Mini review roles of the bZIP gene family in rice

The basic leucine zipper domain (bZIP) transcription factor BbYap1 promotes evasion of host humoral immunity and regulates lipid homeostasis contributing to fungal virulence in Beauveria bassiana

Basic leucine zipper domain transcription factors (TFs), of which yeast activator protein (Yap) is a significant class, are crucial for the development of sclerotia, the stress response, vegetative growth, and spore adhesion. Nevertheless, nothing is known about how Yap TFs contribute to the pathogenicity of entomopathogenic fungus. In this work, Beauveria bassiana was used to identify and knock out the yeast gene BbYap1, which is similar to Yap. The BbYap1 gene deletion has an impact on lipid homeostasis of B. bassiana; oleic acid, for example, dropped by 95.69%. The BbYap1 mutant exhibited much less virulence and vegetative development in comparison to the wild strain, while demonstrating a greater sensitivity to chemical stress. It is noteworthy that the physiological abnormalities brought on by BbYap1 deletion were largely repaired by the addition of exogenous oleic acid, as seen by the notable increase in insect survival in the blood cavity injection group. Following infection with the BbYap1 mutant, the host exhibits a considerable down-regulation of the expression of β-1,3-glucan recognition protein, gallerimycin, gloverin, and moricin-like protein genes. Likewise, the introduction of exogenous oleic acid markedly increased the host's expression of the aforementioned genes. In summary, BbYap1 regulates cellular enzyme lipid homeostasis and fungal virulence by eluding host humoral defense, which contributes to fungal chemical stress and vegetative development.

IMPORTANCE

Entomopathogenic fungi (EPF) offer an effective and eco-friendly alternative to curb insect populations in biocontrol strategy. When EPF enter the hemolymph of their host, they encounter a variety of stress reactions, such as immunological and oxidative stress. Basic leucine zipper domain transcription factors, of which yeast activator protein (Yap) is a significant class, have diverse biological functions related to metabolism, development, reproduction, conidiation, stress responses, and pathogenicity. This study demonstrates that BbYap1 of Beauveria bassiana regulates cellular enzyme lipid homeostasis and fungal virulence by eluding host humoral defense, which contributes to fungal chemical stress and vegetative development. These findings offer fresh perspectives for comprehending molecular roles of YAP in EPF.

In silico analysis identified bZIP transcription factors genes responsive to abiotic stress in Alfalfa (Medicago sativa L.)

BACKGROUND

Alfalfa (Medicago sativa L.) is the most cultivated forage legume around the world. Under a variety of growing conditions, forage yield in alfalfa is stymied by biotic and abiotic stresses including heat, salt, drought, and disease. Given the sessile nature of plants, they use strategies including, but not limited to, differential gene expression to respond to environmental cues. Transcription factors control the expression of genes that contribute to or enable tolerance and survival during periods of stress. Basic-leucine zipper (bZIP) transcription factors have been demonstrated to play a critical role in regulating plant growth and development as well as mediate the responses to abiotic stress in several species, including Arabidopsis thaliana, Oryza sativa, Lotus japonicus and Medicago truncatula. However, there is little information about bZIP transcription factors in cultivated alfalfa.

RESULT

In the present study, 237 bZIP genes were identified in alfalfa from publicly available sequencing data. Multiple sequence alignments showed the presence of intact bZIP motifs in the identified sequences. Based on previous phylogenetic analyses in A. thaliana, alfalfa bZIPs were similarly divided and fell into 10 groups. The physico-chemical properties, motif analysis and phylogenetic study of the alfalfa bZIPs revealed high specificity within groups. The differential expression of alfalfa bZIPs in a suite of tissues indicates that bZIP genes are specifically expressed at different developmental stages in alfalfa. Similarly, expression analysis in response to ABA, cold, drought and salt stresses, indicates that a subset of bZIP genes are also differentially expressed and likely play a role in abiotic stress signaling and/or tolerance. RT-qPCR analysis on selected genes further verified these differential expression patterns.

CONCLUSIONS

Taken together, this work provides a framework for the future study of bZIPs in alfalfa and presents candidate bZIPs involved in stress-response signaling.

Genome-Wide Analysis of C/S1-bZIP Subfamilies in Populus tomentosa and Unraveling the Role of PtobZIP55/21 in Response to Low Energy

C/S1 basic leucine zipper (bZIP) transcription factors are essential for plant survival under energy deficiency. However, studies on the responses of C/S1-bZIPs to low energy in woody plants have not yet been reported. In this study, members of C/S1-bZIP subfamilies in Populus tomentosa were systematically analyzed using bioinformatic approaches. Four C-bZIPs and 10 S1-bZIPs were identified, and their protein properties, phylogenetic relationships, gene structures, conserved motifs, and uORFs were systematically investigated. In yeast two-hybrid assays, direct physical interactions between C-bZIP and S1-bZIP members were observed, highlighting their potential functional synergy. Moreover, expression profile analyses revealed that low energy induced transcription levels of most C/S1-bZIP members, with bZIP55 and bZIP21 (a homolog of bZIP55) exhibiting particularly significant upregulation. When the expression of bZIP55 and bZIP21 was co-suppressed using artificial microRNA mediated gene silencing in transgenic poplars, root growth was promoted. Further analyses revealed that bZIP55/21 negatively regulated the root development of P. tomentosa in response to low energy. These findings provide insights into the molecular mechanisms by which C/S1-bZIPs regulate poplar growth and development in response to energy deprivation.

The bZIP transcription factor MpbZIP9 regulates anthocyanin biosynthesis in Malus 'Pinkspire' fruit

Malus 'Pinkspire' is regulated by abscisic acid (ABA), which results in a red colour, but the regulatory relationship between ABA and anthocyanin synthesis has not been determined. The key factors affecting the colour change of M. 'Pinkspire' peel were investigated during the periods of significant colour changes during fruit ripening. The results showed that the transcription factor MpbZIP9 associated with ABA was screened by transcriptomic analysis. MpbZIP9 expression was consistent with the trend of structural genes expression for anthocyanin synthesis in the peel during fruit ripening, as well as with changes in the content of ABA, which is a positive regulator. A yeast one-hybrid assay showed that MpbZIP9 can directly bind to the promoter of MpF3'H. Dual luciferase reporter gene assays and GUS staining experiments showed that MpbZIP9 significantly activate MpF3'H expression. In addition, overexpression of the MpbZIP9 significantly enhanced anthocyanin accumulation and the expression of genes involved in anthocyanin synthesis. In contrast, virus-induced silencing of the MpbZIP9 significantly reduced the expression of structural genes involved in anthocyanin synthesis. These results suggest that the MpbZIP9 transcription factor can regulate the synthesis of peel anthocyanin and is a positive regulator that promotes anthocyanin biosynthesis by activating MpF3'H expression.

Genome-wide analysis of bZIP gene family members in Pleurotus ostreatus, and potential roles of PobZIP3 in development and the heat stress response

The basic leucine zipper (bZIP) transcription factor (TF) is widespread among eukaryotes and serves different roles in fungal processes including nutrient utilization, growth, stress responses and development. The oyster mushroom (Pleurotus ostreatus) is an important and widely cultivated edible mushroom worldwide; nevertheless, reports are lacking on the identification or function of bZIP gene family members in P. ostreatus. Herein, 11 bZIPs on 6 P. ostreatus chromosomes were systematically identified, which were classified into 3 types according to their protein sequences. Phylogenetic analysis of PobZIPs with other fungal bZIPs indicated that PobZIPs may have differentiated late. Cis-regulatory element analysis revealed that at least one type of stress-response-related element was present on each bZIP promoter. RNA-seq and RT-qPCR analyses revealed that bZIP expression patterns were altered under heat stress and different developmental stages. We combined results from GST-Pull-down, EMSA and yeast two-hybrid assays to screen a key heat stress-responsive candidate gene PobZIP3. PobZIP3 overexpression in P. ostreatus enhanced tolerance to high temperature and cultivation assays revealed that PobZIP3 positively regulates the development of P. ostreatus. RNA-seq analysis showed that PobZIP3 plays a role in glucose metabolism pathways, antioxidant enzyme activity and sexual reproduction. These results may support future functional studies of oyster mushroom bZIP TFs.

Genome-Wide Identification of bZIP Transcription Factors in Cymbidium ensifolium and Analysis of Their Expression under Low-Temperature Stress

The basic leucine zipper (bZIP) transcription factors constitute the most widely distributed and conserved eukaryotic family. They play crucial roles in plant growth, development, and responses to both biotic and abiotic stresses, exerting strong regulatory control over the expression of downstream genes. In this study, a genome-wide characterization of the CebZIP transcription factor family was conducted using bioinformatic analysis. Various aspects, including physicochemical properties, phylogenetics, conserved structural domains, gene structures, chromosomal distribution, gene covariance relationships, promoter cis-acting elements, and gene expression patterns, were thoroughly analyzed. A total of 70 CebZIP genes were identified from the C. ensifolium genome, and they were randomly distributed across 18 chromosomes. The phylogenetic tree clustered them into 11 subfamilies, each exhibiting complex gene structures and conserved motifs arranged in a specific order. Nineteen pairs of duplicated genes were identified among the 70 CebZIP genes, with sixteen pairs affected by purifying selection. Cis-acting elements analysis revealed a plethora of regulatory elements associated with stress response, plant hormones, and plant growth and development. Transcriptome and qRT-PCR results demonstrated that the expression of CebZIP genes was universally up-regulated under low temperature conditions. However, the expression patterns varied among different members. This study provides theoretical references for identifying key bZIP genes in C. ensifolium that confer resistance to low-temperature stress, and lays the groundwork for further research into their broader biological functions.

Identification of a Branch Number Locus in Soybean Using BSA-Seq and GWAS Approaches

The determination of the soybean branch number plays a pivotal role in plant morphogenesis and yield components. This polygenic trait is subject to environmental influences, and despite its significance, the genetic mechanisms governing the soybean branching number remain incompletely understood. To unravel these mechanisms, we conducted a comprehensive investigation employing a genome-wide association study (GWAS) and bulked sample analysis (BSA). The GWAS revealed 18 SNPs associated with the soybean branch number, among which qGBN3 on chromosome 2 emerged as a consistently detected locus across two years, utilizing different models. In parallel, a BSA was executed using an F2 population derived from contrasting cultivars, Wandou35 (low branching number) and Ruidou1 (high branching number). The BSA results pinpointed a significant quantitative trait locus (QTL), designated as qBBN1, located on chromosome 2 by four distinct methods. Importantly, both the GWAS and BSA methods concurred in co-locating qGBN3 and qBBN1. In the co-located region, 15 candidate genes were identified. Through gene annotation and RT-qPCR analysis, we predicted that Glyma.02G125200 and Glyma.02G125600 are candidate genes regulating the soybean branch number. These findings significantly enhance our comprehension of the genetic intricacies regulating the branch number in soybeans, offering promising candidate genes and materials for subsequent investigations aimed at augmenting the soybean yield. This research represents a crucial step toward unlocking the full potential of soybean cultivation through targeted genetic interventions.

Genome-wide identification of bZIP gene family and expression analysis of BhbZIP58 under heat stress in wax gourd

BACKGROUND

The basic leucine zipper (bZIP) transcription factor family is one of the most abundant and evolutionarily conserved gene families in plants. It assumes crucial functions in the life cycle of plants, including pathogen defense, secondary metabolism, stress response, seed maturation, and flower development. Although the genome of wax gourd has been published, little is known about the functions, evolutionary background, and gene expression patterns of the bZIP gene family, which limits its utilization.

RESULTS

A total of 61 bZIP genes (BhbZIPs) were identified from wax gourd (Benincasa hispida) genome and divided into 12 subgroups. Whole-genome duplication (WGD) and dispersed duplication (DSD) were the main driving forces of bZIP gene family expansion in wax gourd, and this family may have undergone intense purifying selection pressure during the evolutionary process. We selected BhbZIP58, only one in the member of subgroup B, to study its expression patterns under different stresses, including heat, salt, drought, cold stress, and ABA treatment. Surprisingly, BhbZIP58 had a dramatic response under heat stress. BhbZIP58 showed the highest expression level in the root compared with leaves, stem, stamen, pistil, and ovary. In addition, BhbZIP58 protein was located in the nucleus and had transcriptional activation activity. Overexpression of BhbZIP58 in Arabidopsis enhanced their heat tolerance.

CONCLUSIONS

In this study, bZIP gene family is systematically bioinformatically in wax gourd for the first time. Particularly, BhbZIP58 may have an important role in heat stress. It will facilitate further research on the bZIP gene family regarding their evolutionary history and biological functions.

Comprehensive Functional Analysis of the bZIP Family in Bletilla striata Reveals That BsbZIP13 Could Respond to Multiple Abiotic Stresses

Basic leucine zipper (bZIP) transcription factors (TFs) are one of the largest families involved in plant physiological processes such as biotic and abiotic responses, growth, and development, etc. In this study, 66 members of the bZIP family were identified in Bletilla striata, which were divided into 10 groups based on their phylogenetic relationships with AtbZIPs. A structural analysis of BsbZIPs revealed significant intron-exon differences among BsbZIPs. A total of 63 bZIP genes were distributed across 16 chromosomes in B. striata. The tissue-specific and germination stage expression patterns of BsbZIPs were based on RNA-seq. Stress-responsive expression analysis revealed that partial BsbZIPs were highly expressed under low temperatures, wounding, oxidative stress, and GA treatments. Furthermore, subcellular localization studies indicated that BsbZIP13 was localized in the nucleus. Yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) assays suggested that BsbZIP13 could interact with multiple BsSnRK2s. The results of this study provide insightful data regarding bZIP TF as one of the stress response regulators in B. striata, while providing a theoretical basis for transgenic and functional studies of the bZIP gene family in B. striata.

Systematic evolution of bZIP transcription factors in Malvales and functional exploration of AsbZIP14 and AsbZIP41 in Aquilaria sinensis

Introduction

Agarwood, the dark-brown resin produced by Aquilaria trees, has been widely used as incense, spice, perfume or traditional medicine and 2-(2-phenethyl) chromones (PECs) are the key markers responsible for agarwood formation. But the biosynthesis and regulatory mechanism of PECs were still not illuminated. The transcription factor of basic leucine zipper (bZIP) presented the pivotal regulatory roles in various secondary metabolites biosynthesis in plants, which might also contribute to regulate PECs biosynthesis. However, molecular evolution and function of bZIP are rarely reported in Malvales plants, especially in Aquilaria trees.

Methods and results

Here, 1,150 bZIPs were comprehensively identified from twelve Malvales and model species genomes and the evolutionary process were subsequently analyzed. Duplication types and collinearity indicated that bZIP is an ancient or conserved TF family and recent whole genome duplication drove its evolution. Interesting is that fewer bZIPs in A. sinensis than that species also experienced two genome duplication events in Malvales. 62 AsbZIPs were divided into 13 subfamilies and gene structures, conservative domains, motifs, cis-elements, and nearby genes of AsbZIPs were further characterized. Seven AsbZIPs in subfamily D were significantly regulated by ethylene and agarwood inducer. As the typical representation of subfamily D, AsbZIP14 and AsbZIP41 were localized in nuclear and potentially regulated PECs biosynthesis by activating or suppressing type III polyketide synthases (PKSs) genes expression via interaction with the AsPKS promoters.

Discussion

Our results provide a basis for molecular evolution of bZIP gene family in Malvales and facilitate the understanding the potential functions of AsbZIP in regulating 2-(2-phenethyl) chromone biosynthesis and agarwood formation.

Genome-Wide Identification of bZIP Transcription Factors in Faba Bean Based on Transcriptome Analysis and Investigation of Their Function in Drought Response

Faba bean is an important cool-season edible legume crop that is constantly threatened by abiotic stresses such as drought. The basic leucine zipper (bZIP) gene family is one of the most abundant and diverse families of transcription factors in plants. It regulates plant growth and development and plays an important role in the response to biotic and abiotic stresses. In this study, we identified 18 members of the faba bean bZIP transcription factor family at the genome-wide level based on previous faba bean drought stress transcriptome sequencing data. A phylogenetic tree was constructed to group the 18 VfbZIP proteins into eight clades. Analysis of cis-acting elements in the promoter region suggested that these 18 VfbZIPs may be involved in regulating abiotic stress responses such as drought. Transcriptome data showed high expression of seven genes (VfbZIP1, VfbZIP2, VfbZIP5, VfbZIP7, VfbZIP15, VfbZIP17, and VfbZIP18) in the drought-tolerant cultivar under drought stress, in which VfbZIP1, VfbZIP2, and VfbZIP5 were consistently expressed as detected by quantitative real-time polymerase chain reaction (qRT-PCR) compared to the transcriptome data. Ectopic overexpression of the three VfbZIPs in tobacco, based on the potato Virus X (PVX) vector, revealed that VfbZIP5 enhanced the drought tolerance. Overexpressed VfbZIP5 in plants showed lower levels of proline (PRO), malondialdehyde (MDA), and peroxidase (POD) compared to those overexpressing an empty vector under 10 days of drought stress. Protein-protein interaction (PPI) analysis showed that VfbZIP5 interacted with seven proteins in faba bean, including VfbZIP7 and VfbZIP10. The results depict the importance of VfbZIPs in response to drought stress, and they would be useful for the improvement of drought tolerance.

The transcriptional hub SHORT INTERNODES1 integrates hormone signals to orchestrate rice growth and development

Plants have evolved sophisticated mechanisms to coordinate their growth and stress responses via integrating various phytohormone signaling pathways. However, the precise molecular mechanisms orchestrating integration of the phytohormone signaling pathways remain largely obscure. In this study, we found that the rice (Oryza sativa) short internodes1 (shi1) mutant exhibits typical auxin-deficient root development and gravitropic response, brassinosteroid (BR)-deficient plant architecture and grain size as well as enhanced abscisic acid (ABA)-mediated drought tolerance. Additionally, we found that the shi1 mutant is also hyposensitive to auxin and BR treatment but hypersensitive to ABA. Further, we showed that OsSHI1 promotes the biosynthesis of auxin and BR by activating the expression of OsYUCCAs and D11, meanwhile dampens ABA signaling by inducing the expression of OsNAC2, which encodes a repressor of ABA signaling. Furthermore, we demonstrated that 3 classes of transcription factors, AUXIN RESPONSE FACTOR 19 (OsARF19), LEAF AND TILLER ANGLE INCREASED CONTROLLER (LIC), and OsZIP26 and OsZIP86, directly bind to the promoter of OsSHI1 and regulate its expression in response to auxin, BR, and ABA, respectively. Collectively, our results unravel an OsSHI1-centered transcriptional regulatory hub that orchestrates the integration and self-feedback regulation of multiple phytohormone signaling pathways to coordinate plant growth and stress adaptation.

The role of walnut bZIP genes in explant browning

BACKGROUND

Basic leucine zipper (bZIP) proteins are important transcription factors in plants. To study the role of bZIP transcription factors in walnut explant browning, this study used bioinformatics software to analyze walnut bZIP gene family members, along with their transcript levels in different walnut tissues, to evaluate the transcriptional expression of this gene family during the primary culture of walnut explants and to reveal the mechanism of action of walnut bZIP genes in walnut explant browning.

RESULTS

The results identified 65 JrbZIP genes in the walnut genome, which were divided into 8 subfamilies and distributed on 16 chromosomes. The results of transcriptome data analysis showed that there were significant differences in the expression of four genes, namely, JrbZIP55, JrbZIP70, JrbZIP72, and JrbZIP88, under both vermiculite and agar culture conditions. There were multiple hormone (salicylic acid, abscisic acid, auxin, and gibberellin) signaling and regulatory elements that are responsive to stress (low temperature, stress, and defense) located in the promoter regions of JrbZIP55, JrbZIP70, JrbZIP72, and JrbZIP88. The walnut JrbZIP55 protein and Arabidopsis bZIP42 protein are highly homologous, and the proteins interacting with Arabidopsis bZIP42 include the AT2G19940 oxidoreductases, which act on aldehyde or oxygen-containing donors.

CONCLUSION

It is speculated that JrbZIP55 may participate in the regulation of browning in walnut explants.

Global transcriptome and gene co-expression network analyses reveal regulatory and non-additive effects of drought and heat stress in grapevine

Despite frequent co-occurrence of drought and heat stress, the molecular mechanisms governing plant responses to these stresses in combination have not often been studied. This is particularly evident in non-model, perennial plants. We conducted large scale physiological and transcriptome analyses to identify genes and pathways associated with grapevine response to drought and/or heat stress during stress progression and recovery. We identified gene clusters with expression correlated to leaf temperature and water stress and five hub genes for the combined stress co-expression network. Several differentially expressed genes were common to the individual and combined stresses, but the majority were unique to the individual or combined stress treatments. These included heat-shock proteins, mitogen-activated kinases, sugar metabolizing enzymes, and transcription factors, while phenylpropanoid biosynthesis and histone modifying genes were unique to the combined stress treatment. Following physiological recovery, differentially expressed genes were found only in plants under heat stress, both alone and combined with drought. Taken collectively, our results suggest that the effect of the combined stress on physiology and gene expression is more severe than that of individual stresses, but not simply additive, and that epigenetic chromatin modifications may play an important role in grapevine responses to combined drought and heat stress.

Up-regulation of bZIP88 transcription factor is involved in resistance to three different herbicides in both Echinochloa crus-galli and E. glabrescens

The resistance of weeds to herbicides poses a major threat to agricultural production, and non-target-site resistance (NTSR) is often a serious problem as its mechanisms can in some cases confer resistance to herbicides with different modes of action. In this study, we hypothesized that bZIP transcription factors (TFs), which regulate abiotic stress responses in many plants, play a regulatory role in NTSR. Whole-plant assays indicated that the wild grasses Echinochloa crus-galli and E. glabrescens are resistant to the herbicides penoxsulam, cyhalofop-butyl, and quintrione. Transcriptome sequencing then identified 101 and 49 bZIP TFs with differential expression following penoxsulam treatment in E. crus-galli and E. glabrescens, respectively. Twelve of these genes had >60% homology with rice genes. The expression of bZIP88 was considerably up-regulated 6 h after treatment with the three different herbicides, and it was similar between resistant and susceptible populations; however, the relative expression levels before herbicide treatment and 24 h after were the same. We used rice (Oryza sativa ssp. japonica cv Nipponbare) as a model system for functional validation and found that CRISPR-Cas9-knockout of the rice bZIP88 ortholog increased the sensitivity to herbicide, whereas overexpression reduced it. The OsbZIP88 protein was localized to the nucleus. Using ChIP coupled with high-throughput sequencing, OsbZIP88 was found to form a network regulatory center with other TFs such as bZIP20/52/59 to regulate OsKS1, OsCOE1, and OsIM1, which are related to auxin, abscisic acid, brassinosteroids, and gibberellic acid. Based on these results, we have established a database of bZIP TFs corresponding to herbicide stress, and resolved the mechanisms of the positive regulation of herbicide resistance by bZIP88, thereby providing new insights for NTSR.

Genome-Wide Identification and Salt Stress Response Analysis of the bZIP Transcription Factor Family in Sugar Beet

As one of the largest transcription factor families in plants, bZIP transcription factors play important regulatory roles in different biological processes, especially in the process of stress response. Salt stress inhibits the growth and yield of sugar beet. However, bZIP-related studies in sugar beet (Beta vulgaris L.) have not been reported. This study aimed to identify the bZIP transcription factors in sugar beet and analyze their biological functions and response patterns to salt stress. Using bioinformatics, 48 BvbZIP genes were identified in the genome of sugar beet, encoding 77 proteins with large structural differences. Collinearity analysis showed that three pairs of BvbZIP genes were fragment replication genes. The BvbZIP genes were grouped according to the phylogenetic tree topology and conserved structures, and the results are consistent with those reported in Arabidopsis. Under salt stress, the expression levels of most BvbZIP genes were decreased, and only eight genes were up-regulated. GO analysis showed that the BvbZIP genes were mainly negatively regulated in stress response. Protein interaction prediction showed that the BvbZIP genes were mainly involved in light signaling and ABA signal transduction, and also played a certain role in stress responses. In this study, the structures and biological functions of the BvbZIP genes were analyzed to provide foundational data for further mechanistic studies and for facilitating the efforts toward the molecular breeding of stress-resilient sugar beet.

Phosphorylation of OsTGA5 by casein kinase II compromises its suppression of defense-related gene transcription in rice

Plants manage the high cost of immunity activation by suppressing the expression of defense genes during normal growth and rapidly switching them on upon pathogen invasion. TGAs are key transcription factors controlling the expression of defense genes. However, how TGAs function, especially in monocot plants like rice with continuously high levels of endogenous salicylic acid (SA) remains elusive. In this study, we characterized the role of OsTGA5 as a negative regulator of rice resistance against blast fungus by transcriptionally repressing the expression of various defense-related genes. Moreover, OsTGA5 repressed PTI responses and the accumulation of endogenous SA. Importantly, we showed that the nucleus-localized casein kinase II (CK2) complex interacts with and phosphorylates OsTGA5 on Ser-32, which reduces the affinity of OsTGA5 for the JIOsPR10 promoter, thereby alleviating the repression of JIOsPR10 transcription and increasing rice resistance. Furthermore, the in vivo phosphorylation of OsTGA5 Ser-32 was enhanced by blast fungus infection. The CK2 α subunit, depending on its kinase activity, positively regulated rice defense against blast fungus. Taken together, our results provide a mechanism for the role of OsTGA5 in negatively regulating the transcription of defense-related genes in rice and the repressive switch imposed by nuclear CK2-mediated phosphorylation during blast fungus invasion.

Integration of eQTL Analysis and GWAS Highlights Regulation Networks in Cotton under Stress Condition

The genus Gossypium is one of the most economically important crops in the world. Here, we used RNA-seq to quantify gene expression in a collection of G. arboreum seedlings and performed eGWAS on 28,382 expressed genes. We identified a total of 30,089 eQTLs in 10,485 genes, of which >90% were trans-regulate target genes. Using luciferase assays, we confirmed that different cis-eQTL haplotypes could affect promoter activity. We found ~6600 genes associated with ~1300 eQTL hotspots. Moreover, hotspot 309 regulates the expression of 325 genes with roles in stem length, fresh weight, seed germination rate, and genes related to cell wall biosynthesis and salt stress. Transcriptome-wide association study (TWAS) identified 19 candidate genes associated with the cotton growth and salt stress response. The variation in gene expression across the population played an essential role in population differentiation. Only a small number of the differentially expressed genes between South China, the Yangtze River region, and the Yellow River region sites were located in different chromosomal regions. The eQTLs found across the duplicated gene pairs showed conservative cis- or trans- regulation and that the expression levels of gene pairs were correlated. This study provides new insights into the evolution of gene expression regulation in cotton, and identifies eQTLs in stress-related genes for use in breeding improved cotton varieties.

Genome-Wide Identification and Functional Analysis of the bZIP Transcription Factor Family in Rice Bakanae Disease Pathogen, Fusarium fujikuroi

Fungal basic leucine zipper (bZIP) proteins play a vital role in biological processes such as growth, biotic/abiotic stress responses, nutrient utilization, and invasion. In this study, genome-wide identification of bZIP genes in the fungus Fusarium fujikuroi, the pathogen of bakanae disease, was carried out. Forty-four genes encoding bZIP transcription factors (TFs) from the genome of F. fujikuroi (FfbZIP) were identified and functionally characterized. Structures, domains, and phylogenetic relationships of the sequences were analyzed by bioinformatic approaches. Based on the phylogenetic relationships with the FfbZIP proteins of eight other fungi, the bZIP genes can be divided into six groups (A–F). The additional conserved motifs have been identified and their possible functions were predicted. To analyze functions of the bZIP genes, 11 FfbZIPs were selected according to different motifs they contained and were knocked out by genetic recombination. Results of the characteristic studies revealed that these FfbZIPs were involved in oxygen stress, osmotic stress, cell wall selection pressure, cellulose utilization, cell wall penetration, and pathogenicity. In conclusion, this study enhanced understandings of the evolution and regulatory mechanism of the FfbZIPs in fungal growth, abiotic/biotic stress resistance, and pathogenicity, which could be the reference for other fungal bZIP studies.

The bZIP Transcription Factor Family in Adzuki Bean (Vigna Angularis): Genome-Wide Identification, Evolution, and Expression Under Abiotic Stress During the Bud Stage

Adzuki bean (Vigna angularis) is an important dietary legume crop that was first cultivated and domesticated in Asia. Currently, little is known concerning the evolution and expression patterns of the basic leucine zipper (bZIP) family transcription factors in the adzuki bean. Through the PFAM search, 72 bZIP members of adzuki bean (VabZIP) were identified from the reference genome. Most of them were located on 11 chromosomes and seven on an unknown chromosome. A comprehensive analysis, including evolutionary, motifs, gene structure, cis-elements, and collinearity was performed to identify VabZIP members. The subcellular localization results showed VabZIPs might locate on the nuclear. Quantitative real-time PCR (qRT-PCR) analysis of the relative expression of VabZIPs in different tissues at the bud stage revealed that VabZIPs had a tissue-specific expression pattern, and its expression was influenced by abiotic stress. These characteristics of VabZIPs provide insights for future research aimed at developing interventions to improve abiotic stress resistance.

Genome-wide identification and expression analysis of the bZIP transcription factor family genes in response to abiotic stress in Nicotiana tabacum L

BACKGROUND

The basic leucine zipper (bZIP) transcription factor (TF) is one of the largest families of transcription factors (TFs). It is widely distributed and highly conserved in animals, plants, and microorganisms. Previous studies have shown that the bZIP TF family is involved in plant growth, development, and stress responses. The bZIP family has been studied in many plants; however, there is little research on the bZIP gene family in tobacco.

RESULTS

In this study, 77 bZIPs were identified in tobacco and named NtbZIP01 through to NtbZIP77. These 77 genes were then divided into eleven subfamilies according to their homology with Arabidopsis thaliana. NtbZIPs were unevenly distributed across twenty-two tobacco chromosomes, and we found sixteen pairs of segmental duplication. We further studied the collinearity between these genes and related genes of six other species. Quantitative real-time polymerase chain reaction analysis identified that expression patterns of bZIPs differed, including in different organs and under various abiotic stresses. NtbZIP49 might be important in the development of flowers and fruits; NtbZIP18 might be an important regulator in abiotic stress.

CONCLUSIONS

In this study, the structures and functions of the bZIP family in tobacco were systematically explored. Many bZIPs may play vital roles in the regulation of organ development, growth, and responses to abiotic stresses. This research has great significance for the functional characterisation of the tobacco bZIP family and our understanding of the bZIP family in higher plants.

CabZIP23 Integrates in CabZIP63-CaWRKY40 Cascade and Turns CabZIP63 on Mounting Pepper Immunity against Ralstonia solanacearum via Physical Interaction

CabZIP63 and CaWRKY40 were previously found to be shared in the pepper defense response to high temperature stress (HTS) and to Ralstonia solanacearum inoculation (RSI), forming a transcriptional cascade. However, how they activate the two distinct defense responses is not fully understood. Herein, using a revised genetic approach, we functionally characterized CabZIP23 in the CabZIP63-CaWRKY40 cascade and its context specific pepper immunity activation against RSI by interaction with CabZIP63. CabZIP23 was originally found by immunoprecipitation-mass spectrometry to be an interacting protein of CabZIP63-GFP; it was upregulated by RSI and acted positively in pepper immunity against RSI by virus induced gene silencing in pepper plants, and transient overexpression in Nicotiana benthamiana plants. By chromatin immunoprecipitation (ChIP)-qPCR and electrophoresis mobility shift assay (EMSA), CabZIP23 was found to be directly regulated by CaWRKY40, and CabZIP63 was directly regulated by CabZIP23, forming a positive feedback loop. CabZIP23-CabZIP63 interaction was confirmed by co-immunoprecipitation (CoIP) and bimolecular fluorescent complimentary (BiFC) assays, which promoted CabZIP63 binding immunity related target genes, including CaPR1, CaNPR1 and CaWRKY40, thereby enhancing pepper immunity against RSI, but not affecting the expression of thermotolerance related CaHSP24. All these data appear to show that CabZIP23 integrates in the CabZIP63-CaWRKY40 cascade and the context specifically turns it on mounting pepper immunity against RSI.

Global N6-Methyladenosine Profiling Revealed the Tissue-Specific Epitranscriptomic Regulation of Rice Responses to Salt Stress

N⁶-methyladenosine (m⁶A) methylation represents a new layer of the epitranscriptomic regulation of plant development and growth. However, the effects of m⁶A on rice responses to environmental stimuli remain unclear. In this study, we performed a methylated-RNA immunoprecipitation sequencing analysis and compared the changes in m⁶A methylation and gene expression in rice under salt stress conditions. Salt stress significantly increased the m⁶A methylation in the shoots (p value < 0.05). Additionally, 2537 and 2304 differential m⁶A sites within 2134 and 1997 genes were identified in the shoots and roots, respectively, under salt stress and control conditions. These differential m⁶A sites were largely regulated in a tissue-specific manner. A unique set of genes encoding transcription factors, antioxidants, and auxin-responsive proteins had increased or decreased m⁶A methylation levels only in the shoots or roots under salt stress, implying m⁶A may mediate salt tolerance by regulating transcription, ROS homeostasis, and auxin signaling in a tissue-specific manner. Integrating analyses of m⁶A modifications and gene expression changes revealed that m⁶A changes regulate the expression of genes controlling plant growth, stress responses, and ion transport under saline conditions. These findings may help clarify the regulatory effects of m⁶A modifications on rice salt tolerance.

OsRLCK160 contributes to flavonoid accumulation and UV-B tolerance by regulating OsbZIP48 in rice

Plants produce specialized metabolites to adapt to the ever-changing environments. Flavonoids are antioxidants essential for growth, development, and breeding with increased stress resistance in crops. However, the mechanism of the involvement of flavonoids in ultraviolet-B (UV-B) stress in rice (Oryza sativa) is largely unknown. In this study, we cloned and functionally identified a receptor-like kinase (OsRLCK160) and a bZIP transcription factor (OsbZIP48) positively regulating flavonoid accumulation through metabolite-based genome-wide association study of the flavonoid content in rice. Meanwhile, OsRLCK160 interacted with and phosphorylated OsbZIP48 to regulate the flavonoid accumulation and participate in UV-B tolerance in rice. Our study indicates the importance of applying OsRLCK160 and OsbZIP48 to advance the fundamental understanding of stable rice production and breed UV-B-tolerant rice varieties, which may contribute to breeding high-yield rice varieties.

OsABF1 Represses Gibberellin Biosynthesis to Regulate Plant Height and Seed Germination in Rice (Oryza sativa L.)

Gibberellins (GAs) are diterpenoid phytohormones regulating various aspects of plant growth and development, such as internode elongation and seed germination. Although the GA biosynthesis pathways have been identified, the transcriptional regulatory network of GA homeostasis still remains elusive. Here, we report the functional characterization of a GA-inducible OsABF1 in GA biosynthesis underpinning plant height and seed germination. Overexpression of OsABF1 produced a typical GA-deficient phenotype with semi-dwarf and retarded seed germination. Meanwhile, the phenotypes could be rescued by exogenous GA₃, suggesting that OsABF1 is a key regulator of GA homeostasis. OsABF1 could directly suppress the transcription of green revolution gene SD1, thus reducing the endogenous GA level in rice. Moreover, OsABF1 interacts with and transcriptionally antagonizes to the polycomb repression complex component OsEMF2b, whose mutant showed as similar but more severe phenotype to OsABF1 overexpression lines. It is suggested that OsABF1 recruits RRC2-mediated H3K27me3 deposition on the SD1 promoter, thus epigenetically silencing SD1 to maintain the GA homeostasis for growth and seed germination. These findings shed new insight into the functions of OsABF1 and regulatory mechanism underlying GA homeostasis in rice.

Genome-Wide Characterization and Expression Analysis of bZIP Gene Family Under Abiotic Stress in Glycyrrhiza uralensis

bZIP gene family is one of the largest transcription factor families. It plays an important role in plant growth, metabolic, and environmental response. However, complete genome-wide investigation of bZIP gene family in Glycyrrhiza uralensis remains unexplained. In this study, 66 putative bZIP genes in the genome of G. uralensis were identified. And their evolutionary classification, physicochemical properties, conserved domain, functional differentiation, and the expression level under different stress conditions were further analyzed. All the members were clustered into 13 subfamilies (A–K, M, and S). A total of 10 conserved motifs were found in GubZIP proteins. Members from the same subfamily shared highly similar gene structures and conserved domains. Tandem duplication events acted as a major driving force for the evolution of bZIP gene family in G. uralensis. Cis-acting elements and protein–protein interaction networks showed that GubZIPs in one subfamily are involved in multiple functions, while some GubZIPs from different subfamilies may share the same functional category. The miRNA network targeting GubZIPs showed that the regulation at the transcriptional level may affect protein–protein interaction networks. We suspected that domain-mediated interactions may categorize a protein family into subfamilies in G. uralensis. Furthermore, the tissue-specific gene expression patterns of GubZIPs were analyzed using the public RNA-seq data. Moreover, gene expression level of 66 bZIP family members under abiotic stress treatments was quantified by using qRT-PCR. The results of this study may serve as potential candidates for functional characterization in the future.

OsRE1 interacts with OsRIP1 to regulate rice heading date by finely modulating Ehd1 expression

Heading date is a key agronomic trait affecting crop yield. In rice, Early heading date 1 (Ehd1) is an important B-type response regulator in determination of heading date. Although many regulatory factors of Ehd1 expression have been functionally characterized, the direct regulators of Ehd1 largely remain to be identified. Here, we identified a new regulator of Ehd1, OsRE1, that directly binds to the A-box motif in the Ehd1 promoter. Osre1 confers an early heading phenotype due to elevated expression levels of Ehd1. OsRE1 is a nucleus-localized bZIP transcription factor with a diurnal rhythmic expression pattern. Furthermore, we identified an OsRE1-interacting protein, OsRIP1, and demonstrated that OsRIP1 can repress the transcript expression of Ehd1 in an OsRE1-dependent manner. Our genetic data showed that OsRE1 and OsRIP1 may function upstream of Ehd1 in regulating heading date. Together, our results suggest that OsRE1 functions cooperatively with OsRIP1 to regulate heading date through finely modulating the expression of Ehd1. In addition, OsRE1 and OsRIP1 are two minor heading date regulators, which are more desirable for fine-tuning heading date to improve rice regional adaptability.

Natural Genetic Resources from Diverse Plants to Improve Abiotic Stress Tolerance in Plants

The current agricultural system is biased for the yield increase at the cost of biodiversity. However, due to the loss of precious genetic diversity during domestication and artificial selection, modern cultivars have lost the adaptability to cope with unfavorable environments. There are many reports on variations such as single nucleotide polymorphisms (SNPs) and indels in the stress-tolerant gene alleles that are associated with higher stress tolerance in wild progenitors, natural accessions, and extremophiles in comparison with domesticated crops or model plants. Therefore, to gain a better understanding of stress-tolerant traits in naturally stress-resistant plants, more comparative studies between the modern crops/model plants and crop progenitors/natural accessions/extremophiles are required. In this review, we discussed and summarized recent progress on natural variations associated with enhanced abiotic stress tolerance in various plants. By applying the recent biotechniques such as the CRISPR/Cas9 gene editing tool, natural genetic resources (i.e., stress-tolerant gene alleles) from diverse plants could be introduced to the modern crop in a non-genetically modified way to improve stress-tolerant traits.

Drought-induced AtbZIP62 transcription factor regulates drought stress response in Arabidopsis

We investigated the role of AtbZIP62, an uncharacterized Arabidopsis bZIP TF, in oxidative, nitro-oxidative and drought stress conditions using reverse genetics approach. We further monitored the expression of AtPYD1 gene (orthologous to rice OsDHODH1 involved in the pyrimidine biosynthesis) in atbzip62 knock-out (KO) plants in order to investigate the transcriptional interplay of AtbZIP62 and AtPYD1. The atbzip62 KO plants showed significant increase in shoot length under oxidative stress, while no significant difference was recorded for root length compared to WT. However, under nitro-oxidative stress conditions, atbzip62 showed differential response to both NO-donors. Further characterization of AtbZIP62 under drought conditions showed that both atbzip62 and atpyd1-2 showed a sensitive phenotype to drought stress, and could not recover after re-watering. Transcript accumulation of AtbZIP62 and AtPYD1 showed that both were highly up-regulated by drought stress in wild type (WT) plants. Interestingly, AtPYD1 transcriptional level significantly decreased in atbzip62 exposed to drought stress. However, AtbZIP62 expression was highly induced in atpyd1-2 under the same conditions. Both AtbZIP62 and AtPYD1 were up-regulated in atnced3 and atcat2 while showing a contrasting expression pattern in atgsnor1-3. The recorded increase in CAT, POD, and PPO-like activities, the accumulation of chlorophylls and total carotenoids, and the enhanced proline and malondialdehyde levels would explain the sensitivity level of atbzip62 towards drought stress. All results collectively suggest that AtbZIP62 could be involved in AtPYD1 transcriptional regulation while modulating cellular redox state and photosynthetic processes. In addition, AtbZIP62 is suggested to positively regulate drought stress response in Arabidopsis.

CaASR1 promotes salicylic acid- but represses jasmonic acid-dependent signaling to enhance the resistance of Capsicum annuum to bacterial wilt by modulating CabZIP63

CabZIP63 acts positively in the resistance of pepper (Capsicum annuum) to bacterial wilt caused by Ralstonia solanacearum or tolerance to high-temperature/high-humidity stress, but it is unclear how CabZIP63 achieves its functional specificity against R. solanacearum. Here, CaASR1, an abscisic acid-, stress-, and ripening-inducible protein of C. annuum, was functionally characterized in modulating the functional specificity of CabZIP63 during the defense response of pepper to R. solanacearum. In pepper plants inoculated with R. solanacearum, CaASR1 was up-regulated before 24 h post-inoculation but down-regulated thereafter, and was down-regulated by high-temperature/high-humidity stress. Data from gene silencing and transient overexpression experiments indicated that CaASR1 acts as a positive regulator in the immunity of pepper against R. solanacearum and a negative regulator of thermotolerance. Pull-down combined with mass spectrometry revealed that CaASR1 interacted with CabZIP63 upon R. solanacearum infection; the interaction was confirmed by microscale thermophoresis and bimolecular fluorescence complementation assays.CaASR1 silencing upon R. solanacearum inoculation repressed CabZIP63-mediated transcription from the promoters of the salicylic acid (SA)-dependent CaPR1 and CaNPR1, but derepressed transcription of CaHSP24 and the jasmonic acid (JA)-dependent CaDEF1. Our findings suggest that CaASR1 acts as a positive regulator of the defense response of pepper to R. solanacearum by interacting with CabZIP63, enabling it to promote SA-dependent but repress JA-dependent immunity and thermotolerance during the early stages of infection.

ABA-responsive transcription factor bZIP1 is involved in modulating biosynthesis of phenolic acids and tanshinones in Salvia miltiorrhiza

Phenolic acids and tanshinones are major bioactive ingredients in Salvia miltiorrhiza, which possess pharmacological activities with great market demand. However, transcriptional regulation of phenolic acid and tanshinone biosynthesis remains poorly understood. Here, a basic leucine zipper transcription factor (TF) named SmbZIP1 was screened from the abscisic acid (ABA)-induced transcriptome library. Overexpression of SmbZIP1 positively promoted phenolic acid biosynthesis by enhancing expression of biosynthetic genes such as cinnamate-4-hydroxylase (C4H1). Furthermore, biochemical experiments revealed that SmbZIP1 bound the G-Box-like1 element in the promoter of the C4H1 gene. Meanwhile, SmbZIP1 inhibited accumulation of tanshinones mainly by suppressing the expression of biosynthetic genes including geranylgeranyl diphosphate synthase (GGPPS) which was confirmed as a target gene by in vitro and in vivo experiments. In contrast, the phenolic acid content was reduced and tanshinone was enhanced in CRISPR/Cas9 [clustered regularly interspaced palindromic repeats (CRISPR)/CRISPR-associated protein 9]-mediated knockout lines. In addition, the previously reported positive regulator of tanshinone biosynthesis, SmERF1L1, was found to be inhibited in SmbZIP1 overexpression lines indicated by RNA sequencing, and was proven to be the target of SmbZIP1. In summary, this work uncovers a novel regulator and deepens our understanding of the transcriptional and regulatory mechanisms of phenolic acid and tanshinone biosynthesis, and also sheds new light on metabolic engineering in S. miltiorrhiza.

RNA-sequencing analysis revealed genes associated drought stress responses of different durations in hexaploid sweet potato

Purple-fleshed sweet potato (PFSP) is an important food crop, as it is a rich source of nutrients and anthocyanin pigments. Drought has become a major threat to sustainable sweetpotato production, resulting in huge yield losses. Therefore, the present study was conducted to identify drought stress-responsive genes using next-generation (NGS) and third-generation sequencing (TGS) techniques. Five cDNA libraries were constructed from seedling leaf segments treated with a 30% solution of polyethylene glycol (PEG-6000) for 0, 1, 6, 12, and 48 h for second-generation sequencing. Leaf samples taken from upper third of sweet potato seedlings after 1, 6, 12, and 48 h of drought stress were used for the construction of cDNA libraries for third-generation sequencing; however, leaf samples from untreated plants were collected as controls. A total of 184,259,679 clean reads were obtained using second and third-generation sequencing and then assembled into 17,508 unigenes with an average length of 1,783 base pairs. Out of 17,508 unigenes, 642 (3.6%) unigenes failed to hit any homologs in any databases, which might be considered novel genes. A total of 2, 920, 1578, and 2,418 up-regulated unigenes and 3,834, 2,131, and 3,337 down-regulated unigenes from 1 h, 6 h, 12 h, and 48 h library were identified, respectively in drought stress versus control. In addition, after 6, 12, and 48 h of drought stress, 540 up-regulated unigenes, 486 down-regulated unigenes and 414 significantly differentially expressed unigenes were detected. It was found that several gene families including Basic Helix-loop-helix (bHLH), basic leucine zipper (bZIP), Cystein2/Histidine2 (C2H2), C3H, Ethylene-responsive transcription factor (ERF), Homo domain-leucine zipper (HD-ZIP), MYB, NAC (NAM, ATAF1/2, and CUC2), Thiol specific antioxidant and WRKY showed responses to drought stress. In total, 17,472 simple sequence repeats and 510,617 single nucleotide polymorphisms were identified based on transcriptome sequencing of the PFSP. About 96.55% of the obtained sequences are not available online in sweet potato genomics resources. Therefore, it will enrich annotated sweet potato gene sequences and enhance understanding of the mechanisms of drought tolerance through genetic manipulation. Moreover, it represents a sequence resource for genetic and genomic studies of sweet potato.

TaABI5, a wheat homolog of Arabidopsis thaliana ABA insensitive 5, controls seed germination

Abscisic acid (ABA) response element (ABRE)-binding factors (ABFs) are basic region/leucine zipper motif (bZIP) transcription factors that regulate the expression of ABA-induced genes containing ABRE in their promoters. The amino acid sequence of the wheat bZIP protein, TaABI5, showed high homology to that of Arabidopsis ABA insensitive 5 (ABI5). TaABI5 was classified into the clade of ABI5s in Arabidopsis and rice, unlike TRAB1 of rice, Wabi5 of wheat, and HvABI5 of barley in the bZIP Group A family, by a phylogenetic analysis. TaABI5 was strongly expressed in seeds during the late ripening and maturing stages; however, its expression level markedly decreased after germination. An in situ hybridization analysis showed that TaABI5 mRNA accumulated in seed embryos, particularly the scutellum. In a transient assay using wheat aleurone cells, TaABI5 activated the promoter of Em containing ABRE, which is an embryogenesis abundant protein gene, indicating that TaABI5 acts as a transcription factor in wheat seeds. Furthermore, the seeds of transgenic Arabidopsis lines introduced with 35S:TaABI5 exhibited high sensitivity to ABA and the inhibition of germination. The seed dormancy of the transgenic Arabidopsis lines was stronger than that of Col. These results support TaABI5 playing an important role in mature seeds, particularly before seed germination, and acting as a functional ortholog to Arabidopsis ABI5.

Characterization of the bZIP Transcription Factor Family in Pepper (Capsicum annuum L.): CabZIP25 Positively Modulates the Salt Tolerance

The basic leucine zipper (bZIP) proteins compose a family of transcription factors (TFs), which play a crucial role in plant growth, development, and abiotic and biotic stress responses. However, no comprehensive analysis of bZIP family has been reported in pepper (Capsicum annuum L.). In this study, we identified and characterized 60 bZIP TF-encoding genes from two pepper genomes. These genes were divided into 10 groups based on their phylogenetic relationships with bZIP genes from Arabidopsis. Six introns/exons structural patterns within the basic and hinge regions and the conserved motifs were identified among all the pepper bZIP proteins, on the basis of which, we classify them into different subfamilies. Based on the transcriptomic data of Zunla-1 genome, expression analyses of 59 pepper bZIP genes (not including CabZIP25 of CM334 genome), indicated that the pepper bZIP genes were differentially expressed in the pepper tissues and developmental stages, and many of the pepper bZIP genes might be involved in responses to various abiotic stresses and phytohormones. Further, gene expression analysis, using quantitative real-time PCR (qRT-PCR), showed that the CabZIP25 gene was expressed at relatively higher levels in vegetative tissues, and was strongly induced by abiotic stresses and phytohormones. In comparing with wild type Arabidopsis, germination rate, fresh weight, chlorophyll content, and root lengths increased in the CabZIP25-overexpressing Arabidopsis under salt stress. Additionally, CabZIP25-silenced pepper showed lower chlorophyll content than the control plants under salt stress. These results suggested that CabZIP25 improved salt tolerance in plants. Taken together, our results provide new opportunities for the functional characterization of bZIP TFs in pepper.

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.

Reversible photo-cross-linking of the GCN4 peptide containing 3-cyanovinylcarbazole amino acid to double-stranded DNA

Interaction analysis in vivo greatly promotes the analyses and understanding of biological functions. The interaction between DNA and peptides or proteins is very important in terms of readout and amplifying information from genomic DNA. In this study, we designed and synthesized a photo-cross-linkable amino acid, l-3-cyanovinlycarbazole amino acid (l-CNVA), to double-stranded DNA. Reversible photo-cross-linking between DNA and peptides containing CNVA, having 3-cyanovinylcarbazole moieties capable of photo-cross-linking to nucleic acids, was demonstrated. As a result, it was shown that the GCN4 peptide, containing CNVA, can be photo-cross-linked to DNA, and its adduct was photo-split into the original peptide and DNA with 312 nm-irradiation. This is the first report that reversibly manipulates photo-crosslinking between double stranded DNA and peptides. In addition, this reversible photo-cross-linking, using l-CNVA, is faster and with higher yield than that using diazirine and psoralen.

Variations in the Structure and Evolution of Rice WRKY Genes in Indica and Japonica Genotypes and their Co-expression Network in Mediating Disease Resistance

WRKY transcription factor (TF) family regulates many functions in plant growth and development and also during biotic and abiotic stress. In this study, 101 WRKY TF gene models in indica and japonica rice were used to conduct evolutionary analysis, gene structure analysis, and motif composition. Co-expression analysis was carried out first by selecting the differentially expressing genes that showed a significant change in response to the pathogens from Rice Oligonucleotide Array Database (ROAD). About 82 genes showed responses to infection by Magnaporthe oryzae or Xanthomonas oryzae pv. oryzae. Co-expression gene network was constructed using direct neighborhood and context associated inbuilt mode in RiceNetv2 tool. Only 41 genes showed interaction with 2299 non-WRKY genes. Variations exist in the structure and evolution of WRKY genes among indica and japonica genotypes which have important implications in their differential roles including disease resistance. WRKY genes mediate a complex networking and co-express along with other WRKY and non-WRKY genes to mediate resistance against fungal and bacterial pathogens in rice.

Transcription factors–DNA interactions in rice: identification and verification

The completion of the rice genome sequence paved the way for rice functional genomics research. Additionally, the functional characterization of transcription factors is currently a popular and crucial objective among researchers. Transcription factors are one of the groups of proteins that bind to either enhancer or promoter regions of genes to regulate expression. On the basis of several typical examples of transcription factor analyses, we herein summarize selected research strategies and methods and introduce their advantages and disadvantages. This review may provide some theoretical and technical guidelines for future investigations of transcription factors, which may be helpful to develop new rice varieties with ideal traits.

Transcriptional regulation of Lonicera japonica Thunb. during flower development as revealed by comprehensive analysis of transcription factors

BACKGROUND

Lonicera japonica Thunb. flower has been used for the treatment of various diseases for a long time and attracted many studies on its potential effects. Transcription factors (TFs) regulate extensive biological processes during plant development. As the restricted reports of L. japonica on TFs, our work was carried out to better understand the TFs' regulatory roles under different developmental stages in L. japonica.

RESULTS

In this study, 1316 TFs belonging to 52 families were identified from the transcriptomic data, and corresponding expression profiles during the L. japonica flower development were comprehensively analyzed. 917 (69.68%) TFs were differentially expressed. TFs in bHLH, ERF, MYB, bZIP, and NAC families exhibited obviously altered expression during flower growth. Based on the analysis of differentially expressed TFs (DETFs), TFs in MYB, WRKY, NAC and LSD families that involved in phenylpropanoids biosynthesis, senescence processes and antioxidant activity were detected. The expression of MYB114 exhibited a positive correlation with the contents of luteoloside; Positive correlation was observed among the expression of MYC12, chalcone synthase (CHS) and flavonol synthase (FLS), while negative correlation was observed between the expression of MYB44 and the synthases; The expression of LSD1 was highly correlated with the expression of SOD and the total antioxidant capacity, while the expression of LOL1 and LOL2 exhibited a negative correlation with them; Many TFs in NAC and WRKY families may be potentially involved in the senescence process regulated by hormones and reactive oxygen species (ROS). The expression of NAC19, NAC29, and NAC53 exhibited a positive correlation with the contents of ABA and H₂O₂, while the expression of WRKY53, WRKY54, and WRKY70 exhibited a negative correlation with the contents of JA, SA and ABA.

CONCLUSIONS

Our study provided a comprehensive characterization of the expression profiles of TFs during the developmental stages of L. japonica. In addition, we detected the key TFs that may play significant roles in controlling active components biosynthesis, antioxidant activity and flower senescence in L. japonica, thereby providing valuable insights into the molecular networks underlying L. japonica flower development.

OsbZIP42 is a positive regulator of ABA signaling and confers drought tolerance to rice

OsbZIP42 is a positive regulator of ABA signaling and drought stress tolerance. The activation of OsbZIP42 depends on stress-/ABA-activated protein kinase 4 (SAPK4) and an additional ABA-dependent modification of OsbZIP42. Basic leucine zipper transcription factors (bZIP TFs) play important roles in the ABA signaling pathway in plants. Rice OsbZIP42 is a member of the group E bZIP, which is an ortholog of Arabidopsis group A bZIP. This latter group includes abscisic acid-responsive element (ABRE)-binding factors (ABFs) involved in abiotic stress tolerance. The expression of OsbZIP42 was induced by ABA treatment, although it was not induced by drought and salt stresses. Unlike other bZIP TFs, OsbZIP42 contained two transcriptional activation domains. Although the full-length OsbZIP42 protein did not, the N-terminus of the protein interacted with SAPK4. Our results suggest that the activation of OsbZIP42 by SAPK4 requires another ABA-dependent modification of OsbZIP42. Transgenic rice overexpressing OsbZIP42 (OsbZIP42-OX) exhibited a rapidly elevated expression of the ABA-responsive LEA3 and Rab16 genes and was hypersensitive to ABA. Analyses of the OsbZIP42-OX plants revealed enhanced tolerance to drought stress. These results suggest that OsbZIP42 is a positive regulator of ABA signaling and drought stress tolerance depending on its activation, which is followed by an additional ABA-dependent modification. We propose that OsbZIP42 is an important player in rice for conferring ABA-dependent drought tolerance.

Genome-wide Association Study of a Panel of Vietnamese Rice Landraces Reveals New QTLs for Tolerance to Water Deficit During the Vegetative Phase

BACKGROUND

Drought tolerance is a major challenge in breeding rice for unfavorable environments. In this study, we used a panel of 180 Vietnamese rice landraces genotyped with 21,623 single-nucleotide polymorphism markers to perform a genome-wide association study (GWAS) for different drought response and recovery traits during the vegetative stage. These landraces originate from different geographical locations and are adapted to different agrosystems characterized by contrasted water regimes. Vietnamese landraces are often underrepresented in international panels used for GWAS, but they can contain original genetic determinants related to drought resistance.

RESULTS

The panel of 180 rice varieties was phenotyped under greenhouse conditions for several drought-related traits in an experimental design with 3 replicates. Plants were grown in pots for 4 weeks and drought-stressed by stopping irrigation for an additional 4 weeks. Drought sensitivity scores and leaf relative water content were measured throughout the drought stress. The recovery capacity was measured 2 weeks after plant rewatering. Several QTLs associated with these drought tolerance traits were identified by GWAS using a mixed model with control of structure and kinship. The number of detected QTLs consisted of 14 for leaf relative water content, 9 for slope of relative water content, 12 for drought sensitivity score, 3 for recovery ability and 1 for relative crop growth rate. This set of 39 QTLs actually corresponded to a total of 17 different QTLs because 9 were simultaneously associated with two or more traits, which indicates that these common loci may have pleiotropic effects on drought-related traits. No QTL was found in association with the same traits in both the indica and japonica subpanels. The possible candidate genes underlying the quantitative trait loci are reviewed.

CONCLUSIONS

Some of the identified QTLs contain promising candidate genes with a function related to drought tolerance by osmotic stress adjustment.

Insights from the crystal structure of the chicken CREB3 bZIP suggest that members of the CREB3 subfamily transcription factors may be activated in response to oxidative stress

cAMP response element binding Protein 3 (CREB3) is an endoplasmic reticulum (ER) membrane‐bound transcription factor, which belongs to the basic leucine zipper (bZIP) superfamily of eukaryotic transcription factors. CREB3 plays a role in the ER‐stress induced unfolded protein response (UPR) and is a multifunctional cellular factor implicated in a number of biological processes including cell proliferation and migration, tumor suppression, and immune‐related gene expression. To gain structural insights into the transcription factor, we determined the crystal structure of the conserved bZIP domain of chicken CREB3 (chCREB3) to a resolution of 3.95 Å. The X‐ray structure provides evidence that chCREB3 can form a stable homodimer. The chCREB3 bZIP has a structured, pre‐formed DNA binding region, even in the absence of DNA, a feature that could potentially enhance both the DNA binding specificity and affinity of chCREB3. Significantly, the homodimeric bZIP possesses an intermolecular disulfide bond that connects equivalent cysteine residues of the parallel helices in the leucine zipper region. This disulfide bond in the hydrophobic core of the bZIP may increase the stability of the homodimer under oxidizing conditions. Moreover, sequence alignment of bZIP sequences from chicken, human, and mouse reveals that only members of the CREB3 subfamily contain this cysteine residue, indicating that it could act as a redox‐sensor. Taken together, these results suggest that the activity of these transcription factors may be redox‐regulated and they may be activated in response to oxidative stress.

PDB Code(s): 6IAK

Whole genome deep sequencing revealed host impact on population structure, variation and evolution of Rice stripe virus

High-throughput deep sequencing and variant detection showed that variations of Rice stripe virus (RSV) populations obtained from small brown planthopper-transmitted rice plants and sap-inoculated N. benthamiana plants were single nucleotide polymorphisms (SNPs) and insertion-deletions (InDels). The SNPs were more uniform across RSV genome, but InDels occurred mainly in the intergenic regions (IRs) and in the 5' or 3' noncoding regions. There were no clear patterns of InDels, although the inserted sequences were all from virus itself. Six, one, and one non-synonymous substitutions were respectively observed in the RdRP ORF, IR and the movement protein ORF. These non-synonymous substitutions were found to be stable, resulting in new consensus sequences in the NBL11 RSV population. Furthermore, the numbers of SNPs and InDels in RSV genome from N. benthamiana plants were much higher than that from O. sativa plants. These differences are likely caused by selection pressures generated by different host plants.

Identification and expression analysis of genes with pathogen-inducible cis-regulatory elements in the promoter regions in Oryza sativa

BACKGROUND

Complex co-regulatory networks in plants may elicit responses during pathogen infections. A number of genes are activated when these responses take place. Identification of these genes would shed new light on understanding the mechanisms of rice response to pathogen infections and the elucidation of crosstalk among diverse signaling networks in rice disease resistance/susceptibility.

RESULTS

Here we report the identification of genes with pathogen-inducible cis-regulatory elements (PICEs) (AS-1, G-box, GCC-box, and H-box) in the promoter regions in rice. Our results showed that a set of 882 rice genes contained these four elements in their promoter regions. Of these genes, 190 encode disease resistance/susceptibility related proteins, and 70 encode transcription factors. Analyses of the available microarray data demonstrated that 357 transcripts were differentially expressed after pathogen infections. 48 out of 53 differentially expressed transcription factors are up-regulated or down-regulated by more than 1.1-fold in response to pathogen infections. Analyses of the public mRNA-Seq data showed that 327 transcripts were differently expressed after pathogen infections. A total of 100 up-regulated genes and 37 down-regulated genes were found in common between the microarray and mRNA-Seq data.

CONCLUSIONS

We report here a set of rice genes that contain the four PICEs, i.e., AS-1, G-box, GCC-box, and H-box, in their promoter regions, of which, 53.5% were up- or down-regulated when pathogens attack. The PICEs in the gene promoters are critical for rice response to pathogen infections. They are also useful markers for identification of rice genes involved in response to pathogen infections.

Early selection of bZIP73 facilitated adaptation of japonica rice to cold climates

Cold stress is a major factor limiting production and geographic distribution of rice (Oryza sativa). Although the growth range of japonica subspecies has expanded northward compared to modern wild rice (O. rufipogon), the molecular basis of the adaptation remains unclear. Here we report bZIP73, a bZIP transcription factor-coding gene with only one functional polymorphism (+511 G>A) between the two subspecies japonica and indica, may have facilitated japonica adaptation to cold climates. We show the japonica version of bZIP73 (bZIP73^Jap) interacts with bZIP71 and modulates ABA levels and ROS homeostasis. Evolutionary and population genetic analyses suggest bZIP73 has undergone balancing selection; the bZIP73^Jap allele has firstly selected from standing variations in wild rice and likely facilitated cold climate adaptation during initial japonica domestication, while the indica allele bZIP73^Ind was subsequently selected for reasons that remain unclear. Our findings reveal early selection of bZIP73^Jap may have facilitated climate adaptation of primitive rice germplasms.

Japonica rice can grow further north than wild or indica rice and is more tolerant of cold climates. Here, the authors show that bZIP73 likely underwent selection in the early phase of rice domestication to facilitate cold tolerance in japonica by modulating ABA and ROS homeostasis.