PtrbZIP12 improves drought resistance in Populus trichocarpa by directly targeting PtrDHN and PtrPOD

Dehydration-responsive element binding factors (DREBs) play important roles in plant growth, development, and stress signaling pathways in model plants. However, little is known about the function of DREBs in apple (Malus × domestica), a widely cultivated crop that is frequently threatened by drought. We isolated a DREB gene from Malus sieversii (Ledeb.) Roem., MsDREB6.2, and investigated its functions using overexpression analysis and chimeric repressor gene-silencing technology (CRES-T). We identified possible target genes of the protein encoded by MsDREB6.2 using electrophoretic mobility shift assays (EMSAs) and chromatin immunoprecipitation (ChIP). Overexpression of MsDREB6.2 increased the expression of a key cytokinin (CK) catabolism gene, MdCKX4a, which led to a significant reduction in endogenous CK levels, and caused a decrease in shoot:root ratio in transgenic apple plants. Overexpression of MsDREB6.2 resulted in a decrease in stomatal aperture and density and an increase in root hydraulic conductance (L0 ), and thereby enhanced drought tolerance in transgenic plants. Furthermore, manipulating the level of MsDREB6.2 expression altered the expression of two aquaporin (AQP) genes. The effect of the two AQP genes on L0 was further characterized using the AQP inhibitor HgCl2 . Based on these observations, we conclude that MsDREB6.2 enhances drought tolerance and that its function may be due, at least in part, to its influence on stomatal opening, root growth, and AQP expression. These results may have applications in apple rootstock breeding programs aimed at developing drought-resistant apple varieties.

Salicylic acid (SA) plays an essential role in the growth and development of plants, and in their response to abiotic stress. Previous studies have mostly focused on the effects of exogenously applied SA on the physiological response of plants to abiotic stresses; however, the underlying genetic mechanisms for the regulatory functions of endogenous SA in the defense response of plants remain unclear. In plants, SA binding protein 2 (SABP2), possessing methyl salicylate (MeSA) esterase activity, catalyzes the conversion of MeSA to SA. Herein, a SABP2-like gene, LcSABP, was cloned from Lycium chinense, which contained a complete open reading frame of 795 bp and encoded a protein of 264 amino acids that shared high sequence similarities with SABP2 orthologs from other plants. Overexpression of LcSABP enhanced the drought tolerance of transgenic tobacco plants. The results indicated that increased levels of LcSABP transcripts and endogenous SA content were involved in the enhanced drought tolerance. Physiological and biochemical studies further demonstrated that higher chlorophyll content, increased photosynthetic capacity, lower malondialdehyde content, and higher activities of superoxide dismutase, peroxidase, and catalase enhanced the drought tolerance of transgenic plants. Moreover, overexpression of LcSABP also increased the expression of reactive oxygen species (ROS)- and stress-responsive genes under drought stress. Overall, our results demonstrate that LcSABP plays a positive regulatory role in drought stress response by enhancing the endogenous SA content, promoting the scavenging of ROS, and regulating of the expression of stress-related transcription factor genes. Our findings indicate that LcSABP functions as a major regulator of the plant’s response to drought stress through a SA-dependent defense pathway.

The basic leucine zipper (bZIP) transcription factor family contains a large number of genes and has been found in many plant species. Previous studies have reported that bZIP family genes play important roles in the regulation of plant development and biotic/abiotic stress responses. However, a comprehensive investigation of this transcription factor family in tea plant (Camellia sinensis) has been lacking. In this study, a total of 61 bZIP genes were identified from the tea plant whole genome. The phylogenetic analysis classified these bZIP genes into 11 groups. The gene structures and composition patterns of the conserved motifs of bZIP genes were also characterized, which was consistent with the phylogenetic result. The gene expression analysis revealed that multiple bZIPs could be involved in response to drought, cold, or tea geometrid (Ectropis oblique) feeding. Our expression profile also indicated that many identified bZIPs were possibly involved in different developmental stages in tea plant. This study has provided an extensive overview of the tea plant bZIP transcription factor family and their possible roles in stress-responses.

Abiotic stresses such as drought, high salinity, and cold are key factors in determining crop yield. Rice is a notoriously drought-susceptible crop due in part to its small root system. Abscisic acid (ABA) involves in abiotic stress resistance in plants. The basic leucine zipper (bZIP) transcription factors play important roles in the ABA signaling pathway in plants. OsbZIP12 is a member of the group E bZIP transcription factor family in rice (Oryza sativa). Expression of OsbZIP12 is induced by abiotic stresses and ABA as well as sugar in rice. It is rapidly and strongly induced by drought stress. Corresponding with expression patterns, several stress and sugar-associated cis-acting elements were found in the OsbZIP12 promoter region. Transgenic rice overexpressing OsbZIP12 showed significantly improved drought tolerance and hypersensitivity to ABA. The elevated levels of expression of the ABA responding LEA3 and Rab16 genes in transgenic rice may enhance drought tolerance. These results indicate that OsbZIP12 is a positive regulator of ABA signaling and drought stress tolerance in rice and that OsbZIP12 could be involved in crosstalk among stress, hormone, and sugar signaling. We propose that OsbZIP12 is an important player in rice for conferring ABA-dependent drought tolerance and has high potential for use in the genetic improvement of stress tolerance.

The basic leucine zipper (bZIP) transcription factors form a large gene family that is important in pathogen defense, light and stress signaling, etc. The Completed whole genome sequences of model plants Arabidopsis (Arabidopsis thaliana), rice (Oryza sativa) and poplar (Populus trichocarpa) constitute a valuable resource for genome-wide analysis and genomic comparative analysis, as they are representatives of the two major evolutionary lineages within the angiosperms: the monocotyledons and the dicotyledons. In this study, bioinformatics analysis identified 74, 89 and 88 bZIP genes respectively in Arabidopsis, rice and poplar. Moreover, a comprehensive overview of this gene family is presented, including the gene structure, phylogeny, chromosome distribution, conserved motifs. As a result, the plant bZIPs were organized into 10 subfamilies on basis of phylogenetic relationship. Gene duplication events during the family evolution history were also investigated. And it was further concluded that chromosomal/segmental duplication might have played a key role in gene expansion of bZIP gene family.

A quantitative understanding of how transcription factors interact with genomic target sites is crucial for reconstructing transcriptional networks in vivo. Here, we use Hac1, a well-characterized basic leucine zipper (bZIP) transcription factor involved in the unfolded protein response (UPR) as a model to investigate interactions between bZIP transcription factors and their target sites. During the UPR, the accumulation of unfolded proteins leads to unconventional splicing and subsequent translation of HAC1 mRNA, followed by transcription of UPR target genes. Initial candidate-based approaches identified a canonical cis-acting unfolded protein response element (UPRE-1) within target gene promoters; however, subsequent studies identified a large set of Hac1 target genes lacking this UPRE-1 and containing a different motif (UPRE-2). Using a combination of unbiased and directed microfluidic DNA binding assays, we established that Hac1 binds in two distinct modes: (i) to short (6-7bp) UPRE-2-like motifs and (ii) to significantly longer (11-13bp) extended UPRE-1-like motifs. Using a genetic screen, we demonstrate that a region of extended homology N-terminal to the basic DNA binding domain is required for this dual site recognition. These results establish Hac1 as the first bZIP transcription factor known to adopt more than one binding mode and unify previously conflicting and discrepant observations of Hac1 function into a cohesive model of UPR target gene activation. Our results also suggest that even structurally simple transcription factors can recognize multiple divergent target sites of very different lengths, potentially enriching their downstream target repertoire.

The basic leucine zipper (bZIP) transcription factor family regulates plant developmental processes and response to stresses. The common bean (Phaseolus vulgaris), an important crop legume, possesses a whole set of 78 bZIP (PvbZIP) genes, the majority of these (59%) are most highly expressed in roots and nodules, root-derived new organs formed in the rhizobia N2-fixing symbiosis. Crop production is highly affected by salinity in Cuba and other countries. In this work we characterized the adverse effect of salinity to common bean plants of the Cuban CC-25-9-N cultivar grown in fertilized (full N-content) or symbiotic N-fixation (rhizobia inoculated) conditions. We assessed if PvbZIP TF participate in CC-25-9-N common bean response to salinity. Quantitative reverse-transcriptase-PCR (qRT-PCR) expression analysis showed that 26 out of 46 root/nodule-enhanced PvbZIP, that responded to salt stress in roots and/or nodules from fertilized and N2-fixing CC-25-9-N plants. From public common bean transcriptomic data, we identified 554 genes with an expression pattern similar to that of salt-responsive PvbZIP genes, and propose that the co-expressed genes are likely to be involved in the stress response. Our data provide a foundation for evaluating the individual roles of salt-responsive genes and to explore the PvbZIP-mediated improvement of salt tolerance in common bean.

Multiorgan Autoimmune Inflammation, Enhanced Lymphoproliferation, and Impaired Homeostasis of Reactive Oxygen Species in Mice Lacking the Antioxidant-Activated Transcription Factor Nrf2

OsbZIP52/RISBZ5 is a member of the basic leucine zipper (bZIP) transcription factor (TF) family in rice (Oryza sativa) isolated from rice (Zhonghua11) panicles. Expression of the OsbZIP52 gene was strongly induced by low temperature (4°C) but not by drought, PEG, salt, or ABA. The subcellular localization of OsbZIP52-GFP in onion (Allium cepa) epidermis cells revealed that OsbZIP52 is a nuclear localized protein. A transactivation assay in yeast demonstrated that OsbZIP52 functions as a transcriptional activator and can specifically bind to the G-box promoter motif. In a yeast two-hybrid (Y-2-H) experiment, OsbZIP52 was able to form homodimeric complexes. Rice plants overexpressing OsbZIP52 showed significantly increased sensitivity to cold and drought stress. Real-time PCR analysis revealed that some abiotic stress-related genes, such as OsLEA3, OsTPP1, Rab25, gp1 precursor, β-gal, LOC_Os05g11910 and LOC_Os05g39250, were down-regulated in OsbZIP52 overexpression lines. These results suggest that OsbZIP52/RISBZ5 could function as a negative regulator in cold and drought stress environments.

Drought stress is a major constraint of crop development and productivity. Plants have evolutionally developed several mechanisms at the molecular, cellular, and physiological levels to overcome drought stress. The basic leucine zipper (bZIP) transcription factor (TF) family members are starting to be concerned about their roles in drought stress responses. In this study, we functionally characterized OsbZIP66, a rice group-E bZIP TF, to be associated with rice drought tolerance mechanisms. Expression of OsbZIP66 was significantly induced upon treatments of rice plants with drought, high salinity, and ABA. These observations and the fact that the OsbZIP66 promoter contains ten ABA-responsive cis-elements suggest that OsbZIP66 is up-regulated by drought stress in an ABA-dependent manner. Overexpression of OsbZIP66 both in a whole plant body and specifically in roots enhanced drought tolerance of rice plants, indicating that the rice drought tolerance positively correlates with the expression levels of OsbZIP66. Thus, our results demonstrated that OsbZIP66 has a potential for use in biotechnological development of high-yielding rice plants under drought conditions.

The basic leucine (Leu) zipper (bZIP) proteins compose a family of transcriptional regulators present exclusively in eukaryotes. The bZIP proteins characteristically harbor a bZIP domain composed of two structural features: a DNA-binding basic region and the Leu zipper dimerization region. They have been shown to regulate diverse plant-specific phenomena, including seed maturation and germination, floral induction and development, and photomorphogenesis, and are also involved in stress and hormone signaling. We have identified 89 bZIP transcription factor-encoding genes in the rice (Oryza sativa) genome. Their chromosomal distribution and sequence analyses suggest that the bZIP transcription factor family has evolved via gene duplication. The phylogenetic relationship among rice bZIP domains as well as with bZIP domains from other plant bZIP factors suggests that homologous bZIP domains exist in plants. Similar intron/exon structural patterns were observed in the basic and hinge regions of their bZIP domains. Detailed sequence analysis has been done to identify additional conserved motifs outside the bZIP domain and to predict their DNA-binding site specificity as well as dimerization properties, which has helped classify them into different groups and subfamilies, respectively. Expression of bZIP transcription factor-encoding genes has been analyzed by full-length cDNA and expressed sequence tag-based expression profiling. This expression profiling was complemented by microarray analysis. The results indicate specific or coexpression patterns of rice bZIP transcription factors starting from floral transition to various stages of panicle and seed development. bZIP transcription factor-encoding genes in rice also displayed differential expression patterns in rice seedlings in response to abiotic stress and light irradiation. An effort has been made to link the structure and expression pattern of bZIP transcription factor-encoding genes in rice to their function, based on the information obtained from our analyses and earlier known results. This information will be important for functional characterization of bZIP transcription factors in rice.

One of the major causes of significant crop loss throughout the world is the myriad of environmental stresses including drought, salinity, cold, heavy metal toxicity, and ultraviolet-B (UV-B) rays. Plants as sessile organisms have evolved various effective mechanism which enable them to withstand this plethora of stresses. Most of such regulatory mechanisms usually follow the abscisic-acid (ABA)-dependent pathway. In this review, we have primarily focussed on the basic leucine zipper (bZIP) transcription factors (TFs) activated by the ABA-mediated signalosome. Upon perception of ABA by specialized receptors, the signal is transduced via various groups of Ser/Thr kinases, which phosphorylate the bZIP TFs. Following such post-translational modification of TFs, they are activated so that they bind to specific cis-acting sequences called abscisic-acid-responsive elements (ABREs) or GC-rich coupling elements (CE), thereby influencing the expression of their target downstream genes. Several in silico techniques have been adopted so far to predict the structural features, recognize the regulatory modification sites, undergo phylogenetic analyses, and facilitate genome-wide survey of TF under multiple stresses. Current investigations on the epigenetic regulation that controls greater accessibility of the inducible regions of DNA of the target gene to the bZIP TFs exclusively under stress situations, along with the evolved stress memory responses via genomic imprinting mechanism, have been highlighted. The potentiality of overexpression of bZIP TFs, either in a homologous or in a heterologous background, in generating transgenic plants tolerant to various abiotic stressors have also been addressed by various groups. The present review will provide a coherent documentation on the functional characterization and regulation of bZIP TFs under multiple environmental stresses, with the major goal of generating multiple-stress-tolerant plant cultivars in near future.

Peach (Prunus persica L.) is prone to chilling injury as exhibited by inhibition of the ethylene production, failure in softening, and the manifestation of internal browning. The basic leucine zipper (bZIP) transcription factors play an essential role in regulatory networks that control many processes associated with physiological, abiotic and biotic stress responses in fruits. Formerly, the underlying molecular and regulatory mechanism of (bZIP) transcription factors responsive to chilling injury in peach fruit is still elusive. In the current experiment, the solute peach 'Zhongyou Peach No. 13' was used as the test material and cold storage at low temperature (4°C). It was found that long-term low-temperature storage induced the production of ethylene, the hardness of the pulp decreased, and the low temperature also induced ABA accumulation. The changes of ABA and ethylene in peach fruits during low-temperature storage were clarified. Since the bZIP transcription factor is involved in the regulation of downstream pathways of ABA signals, 47 peach bZIP transcription factor family genes were identified through bioinformatics analysis. Further based on RT-qPCR analysis, 18 PpbZIP genes were discovered to be expressed in refrigerated peach fruits. Among them, the expression of PpbZIP23 and PpbZIP25 was significantly reduced during the refrigeration process, the promoter analysis of these genes found that this region contains the MYC/MYB/ABRES binding element, but not the DRES/CBFS element, indicating that the expression may be regulated by the ABA-dependent cold induction pathway, thereby responding to chilling injury in peach fruit. Over investigation will provide new insights for further postharvest protocols related to molecular changes during cold storage and will prove a better cope for chilling injury.

The basic leucine zipper (bZIP) transcription factor family plays crucial roles in multiple biological processes, especially stress responses. Cassava (Manihot esculenta Crantz) is an important tropical crop with a strong tolerance to environmental stresses such as drought, heat, and low-fertility environments. Currently, limited information is available regarding the functional identification of bZIP transcription factors in response to abiotic stress in cassava. Herein, a gene encoding an ABA Insensitive 5 (ABI5)-like transcription factor, designated as MeABL5, was identified in cassava. Sequence and phylogenetic analysis showed that MeABL5 is a cassava bZIP transcription factor that is not included in the previously identified cassava bZIP family members, belongs to subfamily A, and has high sequence similarity to ABI5-like proteins. Subcellular localization and transactivation assays revealed that MeABL5 was a nuclear-localized protein and possessed transactivation activity. Furthermore, MeABL5 was able to specifically interact with the ABRE cis-element in the promoter of the cassava major cell wall invertase gene, MeCWINV3, in vitro and in vivo. MeABL5 and MeCWINV3 exhibited similar expression patterns in various organs or tissues and under abiotic stress in cassava. The expressions of MeABL5 and MeCWINV3 within cassava plantlets were both induced by exogenous abscisic acid (ABA), gibberellic acid (GA3), methyl jasmonate (MeJA), and heat. Overexpression of MeABL5 increased the activity of the MeCWINV3 gene, and the up-regulated expressions of MeCWINV3 were significantly activated under ABA-, salicylic acid (SA)-, and MeJA-induced conditions. Overall, these results suggest that MeABL5 is a positive regulator of MeCWINV3 and might participate in the robust resistance of cassava in response to abiotic stress. This study also provides a foundation for further research on ABA-mediated and stress-related signaling pathways in cassava.

Basic leucine zipper (bZIP) transcription factors (TFs) play a crucial role in anthocyanin accumulation in plants. In addition to bZIP TFs, abscisic acid (ABA) increases anthocyanin biosynthesis. Therefore, this study aimed to investigate whether bZIP TFs are involved in ABA-induced anthocyanin accumulation in sweet cherry and elucidate the underlying molecular mechanisms. Specifically, the BLAST method was used to identify bZIP genes in sweet cherry. Additionally, we examined the expression of ABA- and anthocyanin-related genes in sweet cherry following the overexpression or knockdown of a bZIP candidate gene. In total, we identified 54 bZIP-encoding genes in the sweet cherry genome. Basic leucine zipper 6 (bZIP6) showed significantly increased expression, along with increased anthocyanin accumulation in sweet cherry. Additionally, yeast one-hybrid and dual-luciferase assays indicated that PavbZIP6 enhanced the expression of anthocyanin biosynthetic genes (PavDFR, PavANS, and PavUFGT), thereby increasing anthocyanin accumulation. Moreover, PavbZIP6 interacted directly with the PavBBX6 promoter, thereby regulating PavNCED1 to promote abscisic acid (ABA) synthesis and enhance anthocyanin accumulation in sweet cherry fruit. Conclusively, this study reveals a novel mechanism by which PavbZIP6 mediates anthocyanin biosynthesis in response to ABA and contributes to our understanding of the mechanism of bZIP genes in the regulation of anthocyanin biosynthesis in sweet cherry.