in XJ, including a transcription factor. Consistent with the suppression of plant growth resulting from salt stress, the expression of numerous photosynthesis- and growth hormone-related genes decreased more dramatically in XJ than in ZM. By contrast, the expression levels of photosynthetic genes were lower in ZM under low-salt conditions.

CONCLUSIONS

Compared with XJ, ZM is a salt-tolerant alfalfa cultivar possessing specific regulatory mechanisms conferring exceptional salt tolerance, likely by maintaining high transcript levels of abiotic and biotic stress resistance-related genes. Our results suggest that maintaining this specific physiological status and/or plant adaptation to salt stress most likely arises by inhibition of plant growth in ZM through plant hormone interactions. This study identifies new candidate genes that may regulate alfalfa tolerance to salt stress and increases the understanding of the genetic basis for salt tolerance.

SlbZIP38, a Tomato bZIP Family Gene Downregulated by Abscisic Acid, Is a Negative Regulator of Drought and Salt Stress Tolerance

The basic leucine zipper (bZIP) transcription factors have crucial roles in plant stress responses. In this study, the bZIP family gene SlbZIP38 (GenBank accession No: XM004239373) was isolated from a tomato (Solanum lycopersicum cv. Ailsa Craig) mature leaf cDNA library. The DNA sequence of SlbZIP38 encodes a protein of 484 amino acids, including a highly conserved bZIP DNA-binding domain in the C-terminal region. We found that SlbZIP38 was differentially expressed in various organs of the tomato plant and was downregulated by drought, salt stress, and abscisic acid (ABA). However, overexpression of SlbZIP38 significantly decreased drought and salt stress tolerance in tomatoes (Ailsa Craig). The findings that SlbZIP38 overexpression reduced the chlorophyll and free proline content in leaves but increased the malondialdehyde content may explain the reduced drought and salt tolerance observed in these lines. These results suggest that SlbZIP38 is a negative regulator of drought and salt resistance that acts by modulating ABA signaling.

BnaA.bZIP1 Negatively Regulates a Novel Small Peptide Gene, BnaC.SP6, Involved in Pollen Activity

Small peptides secreted to the extracellular matrix control many aspects of the plant's physiological activities which were identified in Arabidopsis thaliana, called ATSPs. Here, we isolated and characterized the small peptide gene Bna.SP6 from Brassica napus. The BnaC.SP6 promoter was cloned and identified. Promoter deletion analysis suggested that the -447 to -375 and -210 to -135 regions are crucial for the silique septum and pollen expression of BnaC.SP6, respectively. Furthermore, the minimal promoter region of p158 (-210 to -52) was sufficient for driving gene expression specifically in pollen and highly conserved in Brassica species. In addition, BnaA.bZIP1 was predominantly expressed in anthers where BnaC.SP6 was also expressed, and was localized to the nuclei. BnaA.bZIP1 possessed transcriptional activation activity in yeast and protoplast system. It could specifically bind to the C-box in p158 in vitro, and negatively regulate p158 activity in vivo. BnaA.bZIP1 functions as a transcriptional repressor of BnaC.SP6 in pollen activity. These results provide novel insight into the transcriptional regulation of BnaC.SP6 in pollen activity and the pollen/anther-specific promoter regions of BnaC.SP6 may have their potential agricultural application for new male sterility line generation.

GaMYB85, an R2R3 MYB gene, in transgenic Arabidopsis plays an important role in drought tolerance

BACKGROUND

MYB transcription factors (TFs) are one of the largest families of TFs in higher plants and are involved in diverse biological, functional, and structural processes. Previously, very few functional validation studies on R2R3 MYB have been conducted in cotton in response to abiotic stresses. In the current study, GaMYB85, a cotton R2R3 MYB TF, was ectopically expressed in Arabidopsis thaliana (Col-0) and was functionally characterized by overexpression in transgenic plants.

RESULTS

The in-silico analysis of GaMYB85 shows the presence of a SANT domain with a conserved R2R3 MYB imperfect repeat. The GaMYB85 protein has a 257-amino acid sequence, a molecular weight of 24.91 kD, and an isoelectric point of 5.58. Arabidopsis plants overexpressing GaMYB85 exhibited a higher seed germination rate in response to mannitol and salt stress, and higher drought avoidance efficiency than wild-type plants upon water deprivation. These plants had notably higher levels of free proline and chlorophyll with subsequent lower water loss rates and higher relative water content. Germination of GaMYB85 transgenics was more sensitive to abscisic acid (ABA) and extremely liable to ABA-induced inhibition of primary root elongation. Moreover, when subjected to treatment with different concentrations of ABA, transgenic plants with ectopically expressed GaMYB85 showed reduced stomatal density, with greater stomatal size and lower stomatal opening rates than those in wild-type plants. Ectopic expression of GaMYB85 led to enhanced transcript levels of stress-related marker genes such as RD22, ADH1, RD29A, P5CS, and ABI5.

CONCLUSIONS

Our results indicate previously unknown roles of GaMYB85, showing that it confers good drought, salt, and freezing tolerance, most probably via an ABA-induced pathway. These findings can potentially be exploited to develop improved abiotic stress tolerance in cotton plants.

Identification of a novel bZIP transcription factor in Camellia sinensis as a negative regulator of freezing tolerance in transgenic arabidopsis

BACKGROUND AND AIMS

Basic region/leucine zipper (bZIP) transcription factors play vital roles in the abiotic stress response of plants. However, little is known about the function of bZIP genes in Camellia sinensis .

METHODS

CsbZIP6 was overexpressed in Arabidopsis thaliana . Effects of CsbZIP6 overexpression on abscisic acid (ABA) sensitivity, freezing tolerance and the expression of cold-responsive genes in arabidopsis were studied.

KEY RESULTS

CsbZIP6 was induced during cold acclimation in tea plant. Constitutive overexpression of CsbZIP6 in arabidopsis lowered the plants' tolerance to freezing stress and ABA exposure during seedling growth. Compared with wild-type (WT) plants, CsbZIP6 overexpression (OE) lines exhibited increased levels of electrolyte leakage (EL) and malondialdehyde (MDA) contents, and reduced levels of total soluble sugars (TSS) under cold stress conditions. Microarray analysis of transgenic arabidopsis revealed that many differentially expressed genes (DEGs) between OE lines and WT plants could be mapped to 'response to cold' and 'response to water deprivation' terms based on Gene Ontology analysis. Interestingly, CsbZIP6 overexpression repressed most of the cold- and drought-responsive genes as well as starch metabolism under cold stress conditions.

CONCLUSIONS

The data suggest that CsbZIP6 functions as a negative regulator of the cold stress response in A. thaliana , potentially by down-regulating cold-responsive genes.

Poplar PtabZIP1-like enhances lateral root formation and biomass growth under drought stress

Developing drought-resistance varieties is a major goal for bioenergy crops, such as poplar (Populus), which will be grown on marginal lands with little or no water input. Root architecture can affect drought resistance, but few genes that affect root architecture in relation to water availability have been identified. Here, using activation tagging in the prime bioenergy crop poplar, we have identified a mutant that overcomes the block of lateral root (LR) formation under osmotic stress. Positioning of the tag, validation of the activation and recapitulation showed that the phenotype is caused by the poplar PtabZIP1-like (PtabZIP1L) gene with highest homology to bZIP1 from Arabidopsis. PtabZIP1L is predominantly expressed in roots, particularly in zones where lateral root primordia (LRP) initiate and LR differentiate and emerge. Transgenics overexpressing PtabZIP1L showed precocious LRP and LR development, while PtabZIP1L suppression significantly delayed both LRP and LR formation. Transgenic overexpression and suppression of PtabZIP1L also resulted in modulation of key metabolites like proline, asparagine, valine and several flavonoids. Consistently, expression of both of the poplar Proline Dehydrogenase orthologs and two of the Flavonol Synthases genes was also increased and decreased in overexpressed and suppressed transgenics, respectively. These findings suggest that PtabZIP1L mediates LR development and drought resistance through modulation of multiple metabolic pathways.

Functional Characterization of Cotton GaMYB62L, a Novel R2R3 TF in Transgenic Arabidopsis

Drought stress can trigger the production of ABA in plants, in response to adverse conditions, which induces the transcript of stress-related marker genes. The R2R3 MYB TFs are implicated in regulation of various plants developmental, metabolic and multiple environmental stress responses. Here, a R2R3-MYB cloned gene, GaMYB62L, was transformed in Arabidopsis and was functionally characterized. The GaMYB62L protein contains two SANT domains with a conserved R2R3 imperfect repeats. The GaMYB62L cDNA is 1,017 bp with a CDS of 879, encodes a 292-residue polypeptide with MW of 38.78 kD and a pI value of 8.91. Overexpressed GaMYB62L transgenic Arabidopsis have increased proline and chlorophyll content, superior seed germination rate under salt and osmotic stress, less water loss rate with reduced stomatal apertures, high drought avoidance as compared to WT on water deprivation and also significant plant survival rates at low temperature. In addition, overexpressed GaMYB62L lines were more sensitive to ABA mediated germination and root elongation assay. Moreover, ABA induced GaMYB62L overexpression, enhanced the expression of ABA stress related marker genes like RD22, COR15A, ADH1, and RD29A. Together, overexpression of GaMYB62L suggested having developed better drought, salt and cold tolerance in transgenic Arabidopsis and thus presented it as a prospective candidate gene to achieve better abiotic stress tolerance in cotton crop.

Definition of a core module for the nuclear retrograde response to altered organellar gene expression identifies GLK overexpressors as gun mutants

Retrograde signaling can be triggered by changes in organellar gene expression (OGE) induced by inhibitors such as lincomycin (LIN) or mutations that perturb OGE. Thus, an insufficiency of the organelle-targeted prolyl-tRNA synthetase PRORS1 in Arabidopsis thaliana activates retrograde signaling and reduces the expression of nuclear genes for photosynthetic proteins. Recently, we showed that mTERF6, a member of the so-called mitochondrial transcription termination factor (mTERF) family, is involved in the formation of chloroplast (cp) isoleucine-tRNA. To obtain further insights into its functions, co-expression analysis of MTERF6, PRORS1 and two other genes for organellar aminoacyl-tRNA synthetases was conducted. The results suggest a prominent role of mTERF6 in aminoacylation activity, light signaling and seed storage. Analysis of changes in whole-genome transcriptomes in the mterf6-1 mutant showed that levels of nuclear transcripts for cp OGE proteins were particularly affected. Comparison of the mterf6-1 transcriptome with that of prors1-2 showed that reduced aminoacylation of proline (prors1-2) and isoleucine (mterf6-1) tRNAs alters retrograde signaling in similar ways. Database analyses indicate that comparable gene expression changes are provoked by treatment with LIN, norflurazon or high light. A core OGE response module was defined by identifying genes that were differentially expressed under at least four of six conditions relevant to OGE signaling. Based on this module, overexpressors of the Golden2-like transcription factors GLK1 and GLK2 were identified as genomes uncoupled mutants.

Functional characterization and expression study of sugarcane MYB transcription factor gene PEaMYBAS1 promoter from Erianthus arundinaceus that confers abiotic stress tolerance in tobacco

This work provides a thorough understanding about the function ofcis-acting elements regarding drought, salt, cold and wounding stress.

Genome-wide analysis of the basic leucine zipper (bZIP) transcription factor gene family in six legume genomes

BACKGROUND

Plant bZIP proteins characteristically harbor a highly conserved bZIP domain with two structural features: a DNA-binding basic region and a leucine (Leu) zipper dimerization region. They have been shown to be diverse transcriptional regulators, playing crucial roles in plant development, physiological processes, and biotic/abiotic stress responses. Despite the availability of six completely sequenced legume genomes, a comprehensive investigation of bZIP family members in legumes has yet to be presented.

RESULTS

In this study, we identified 428 bZIP genes encoding 585 distinct proteins in six legumes, Glycine max, Medicago truncatula, Phaseolus vulgaris, Cicer arietinum, Cajanus cajan, and Lotus japonicus. The legume bZIP genes were categorized into 11 groups according to their phylogenetic relationships with genes from Arabidopsis. Four kinds of intron patterns (a-d) within the basic and hinge regions were defined and additional conserved motifs were identified, both presenting high group specificity and supporting the group classification. We predicted the DNA-binding patterns and the dimerization properties, based on the characteristic features in the basic and hinge regions and the Leu zipper, respectively, which indicated that some highly conserved amino acid residues existed across each major group. The chromosome distribution and analysis for WGD-derived duplicated blocks revealed that the legume bZIP genes have expanded mainly by segmental duplication rather than tandem duplication. Expression data further revealed that the legume bZIP genes were expressed constitutively or in an organ-specific, development-dependent manner playing roles in multiple seed developmental stages and tissues. We also detected several key legume bZIP genes involved in drought- and salt-responses by comparing fold changes of expression values in drought-stressed or salt-stressed roots and leaves.

CONCLUSIONS

In summary, this genome-wide identification, characterization and expression analysis of legume bZIP genes provides valuable information for understanding the molecular functions and evolution of the legume bZIP transcription factor family, and highlights potential legume bZIP genes involved in regulating tissue development and abiotic stress responses.

Isolation and expression analysis of 18 CsbZIP genes implicated in abiotic stress responses in the tea plant (Camellia sinensis)

Basic leucine zipper (bZIP) transcription factors (TFs) play essential roles in regulating stress processes in plants. Despite the economic importance of this woody crop, there is little information about bZIP TFs in tea plants. In this study, 18 bZIP genes were isolated from the tea plant (Camellia sinensis) and named sequentially from CsbZIP1 to CsbZIP18. According to the phylogenetic classification as in Arabidopsis, the CsbZIP genes spanned ten subgroups (Group A, B, C, D, E, F, H, I, S and K) of bZIP TFs. When analyzed for organ specific expression, all CsbZIP genes were found to be ubiquitously expressed in roots, stems, leaves and flowers. Expression analysis of CsbZIP genes in response to four abiotic stresses showed that in leaves, 9, 9, 15 and 11 CsbZIPs have 2-fold greater variation in transcript abundance under cold, exogenous ABA, high salinity and dehydration conditions, respectively. In roots, 5, 12, 14 and 11 CsbZIPs were differentially expressed under conditions of cold, exogenous ABA, high salinity and dehydration stresses. Moreover, CsbZIP genes in Groups F, H, S and K exhibited several folds up-and/or down-regulation against the above four stresses. Notably, CsbZIP18 of group K showed significant up-regulation in response to these same stresses, suggesting a vital functional role in stress response. Together, these findings increase our knowledge of bZIP TFs in the tea plant and suggest the significance of CsbZIP genes in plant abiotic responses.

Molecular and physiological changes in response to salt stress in Citrus macrophylla W plants overexpressing Arabidopsis CBF3/DREB1A

Plant stress induced by high salinity has leading to an important reduction in crop yields. Due to their tropical origin, citrus fruits are highly sensitive to salts. Rootstocks are the root system of fruit trees, regulating ion uptake and transport to the canopy. Therefore, increasing their salt tolerance could improve the salt tolerance of the fruit tree. For this, we genetically-transformed an important rootstock for lemon, Citrus macrophylla W, to constitutively express the CBF3/DREB1A gene from Arabidopsis, a well-studied salinity tolerance transcription factor. Transgenic lines showed normal size, with no dwarfism. Under salt stress, some transgenic lines showed greater growth, similar accumulation of chloride and sodium in the leaves and better stomatal conductance, in comparison to wild-type plants. Quantitative real-time analyses showed a similar expression of several CBF3/DREB1A target genes, such as COR15A, LEA 4/5, INV, SIP1, P5CS, GOLS, ADC2 and LKR/SDH, in transgenic lines and wild type plants, with the exception of INV that shows increased expression in line 4C15. Under salt stress, all measured transcript increased in both wild type and transgenics lines, with the exception of INV. Altogether, these results suggest a higher salt tolerance of transgenic C. macrophylla plants induced by the overexpression of AtCBF3/DREB1A.

A fungal transcription factor gene is expressed in plants from its own promoter and improves drought tolerance

MAIN CONCLUSION

A fungal gene encoding a transcription factor is expressed from its own promoter in Arabidopsis phloem and improves drought tolerance by reducing transpiration and increasing osmotic potential. Horizontal gene transfer from unrelated organisms has occurred in the course of plant evolution, suggesting that some foreign genes may be useful to plants. The CtHSR1 gene, previously isolated from the halophytic yeast Candida tropicalis, encodes a heat-shock transcription factor-related protein. CtHSR1, with expression driven by its own promoter or by the Arabidopsis UBQ10 promoter, was introduced into the model plant Arabidopsis thaliana by Agrobacterium tumefaciens-mediated transformation and the resulting transgenic plants were more tolerant to drought than controls. Fusions of the CtHSR1 promoter with β-glucuronidase reporter gene indicated that this fungal promoter drives expression to phloem tissues. A chimera of CtHSR1 and green fluorescence protein is localized at the cell nucleus. The physiological mechanism of drought tolerance in transgenic plants is based on reduced transpiration (which correlates with decreased opening of stomata and increased levels of jasmonic acid) and increased osmotic potential (which correlates with increased proline accumulation). Transcriptomic analysis indicates that the CtHSR1 transgenic plants overexpressed a hundred of genes, including many relevant to stress defense such as LOX4 (involved in jasmonic acid synthesis) and P5CS1 (involved in proline biosynthesis). The promoters of the induced genes were enriched in upstream activating sequences for water stress induction. These results demonstrate that genes from unrelated organisms can have functional expression in plants from its own promoter and expand the possibilities of useful transgenes for plant biotechnology.

Grafting triggers differential responses between scion and rootstock

Grafting is a well-established practice to facilitate asexual propagation in horticultural and agricultural crops. It has become a method for studying molecular aspects of root-to-shoot and/or shoot-to-root signaling events. The objective of this study was to investigate differences in gene expression between the organs of the scion and rootstock of a homograft (Arabidopsis thaliana). MapMan and Gene Ontology enrichment analysis revealed differentially expressed genes from numerous functional categories related to stress responses in the developing flower buds and leaves of scion and rootstock. Meta-analysis suggested induction of drought-type responses in flower buds and leaves of the scion. The flower buds of scion showed over-representation of the transcription factor genes, such as Homeobox, NAC, MYB, bHLH, B3, C3HC4, PLATZ etc. The scion leaves exhibited higher accumulation of the regulatory genes for flower development, such as SEPALLATA 1-4, Jumonji C and AHL16. Differential transcription of genes related to ethylene, gibberellic acid and other stimuli was observed between scion and rootstock. The study is useful in understanding the molecular basis of grafting and acclimation of scion on rootstock.

The positive regulatory roles of the TIFY10 proteins in plant responses to alkaline stress

The TIFY family is a novel plant-specific protein family, and is characterized by a conserved TIFY motif (TIFF/YXG). Our previous studies indicated the potential roles of TIFY10/11 proteins in plant responses to alkaline stress. In the current study, we focused on the regulatory roles and possible physiological and molecular basis of the TIFY10 proteins in plant responses to alkaline stress. We demonstrated the positive function of TIFY10s in alkaline responses by using the AtTIFY10a and AtTIFY10b knockout Arabidopsis, as evidenced by the relatively lower germination rates of attify10a and attify10b mutant seeds under alkaline stress. We also revealed that ectopic expression of GsTIFY10a in Medicago sativa promoted plant growth, and increased the NADP-ME activity, citric acid content and free proline content but decreased the MDA content of transgenic plants under alkaline stress. Furthermore, expression levels of the stress responsive genes including NADP-ME, CS, H⁺-ppase and P5CS were also up-regulated in GsTIFY10a transgenic plants under alkaline stress. Interestingly, GsTIFY10a overexpression increased the jasmonate content of the transgenic alfalfa. In addition, we showed that neither GsTIFY10a nor GsTIFY10e exhibited transcriptional activity in yeast cells. However, through Y2H and BiFc assays, we demonstrated that GsTIFY10a, not GsTIFY10e, could form homodimers in yeast cells and in living plant cells. As expected, we also demonstrated that GsTIFY10a and GsTIFY10e could heterodimerize with each other in both yeast and plant cells. Taken together, our results provided direct evidence supporting the positive regulatory roles of the TIFY10 proteins in plant responses to alkaline stress.