Basic leucine zipper (bZIP) transcription factors involved in abiotic stresses: A molecular model of a wheat bZIP factor and implications of its structure in function

Genomic characterization of bZIP gene family and patterns of gene regulation on Cercospora beticola Sacc resistance in sugar beet (Beta vulgaris L.)

Sugar beet (Beta vulgaris L.) is one of the most important sugar crops, accounting for nearly 30% of the world's annual sugar production. And it is mainly distributed in the northwestern, northern, and northeastern regions of China. However, Cercospora leaf spot (CLS) is the most serious and destructive foliar disease during the cultivation of sugar beet. In plants, the bZIP gene family is one of important family of transcription factors that regulate many biological processes, including cell and tissue differentiation, pathogen defense, light response, and abiotic stress signaling. Although the bZIP gene family has been mentioned in previous studies as playing a crucial role in plant defense against diseases, there has been no comprehensive study or functional analysis of the bZIP gene family in sugar beet with respect to biotic stresses. In this study, we performed a genome-wide analysis of bZIP family genes (BvbZIPs) in sugar beet to investigate their phylogenetic relationships, gene structure and chromosomal localization. At the same time, we observed the stomatal and cell ultrastructure of sugar beet leaf surface during the period of infestation by Cercospora beticola Sacc (C. beticola). And identified the genes with significant differential expression in the bZIP gene family of sugar beet by qRT-PCR. Finally we determined the concentrations of SA and JA and verified the associated genes by qRT-PCR. The results showed that 48 genes were identified and gene expression analysis indicated that 6 BvbZIPs were significantly differential expressed in C. beticola infection. It is speculated that these BvbZIPs are candidate genes for regulating the response of sugar beet to CLS infection. Meanwhile, the observation stomata of sugar beet leaves infected with C. beticola revealed that there were also differences in the surface stomata of the leaves at different periods of infection. In addition, we further confirmed that the protein encoded by the SA signaling pathway-related gene BVRB_9g222570 in high-resistant varieties was PR1, which is closely related to systemic acquired resistance. One of the protein interaction modes of JA signal transduction pathway is the response of MYC2 transcription factor caused by JAZ protein degradation, and there is a molecular interaction between JA signal transduction pathway and auxin. Despite previous reports on abiotic stresses in sugar beet, this study provides very useful information for further research on the role of the sugar beet bZIP gene family in sugar beet through experiments. The above research findings can promote the development of sugar beet disease resistance breeding.

Genome-wide identification and expression analysis of calmodulin and calmodulin-like genes in passion fruit (Passiflora edulis) and their involvement in flower and fruit development

BACKGROUND

The calmodulin (CaM) and calmodulin-like (CML) proteins play regulatory roles in plant growth and development, responses to biotic and abiotic stresses, and other biological processes. As a popular fruit and ornamental crop, it is important to explore the regulatory mechanism of flower and fruit development of passion fruit.

RESULTS

In this study, 32 PeCaM/PeCML genes were identified from passion fruit genome and were divided into 9 groups based on phylogenetic analysis. The structural analysis, including conserved motifs, gene structure and homologous modeling, illustrates that the PeCaM/PeCML in the same subgroup have relative conserved structural features. Collinearity analysis suggested that the expansion of the CaM/CML gene family likely took place mainly by segmental duplication, and the whole genome replication events were closely related with the rapid expansion of the gene group. PeCaM/PeCMLs were potentially required for different floral tissues development. Significantly, PeCML26 had extremely high expression levels during ovule and fruit development compared with other PeCML genes, suggesting that PeCML26 had potential functions involved in the development of passion fruit flowers and fruits. The co-presence of various cis-elements associated with growth and development, hormone responsiveness, and stress responsiveness in the promoter regions of these PeCaM/PeCMLs might contribute to their diverse regulatory roles. Furthermore, PeCaM/PeCMLs were also induced by various abiotic stresses. This work provides a comprehensive understanding of the CaM/CML gene family and valuable clues for future studies on the function and evolution of CaM/CML genes in passion fruit.

CONCLUSION

A total of 32 PeCaM/PeCML genes were divided into 9 groups. The PeCaM/PeCML genes showed differential expression patterns in floral tissues at different development stages. It is worth noting that PeCML26, which is highly homologous to AtCaM2, not only interacts with multiple BBR-BPC TFs, but also has high expression levels during ovule and fruit development, suggesting that PeCML26 had potential functions involved in the development of passion fruit flowers and fruits. This research lays the foundation for future investigations and validation of the potential function of PeCaM/PeCML genes in the growth and development of passion fruit.

Functional Identification of Malus halliana MhbZIP23 Gene Demonstrates That It Enhances Saline-Alkali Stress Tolerance in Arabidopsis thaliana

Saline-alkali stress is a significant abiotic stress that restricts plant growth globally. Basic region leucine zipper (bZIP) transcription factor proteins are widely involved in plants in response to abiotic stress such as saline-alkali stress. Based on transcriptome and quantitative real-time PCR (qRT-PCR), we found that the MhbZIP23 gene could respond to saline-alkali stress. Despite this discovery, the underlying mechanism by which the MhbZIP23 transcription factor responds to saline-alkaline stress remains unexplored. To address this gap in knowledge, we successfully cloned the MhbZIP23 (MD05G1121500) gene from Malus halliana for heterologous expression in Arabidopsis thaliana, facilitating the investigation of its functional role in stress response. Compared to the wild type (WT), Arabidopsis plants demonstrated enhanced growth and a lower degree of wilting when subjected to saline-alkali stress. Furthermore, several physiological indices of the plants altered under such stress conditions. The transgenic Arabidopsis plants (OE-5, 6, and 8), which grew normally, exhibited a higher chlorophyll content and had greater root length in comparison to the control check (CK). MhbZIP23 effectively regulated the levels of the osmoregulatory substance proline (Pro), enhanced the activities of antioxidant enzymes such as peroxidase (POD) and superoxide dismutase (SOD), and reduced the levels of malondialdehyde (MDA) and relative conductivity (REC). These actions improved the ability of plant cells in transgenic Arabidopsis to counteract ROS, as evidenced by the decreased accumulation of O2- and hydrogen peroxide (H2O2). In summary, the MhbZIP23 gene demonstrated effectiveness in alleviating saline-alkali stress in M. halliana, presenting itself as an outstanding resistance gene for apples to combat saline-alkali stress.

Genome-Wide Identification of the TGA Gene Family and Expression Analysis under Drought Stress in Brassica napus L

TGA transcription factors belong to Group D of the bZIP transcription factors family and play vital roles in the stress response of plants. Brassica napus is an oil crop with rich economic value. However, a systematic analysis of TGA gene family members in B. napus has not yet been reported. In this study, we identified 39 full-length TGA genes in B. napus, renamed TGA1~TGA39. Thirty-nine BnTGA genes were distributed on 18 chromosomes, mainly located in the nucleus, and differences were observed in their 3D structures. Phylogenetic analysis showed that 39 BnTGA genes could be divided into five groups. The BnTGA genes in the same group had similar structure and motif compositions, and all the BnTGA genes had the same conserved bZIP and DOG1 domains. Phylogenetic and synteny analysis showed that the BnTGA genes had a close genetic relationship with the TGA genes of the Brassica juncea, and BnTGA11 and BnTGA29 may play an important role in evolution. In addition, qRT-PCR revealed that three genes (BnTGA14/17/23) showed significant changes in eight experimental materials after drought treatment. Meanwhile, it can be inferred from the results of drought treatment on different varieties of rapeseed that the stress tolerance of parental rapeseed can be transmitted to the offspring through hybridization. In short, these findings have promoted the understanding of the B. napus TGA gene family and will contribute to future research aimed at B. napus resistant breeding.

An Accurate Representation of the Number of bZIP Transcription Factors in the Triticum aestivum (Wheat) Genome and the Regulation of Functional Genes during Salt Stress

Climate change is dramatically increasing the overall area of saline soils around the world, which is increasing by approximately two million hectares each year. Soil salinity decreases crop yields and, thereby, makes farming less profitable, potentially causing increased poverty and hunger in many areas. A solution to this problem is increasing the salt tolerance of crop plants. Transcription factors (TFs) within crop plants represent a key to understanding salt tolerance, as these proteins play important roles in the regulation of functional genes linked to salt stress. The basic leucine zipper (bZIP) TF has a well-documented role in the regulation of salt tolerance. To better understand how bZIP TFs are linked to salt tolerance, we performed a genome-wide analysis in wheat using the Chinese spring wheat genome, which has been assembled by the International Wheat Genome Sequencing Consortium. We identified 89 additional bZIP gene sequences, which brings the total of bZIP gene sequences in wheat to 237. The majority of these 237 sequences included a single bZIP protein domain; however, different combinations of five other domains also exist. The bZIP proteins are divided into ten subfamily groups. Using an in silico analysis, we identified five bZIP genes (ABF2, ABF4, ABI5, EMBP1, and VIP1) that were involved in regulating salt stress. By scrutinizing the binding properties to the 2000 bp upstream region, we identified putative functional genes under the regulation of these TFs. Expression analyses of plant tissue that had been treated with or without 100 mM NaCl revealed variable patterns between the TFs and functional genes. For example, an increased expression of ABF4 was correlated with an increased expression of the corresponding functional genes in both root and shoot tissues, whereas VIP1 downregulation in root tissues strongly decreased the expression of two functional genes. Identifying strategies to sustain the expression of the functional genes described in this study could enhance wheat's salt tolerance.

Genome-wide analysis of bZIP transcription factors and their expression patterns in response to methyl jasmonate and low-temperature stresses in Platycodon grandiflorus

Background

Platycodon grandiflorus belongs to the genus Platycodon and has many pharmacological effects, such as expectorant, antitussive, and anti-tumor properties. Among transcription factor families peculiar to eukaryotes, the basic leucine zipper (bZIP) family is one of the most important, which exists widely in plants and participates in many biological processes, such as plant growth, development, and stress responses. However, genomic analysis of the bZIP gene family and related stress response genes has not yet been reported in P. grandiflorus.

Methods

P. grandiflorus bZIP (PgbZIP) genes were first identified here, and the phylogenetic relationships and conserved motifs in the PgbZIPs were also performed. Meanwhile, gene structures, conserved domains, and the possible protein subcellular localizations of these PgbZIPs were characterized. Most importantly, the cis-regulatory elements and expression patterns of selected genes exposed to two different stresses were analyzed to provide further information on PgbZIPs potential biological roles in P. grandiflorus upon exposure to environmental stresses.

Conclusions

Forty-six PgbZIPs were identified in P. grandiflorus and divided into nine groups, as displayed in the phylogenetic tree. The results of the chromosomal location and the collinearity analysis showed that forty-six PgbZIP genes were distributed on eight chromosomes, with one tandem duplication event and eleven segmental duplication events identified. Most PgbZIPs in the same phylogenetic group have similar conserved motifs, domains, and gene structures. There are cis-regulatory elements related to the methyl jasmonate (MeJA) response, low-temperature response, abscisic acid response, auxin response, and gibberellin response. Ten PgbZIP genes were selected to study their expression patterns upon exposure to low-temperature and MeJA treatments, and all ten genes responded to these stresses. The real-time quantitative polymerase chain reaction (RT-qPCR) results suggest that the expression levels of most PgbZIPs decreased significantly within 6 h and then gradually increased to normal or above normal levels over the 90 h following MeJA treatment. The expression levels of all PgbZIPs were significantly reduced after 3 h of the low-temperature treatment. These results reveal the characteristics of the PgbZIP family genes and provide valuable information for improving P. grandiflorus's ability to cope with environmental stresses during growth and development.

Thaumatin-like Proteins in Legumes: Functions and Potential Applications-A Review

Thaumatin-like proteins (TLPs) comprise a complex and evolutionarily conserved protein family that participates in host defense and several developmental processes in plants, fungi, and animals. Importantly, TLPs are plant host defense proteins that belong to pathogenesis-related family 5 (PR-5), and growing evidence has demonstrated that they are involved in resistance to a variety of fungal diseases in many crop plants, particularly legumes. Nonetheless, the roles and underlying mechanisms of the TLP family in legumes remain unclear. The present review summarizes recent advances related to the classification, structure, and host resistance of legume TLPs to biotic and abiotic stresses; analyzes and predicts possible protein-protein interactions; and presents their roles in phytohormone response, root nodule formation, and symbiosis. The characteristics of TLPs provide them with broad prospects for plant breeding and other uses. Searching for legume TLP genetic resources and functional genes, and further research on their precise function mechanisms are necessary.

PhbZIP2 regulates photosynthesis-related genes in an intertidal macroalgae, Pyropia haitanensis, under stress

Intertidal macroalgae are important research subjects in stress biology. Basic region-leucine zipper transcription factors (bZIPs) play an important regulatory role in the expression of target genes under abiotic stress. We herein identified a bZIP2 gene PhbZIP2 to regulate abiotic stress tolerance in Pyropia haitanensis, a representative intertidal macroalgal species. Cloning and sequencing of the cDNA characterized a BRLZ structure and an α coiled-coil structure between amino acids and Expression of PhbZIP2 was detected to upregulate under both high temperature and salt stresses. A DAP-seq analysis revealed the PhbZIP2-binding motifs of (T/C)TCCA(C/G) and A (A/G)AAA (G/A), which differed from the conserved motifs in plants. Overexpression of PhbZIP2 was indicative of a high temperature and salt stress tolerances in transgenic Chlamydomonas reinhardtii. It was suggested that PhbZIP2 was probably involved in regulating expression of the photosynthetic-related genes and the response to the abiotic stresses in P. haitanensis, which provide new insights for elucidating efficient adaptation strategies of intertidal macroalgae.

"Genome-wide identification of bZIP gene family in Pearl millet and transcriptional profiling under abiotic stress, phytohormonal treatments; and functional characterization of PgbZIP9"

Abiotic stresses are major constraints in crop production, and are accountable for more than half of the total crop loss. Plants overcome these environmental stresses using coordinated activities of transcription factors and phytohormones. Pearl millet an important C4 cereal plant having high nutritional value and climate resilient features is grown in marginal lands of Africa and South-East Asia including India. Among several transcription factors, the basic leucine zipper (bZIP) is an important TF family associated with diverse biological functions in plants. In this study, we have identified 98 bZIP family members (PgbZIP) in pearl millet. Phylogenetic analysis divided these PgbZIP genes into twelve groups (A-I, S, U and X). Motif analysis has shown that all the PgbZIP proteins possess conserved bZIP domains and the exon-intron organization revealed conserved structural features among the identified genes. Cis-element analysis, RNA-seq data analysis, and real-time expression analysis of PgbZIP genes suggested the potential role of selected PgbZIP genes in growth/development and abiotic stress responses in pearl millet. Expression profiling of selected PgbZIPs under various phytohormones (ABA, SA and MeJA) treatment showed differential expression patterns of PgbZIP genes. Further, PgbZIP9, a homolog of AtABI5 was found to localize in the nucleus and modulate gene expression in pearl millet under stresses. Our present findings provide a better understanding of bZIP genes in pearl millet and lay a good foundation for the further functional characterization of multi-stress tolerant PgbZIP genes, which could become efficient tools for crop improvement.

A Molecular Orchestration of Plant Translation under Abiotic Stress

The complexities of translational strategies make this stage of implementing genetic information one of the most challenging to comprehend and, simultaneously, perhaps the most engaging. It is evident that this diverse range of strategies results not only from a long evolutionary history, but is also of paramount importance for refining gene expression and metabolic modulation. This notion is particularly accurate for organisms that predominantly exhibit biochemical and physiological reactions with a lack of behavioural ones. Plants are a group of organisms that exhibit such features. Addressing unfavourable environmental conditions plays a pivotal role in plant physiology. This is particularly evident with the changing conditions of global warming and the irrevocable loss or depletion of natural ecosystems. In conceptual terms, the plant response to abiotic stress comprises a set of elaborate and intricate strategies. This is influenced by a range of abiotic factors that cause stressful conditions, and molecular genetic mechanisms that fine-tune metabolic pathways allowing the plant organism to overcome non-standard and non-optimal conditions. This review aims to focus on the current state of the art in the field of translational regulation in plants under abiotic stress conditions. Different regulatory elements and patterns are being assessed chronologically. We deem it important to focus on significant high-performance techniques for studying the genetic information dynamics during the translation phase.

Comparative transcriptome analysis reveals key genes and coordinated mechanisms in two rice cultivars differing in cadmium accumulation

Although Cd accumulation varies among rice varieties is recognized, the underlying mechanisms are not well clarified. In this study, comparative transcriptome analysis were performed by hydroponic culture system with two rice varieties, Y1540 (high Cd accumulator) and Y15 (low Cd accumulator) under 20 μM Cd stress. Results revealed 17,320 differentially expressed genes (DEGs) in roots of Y15 (7,655 upregulated and 9,665 downregulated) and 17,386 DEGs in roots of Y1540 (8,823 upregulated and 8,563 downregulated) expose to 20 μM Cd stress. Gene ontology (GO) analysis enriched 24 and 26 terms in Y15 and Y1540 respectively, including 23 common terms. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment showed 27 and 28 significant pathways in Y15 and Y1540 respectively, with 19 common pathways. Different responses to Cd stress between cultivars were not only reflected in differently enriched GO terms and KEGG pathways but also in different DEGs of 23 common GO terms and significant sequences represented by p-values of 19 common KEGG pathways. Both cultivars resist Cd through common processes with different weights; hence glutathione metabolism, mineral absorption, biosynthesis of secondary metabolites, and degradation of aromatic compounds could be playing a more important role in Y1540, whereas ribosome biogenesis in eukaryotes, mismatch repair, aminoacyl-tRNA biosynthesis, and the cell cycle maybe playing a more important role in Y15. Weighted gene co-expression network analysis (WGCNA) showed that five and three modules were clustered in Y15 and Y1540, respectively, with yellow and brown modules in Y15 and brown modules in Y1540 being significantly related to Cd stress. Further analysis showed that most of hub genes in Y15 were related to signal transduction or transcription factors, while most of hub genes in Y1540 were related to binding, metabolic, and secondary metabolic processes, which demonstrated their different response patterns at transcriptomic level to Cd stress.

An insight into Pisum sativum HSF gene family-Genome-wide identification, phylogenetic, expression, and analysis of transactivation potential of pea heat shock transcription factor

Field pea (Pisum sativum L, 2n = 14) is a popular temperate legume with high economic value. Heat shock factors (HSFs) are the core element in the regulatory mechanism of heat stress responses. HSFs in pea (P. sativum) have not been characterized and their role remains unclear in different abiotic stresses. To address this knowledge gap, the current study aimed to characterize the HSF gene family in pea. We identified 38 PsHsf members in P. sativum, which are distributed on the seven chromosomes, and based on phylogenetic analysis, we classified them into three representative classes i.e. A, B, and C. Conserved motif and gene structure analysis confirmed a high degree of similarity among the members of the same class. Additionally, identified cis-acting regulatory elements (CAREs) related to abiotic responses, development, growth, and hormone signaling provides crucial insights into the regulatory mechanisms of PsHsfs. Our research revealed instances of gene duplication in PsHsf gene family, suggesting that this mechanism could be driving the expansion of the PsHsf gene family. Moreover, Expression analysis of PsHsfs exhibited upregulation under heat stress (HS), salt stress (SS), and drought stress (DS) showing their phenomenal role in stress conditions. PsHsfs protein interaction network suggested their involvement in stress-responsive mechanisms. Further transactivation potential was checked for spliced variant of PsHsfA2a (PsHsfA2aI, PsHsfA2aII, and PsHsfA2aIII), PsHsfA3, PsHsfA6b, PsHsfA9, PsHsfB1a, and PsHsfB2a. Overall, these findings provide valuable insight into the evolutionary relationship of PsHsf gene family and their role in abiotic stress responses.

Banana MKK1 modulates fruit ripening via the MKK1-MPK6-3/11-4-bZIP21 module

The mitogen-activated protein kinase (MAPK) cascade consisting of MKKK, MKK, and MPK plays an indispensable role in various plant physiological processes. Previously, we showed that phosphorylation of MabZIP21 by MaMPK6-3 is involved in banana fruit ripening, but the regulatory mechanism by which MKK controls banana fruit ripening remains unclear. Here, ripening-induced MaMKK1 from banana fruit is characterized, and transiently overexpressing and silencing of MaMKK1 in banana fruit accelerates and inhibits fruit ripening, respectively, possibly by influencing phosphorylation and activity of MPK. MaMKK1 interacts with and phosphorylates MaMPK6-3 and MaMPK11-4 mainly at the pTEpY residues, resulting in MPK activation. MaMPK11-4 phosphorylates MabZIP21 to elevate its transcriptional activation ability. Transgenic tomato fruit expressing MabZIP21 ripen quickly with a concomitant increase in MabZIP21 phosphorylation. Additionally, MabZIP21 activates MaMPK11-4 and MaMKK1 transcription to form a regulatory feedback loop. Collectively, here we report a regulatory pathway of the MaMPK6-3/11-4-MabZIP21 module in controlling banana fruit ripening.

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.

Identification of passion fruit HSF gene family and the functional analysis of PeHSF-C1a in response to heat and osmotic stress

Heat stress transcription factors (HSFs) are the major regulators of plant response to environmental stress, especially heat and drought stress. To gain a deeper understanding of the mechanisms underlying HSFs in the abiotic stress response of passion fruit, we conducted an in silico analysis of the HSF gene family. Through bioinformatics and phylogenetic analyses, we identified 18 PeHSF members and classified them into A, B, and C groups. Collinearity analysis results revealed that the expansion of the PeHSF gene family was due to the presence of segmental duplication. Furthermore, gene structure and protein domain analysis illustrated that PeHSFs in the same subgroup are relatively conserved. Conserved motif and function domain analysis suggested that PeHSF proteins possess typical conserved functional domains of the HSF family. A protein interaction network and 3D structure prediction were used to study the potential regulatory relationship of PeHSFs. Additionally, the subcellular localization results of PeHSF-A6a, PeHSF-B4b, and PeHSF-C1a were consistent with the predictions. RNA-seq and RT-qPCR analysis revealed the expression patterns of PeHSFs in different tissues of passion fruit floral organs. Promoter analysis and the expression patterns of the PeHSFs under different treatments demonstrated their involvement in various abiotic stress processes. Notably, overexpression of PeHSF-C1a consistently enhanced tolerance to drought and heat stress in Arabidopsis. Overall, our findings provide a scientific basis for further functional studies of PeHSFs that could contribute to improvement of passion fruit breeding.

Domain tethering impacts dimerization and DNA-mediated allostery in the human transcription factor FoxP1

Transcription factors are multidomain proteins with specific DNA binding and regulatory domains. In the human FoxP subfamily (FoxP1, FoxP2, FoxP3, and FoxP4) of transcription factors, a 90 residue-long disordered region links a Leucine Zipper (ZIP)-known to form coiled-coil dimers-and a Forkhead (FKH) domain-known to form domain swapping dimers. We used replica exchange discrete molecular dynamics simulations, single-molecule fluorescence experiments, and other biophysical tools to understand how domain tethering in FoxP1 impacts dimerization at ZIP and FKH domains and how DNA binding allosterically regulates their dimerization. We found that domain tethering promotes FoxP1 dimerization but inhibits a FKH domain-swapped structure. Furthermore, our findings indicate that the linker mediates the mutual organization and dynamics of ZIP and FKH domains, forming closed and open states with and without interdomain contacts, thus highlighting the role of the linkers in multidomain proteins. Finally, we found that DNA allosterically promotes structural changes that decrease the dimerization propensity of FoxP1. We postulate that, upon DNA binding, the interdomain linker plays a crucial role in the gene regulatory function of FoxP1.

Molecular analysis of the 14-3-3 genes in Panax ginseng and their responses to heat stress

Background

Panax Ginseng is a perennial and semi-shady herb with tremendous medicinal value. Due to its unique botanical characteristics, ginseng is vulnerable to various abiotic factors during its growth and development, especially in high temperatures. Proteins encoded by 14-3-3 genes form a highly conserved protein family that widely exists in eukaryotes. The 14-3-3 family regulates the vital movement of cells and plays an essential role in the response of plants to abiotic stresses, including high temperatures. Currently, there is no relevant research on the 14-3-3 genes of ginseng.

Methods

The identification of the ginseng 14-3-3 gene family was mainly based on ginseng genomic data and Hidden Markov Models (HMM). We used bioinformatics-related databases and tools to analyze the gene structure, physicochemical properties, cis-acting elements, gene ontology (GO), phylogenetic tree, interacting proteins, and transcription factor regulatory networks. We analyzed the transcriptome data of different ginseng tissues to clarify the expression pattern of the 14-3-3 gene family in ginseng. The expression level and modes of 14-3-3 genes under heat stress were analyzed by quantitative real-time PCR (qRT-PCR) technology to determine the genes in the 14-3-3 gene family responding to high-temperature stress.

Results

In this study, 42 14-3-3 genes were identified from the ginseng genome and renamed PgGF14-1 to PgGF14-42. Gene structure and evolutionary relationship research divided PgGF14s into epsilon (ε) and non-epsilon (non-ε) groups, mainly located in four evolutionary branches. The gene structure and motif remained highly consistent within a subgroup. The physicochemical properties and structure of the predicted PgGF14 proteins conformed to the essential characteristics of 14-3-3 proteins. RNA-seq results indicated that the detected PgGF14s existed in different organs and tissues but differed in abundance; their expression was higher in roots, stems, leaves, and fruits but lower in seeds. The analysis of GO, cis-acting elements, interacting proteins, and regulatory networks of transcription factors indicated that PgGF14s might participate in physiological processes, such as response to stress, signal transduction, material synthesis-metabolism, and cell development. The qRT-PCR results indicated PgGF14s had multiple expression patterns under high-temperature stress with different change trends in several treatment times, and 38 of them had an apparent response to high-temperature stress. Furthermore, PgGF14-5 was significantly upregulated, and PgGF14-4 was significantly downregulated in all treatment times. This research lays a foundation for further study on the function of 14-3-3 genes and provides theoretical guidance for investigating abiotic stresses in ginseng.

Insight into the bZIP gene family in Lagenaria siceraria: Genome and transcriptome analysis to understand gene diversification in Cucurbitaceae and the roles of LsbZIP gene expression and function under cold stress

The basic leucine zipper (bZIP) as a well-known transcription factor family, figures prominently in diverse biological and developmental processes and response to abiotic/biotic stresses. However, no knowledge of the bZIP family is available for the important edible Cucurbitaceae crop bottle gourd. Herein, we identified 65 putative LsbZIP genes and characterized their gene structure, phylogenetic and orthologous relationships, gene expression profiles in different tissues and cultivars, and responsive genes under cold stress. The phylogenetic tree of 16 released Cucurbitaceae plant genomes revealed the evolutionary convergence and divergence of bZIP family. Based on the specific domains, LsbZIP family were classified into 12 clades (A-K, S) with similar motifs and exon-intron distribution. 65 LsbZIP genes have undergone 19 segmental and two tandem duplication events with purifying selection. The expression profiling of LsbZIP genes showed tissue-specific but no cultivar-specific pattern. The cold stress-responsive candidate LsbZIP genes were analyzed and validated by RNA-Seq and RT-PCR, providing new insights of transcriptional regulation of bZIP family genes in bottle gourd and their potential functions in cold-tolerant variety breeding.

Characterization and expression analysis of basic leucine zipper (bZIP) transcription factors responsive to chilling injury in peach fruit

BACKGROUND

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.

METHODS AND RESULTS

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.

CONCLUSIONS

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.

TcbZIP60 positively regulates pyrethrins biosynthesis in Tanacetum cinerariifolium

Pyrethrins, synthesized in the perennial plant Tanacetum cinerariifolium, are a class of terpene mixtures with high insecticidal activity and low human toxicity, which are widely used in plant-derived pesticides. Numerous studies have identified multiple pyrethrins biosynthesis enzymes, which can be enhanced by exogenous hormones such as methyl jasmonate (MeJA). However, the mechanism by which hormone signaling regulates pyrethrins biosynthesis and the potential involvement of certain transcription factors (TFs) remain unclear. In this study, we found that the expression level of a TF in T. cinerariifolium was significantly increased after treatment with plant hormones (MeJA, abscisic acid). Subsequent analysis identified this TF as a member of the basic region/leucine zipper (bZIP) family and was thus named TcbZIP60. TcbZIP60 was localized in the nucleus, suggesting that it is involved in the transcription process. The expression profiles of TcbZIP60 were similar to those of pyrethrins synthesis genes in different flower organs and at different flowering stages. Furthermore, TcbZIP60 could directly bind to the E-box/G-box motifs in the promoters of the pyrethrins synthesis genes TcCHS and TcAOC to activate their expression. Transient overexpression of TcbZIP60 increased the expression levels of pyrethrins biosynthesis genes, leading to the significant accumulation of pyrethrins. Silencing of TcbZIP60 significantly downregulated pyrethrins accumulation and the expression of related genes. Overall, our results reveal a novel TF, TcbZIP60, that regulates both the terpenoid and jasmonic acid pathways of pyrethrins biosynthesis in T. cinerariifolium.

Conserved and divergent evolution of the bZIP transcription factor in five diploid Gossypium species

495 bZIP members with 12 subfamilies were identified in the five diploid cottons. Segmental duplication events in cotton ancestor might have led to primary expansion of the cotton bZIP members. The basic leucine zipper (bZIP) transcription factor is one of the largest and most diverse families in plants. The evolutionary history of the bZIP family is still unclear in cotton. In this study, a total of 495 bZIP members were identified in five diploid Gossypium species, including 100 members in Gossypium arboreum, 104 members in Gossypium herbaceum, 95 members in Gossypium raimondii, 96 members in Gossypium longicalyx, and 100 members in Gossypium turneri. The bZIP members could be divided into 12 subfamilies with biased gene proportions, gene structures, conserved motifs, expansion rates, gene loss rates, and cis-regulatory elements. A total of 239 duplication events were identified in the five Gossypium species, and mainly occurred in their common ancestor. Furthermore, some GabZIPs and GhebZIPs could be regarded as important candidates in cotton breeding. The bZIP members had a conserved and divergent evolution in the five diploid Gossypium species. The current study laid an important foundation on the evolutionary history of the bZIP family in cotton.

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 of the TGA gene family in kiwifruit (Actinidia chinensis spp.) and revealing its roles in response to Pseudomonas syringae pv. actinidiae (Psa) infection

Kiwifruit bacterial canker, caused by Pseudomonas syringae pv. actinidiae (Psa), is a destructive disease of kiwifruit worldwide. Functional genes in response to Psa infection are needed, as they could be utilized to control disease. TGACG-binding transcription factor (TGA), as an essential regulator, involved in the process of plant against pathogens. However, the function of TGA regulators has not been reported in kiwifruit. It is unclear that whether TGA genes play a role in response to Psa infection. Here, we performed genome-wide screening and identified 13 TGA genes in kiwifruit. Phylogenetic analysis showed that 13 members of the AcTGA gene family could be divided into five groups. AcTGA proteins were mainly located in the nucleus, and significant differences were identified in their 3D structures. Segmental duplications promoted the expansion of the AcTGA family. Additionally, RNA-Seq and qRT-PCR revealed that four genes (AcTGA01/06/07/09) were tissue-specific and responsive to hormones at different levels. Subcellular localization showed that four proteins located in the nucleus, and among them, three (AcTGA01/06/07) had transcriptional activation activity. Lastly, transient overexpression proved that these three genes (AcTGA01/06/07) potentially played a role in the resistance to kiwifruit canker. These results provided a theoretical basis for revealing TGA involved in kiwifruit regulation against Psa.

Genome-wide Association Study for Yield and Yield-Related Traits in Diverse Blackgram Panel (Vigna mungo L. Hepper) Reveals Novel Putative Alleles for Future Breeding Programs

Blackgram (Vigna mungo L. Hepper) is an important tropical and sub-tropical short-duration legume that is rich in dietary protein and micronutrients. Producing high-yielding blackgram varieties is hampered by insufficient genetic variability, absence of suitable ideotypes, low harvest index and susceptibility to biotic-abiotic stresses. Seed yield, a complex trait resulting from the expression and interaction of multiple genes, necessitates the evaluation of diverse germplasm for the identification of novel yield contributing traits. Henceforth, a panel of 100 blackgram genotypes was evaluated at two locations (Ludhiana and Gurdaspur) across two seasons (Spring 2019 and Spring 2020) for 14 different yield related traits. A wide range of variability, high broad-sense heritability and a high correlation of grain yield were observed for 12 out of 14 traits studied among all environments. Investigation of population structure in the panel using a set of 4,623 filtered SNPs led to identification of four sub-populations based on ad-hoc delta K and Cross entropy value. Using Farm CPU model and Mixed Linear Model algorithms, a total of 49 significant SNP associations representing 42 QTLs were identified. Allelic effects were found to be statistically significant at 37 out of 42 QTLs and 50 known candidate genes were identified in 24 of QTLs.

Systemic effects of Tuber melanosporum inoculation in two Corylus avellana genotypes

Roots of the European hazelnut (Corylus avellana L.), i.e., one of the most economically important nut species, form symbiosis with ectomycorrhizal (ECM) fungi, including truffles. Although physical interactions only occur in roots, the presence of mycorrhizal fungi can lead to metabolic changes at a systemic level, i.e., in leaves. However, how root colonization by ECM fungi modifies these processes in the host plant has so far not been widely studied. This work aimed to investigate the response in two C. avellana genotypes, focusing on leaves from plants inoculated with the black truffle Tuber melanosporum Vittad. Transcriptomic profiles of leaves of colonized plants were compared with those of non-colonized plants, as well as sugar and polyphenolic content. Results suggested that T. melanosporum has the potential to support plants in stressed conditions, leading to the systemic regulation of several genes involved in signaling and defense responses. Although further confirmation is needed, our results open new perspectives for future research aimed to highlight novel aspects in ECM symbiosis.

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

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

Methyl-CpG binding proteins (MBD) family evolution and conservation in plants

DNA methylation is an epigenetic mechanism that acts on cytosine residues. The methyl-CpG-binding domain proteins (MBD) are involved in the recognition of methyl-cytosines by activating a signaling cascade that induces the formation of heterochromatin or euchromatin, thereby regulating gene expression. In this study, we analyzed the evolution and conservation of MBD proteins in plants. First, we performed a genome-wide identification and analysis of the MBD family in common bean and soybean, since they have experienced one and two whole-genome duplication events, respectively. We found one pair of MBD paralogs in soybean (GmMBD2) has subfunctionalized after their recent divergence, which was corroborated with their expression profile. Phylogenetic analysis revealed that classes of MBD proteins clustered with human MBD. Interestingly, the MBD9 may have emerged after the hexaploidization event in eudicots. We found that plants and humans share a great similarity in MBDs' binding affinity in the mCpG context. MBD2 and MBD4 from different plant species have the conserved four amino acid residues -Arg (R), Asp (D), Tyr (Y) and Arg (R)- reported to be responsible for MBD-binding in the mCpG. However, MBD8, MBD9, MBD10, and MBD11 underwent substitutions in these residues, suggesting the non-interaction in the mCpG context, but a heterochromatin association as MBD5 and MBD6 from human. This study represents the first genome-wide analysis of the MBD gene family in eurosids I - soybean and common bean. The data presented here contribute towards understanding the evolution of MBDs proteins in plants and their specific binding affinity on mCpG site.

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.

The co-modulation of RAV transcription factors in ROS burst and extensive transcriptional reprogramming underlies disease resistance in cassava

MeRAVs positively regulate ROS burst and the expression of downstream disease resistance-related genes, which underlie improved disease resistance to Xam. Cassava (Manihot esculenta Crantz) is an important food crop and energy crop, but its yield is seriously affected by cassava bacterial blight (CBB) caused by Xanthomonas axonopodis pv. manihotis (Xam). Related to ABI3/VP1 (RAV) transcription factor family belongs to the APETALA2/Ethylene-Responsive Factor (AP2/ERF) family, which plays an important role in plant growth, development and response to biotic and abiotic stresses. In this study, we found that MeRAVs positively co-regulates the resistance to Xam and stimulates the innate immune response by regulating reactive oxygen species (ROS) burst in cassava. Dual-luciferase assay showed that seven MeRAVs exhibited transcriptional activate activity by binding CAACA motif and CACCTG motif. A large number of differentially expressed genes (DEGs) were identified through RNA-seq analysis of MeRAVs-silenced lines, and the DEGs co-regulated by seven MeRAVs accounted for more than 45% of the total DEGs. In addition, seven MeRAVs positively regulate expression of disease resistance-related genes through directly binding to their promoters. In summary, MeRAVs co-regulate ROS burst and the expression of downstream disease resistance-related genes, which underlie improved disease resistance to Xam.

Genome-Wide Identification and Expression Analysis of the Basic Leucine Zipper (bZIP) Transcription Factor Gene Family in Fusarium graminearum

The basic leucine zipper (bZIP) is a widely found transcription factor family that plays regulatory roles in a variety of cellular processes including cell growth and development and various stress responses. However, the bZIP gene family has not been well studied at a genome-wide scale in Fusarium graminearum (Fg), a potent pathogen of cereal grains. In the present study, we conducted a genome-wide identification, characterization, and expression profiling of 22 F. graminearum bZIP (FgbZIP) genes at different developmental stages and under various abiotic stresses. All identified FgbZIPs were categorized into nine groups based on their sequence similarity and phylogenetic tree analysis. Furthermore, the gene structure analysis, conserved motif analysis, chromosomal localization, protein network studies, and synteny analysis were performed. The symmetry of the exon and intron varied with the phylogenetic groups. The post-translational modifications (PTMs) analysis also predicted several phosphorylation sites in FgbZIPs, indicating their functional diversity in cellular processes. The evolutionary study identified many orthogroups among eight species and also predicted several gene duplication events in F. graminearum. The protein modeling indicated the presence of a higher number of α-helices and random coils in their structures. The expression patterns of FgbZIP genes showed that 5 FgbZIP genes, including FgbZIP_1.1, FgbZIP_1.3, FgbZIP_2.6 FgbZIP_3.1 and FgbZIP_4.3, had high expression at different growth and conidiogenesis stages. Similarly, eight genes including FgbZIP_1.1, FgbZIP_1.6, FgbZIP_2.3, FgbZIP_2.4, FgbZIP_4.1, FgbZIP_4.2, FgbZIP_4.3 and FgbZIP_4.6 demonstrated their putative role in response to various abiotic stresses. In summary, these results provided basic information regarding FgbZIPs which are helpful for further functional analysis.

Genome-wide identification and expression analysis of bZIP transcription factors in oil palm (Elaeis guineensis Jacq.) under abiotic stress

The bZIP transcription factors are well-known transcription regulators and play a key role in regulating various developmental, biological processes, and stress responses in plants. However, information on bZIP transcription factors is not yet available in oil palm, an important oil yielding crop. The present study identified the 97 bZIP transcription factor family members in oil palm genome via a genome-wide approach. Phylogenetic analysis clustered all EgbZIPs into 12 clusters with Arabidopsis and rice bZIPs. EgbZIP gene structure analysis showed a distinct variation in the intron-exon organization among all EgbZIPs. Conserved motif analysis demonstrated the occurrence of ten additional conserved motifs besides having a common bZIP domain. All the identified 97 EgbZIPs were unevenly distributed on 16 chromosomes and exhibited tandem duplication in oil palm genome. Our results aslo demonstrated that tissue-specific expression patterns of EgbZIPs based on the available transcriptome data of six different tissue of oil palm. Stress-responsive expression analysis showed that 11EgbZIP transcription factors were highly expressed under cold, salinity, drought stress conditions. Taken together, our findings will provide insightful information on bZIP transcription factors as one of the stress-responsive regulators in oil palm.

Approaches Involved in the Vegetable Crops Salt Stress Tolerance Improvement: Present Status and Way Ahead

Salt stress is one of the most important abiotic stresses as it persists throughout the plant life cycle. The productivity of crops is prominently affected by soil salinization due to faulty agricultural practices, increasing human activities, and natural processes. Approximately 10% of the total land area (950 Mha) and 50% of the total irrigated area (230 Mha) in the world are under salt stress. As a consequence, an annual loss of 12 billion US$ is estimated because of reduction in agriculture production inflicted by salt stress. The severity of salt stress will increase in the upcoming years with the increasing world population, and hence the forced use of poor-quality soil and irrigation water. Unfortunately, majority of the vegetable crops, such as bean, carrot, celery, eggplant, lettuce, muskmelon, okra, pea, pepper, potato, spinach, and tomato, have very low salinity threshold (ECt, which ranged from 1 to 2.5 dS m-1 in saturated soil). These crops used almost every part of the world and lakes' novel salt tolerance gene within their gene pool. Salt stress severely affects the yield and quality of these crops. To resolve this issue, novel genes governing salt tolerance under extreme salt stress were identified and transferred to the vegetable crops. The vegetable improvement for salt tolerance will require not only the yield influencing trait but also target those characters or traits that directly influence the salt stress to the crop developmental stage. Genetic engineering and grafting is the potential tool which can improve salt tolerance in vegetable crop regardless of species barriers. In the present review, an updated detail of the various physio-biochemical and molecular aspects involved in salt stress have been explored.

S1-bZIP Transcription Factors Play Important Roles in the Regulation of Fruit Quality and Stress Response

Sugar metabolism not only determines fruit sweetness and quality but also acts as signaling molecules to substantially connect with other primary metabolic processes and, therefore, modulates plant growth and development, fruit ripening, and stress response. The basic region/leucine zipper motif (bZIP) transcription factor family is ubiquitous in eukaryotes and plays a diverse array of biological functions in plants. Among the bZIP family members, the smallest bZIP subgroup, S1-bZIP, is a unique one, due to the conserved upstream open reading frames (uORFs) in the 5' leader region of their mRNA. The translated small peptides from these uORFs are suggested to mediate Sucrose-Induced Repression of Translation (SIRT), an important mechanism to maintain sucrose homeostasis in plants. Here, we review recent research on the evolution, sequence features, and biological functions of this bZIP subgroup. S1-bZIPs play important roles in fruit quality, abiotic and biotic stress responses, plant growth and development, and other metabolite biosynthesis by acting as signaling hubs through dimerization with the subgroup C-bZIPs and other cofactors like SnRK1 to coordinate the expression of downstream genes. Direction for further research and genetic engineering of S1-bZIPs in plants is suggested for the improvement of quality and safety traits of fruit.

Genome-wide identification and expression analysis of the bZIP transcription factors, and functional analysis in response to drought and cold stresses in pear (Pyrus breschneideri)

BACKGROUND

Transcription factors (TFs) are involved in many important biological processes, including cell stretching, histological differentiation, metabolic activity, seed storage, gene regulation, and response to abiotic and biotic stresses. Little is known about the functions, evolutionary history, and expression patterns of basic region-leucine zipper TF family genes in pear, despite the release of the genome of Chinese white pears ("Dangshansuli").

RESULTS

Overall, 92 bZIP genes were identified in the pear genome (Pyrus breschneideri). Of these, 83 were randomly distributed on all 17 chromosomes except chromosome 4, and the other 9 genes were located on loose scaffolding. The genes were divided into 14 subgroups. Whole-genome duplications, dispersed duplication, and purifying selection for whole-genome duplications are the main reasons for the expansion of the PbrbZIP gene family. The analysis of functional annotation enrichment indicated that most of the functions of PbrbZIP genes were enriched in Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathways involved in the abiotic stress response. Next, expression analysis and virus-induced gene silencing results indicated that PbrbZIP genes might play critical roles in response to drought and cold stresses, especially for the genes from subgroups A, C, G, I, and S.

CONCLUSIONS

Ninety-two PbrbZIP genes were identified from the pear genome and classified into 14 subgroups. PbrbZIP genes were mainly expanded from whole-genome duplications and dispersed duplications and retained by purifying selection. PbrbZIP genes were induced by cold and drought stresses and played important roles in drought and cold tolerance. These results provided useful information for further increasing the tolerance of pears to stresses and a foundation to study the cold and drought tolerance mechanism of PbrbZIP genes.

Identifying the genetic control of salinity tolerance in the bread wheat landrace Mocho de Espiga Branca

Salinity tolerance in bread wheat is frequently reported to be associated with low leaf sodium (Na+) concentrations. However, the Portuguese landrace, Mocho de Espiga Branca, accumulates significantly higher leaf Na+ but has comparable salinity tolerance to commercial bread wheat cultivars. To determine the genetic loci associated with the salinity tolerance of this landrace, an F2 mapping population was developed by crossing Mocho de Espiga Branca with the Australian cultivar Gladius. The population was phenotyped for 19 salinity tolerance subtraits using both non-destructive and destructive techniques. Genotyping was performed using genotyping-by-sequencing (GBS). Genomic regions associated with salinity tolerance were detected on chromosomes 1A, 1D, 4B and 5A for the subtraits of relative and absolute growth rate (RGR, AGR respectively), and on chromosome 2A, 2B, 4D and 5D for Na+, potassium (K+) and chloride (Cl-) accumulation. Candidate genes that encode proteins associated with salinity tolerance were identified within the loci including Na+/H+ antiporters, K+ channels, H+-ATPase, calcineurin B-like proteins (CBLs), CBL-interacting protein kinases (CIPKs), calcium dependent protein kinases (CDPKs) and calcium-transporting ATPase. This study provides a new insight into the genetic control of salinity tolerance in a Na+ accumulating bread wheat to assist with the future development of salt tolerant cultivars.

Two FD homologs from London plane (Platanus acerifolia) are associated with floral initiation and flower morphology

The flowering-time gene FD encodes a bZIP transcription factor that interacts with FLOWERING LOCUS T (FT) to induce flowering in Arabidopsis. Previous research has identified two FT homologs of Platanus acerifolia, PaFT and PaFTL, which each have different expression patterns and are involved in diverse developmental processes. However, it is not known whether such FT/FD complexes participate in the flowering processes in P. acerifolia. Therefore, we isolated two closely related FD homologs, PaFDL1 and PaFDL2, and investigated their functions through the analysis of expression profiles, transgenic phenotypes, their interactions with different FT proteins, and potential cis-regulatory elements in their promoters. The PaFDL genes were found to display their maximal expression levels during the stage of floral transition, and subsequent expression patterns were also seen to be related to inflorescence developmental stage. In addition, both PaFDL1 and PaFDL2 were found to be subject to post-transcriptional alternative splicing, each gene producing two transcript forms. Transgenic tobacco overexpressing each of the four resulting transcript types displayed accelerated floral initiation and produced abnormal flowers. The results suggested that the complete PaFDL proteins may interact with different PaFT/PaFTL proteins in order to fulfill both conservative and diverse functions in floral initiation and floral development.

Plant Transcription Factors Involved in Drought and Associated Stresses

Transcription factors (TFs) play a significant role in signal transduction networks spanning the perception of a stress signal and the expression of corresponding stress-responsive genes. TFs are multi-functional proteins that may simultaneously control numerous pathways during stresses in plants-this makes them powerful tools for the manipulation of regulatory and stress-responsive pathways. In recent years, the structure-function relationships of numerous plant TFs involved in drought and associated stresses have been defined, which prompted devising practical strategies for engineering plants with enhanced stress tolerance. Vast data have emerged on purposely basic leucine zipper (bZIP), WRKY, homeodomain-leucine zipper (HD-Zip), myeloblastoma (MYB), drought-response elements binding proteins/C-repeat binding factor (DREB/CBF), shine (SHN), and wax production-like (WXPL) TFs that reflect the understanding of their 3D structure and how the structure relates to function. Consequently, this information is useful in the tailored design of variant TFs that enhances our understanding of their functional states, such as oligomerization, post-translational modification patterns, protein-protein interactions, and their abilities to recognize downstream target DNA sequences. Here, we report on the progress of TFs based on their interaction pathway participation in stress-responsive networks, and pinpoint strategies and applications for crops and the impact of these strategies for improving plant stress tolerance.

Transcription Factor ChbZIP1 from Alkaliphilic Microalgae Chlorella sp. BLD Enhancing Alkaline Tolerance in Transgenic Arabidopsis thaliana

Saline-alkali soil has become an important environmental problem for crop productivity. One of the most effective approaches is to cultivate new stress-tolerant plants through genetic engineering. Through RNA-seq analysis and RT-PCR validation, a novel bZIP transcription factor ChbZIP1, which is significantly upregulated at alkali conditions, was obtained from alkaliphilic microalgae Chlorella sp. BLD. Overexpression of ChbZIP1 in Saccharomyces cerevisiae and Arabidopsis increased their alkali resistance, indicating ChbZIP1 may play important roles in alkali stress response. Through subcellular localization and transcriptional activation activity analyses, we found that ChbZIP1 is a nuclear-localized bZIP TF with transactivation activity to bind with the motif of G-box 2 (TGACGT). Functional analysis found that genes such as GPX1, DOX1, CAT2, and EMB, which contained G-box 2 and were associated with oxidative stress, were significantly upregulated in Arabidopsis with ChbZIP1 overexpression. The antioxidant ability was also enhanced in transgenic Arabidopsis. These results indicate that ChbZIP1 might mediate plant adaptation to alkali stress through the active oxygen detoxification pathway. Thus, ChbZIP1 may contribute to genetically improving plants’ tolerance to alkali stress.

Regulatory Network of Cotton Genes in Response to Salt, Drought and Wilt Diseases (Verticillium and Fusarium): Progress and Perspective

In environmental conditions, crop plants are extremely affected by multiple abiotic stresses including salinity, drought, heat, and cold, as well as several biotic stresses such as pests and pathogens. However, salinity, drought, and wilt diseases (e.g., Fusarium and Verticillium) are considered the most destructive environmental stresses to cotton plants. These cause severe growth interruption and yield loss of cotton. Since cotton crops are central contributors to total worldwide fiber production, and also important for oilseed crops, it is essential to improve stress tolerant cultivars to secure future sustainable crop production under adverse environments. Plants have evolved complex mechanisms to respond and acclimate to adverse stress conditions at both physiological and molecular levels. Recent progresses in molecular genetics have delivered new insights into the regulatory network system of plant genes, which generally includes defense of cell membranes and proteins, signaling cascades and transcriptional control, and ion uptake and transport and their relevant biochemical pathways and signal factors. In this review, we mainly summarize recent progress concerning several resistance-related genes of cotton plants in response to abiotic (salt and drought) and biotic (Fusarium and Verticillium wilt) stresses and classify them according to their molecular functions to better understand the genetic network. Moreover, this review proposes that studies of stress related genes will advance the security of cotton yield and production under a changing climate and that these genes should be incorporated in the development of cotton tolerant to salt, drought, and fungal wilt diseases (Verticillium and Fusarium).

Genome-wide identification and expression analysis of bZIP gene family in Carthamus tinctorius L

The basic leucine zipper (bZIP) is a widely known transcription factors family in eukaryotes. In plants, the role of bZIP proteins are crucial in various biological functions such as plant growth and development, seed maturation, response to light signal and environmental stress. To date, bZIP protein family has been comprehensively identified in Arabidopsis, castor, rice, ramie, soybean and other plant species, however, the complete genome-wide investigation of Carthamus tinctorius-bZIP family still remains unexplained. Here, we identified 52 putative bZIP genes from Carthamus tinctorius using a draft genome assembly and further analyzed their evolutionary classification, physicochemical properties, Conserved domain analysis, functional differentiation and the investigation of expression level in different tissues. Based on the common bZIP domain, CtbZIP family were clustered into 12 subfamilies renamed as (A-J, S, X), of which the X is a unique subfamily to Carthamus tinctorius. A total of 20 conserved protein motifs were found in CtbZIP proteins. The expression profiling of CtbZIP genes deciphered their tissue-specific pattern. Furthermore, the changes in CtbZIP transcript abundance suggested that their transcription regulation could be highly influenced by light intensity and hormones. Collectively, this study highlights all functional and regulatory elements of bZIP transcription factors family in Carthamus tinctorius which may serve as potential candidates for functional characterization in future.

Analysis of TabZIP15 transcription factor from Trichoderma asperellum ACCC30536 and its function under pathogenic toxin stress

The TabZIP15 gene encoding a 396 amino acid (aa) polypeptide in the fungus Trichoderma asperellum ACCC30536 was cloned and characterised. The protein includes a basic region motif (NR-x2-QR-x2-R) and has a pillar-like structure. The 25 basic region/leucine zipper transcription factors (TFs) identified in the T. asperellum genome were divided into YAP (14 TFs), ATF2 (5), GCN4 (2), Zip1 (2), BRLZ (1) and u1 (1) subfamilies based on conserved domains. T. asperellum was cultured in minimal media (MM) control, C-Hungry and N-Hungry medium (to simulate nutrient competition and interaction with pathogens, respectively), and differential expression analysis showed that 14 TabZIP genes (including TabZIP15) were significantly altered under both conditions; TabZIP23 responded strongly to N-Hungry media and TabZIP24 responded strongly to C-Hungry media. However, only YAP genes TabZIP15, TabZIP12 and TabZIP2 were significantly upregulated under both conditions, and expression levels of TabZIP15 were highest. T. asperellum was also cultured in the presence of five fungal pathogenic toxins, and RT-qPCR results showed that TabZIP15 was significantly upregulated in four of the five toxin stress conditions (MM + Rhizoctonia solani, MM + Fusarium oxysporum, MM + Alternaria alternata and MM + Cytospora chrysosperma).

Genome-Wide Identification and Expression Analysis of the Strawberry FvbZIP Gene Family and the Role of Key Gene FabZIP46 in Fruit Resistance to Gray Mold

A total of 54 FvbZIP genes were identified from the strawberry genome. These genes were found to be unevenly distributed on seven different chromosomes, and two of the genes had no matching chromosomal localization. FvbZIP genes were divided into 10 subfamilies according to protein sequence, and the structures of these genes were found to be highly conserved. Based on the bioinformatics analysis of FvbZIP genes, the expression of FabZIP genes changed during different stages of its growth and of its infection with gray mold disease. FabZIP46 was substantially upregulated, and its expression remained relatively high. FabZIP46 was cloned from cultivated strawberries by homologous cloning. The results of a transient transgenic assay revealed that the damage to the fruit tissue was markedly alleviated in strawberries overexpressing FabZIP46, with the incidence rate being substantially lower than that in the control group. By contrast, a brief silencing of FabZIP46 had the opposite effect. The results revealed that FabZIP46 played a positive role in the resistance of strawberries to Botrytis cinerea. The study findings provide valuable insights into the role of bZIP transcription factors as well as a theoretical reference for the regulation of resistance to gray mold disease in strawberry fruit.

Development and characterization of bZIP transcription factor based SSRs in wheat

Assessment of existing diversity is the key for germplasm conservation and crop improvement. Wheat (Triticum aestivum L.) is among the most important cereal crop and consumed by two billion world's populations. DNA-based markers are predominantly used for diversity characterization because they are easy to develop and not influenced by environment. Among them microsatellites (simple sequence repeats, SSRs) are most suitable due to their genome-wide distribution, hypervariability and reproducibility for their applications in diversity, genetic improvement, and molecular breeding. bZIP transcription factors play major roles in plants in light and stress signalling, seed development, and defence. A total of 846 SSRs were identified from 370 wheat cDNA sequences and a sub-set of 35 polymorphic TabZIPMS (TriticumaestivumbZIP MicroSatellites) was used for diversity and genetic structure analysis of 92 Indian wheat varieties and related species. 114 SSR variants ranging from 2 to 5 per SSR locus were detected for 35 SSRs in the varieties. Average polymorphic information content (PIC) and observed heterozygosity was found to be 0.135 and 0.838, respectively. Thirty-four SSRs showed cross-transferability into different related species. Combined Bayesian model and Jaccard's similarity based genetic clustering analysis revealed two clusters of 80 bread wheat varieties and one separate cluster of related species. In this study, a total 35 novel bZIP-derived SSRs were identified in a set 370 bZIP genes and shown high polymorphism and cross-species transferability in wheat. The findings provide resources for future utilization in genetic resource conservation, trait introgression, breeding and varietal development.

A genome-wide comparative analysis of bZIP transcription factors in G. arboreum and G. raimondii (Diploid ancestors of present-day cotton)

Basic leucine zipper motif (bZIP) transcription factors (TFs) are involved in plant growth regulation, development, and environmental stress responses. These genes have been well characterized in model plants. In current study, a genome-wide analysis of bZIP genes was performed in Gossypium raimondii and Gossypium arboreum taking Arabidopsis thaliana as a reference genome. In total, 85 members of G. raimondii and 87 members of G. arboreum were identified and designated as GrbZIPs and GabZIPs respectively. Phylogenetic analysis clustered bZIP genes into 11 subgroups (A, B, C, D, F, G, H, I, S and X). Gene structure analysis to find the intro-exon structures revealed 1-14 exons in both species. The maximum number of introns were present in subgroup G and D while genes in subgroup S were intron-less except GrbZIP78, which is a unique characteristic as compared to other groups. Results of motif analysis predicted that all three species share a common bZIP motif. A detailed comparison of bZIPs gene distribution on chromosomes has shown a diverse arrangement of genes in both cotton species. Moreover, the functional similarity with orthologs was also predicted. The findings of this study revealed close similarity in gene structure of both cotton species and diversity in gene distribution on chromosomes. This study supports the divergence of both species from the common ancestor and later diversity in gene distribution on chromosomes due to evolutionary changes. Additionally, this work will facilitate the functional characterization of bZIP genes in cotton. Outcomes of this study represent foundation research on the bZIP TFs family in cotton and as a reference for other crops.

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.

Transcription Factors Associated with Abiotic and Biotic Stress Tolerance and Their Potential for Crops Improvement

In field conditions, crops are adversely affected by a wide range of abiotic stresses including drought, cold, salt, and heat, as well as biotic stresses including pests and pathogens. These stresses can have a marked effect on crop yield. The present and future effects of climate change necessitate the improvement of crop stress tolerance. Plants have evolved sophisticated stress response strategies, and genes that encode transcription factors (TFs) that are master regulators of stress-responsive genes are excellent candidates for crop improvement. Related examples in recent studies include TF gene modulation and overexpression approaches in crop species to enhance stress tolerance. However, much remains to be discovered about the diverse plant TFs. Of the >80 TF families, only a few, such as NAC, MYB, WRKY, bZIP, and ERF/DREB, with vital roles in abiotic and biotic stress responses have been intensively studied. Moreover, although significant progress has been made in deciphering the roles of TFs in important cereal crops, fewer TF genes have been elucidated in sorghum. As a model drought-tolerant crop, sorghum research warrants further focus. This review summarizes recent progress on major TF families associated with abiotic and biotic stress tolerance and their potential for crop improvement, particularly in sorghum. Other TF families and non-coding RNAs that regulate gene expression are discussed briefly. Despite the emphasis on sorghum, numerous examples from wheat, rice, maize, and barley are included. Collectively, the aim of this review is to illustrate the potential application of TF genes for stress tolerance improvement and the engineering of resistant crops, with an emphasis on sorghum.

MaMPK2 enhances MabZIP93-mediated transcriptional activation of cell wall modifying genes during banana fruit ripening

Transcriptional regulation is an essential molecular machinery in controlling gene expression in diverse plant developmental processes including fruit ripening. This involves the interaction of transcription factors (TFs) and promoters of target genes. In banana, although a number of fruit ripening-associated TFs have been characterized, their number is relatively small. Here we identified a nuclear-localized basic leucine zipper (bZIP) TF, MabZIP93, associated with banana ripening. MabZIP93 activated cell wall modifying genes MaPL2, MaPE1, MaXTH23 and MaXGT1 by directly binding to their promoters. Transient over-expression of MabZIP93 in banana fruit resulted in the increased expression of MaPL2, MaPE1, MaXTH23 and MaXGT1. Moreover, a mitogen-activated protein kinase MaMPK2 and MabZIP93 were found to interact with MabZIP93. The interaction of MabZIP93 with MaMPK2 enhanced MabZIP93 activation of cell wall modifying genes, which was likely due to the phosphorylation of MabZIP93 mediated by MaMPK2. Overall, this study shows that MaMPK2 interacts with and phosphorylates MabZIP93 to promote MabZIP93-mediated transcriptional activation of cell wall modifying genes, thereby expanding our understanding of gene networks associated with banana fruit ripening.

Acidic residues and a predicted, highly conserved α-helix are critical for the endonuclease/strand separation functions of bacteriophage λ's TerL

Complementation, endonuclease, strand separation, and packaging assays using mutant TerL^λ 's, coupled with bioinformatic information and modeling of its endonuclease, identified five residues, D401, E408, D465, E563, and E586, as critical acidic residues of TerL^λ 's endonuclease. Studies of phage and viral TerL nucleases indicate acidic residues participate in metal ion-binding, part of a two-ion metal catalysis mechanism, where metal ion A activates a water for DNA backbone hydrolysis. Modeling places D401, D465, and E586 in locations analogous to those of the metal-binding residues of many phage and viral TerLs. Our work leads to a model of TerL^λ 's endonuclease domain where at least three acidic residues from a ~185 residue segment (D401 to E586) are near each other in the structure, forming the endonuclease catalytic center at cosN, the nicking site. DNA interactions required to bring the rotationally symmetric cosN precisely to the catalytic center are proposed to rely on an ~60 residue region that includes a conserved α-helix for dimerization. Metal ion A, positioned by TerL^λ 's acidic D401 and E586, would be placed at cosN for water activation, ensuring high accuracy for DNA backbone hydrolysis.