Genome-wide analysis of WRKY gene family in Cucumis sativus

Genome-wide identification and transcriptional expression profiles of the transcription factor WRKY in Gentiana macrophylla

Gentiana macrophylla Pall., a valuable Chinese traditional medicinal herb, exhibits notable anti-inflammatory and analgesic effects. The WRKY transcription factor plays a pivotal role in regulating development and stress responses. Although the WRKY family extensively characterized in diverse plant species, a comprehensive analysis of this gene family in G. macrophylla remains unexplored. In this study, we systematically identified 84 WRKY genes (GmWRKYs) from the G. macrophylla genome and classified them into three primary clades based on phylogenetic analysis. Further characterization of motif architectures, gene structures, chromosomal distributions, and syntenic relationships revealed conserved evolutionary patterns within this gene family. Notably, both phylogenetic evidence and whole-genome duplication (WGD) event analyses suggested that GmWRKYs originated from a common ancestor and underwent expansion through lineage-specific WGDs. RNA-seq and qRT-PCR analysis revealed that GmWRKYs had different expression patterns in different tissues of G. macrophylla. Weighted gene co-expression network analysis (WGCNA) further identified significant co-expression relationships between GmWRKYs and key genes involved in iridoid biosynthesis. Our results provide a potential theoretical basis for future investigation on the role of WRKY genes in the biosynthesis of iridoid in G. macrophylla.

Members of WRKY Group III Transcription Factors Are Important in Mite Infestation in Strawberry (Fragaria × ananassa Duch.)

Strawberry is frequently attacked by mites, which directly affects the yield and quality of this fruit species. The WRKY Group III transcription factors (TFs) play an important role in plant tolerance to biotic sources of stress, such as pathogens and insect pests. In this study, six Group III WRKY TFs (FaWRKY25, FaWRKY31, FaWRKY32, FaWRKY43, FaWRKY44, and FaWRKY45) were identified in strawberry. A phylogenetic analysis showed that the six WRKY III TFs were divided into two clades and all had a conserved WRKYGQK domain and the C-X7-C-X23-H-T-C zinc finger motif. An interaction network analysis revealed that FaWRKY44 was co-expressing with FaWRKY25 and FaWRKY45. The expression patterns showed that the WRKY Group III genes responded to plant hormones and mite infestation in strawberry. To further verify the role of FaWRKY25 in plant resistance to mites, we cloned the FaWRKY25 gene and overexpressed it in transgenic plants. An in vivo subcellular localization analysis indicated that the FaWRKY25 protein was localized in the nucleus. Fewer mites were also detected on the wild-type plants than on FaWRKY25-overexpressing transgenic plants, suggesting that FaWRKY25 negatively regulates the resistance of strawberry to mites. The present study advances our understanding on a potential target that mites use to manipulate host plant defenses.

Genome-wide investigation of WRKY gene family in Lavandula angustifolia and potential role of LaWRKY57 and LaWRKY75 in the regulation of terpenoid biosynthesis

The WRKY transcription factors are integral to plant biology, serving essential functions in growth, development, stress responses, and the control of secondary metabolism. Through the use of bioinformatics techniques, this research has effectively characterized 207 members of the WRKY family (LaWRKY) present in the entire genome of Lavandula angustifolia. Phylogenetic analysis classified LaWRKYs into three distinct categories based on conserved domains. Collinearity analysis revealed tandem repeats, segmental duplications, and whole genome duplications in LaWRKYs, especially for segmental duplication playing a significant role in gene family expansion. LaWRKYs displayed distinct tissue-specific expression profiles across six different tissues of L. angustifolia. Particularly noteworthy were 12 genes exhibiting high expression in flower buds and calyx, the primary sites of volatile terpenoid production, indicating their potential role in terpenoid biosynthesis in L. angustifolia. RT-qPCR analysis revealed a notable increase in the expression levels of most examined LaWRKY genes in flower buds in response to both intense light and low-temperature conditions, whereas the majority of these genes in leaves were primarily induced by drought stress. However, all genes exhibited downregulation following GA treatment in both flower buds and leaves. Overexpression of LaWRKY57 (La13G01665) and LaWRKY75 (La16G00030) in tobacco led to a reduction in the density of glandular trichomes on leaf surfaces, resulting in changes to the volatile terpenoid composition in the leaves. Specifically, the content of Neophytadiene was significantly elevated compared to wild-type tobacco, while compounds such as eucalyptol, cis-3-Hexenyl iso-butyrate, and D-Limonene were produced, which were absent in the wild type. These findings provide a valuable reference for future investigations into the biological functions of the WRKY gene family in L. angustifolia.

Unlocking nature's secrets: The pivotal role of WRKY transcription factors in plant flowering and fruit development

The WRKY transcription factor family is a key player in the regulatory mechanisms of flowering plants, significantly influencing both their biotic and abiotic response systems as well as being vital to numerous physiological and biological functions. Over the past two decades, the functionality of WRKY proteins has been the subject of extensive research in over 50 plant species, with a strong focus on their roles in responding to various stresses. Despite this extensive research, there remains a notable gap in comprehensive studies aimed at understanding how specific WRKY genes directly influence the timing of flowering and fruit development. This review offers an up-to-date look at WRKY family genes and provides insights into the key genes of WRKY to control flowering, enhance fruit ripening and secondary metabolism synthesis, and maintain fruit quality of various plants, including annuals, perennials, medicinal, and crop plants. The WRKY transcription factors serve as critical regulators within the transcriptional regulatory network, playing a crucial role in the precise enhancement of flowering processes. It is also involved in the up-regulation of fruit ripening was strongly demonstrated by combined transcriptomics and metabolomic investigation. Therefore, we speculated that the WRKY family is known to be a key regulator of flowering and fruiting in plants. This detailed insight will enable the identification of the series of molecular occurrences featuring WRKY proteins throughout the stages of flowering and fruiting.

Genome-wide identification of the WRKY gene family in blueberry (Vaccinium spp.) and expression analysis under abiotic stress

Introduction

The WRKY transcription factor (TF) family is one of the largest TF families in plants and is widely involved in responses to both biotic and abiotic stresses.

Methods

To clarify the function of the WRKY family in blueberries, this study identified the WRKY genes within the blueberry genome and systematically analyzed gene characteristics, phylogenetic evolution, promoter cis-elements, expression patterns, and subcellular localization of the encoded products.

Results

In this study, 57 VcWRKY genes were identified, and all encoding products had a complete WRKY heptapeptide structure and zinc-finger motif. The VcWRKY genes were divided into three subgroups (I-III) by phylogenetic analysis. Group II was divided into five subgroups: IIa, IIb, IIc, IId, and IIe. 57 VcWRKY genes were distributed unevenly across 32 chromosomes. The amino acids ranged from 172 to 841, and molecular weights varied from 19.75 to 92.28 kD. Intra-group syntenic analysis identified 12 pairs of duplicate segments. Furthermore, 34 cis-element recognition sites were identified in the promoter regions of VcWRKY genes, primarily comprising phytohormone-responsive and light-responsive elements. Comparative syntenic maps were generated to investigate the evolutionary relationships of VcWRKY genes, revealing the closest homology to dicotyledonous WRKY gene families. VcWRKY genes were predominantly expressed in the fruit flesh and roots of blueberries. Gene expression analysis showed that the responses of VcWRKY genes to stress treatments were more strongly in leaves than in roots. Notably, VcWRKY13 and VcWRKY25 exhibited significant upregulation under salt stress, alkali stress, and saline-alkali stress, and VcWRKY1 and VcWRKY13 showed notable induction under drought stress. Subcellular localization analysis confirmed that VcWRKY13 and VcWRKY25 function within the nucleus.

Conclusion

These findings establish a foundation for further investigation into the functions and regulatory mechanisms of VcWRKY genes and provide guidance for selecting stress-tolerant genes in the development of blueberry cultivars.

WRKY Transcription Factor Responses and Tolerance to Abiotic Stresses in Plants

Plants are subjected to abiotic stresses throughout their developmental period. Abiotic stresses include drought, salt, heat, cold, heavy metals, nutritional elements, and oxidative stresses. Improving plant responses to various environmental stresses is critical for plant survival and perpetuation. WRKY transcription factors have special structures (WRKY structural domains), which enable the WRKY transcription factors to have different transcriptional regulatory functions. WRKY transcription factors can not only regulate abiotic stress responses and plant growth and development by regulating phytohormone signalling pathways but also promote or suppress the expression of downstream genes by binding to the W-box [TGACCA/TGACCT] in the promoters of their target genes. In addition, WRKY transcription factors not only interact with other families of transcription factors to regulate plant defence responses to abiotic stresses but also self-regulate by recognising and binding to W-boxes in their own target genes to regulate their defence responses to abiotic stresses. However, in recent years, research reviews on the regulatory roles of WRKY transcription factors in higher plants have been scarce and shallow. In this review, we focus on the structure and classification of WRKY transcription factors, as well as the identification of their downstream target genes and molecular mechanisms involved in the response to abiotic stresses, which can improve the tolerance ability of plants under abiotic stress, and we also look forward to their future research directions, with a view of providing theoretical support for the genetic improvement of crop abiotic stress tolerance.

Genome-Wide Identification, Characterisation, and Evolution of the Transcription Factor WRKY in Grapevine (Vitis vinifera): New View and Update

WRKYs are a multigenic family of transcription factors that are plant-specific and involved in the regulation of plant development and various stress response processes. However, the evolution of WRKY genes is not fully understood. This family has also been incompletely studied in grapevine, and WRKY genes have been named with different numbers in different studies, leading to great confusion. In this work, 62 Vitis vinifera WRKY genes were identified based on six genomes of different cultivars. All WRKY genes were numbered according to their chromosomal location, and a complete revision of the numbering was performed. Amino acid variability between different cultivars was assessed for the first time and was greater than 5% for some WRKYs. According to the gene structure, all WRKYs could be divided into two groups: more exons/long length and fewer exons/short length. For the first time, some chimeric WRKY genes were found in grapevine, which may play a specific role in the regulation of different processes: VvWRKY17 (an N-terminal signal peptide region followed by a non-cytoplasmic domain) and VvWRKY61 (Frigida-like domain). Five phylogenetic clades A-E were revealed and correlated with the WRKY groups (I, II, III). The evolution of WRKY was studied, and we proposed a WRKY evolution model where there were two dynamic phases of complexity and simplification in the evolution of WRKY.

Identification of WRKY Family Members and Characterization of the Low-Temperature-Stress-Responsive WRKY Genes in Luffa (Luffa cylindrica L.)

The plant-specific WRKY transcription factor family members have diverse regulatory effects on the genes associated with many plant processes. Although the WRKY proteins in Arabidopsis thaliana and other species have been thoroughly investigated, there has been relatively little research on the WRKY family in Luffa cylindrica, which is one of the most widely grown vegetables in China. In this study, we performed a genome-wide analysis to identify L. cylindrica WRKY genes, which were subsequently classified and examined in terms of their gene structures, chromosomal locations, promoter cis-acting elements, and responses to abiotic stress. A total of 62 LcWRKY genes (471-2238 bp) were identified and divided into three phylogenetic groups (I, II, and III), with group II further divided into five subgroups (IIa, IIb, IIc, IId, and IIe) in accordance with the classification in other plants. The LcWRKY genes were unevenly distributed across 13 chromosomes. The gene structure analysis indicated that the LcWRKY genes contained 0-11 introns (average of 4.4). Moreover, 20 motifs were detected in the LcWRKY proteins with conserved motifs among the different phylogenetic groups. Two subgroup IIc members (LcWRKY16 and LcWRKY31) contained the WRKY sequence variant WRKYGKK. Additionally, nine cis-acting elements related to diverse responses to environmental stimuli were identified in the LcWRKY promoters. The subcellular localization analysis indicated that three LcWRKY proteins (LcWRKY43, LcWRKY7, and LcWRKY23) are localized in the nucleus. The tissue-specific LcWRKY expression profiles reflected the diversity in LcWRKY expression. The RNA-seq data revealed the effects of low-temperature stress on LcWRKY expression. The cold-induced changes in expression were verified via a qRT-PCR analysis of 24 differentially expressed WRKY genes. Both LcWRKY7 and LcWRKY12 were highly responsive to the low-temperature treatment (approximately 110-fold increase in expression). Furthermore, the LcWRKY8, LcWRKY12, and LcWRKY59 expression levels increased by more than 25-fold under cold conditions. Our findings will help clarify the evolution of the luffa WRKY family while also providing valuable insights for future studies on WRKY functions.

Genome-wide identification, structural characterization and gene expression analysis of the WRKY transcription factor family in pea (Pisum sativum L.)

BACKGROUND

The WRKY gene family is one of the largest families of transcription factors in higher plants, and WRKY transcription factors play important roles in plant growth and development as well as in response to abiotic stresses; however, the WRKY gene family in pea has not been systematically reported.

RESULTS

In this study, 89 pea WRKY genes were identified and named according to the random distribution of PsWRKY genes on seven chromosomes. The gene family was found to have nine pairs of tandem duplicates and 19 pairs of segment duplicates. Phylogenetic analyses of the PsWRKY and 60 Arabidopsis WRKY proteins were performed to determine their homology, and the PsWRKYs were classified into seven subfamilies. Analysis of the physicochemical properties, motif composition, and gene structure of pea WRKYs revealed significant differences in the physicochemical properties within the PsWRKY family; however, their gene structure and protein-conserved motifs were highly conserved among the subfamilies. To further investigate the evolutionary relationships of the PsWRKY family, we constructed comparative syntenic maps of pea with representative monocotyledonous and dicotyledonous plants and found that it was most recently homologous to the dicotyledonous WRKY gene families. Cis-acting element analysis of PsWRKY genes revealed that this gene family can respond to hormones, such as abscisic acid (ABA), indole-3-acetic acid (IAA), gibberellin (GA), methyl jasmonate (MeJA), and salicylic acid (SA). Further analysis of the expression of 14 PsWRKY genes from different subfamilies in different tissues and fruit developmental stages, as well as under five different hormone treatments, revealed differences in their expression patterns in the different tissues and fruit developmental stages, as well as under hormone treatments, suggesting that PsWRKY genes may have different physiological functions and respond to hormones.

CONCLUSIONS

In this study, we systematically identified WRKY genes in pea for the first time and further investigated their physicochemical properties, evolution, and expression patterns, providing a theoretical basis for future studies on the functional characterization of pea WRKY genes during plant growth and development.

Genome-Wide Identification and Characterization of the WRKY Gene Family in Cucurbita maxima

In higher plants, WRKY transcription factors are broadly involved in a variety of life activities and play an important role in both biotic and abiotic stress responses. However, little is known about the functions of WRKY genes in the popular species, such as Cucurbita maxima (pumpkin), which is planted worldwide. In the present study, 102 CmWRKY genes were identified in the C. maxima genome. Chromosome location, multiple sequence alignment, phylogenetic analysis, and synteny analysis of the CmWRKYs were performed. Notably, we found that silencing CmWRKY22 promoted cucumber mosaic virus (CMV) infection, whereas overexpression of CmWRKY22 inhibited the CMV infection. Subsequently, an electrophoretic mobility shift assay (EMSA) confirmed that CmWRKY22 was able to bind to the W-box at the promoter of CmPR1b, which is a responsive gene of the salicylic acid (SA) signaling pathway. In summary, this study has provided a foundation for the antiviral functions of WRKY transcription factors in C. maxima.

Genome-wide identification and comprehensive analysis of WRKY transcription factor family in safflower during drought stress

The WRKY family is an important family of transcription factors in plant development and stress response. Currently, there are few reports on the WRKY gene family in safflower (Carthamus tinctorius L.). In this study, a total of 82 CtWRKY genes were identified from the safflower genome and could be classified into 3 major groups and 5 subgroups based on their structural and phylogenetic characteristics. The results of gene structure, conserved domain and motif analyses indicated that CtWRKYs within the same subfamily maintained a consistent exon/intron organization and composition. Chromosomal localization and gene duplication analysis results showed that CtWRKYs were randomly localized on 12 chromosomes and that fragment duplication and purification selection may have played an important role in the evolution of the WRKY gene family in safflower. Promoter cis-acting element analysis revealed that the CtWRKYs contain many abiotic stress response elements and hormone response elements. Transcriptome data and qRT-PCR analyses revealed that the expression of CtWRKYs showed tissue specificity and a strong response to drought stress. Notably, the expression level of the CtWRKY55 gene rapidly increased more than eightfold under drought treatment and rehydration, indicating that it may be a key gene in response to drought stress. These results provide useful insights for investigating the regulatory function of the CtWRKY gene in safflower growth and development, as well as identifying key genes for future molecular breeding programmes.

Genome-Wide Identification and Analysis of the WRKY Gene Family in Asparagus officinalis

In recent years, the related research of the WRKY gene family has been gradually promoted, which is mainly reflected in the aspects of environmental stress and hormone response. However, to make the study of the WRKY gene family more complete, we also need to focus on the whole-genome analysis and identification of the family. In previous studies, the whole WRKY gene family of Arabidopsis, legumes and other plants has been thoroughly studied. However, since the publication of Asparagus officinalis genome-wide data, there has never been an analysis of the whole WRKY gene family. To understand more broadly the function of the WRKY gene family, the whole genome and salt stress transcriptome data of asparagus were used for comprehensive analysis in this study, including WRKY gene family identification, phylogenetic tree construction, analysis of conserved mods and gene domains, extraction of cis-acting elements, intron/exon analysis, species collinearity analysis, and WRKY expression analysis under salt stress. The results showed that a total of 70 genes were selected and randomly distributed on 10 chromosomes and one undefined chromosome. According to the functional classification of Arabidopsis thaliana, the WRKY family of asparagus was divided into 11 subgroups (C1-C9, U1, U2). It is worth considering that the distribution rules of gene-conserved motifs, gene domains and introns/exons in the same subfamily are similar, which suggests that genes in the same subfamily may regulate similar physiological processes. In this study, 11 cis-acting elements of WRKY family were selected, among which auxin, gibberellin, abscisic acid, salicylic acid and other hormone-regulated induction elements were involved. In addition, environmental stress (such as drought stress and low-temperature response) also accounted for a large proportion. Interestingly, we analyzed a total of two tandem duplicate genes and 13 segmental duplication genes, suggesting that this is related to the amplification of the WRKY gene family. Transcriptome data analysis showed that WRKY family genes could regulate plant growth and development by up-regulating and down-regulating gene expression under salt stress. Volcanic maps showed that 3 and 15 AoWRKY genes were significantly up-regulated or down-regulated in NI&NI+S and AMF&AMF+S, respectively. These results provide a new way to analyze the evolution and function of the WRKY gene family, and can provide a reference for the production and research of asparagus.

Multi-algorithm cooperation research of WRKY genes under nitrogen stress in Panax notoginseng

WRKY transcription factors play an important role in the immune system and the innate defense response of plants. WRKY transcription factors have great feedback on nitrogen stress. In this study, bioinformatics was used to detect the WRKYs of Panax notoginseng (PnWRKYs). The response of PnWRKYs under nitrogen stress was also well studied. PnWRKYs were distributed on 11 chromosomes. According to PnWRKY and Arabidopsis thaliana WRKY (AtWRKY) domains, these PnWRKY proteins were divided into three groups by phylogenetic analysis. MEME analysis showed that almost every member contained motif 1 and motif 2. PlantCARE online predicted the cis-acting elements of the promoter. PnWRKY gene family members obtained 22 pairs of repeat fragments by collinearity analysis. The expression levels of PnWRKYs in different parts (roots, flowers, and leafs) were analyzed by the gene expression pattern. They reflected tissue-specific expressions. The qRT-PCR experiments were used to detect 74 PnWRKYs under nitrogen stress. The results showed that the expression levels of 8 PnWRKYs were significantly induced. The PnWRKY gene family may be involved in biotic/abiotic stresses and hormone induction. This study will not only lay the foundation to explore the functions of PnWRKYs but also provide candidate genes for the future improvement of P. notoginseng.

Revealing the Roles of the JAZ Family in Defense Signaling and the Agarwood Formation Process in Aquilaria sinensis

Jasmonate ZIM-domain family proteins (JAZs) are repressors in the signaling cascades triggered by jasmonates (JAs). It has been proposed that JAs play essential roles in the sesquiterpene induction and agarwood formation processes in Aquilaria sinensis. However, the specific roles of JAZs in A. sinensis remain elusive. This study employed various methods, including phylogenetic analysis, real-time quantitative PCR, transcriptomic sequencing, yeast two-hybrid assay, and pull-down assay, to characterize A. sinensis JAZ family members and explore their correlations with WRKY transcription factors. The bioinformatic analysis revealed twelve putative AsJAZ proteins in five groups and sixty-four putative AsWRKY transcription factors in three groups. The AsJAZ and AsWRKY genes exhibited various tissue-specific or hormone-induced expression patterns. Some AsJAZ and AsWRKY genes were highly expressed in agarwood or significantly induced by methyl jasmonate in suspension cells. Potential relationships were proposed between AsJAZ4 and several AsWRKY transcription factors. The interaction between AsJAZ4 and AsWRKY75n was confirmed by yeast two-hybrid and pull-down assays. This study characterized the JAZ family members in A. sinensis and proposed a model of the function of the AsJAZ4/WRKY75n complex. This will advance our understanding of the roles of the AsJAZ proteins and their regulatory pathways.

Bioinformatics Analysis of WRKY Family Genes in Flax (Linum usitatissimum)

WRKY gene family is one of the largest transcription factor families involved in various physiological processes of plants. Flax (Linum usitatissimum) is an important stem fiber crop, and it is also an economically important crop in natural fiber and textile industries around the world. In this study, 105 WRKY genes were obtained by screening the whole genome of flax. There were 26 in group I, 68 in group II, 8 in group III and 3 in group UN. The characteristics of the WRKY motif and gene structure in each group are similar. The promoter sequence of WRKY genes includes photoresponsive elements, core regulatory elements and 12 cis-acting elements under abiotic stress. Similar to A. thaliana and Compositae plants, WRKY genes are evenly distributed on each chromosome, with segmental and tandem repeated events, which play a major role in the evolution of WRKY genes. The flax WRKY gene family is mainly concentrated in group I and group II. This study is mainly based on genome-wide information to classify and analyze the flax WRKY gene family, laying a foundation for further understanding the role of WRKY transcription factors in species evolution and functional analysis.

Chromosome-scale genome assembly of Prunus pusilliflora provides novel insights into genome evolution, disease resistance, and dormancy release in Cerasus L

Prunus pusilliflora is a wild cherry germplasm resource distributed mainly in Southwest China. Despite its ornamental and economic value, a high-quality assembled P. pusilliflora genome is unavailable, hindering our understanding of its genetic background, population diversity, and evolutionary processes. Here, we de novo assembled a chromosome-scale P. pusilliflora genome using Oxford Nanopore, Illumina, and chromosome conformation capture sequencing. The assembled genome size was 309.62 Mb, with 76 scaffolds anchored to eight pseudochromosomes. We predicted 33 035 protein-coding genes, functionally annotated 98.27% of them, and identified repetitive sequences covering 49.08% of the genome. We found that P. pusilliflora is closely related to Prunus serrulata and Prunus yedoensis, having diverged from them ~41.8 million years ago. A comparative genomic analysis revealed that P. pusilliflora has 643 expanded and 1128 contracted gene families. Furthermore, we found that P. pusilliflora is more resistant to Colletotrichum viniferum, Phytophthora capsici, and Pseudomonas syringae pv. tomato (Pst) DC3000 infections than cultivated Prunus avium. P. pusilliflora also has considerably more nucleotide-binding site-type resistance gene analogs than P. avium, which explains its stronger disease resistance. The cytochrome P450 and WRKY families of 263 and 61 proteins were divided into 42 and 8 subfamilies respectively in P. pusilliflora. Furthermore, 81 MADS-box genes were identified in P. pusilliflora, accompanying expansions of the SVP and AGL15 subfamilies and loss of the TM3 subfamily. Our assembly of a high-quality P. pusilliflora genome will be valuable for further research on cherries and molecular breeding.

LcWRKY17, a WRKY Transcription Factor from Litsea cubeba, Effectively Promotes Monoterpene Synthesis

The WRKY gene family is one of the most significant transcription factor (TF) families in higher plants and participates in many secondary metabolic processes in plants. Litsea cubeba (Lour.) Person is an important woody oil plant that is high in terpenoids. However, no studies have been conducted to investigate the WRKY TFs that regulate the synthesis of terpene in L. cubeba. This paper provides a comprehensive genomic analysis of the LcWRKYs. In the L. cubeba genome, 64 LcWRKY genes were discovered. According to a comparative phylogenetic study with Arabidopsis thaliana, these L. cubeba WRKYs were divided into three groups. Some LcWRKY genes may have arisen from gene duplication, but the majority of LcWRKY evolution has been driven by segmental duplication events. Based on transcriptome data, a consistent expression pattern of LcWRKY17 and terpene synthase LcTPS42 was found at different stages of L. cubeba fruit development. Furthermore, the function of LcWRKY17 was verified by subcellular localization and transient overexpression, and overexpression of LcWRKY17 promotes monoterpene synthesis. Meanwhile, dual-Luciferase and yeast one-hybrid (Y1H) experiments showed that the LcWRKY17 transcription factor binds to W-box motifs of LcTPS42 and enhances its transcription. In conclusion, this research provided a fundamental framework for future functional analysis of the WRKY gene families, as well as breeding improvement and the regulation of secondary metabolism in L. cubeba.

Comprehensive analysis of the WRKY gene family in Cucumis metuliferus and their expression profile in response to an early stage of root knot nematode infection

Root-knot nematode (RKN) is a major factor that limits the growth and productivity of important Cucumis crops, such as cucumber and melon, which lack RKN-resistance genes in their genome. Cucumis metuliferus is a wild Cucumis species that displays a high degree of RKN-resistance. WRKY transcription factors were involved in plant response to biotic stresses. However, little is known on the function of WRKY genes in response to RKN infection in Cucumis crops. In this study, Cucumis metuliferus 60 WRKY genes (CmWRKY) were identified in the C. metuliferus genome, and their conserved domains were classified into three main groups based on multiple sequence alignment and phylogenetic analysis. Synteny analysis indicated that the WRKY genes were highly conserved in Cucumis crops. Transcriptome data from of C. metuliferus roots inoculated with RKN revealed that 16 CmWRKY genes showed differential expression, of which 13 genes were upregulated and three genes were downregulated, indicating that these CmWRKY genes are important to C. metuliferus response to RKN infection. Two differentially expression CmWRKY genes (CmWRKY10 and CmWRKY28) were selected for further functional analysis. Both CmWRKY genes were localized in nucleus, indicating they may play roles in transcriptional regulation. This study provides a foundation for further research on the function of CmWRKY genes in RKN stress resistance and elucidation of the regulatory mechanism.

Comparative bioinformatics analysis and abiotic stress responses of expansin proteins in Cucurbitaceae members: watermelon and melon

Watermelon and melon are members of the Cucurbitaceae family including economically significant crops in the world. The expansin protein family, which is one of the members of the cell wall, breaks down the non-covalent bonds between cell wall polysaccharides, causing pressure-dependent cell expansion. Comparative bioinformatics and molecular characterization analysis of the expansin protein family were carried out in the watermelon (Citrullus lanatus) and melon (Cucumis melo) plants in the study. Gene expression levels of expansin family members were analyzed in leaf and root tissues of watermelon and melon under ABA, drought, heat, cold, and salt stress conditions by quantitative real-time PCR analysis. After comprehensive searches, 40 expansin proteins (22 ClaEXPA, 14 ClaEXPLA, and 4 ClaEXPB) in watermelon and 43 expansin proteins (19 CmEXPA, 15 CmEXPLA, 3 CmEXPB, and 6 CmEXPLB) in melon were identified. The greatest orthologous genes were identified with soybean expansin genes for watermelon and melon. However, the latest divergence time between orthologous genes was determined with poplar expansin genes for watermelon and melon expansin genes. ClaEXPA-04, ClaEXPA-09, ClaEXPB-01, ClaEXPB-03, and ClaEXPLA-13 genes in watermelon and CmEXPA-12, CmEXPA-10, and CmEXPLA-01 genes in melon can be involved in tissue development and abiotic stress response of the plant. The current study combining bioinformatics and experimental analysis can provide a detailed characterization of the expansin superfamily which has roles in growth and reaction to the stress of the plant. The study ensures detailed data for future studies examining gene functions including the roles in plant growth and stress conditions.

Genome-Wide Identification, Evolutionary and Functional Analyses of WRKY Family Members in Ginkgo biloba

WRKY transcription factors (TFs) are one of the largest families in plants which play essential roles in plant growth and stress response. Ginkgo biloba is a living fossil that has remained essentially unchanged for more than 200 million years, and now has become widespread worldwide due to the medicinal active ingredients in its leaves. Here, 37 WRKY genes were identified, which were distributed randomly in nine chromosomes of G. biloba. Results of the phylogenetic analysis indicated that the GbWRKY could be divided into three groups. Furthermore, the expression patterns of GbWRKY genes were analyzed. Gene expression profiling and qRT-PCR revealed that different members of GbWRKY have different spatiotemporal expression patterns in different abiotic stresses. Most of the GbWRKY genes can respond to UV-B radiation, drought, high temperature and salt treatment. Meanwhile, all GbWRKY members performed phylogenetic tree analyses with the WRKY proteins of other species which were known to be associated with abiotic stress. The result suggested that GbWRKY may play a crucial role in regulating multiple stress tolerances. Additionally, GbWRKY13 and GbWRKY37 were all located in the nucleus, while GbWRKY15 was located in the nucleus and cytomembrane.

Genome-Wide Identification of the Hypericum perforatum WRKY Gene Family Implicates HpWRKY85 in Drought Resistance

WRKY, named for its special heptapeptide conserved sequence WRKYGOK, is one of the largest transcription factor families in plants and is widely involved in plant responses to biotic, abiotic, and hormonal stresses, especially the important regulatory function in response to drought stress. However, there is no complete comprehensive analysis of this family in H. perforatum, which is one of the most extensively studied plants and is probably the best-known herbal medicine on the market today, serving as an antidepressant, neuroprotective, an antineuralgic, and an antiviral. Here, we identified 86 HpWRKY genes according to the whole genome database of H. perforatum, and classified them into three groups through phylogenetic analysis. Gene structure, conserved domain, motif, cis-elements, gene ontology, and expression profiling were performed. Furthermore, it was found that HpWRKY85, a homologous gene of AtWRKY75, showed obvious responses to drought treatment. Subcellular localization analysis indicated that this protein was localized in the nucleus by the Arabidopsis protoplasts transient transfection. Meanwhile, HpWRKY85-overexpressing Arabidopsis plants showed a stronger ability of root growth and scavenging endogenous reactive oxygen species. The results provide a reference for further understanding the role of HpWRKY85 in the molecular mechanism of drought resistance of H. perforatum.

Comprehensive Genomic Survey, Structural Classification, and Expression Analysis of WRKY Transcription Factor Family in Rhododendron simsii

(1) Rhododendron is one of the top ten traditional flowers in China, with both high ornamental and economic values. However, with the change of the environment, Rhododendron suffers from various biological stresses. The WRKY transcription factor is a member of the most crucial transcription factor families, which plays an essential regulatory role in a variety of physiological processes and developmental stresses. (2) In this study, 57 RsWRKYs were identified using genome data and found to be randomly distributed on 13 chromosomes. Based on gene structure and phylogenetic relationships, 57 proteins were divided into three groups: I, II, and III. Multiple alignments of RsWRKYs with Arabidopsis thaliana homologous genes revealed that WRKY domains in different groups had different conserved sites. RsWRKYs have a highly conserved domain, WRKYGQK, with three variants, WRKYGKK, WRKYGEK, and WRKYGRK. Furthermore, cis-acting elements analysis revealed that all of the RsWRKYs had stress and plant hormone cis-elements, with figures varying by group. Finally, the expression patterns of nine WRKY genes treated with gibberellin acid (GA), methyl jasmonate (MeJA), heat, and drought in Rhododendron were also measured using quantitative real-time PCR (qRT-PCR). The results showed that the expression levels of the majority of RsWRKY genes changed in response to multiple phytohormones and abiotic stressors. (3) This current study establishes a theoretical basis for future studies on the response of RsWRKY transcription factors to various hormone and abiotic stresses as well as a significant foundation for the breeding of new stress-tolerant Rhododendron varieties.

Genome-wide identification and expression analysis response to GA3 stresses of WRKY gene family in seed hemp (Cannabis sativa L)

WRKY transcription factor is one of the largest transcription factor families in higher plants. However, the investigations of the WRKY gene family have not yet been reported in seed hemp. In the present study, we identified 39 CasWRKYs at the genome-wide level and analyzed phylogenetic relationship, chromosome location, cis-acting elements, gene structure, conserved motif, and expression pattern. Based on the gene structure and phylogenetic analyses, CasWRKY proteins were divided into 3 groups and 7 subgroups. The gene duplication investigation revealed that 6 and 5 pairs of CasWRKY genes underwent tandem and segmental duplication events, respectively. These events may contribute to the diversity and expansion of the CasWRKY gene family. The regulatory elements in the promoter regions of CasWRKYs contained diverse cis-regulatory elements, among which P-box cis-regulatory elements showed high frequency, indicating that CasWRKYs can respond to the regulation of gibberellin. The expression profiles derived from RNA-seq and qRT-PCR showed that 13 CasWRKY genes could respond to GA₃ stress and affect fiber development, as well as play significant roles in stem growth and development. This study will serve as molecular basis and practical reference for further exploring the genetic evolution and biological function of CasWRKY genes in seed hemp.

Genome-Wide Analysis and Exploration of WRKY Transcription Factor Family Involved in the Regulation of Shoot Branching in Petunia

The WRKY transcription factors (TFs) participate in various physiological, growth and developmental processes of plants. In our study, a total of 79 WRKY family members were identified and classified into three groups (Group I, Group IIa-e, and Group III) based on phylogenetic and conservative domain analyses. Conserved motif analysis showed that seven WRKYGQK domains changed. The promoter sequence analysis suggested that there were multiple stress- and hormone-related cis-regulatory elements in the promoter regions of PhWRKY genes. Expression patterns of PhWRKYs based on RNA-seq data revealed their diverse expression profiles in five tissues and under different treatments. Subcellular localization analysis showed that PhWRKY71 was located in the nucleus. In addition, overexpression of PhWRKY71 caused a significant increase in branch number. This indicated that PhWRKY71 played a critical role in regulating the shoot branching of Petuniahybrida. The above results lay the foundation for further revealing the functions of PhWRKY genes.

Genome-Wide Identification of the B-Box Gene Family and Expression Analysis Suggests Their Potential Role in Photoperiod-Mediated β-Carotene Accumulation in the Endocarp of Cucumber (Cucumis sativus L.) Fruit

Carotenoids are indispensable to plants and essential for human nutrition and health. Carotenoid contents are strongly influenced by light through light-responsive genes such as B-Box (BBX) genes. BBX proteins, a class of zinc-finger transcription factors, mediate many light-signaling pathways, leading to the biosynthesis of important metabolites in plants. However, the identification of the BBX gene family and expression analysis in response to photoperiod-mediated carotenoid accumulation in cucumber remains unexplored. We performed a genome-wide study and determined the expression of cucumber BBX genes (hereafter referred to as CsaBBXs genes) in the endocarp of Xishuangbanna cucumber fruit (a special type of cucumber accumulating a high level of β-carotene in the endocarp) using an RNA-seq analysis of plants previously subjected to two photoperiodic conditions. Here, 26 BBX family genes were identified in the cucumber genome and named serially CsaBBX1 through CsaBBX26. We characterized CsaBBX genes in terms of their phylogenetic relationships, exon-intron structures, cis-acting elements, and syntenic relationships with Arabidopsis thaliana (L.) Heynh. RNA-seq analysis revealed a varied expression of CsaBBX genes under photoperiod treatment. The analysis of CsaBBXs genes revealed a strong positive correlation between CsaBBX17 and carotenoid biosynthetic pathway genes (phytoene synthase, ζ-carotene desaturase, lycopene ε-cyclase, β-carotene hydroxylase-1), thus suggesting its involvement in β-carotene biosynthesis. Additionally, nine CsaBBX genes (CsaBBX 4, 5, 7, 9, 11, 13, 15, 17 and 22) showed a significant positive correlation with β-carotene content. The selected CsaBBX genes were verified by qRT-PCR and confirmed the validity of RNA-seq data. The results of this study established the genome-wide analysis of the cucumber BBX family and provide a framework for understanding their biological role in carotenoid accumulation and photoperiodic responses. Further investigations of CsaBBX genes are vital since they are promising candidate genes for the functional analysis of carotenoid biosynthesis and can provide genetic tools for the molecular breeding of carotenoids in plants.

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.

Genome Wide Identification and Characterization of Apple WD40 Proteins and Expression Analysis in Response to ABA, Drought, and Low Temperature

Basic WD40 proteins, which are characterized by a conserved WD40 domain, comprise a superfamily of regulatory proteins in plants and play important roles in plant growth and development. However, WD40 genes have been rarely studied in apple (Malus × domestica Borkh.). In this study, 346 WD40 genes classified in 12 subfamilies, were identified in the apple genome. Evolutionary analysis of WD40 proteins in apple and Arabidopsis revealed that the genes were classifiable into 14 groups, and the exon/intron structure of each group showed a similar structure. Analysis of collinearity showed that the large-scale amplification of WD40 genes in apple was largely attributable to recent whole-genome replication events. Nineteen candidate stress-related genes, selected by GO annotation and comparison with Arabidopsis homologs, showed different expression profiles in six organs at different developmental stages in response to exogenous abscisic acid (ABA), drought, and low temperature. Eight genes (MdWD40-17, 24, 70, 74, 219, 256, 283, and 307) showed a distinct response to one or more treatments (ABA, drought, and low temperature) as indicated by quantitative real-time PCR analysis. Taken together, these data provide rich resources for further study of MdWD40 genes and their potential roles in stress responses in apple.

Identification and Expression Analysis of WRKY Gene Family in Response to Abiotic Stress in Dendrobium catenatum

Dendrobium catenatum has become a rare and endangered medicinal plant due to habitat loss in China. As one of the most important and largest transcription factors, WRKY plays a critical role in response to abiotic stresses in plants. However, little is known regarding the functions of the WRKY family in D. catenatum. In this study, a total of 62 WRKY genes were identified from the D. catenatum genome. Phylogenetic analysis revealed that DcWRKY proteins could be divided into three groups, a division supported by the conserved motif compositions and intron/exon structures. DcWRKY gene expression and specific responses under drought, heat, cold and salt stresses were analyzed through RNA-seq data and RT-qPCR assay. The results showed that these genes had tissue-specificity and displayed different expression patterns in response to abiotic stresses. The expression levels of DcWRKY22, DcWRKY36 and DcWRKY45 were up-regulated by drought stress. Meanwhile, DcWRKY22 was highly induced by heat in roots, and DcWRKY45 was significantly induced by cold stress in leaves. Furthermore, DcWRKY27 in roots and DcWRKY58 in leaves were extremely induced under salt treatment. Finally, we found that all the five genes may function in ABA- and SA-dependent manners. This study identified candidate WRKY genes with possible roles in abiotic stress and these findings not only contribute to our understanding of WRKY family genes, but also provide valuable information for stress resistance development in D. catenatum.

Genome-wide identification of the Liriodendron chinense WRKY gene family and its diverse roles in response to multiple abiotic stress

BACKGROUND

Liriodendron chinense (Lchi) is a tree species within the Magnoliaceae family and is considered a basal angiosperm. The too low or high temperature or soil drought will restrict its growth as the adverse environmental conditions, thus improving L. chinense abiotic tolerance was the key issues to study. WRKYs are a major family of plant transcription factors known to often be involved in biotic and abiotic stress responses. So far, it is still largely unknown if and how the LchiWRKY gene family is tied to regulating L. chinense stress responses. Therefore, studying the involvement of the WRKY gene family in abiotic stress regulation in L. chinense could be very informative in showing how this tree deals with such stressful conditions.

RESULTS

In this research, we performed a genome-wide analysis of the Liriodendron chinense (Lchi) WRKY gene family, studying their classification relationships, gene structure, chromosomal locations, gene duplication, cis-element, and response to abiotic stress. The 44 members of the LchiWRKY gene family contain a significant amount of sequence diversity, with their lengths ranging from 525 bp to 40,981 bp. Using classification analysis, we divided the 44 LchiWRKY genes into three phylogenetic groups (I, II, II), with group II then being further divided into five subgroups (IIa, IIb, IIc, IId, IIe). Comparative phylogenetic analysis including the WRKY families from 17 plant species suggested that LchiWRKYs are closely related to the Magnolia Cinnamomum kanehirae WRKY family, and has fewer family members than higher plants. We found the LchiWRKYs to be evenly distributed across 15 chromosomes, with their duplication events suggesting that tandem duplication may have played a major role in LchiWRKY gene expansion model. A Ka/Ks analysis indicated that they mainly underwent purifying selection and distributed in the group IId. Motif analysis showed that LchiWRKYs contained 20 motifs, and different phylogenetic groups contained conserved motif. Gene ontology (GO) analysis showed that LchiWRKYs were mainly enriched in two categories, i.e., biological process and molecular function. Two group IIc members (LchiWRKY10 and LchiWRKY37) contain unique WRKY element sequence variants (WRKYGKK and WRKYGKS). Gene structure analysis showed that most LchiWRKYs possess 3 exons and two different types of introns: the R- and V-type which are both contained within the WRKY domain (WD). Additional promoter cis-element analysis indicated that 12 cis-elements that play different functions in environmental adaptability occur across all LchiWRKY groups. Heat, cold, and drought stress mainly induced the expression of group II and I LchiWRKYs, some of which had undergone gene duplication during evolution, and more than half of which had three exons. LchiWRKY33 mainly responded to cold stress and LchiWRKY25 mainly responded to heat stress, and LchiWRKY18 mainly responded to drought stress, which was almost 4-fold highly expressed, while 5 LchiWRKYs (LchiWRKY5, LchiWRKY23, LchiWRKY14, LchiWRKY27, and LchiWRKY36) responded equally three stresses with more than 6-fold expression. Subcellular localization analysis showed that all LchiWRKYs were localized in the nucleus, and subcellular localization experiments of LchiWRKY18 and 36 also showed that these two transcription factors were expressed in the nucleus.

CONCLUSIONS

This study shows that in Liriodendron chinense, several WRKY genes like LchiWRKY33, LchiWRKY25, and LchiWRKY18, respond to cold or heat or drought stress, suggesting that they may indeed play a role in regulating the tree's response to such conditions. This information will prove a pivotal role in directing further studies on the function of the LchiWRKY gene family in abiotic stress response and provides a theoretical basis for popularizing afforestation in different regions of China.

MeWRKY IIas, Subfamily Genes of WRKY Transcription Factors From Cassava, Play an Important Role in Disease Resistance

Cassava (Manihot esculenta Crantz) is an important tropical crop for food, fodder, and energy. Cassava bacterial blight (CBB) caused by Xanthomonas axonopodis pv. manihotis (Xam) occurs in all cassava growing regions and threatens global cassava production. WRKY transcription factor family plays the essential roles during plant growth, development, and abiotic or biotic stress. Particularly, previous studies have revealed the important role of the group IIa WRKY genes in plant disease resistance. However, a comprehensive analysis of group IIa subfamily in cassava is still missing. Here, we identified 102 WRKY members, which were classified into three groups, I, II, and III. Transient expression showed that six MeWRKY IIas were localized in the nucleus. MeWRKY IIas transcripts accumulated significantly in response to SA, JA, and Xam. Overexpression of MeWRKY27 and MeWRKY33 in Arabidopsis enhanced its resistance to Pst DC3000. In contrast, silencing of MeWRKY27 and MeWRKY33 in cassava enhanced its susceptibility to Xam. Co-expression network analysis showed that different downstream genes are regulated by different MeWRKY IIa members. The functional analysis of downstream genes will provide clues for clarifying molecular mechanism of cassava disease resistance. Collectively, our results suggest that MeWRKY IIas are regulated by SA, JA signaling, and coordinate response to Xam infection.

Deciphering Evolutionary Dynamics of WRKY I Genes in Rosaceae Species

WRKY transcription factors participate in various regulation processes at different developmental stages in higher plants. Here, 98 WRKY I genes were identified in seven Rosaceae species. The WRKY I genes are highly enriched in some subgroups and are selectively expanded in Chinese pear [Pyrus bretschneideri (P. bretschneideri)] and apple [Malus domestica (M. domestica)]. By searching for intra-species gene microsynteny, we found the majority of chromosomal segments for WRKY I-containing segments in both P. bretschneideri and M. domestica genomes, while paired segments were hardly identified in the other five genomes. Furthermore, we analyzed the environmental selection pressure of duplicated WRKY I gene pairs, which indicated that the strong purifying selection for WRKY domains may contribute to the stability of its structure and function. The expression patterns of duplication PbWRKY genes revealed that functional redundancy for some of these genes was derived from common ancestry and neo-functionalization or sub-functionalization for some of them. This study traces the evolution of WRKY I genes in Rosaceae genomes and lays the foundation for functional studies of these genes in the future. Our results also show that the rates of gene loss and gain in different Rosaceae genomes are far from equilibrium.

Comparative genomic analysis of expansin superfamily gene members in zucchini and cucumber and their expression profiles under different abiotic stresses

Zucchini and cucumber belong to the Cucurbitaceae family, a group of economical and nutritious food plants that is consumed worldwide. Expansin superfamily proteins are generally localized in the cell wall of plants and are known to possess an effect on cell wall modification by causing the expansion of this region. Although the whole genome sequences of cucumber and zucchini plants have been resolved, the determination and characterization of expansin superfamily members in these plants using whole genomic data have not been implemented yet. In the current study, a genome-wide analysis of zucchini (Cucurbita pepo) and cucumber (Cucumis sativus) genomes was performed to determine the expansin superfamily genes. In total, 49 and 41 expansin genes were identified in zucchini and cucumber genomes, respectively. All expansin superfamily members were subjected to further bioinformatics analysis including gene and protein structure, ontology of the proteins, phylogenetic relations and conserved motifs, orthologous relations with other plants, targeting miRNAs of those genes and in silico gene expression profiles. In addition, various abiotic stress responses of zucchini and cucumber expansin genes were examined to determine their roles in stress tolerance. CsEXPB-04 and CsEXPA-11 from cucumber and CpEXPA-20 and CpEXPLA-14 from zucchini can be candidate genes for abiotic stress response and tolerance in addition to their roles in the normal developmental processes, which are supported by the gene expression analysis. This work can provide new perspectives for the roles of expansin superfamily genes and offers comprehensive knowledge for future studies investigating the modes of action of expansin proteins.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-021-01108-w.

Identification of the Golden-2-like transcription factors gene family in Gossypium hirsutum

Background

Golden2-Like (GLK) transcription factors are a type of transcriptional regulator in plants. They play a pivotal role in the plant physiological activity process and abiotic stress response.

Methods

In this study, the potential function of GLK family genes in Gossypium hirsutum was studied based on genomic identification, phylogenetic analysis, chromosome mapping and cis-regulatory elements prediction. Gene expression of nine key genes were analyzed by qRT-PCR experiments.

Results

Herein, we identified a total of 146 GhGLK genes in Gossypium hirsutum, which were unevenly distributed on each of the chromosomes. There were significant differences in the number and location of genes between the At sub-genome and the Dt sub-genome. According to the phylogenetic analysis, they were divided into ten subgroups, each of which had very similar number and structure of exons and introns. Some cis-regulatory elements were identified through promoter analysis, including five types of elements related to abiotic stress response, five types of elements related to phytohormone and five types of elements involved in growth and development. Based on public transcriptome data analysis, we identified nine key GhGLKs involved in salt, cold, and drought stress. The qRT-PCR results showed that these genes had different expression patterns under these stress conditions, suggesting that GhGLK genes played an important role in abiotic stress response. This study laid a theoretical foundation for the screening and functional verification of genes related to stress resistance of GLK gene family in cotton.

Genome-Wide Identification and Analysis of the WRKY Gene Family and Cold Stress Response in Acer truncatum

WRKY transcription factors constitute one of the largest gene families in plants and are involved in many biological processes, including growth and development, physiological metabolism, and the stress response. In earlier studies, the WRKY gene family of proteins has been extensively studied and analyzed in many plant species. However, information on WRKY transcription factors in Acer truncatum has not been reported. In this study, we conducted genome-wide identification and analysis of the WRKY gene family in A. truncatum, 54 WRKY genes were unevenly located on all 13 chromosomes of A. truncatum, the highest number was found in chromosomes 5. Phylogenetic relationships, gene structure, and conserved motif identification were constructed, and the results affirmed 54 AtruWRKY genes were divided into nine subgroup groups. Tissue species analysis of AtruWRKY genes revealed which were differently exhibited upregulation in flower, leaf, root, seed and stem, and the upregulation number were 23, 14, 34, 18, and 8, respectively. In addition, the WRKY genes expression in leaf under cold stress showed that more genes were significantly expressed under 0, 6 and 12 h cold stress. The results of this study provide a new insight the regulatory function of WRKY genes under abiotic and biotic stresses.

Overexpression of the maize WRKY114 gene in transgenic rice reduce plant height by regulating the biosynthesis of GA

WRKYs represent an important family of transcription factors that are widely involved in plant development, defense regulation and stress response. Transgenic rice that constitutively expressed ZmWRKY114 had shorter plant height and showed less sensitivity to gibberellic acid (GA₃). Further investigation proved that transgenic rice accumulated lower levels of bioactive GAs than that in wild-type plants. Application of exogenous GA₃ fully rescued the semi-dwarf phenotype of ZmWRKY114 transgenic plants. Transcriptome and qRT-PCR analyses indicated that the expression of OsGA2ox4, encoding the repressor of GA biosynthesis, was markedly increased. Electrophoretic mobility shift assay and dual-luciferase reporter assay indicated that ZmWRKY114 directly binds to a W-box motif in the OsGA2ox4 promoter. Taken together, these results confirm that ZmWRKY114 is a GA-responsive gene and is participated in the regulation of plant height in rice.

A salicylic acid inducible mulberry WRKY transcription factor, MiWRKY53 is involved in plant defence response

MiWRKY53 is expressed in response to various stresses and hormones. Although it is localized in the nucleus, it shows no transcriptional activation. Role of SA-mediated plant defence response is demonstrated. WRKY transcription factors are one the largest gene families in plants involved in almost every process in plants including development, physiological processes, and stress response. Salicylic acid (SA) is key regulator of biotic stress against various pathogens in plants acting via its multiple mechanisms to induce defence response. Herein, we have identified and functionally validated WRKY53 from mulberry (Morus indica var. K2). MiWRKY53 expressed differentially in response to different stress and hormonal treatments. MiWRKY53 belongs to group III of WKRY gene family, localized in nucleus, and lacks transcriptional activation activity in yeast. Hormone responsive behaviour of MiWRKY53 Arabidopsis overexpression (OE) transgenics preferentially was noted in root growth assay in response to Salicylic acid (SA). Arabidopsis overexpression plants also displayed alteration in leaf phenotype having wider leaves than the wild-type plants. PR-1 transcripts were higher in MiWRKY53 Arabidopsis OE plants and they displayed resistance towards biotrophic pathogen Pseudomonas syringae PstDC3000. MiWRKY53 Mulberry OE transgenics also depicted SA-responsive behaviour. Several hormones and stress-related cis-acting elements were also identified in the 1.2-Kb upstream regulatory region (URR) of MiWRKY53. Functional characterization of full-length promoter region revealed that it is induced by SA and further analysis of deletion constructs helped in the identification of minimal promoter responsible for its inducibility by SA. Altogether, the findings from this study point towards the SA preferential behaviour of MiWRKY53 and its function as regulator of plant defence response through SA-mediated mechanisms.

Genome-wide analysis of valine-glutamine motif-containing proteins related to abiotic stress response in cucumber (Cucumis sativus L.)

BACKGROUND

Cucumber (Cucumis sativus L.) is one of the most important economic crops and is susceptible to various abiotic stresses. The valine-glutamine (VQ) motif-containing proteins are plant-specific proteins with a conserved "FxxhVQxhTG" amino acid sequence that regulates plant growth and development. However, little is known about the function of VQ proteins in cucumber.

RESULTS

In this study, a total of 32 CsVQ proteins from cucumber were confirmed and characterized using comprehensive genome-wide analysis, and they all contain a conserved motif with 10 variations. Phylogenetic tree analysis revealed that these CsVQ proteins were classified into nine groups by comparing the CsVQ proteins with those of Arabidopsis thaliana, melon and rice. CsVQ genes were distributed on seven chromosomes. Most of these genes were predicted to be localized in the nucleus. In addition, cis-elements in response to different stresses and hormones were observed in the promoters of the CsVQ genes. A network of CsVQ proteins interacting with WRKY transcription factors (CsWRKYs) was proposed. Moreover, the transcripts of CsVQ gene were spatio-temporal specific and were induced by abiotic adversities. CsVQ4, CsVQ6, CsVQ16-2, CsVQ19, CsVQ24, CsVQ30, CsVQ32, CsVQ33, and CsVQ34 were expressed in the range of organs and tissues at higher levels and could respond to multiple hormones and different stresses, indicating that these genes were involved in the response to stimuli.

CONCLUSIONS

Together, our results reveal novel VQ resistance gene resources, and provide critical information on CsVQ genes and their encoded proteins, which supplies important genetic basis for VQ resistance breeding of cucumber plants.

Genome-Wide Identification, Phylogenetic and Expression Pattern Analysis of GATA Family Genes in Cucumber (Cucumis sativus L.)

GATA transcription factors are a class of transcriptional regulatory proteins that contain a characteristic type-IV zinc finger DNA-binding domain, which play important roles in plant growth and development. The GATA gene family has been characterized in various plant species. However, GATA family genes have not been identified in cucumber. In this study, 26 GATA family genes were identified in cucumber genome, whose physicochemical characteristics, chromosomal distributions, phylogenetic tree, gene structures conserved motifs, cis-regulatory elements in promoters, homologous gene pairs, downstream target genes were analyzed. Tissue expression profiles of cucumber GATA family genes exhibited that 17 GATA genes showed constitutive expression, and some GATA genes showed tissue-specific expression patterns. RNA-seq analysis of green and virescent leaves revealed that seven GATA genes might be involved in the chloroplast development and chlorophyll biosynthesis. Importantly, expression patterns analysis of GATA genes in response to abiotic and biotic stresses indicated that some GATA genes respond to either abiotic stress or biotic stress, some GATA genes such as Csa2G162660, Csa3G017200, Csa3G165640, Csa4G646060, Csa5G622830 and Csa6G312540 were simultaneously functional in resistance to abiotic and biotic stresses. Overall, this study will provide useful information for further analysis of the biological functions of GATA factors in cucumber.

Identification of the Group III WRKY Subfamily and the Functional Analysis of GhWRKY53 in Gossypium hirsutum L

WRKY transcription factors had multiple functions in plant secondary metabolism, leaf senescence, fruit ripening, adaptation to biotic and abiotic stress, and plant growth and development. However, knowledge of the group III WRKY subfamily in fiber development in upland cotton (Gossypium hirsutum L.) is largely absent. Previous studies have shown that there were 21 putative group III WRKY members in G. hirsutum L. These putative amino acid sequences from the III WRKY group were phylogenetically clustered into three clades. Multiple alignment, conservative motif analysis, and gene structure analysis showed that the members clustered together in the phylogenetic tree had similar motifs and gene structures. Expression pattern analysis revealed that variation in the expression levels of these genes in different tissues and fiber development stages. To better understand the functions of putative group III WRKY genes in G. hirsutum L., we selected the cotton fiber initiation-related gene GhWRKY53 for cloning and functional identification. The subcellular localization experiment of GhWRKY53 in Nicotiana tabacum leaves showed that it was located in the nucleus. The heterologous expression of GhWRKY53 in Arabidopsis thaliana could significantly increase the density of trichomes. Twelve proteins that interacted with GhWRKY53 were screened from the cotton fiber cDNA library by yeast two-hybrid experiment. This study findings lay a foundation for further research on the role of the GhWRKY53 during cotton fiber development and provide a new insight for further studying putative group III WRKY genes in G. hirsutum L. Our research results also provide vital information for the genetic mechanism of high-quality cotton fiber formation and essential genetic resources for cotton fiber quality improvement.

Genome-Wide Profiling of WRKY Genes Involved in Benzylisoquinoline Alkaloid Biosynthesis in California Poppy (Eschscholzia californica)

Transcription factors of the WRKY family play pivotal roles in plant defense responses, including the biosynthesis of specialized metabolites. Based on the previous findings of WRKY proteins regulating benzylisoquinoline alkaloid (BIA) biosynthesis, such as CjWRKY1-a regulator of berberine biosynthesis in Coptis japonica-and PsWRKY1-a regulator of morphine biosynthesis in Papaver somniferum-we performed genome-wide characterization of the WRKY gene family in Eschscholzia californica (California poppy), which produces various BIAs. Fifty WRKY genes were identified by homology search and classified into three groups based on phylogenetic, gene structure, and conserved motif analyses. RNA sequencing showed that several EcWRKY genes transiently responded to methyl jasmonate, a known alkaloid inducer, and the expression patterns of these EcWRKY genes were rather similar to those of BIA biosynthetic enzyme genes. Furthermore, tissue expression profiling suggested the involvement of a few subgroup IIc EcWRKYs in the regulation of BIA biosynthesis. Transactivation analysis using luciferase reporter genes harboring the promoters of biosynthetic enzyme genes indicated little activity of subgroup IIc EcWRKYs, suggesting that the transcriptional network of BIA biosynthesis constitutes multiple members. Finally, we investigated the coexpression patterns of EcWRKYs with some transporter genes and discussed the diversified functions of WRKY genes based on a previous finding that CjWRKY1 overexpression in California poppy cells enhanced BIA secretion into the medium.

Transcriptome-wide characterization of the WRKY family genes in Lonicera macranthoides and the role of LmWRKY16 in plant senescence

BACKGROUND

Lonicera macranthoides is an important woody plant with high medicinal values widely cultivated in southern China. WRKY, one of the largest transcription factor families, participates in plant development, senescence, and stress responses. However, a comprehensive study of the WRKY family in L. macranthoides hasn't been reported previously.

OBJECTIVE

To establish an extensive overview of the WRKY family in L. macranthoides and identify senescence-responsive members of LmWRKYs.

METHODS

RNA-Seq and phylogenetic analysis were employed to identify the LmWRKYs and their evolutionary relationships. Quantitative real-time (qRT-PCR) and transgenic technology was utilized to investigate the roles of LmWRKYs in response to developmental-, cold-, and ethylene-induced senescence.

RESULTS

A total of 61 LmWRKY genes with a highly conserved motif WRKYGQK were identified. Phylogenetic analysis of LmWRKYs together with their orthologs from Arabidopsis classified them into three groups, with the number of 15, 39, and 7, respectively. 17 LmWRKYs were identified to be differentially expressed between young and aging leaves by RNA-Seq. Further qRT-PCR analysis showed 15 and 5 LmWRKY genes were significantly induced responding to tissue senescence in leaves and stems, respectively. What's more, five LmWRKYs, including LmWRKY4, LmWRKY5, LmWRKY6, LmWRKY11, and LmWRKY16 were dramatically upregulated under cold and ethylene treatment in both leaves and stems, indicating their involvements commonly in developmental- and stress-induced senescence. In addition, function analysis revealed LmWRKY16, a homolog of AtWRKY75, can accelerate plant senescence, as evidenced by leaf yellowing during reproductive growth in LmWRKY16-overexpressing tobaccos.

CONCLUSION

The results lay the foundation for molecular characterization of LmWRKYs in plant senescence.

Computational Identification of miRNAs and Temperature-Responsive lncRNAs From Mango (Mangifera indica L.)

Mango is a major tropical fruit in the world and is known as the king of fruits because of its flavor, aroma, taste, and nutritional values. Although various regulatory roles of microRNAs (miRNAs) and long non-coding RNAs (lncRNAs) have been investigated in many plants, there is yet an absence of such study in mango. This is the first study to provide information on non-coding RNAs (ncRNAs) of mango with the aims of identifying miRNAs and lncRNAs and discovering their potential functions by interaction prediction of the miRNAs, lncRNAs, and their target genes. In this analysis, about a hundred miRNAs and over 7,000 temperature-responsive lncRNAs were identified and the target genes of these ncRNAs were characterized. According to these results, the newly identified mango ncRNAs, like other plant ncRNAs, have a potential role in biological and metabolic pathways including plant growth and developmental process, pathogen defense mechanism, and stress-responsive process. Moreover, mango lncRNAs can target miRNAs to reduce the stability of lncRNAs and can function as molecular decoys or sponges of miRNAs. This paper would provide information about miRNAs and lncRNAs of mango and would help for further investigation of the specific functions of mango ncRNAs through wet lab experiments.

Enhanced tolerance to drought stress resulting from Caragana korshinskii CkWRKY33 in transgenic Arabidopsis thaliana

Background

It is well known that WRKY transcription factors play important roles in plant growth and development, defense regulation and stress responses.

Results

In this study, a WRKY transcription factor, WRKY33, was cloned from Caragana korshinskii. A sequence structure analysis showed that it belonged to the Group-I type. Subcellular localization experiments in tobacco epidermal cells showed the presence of CkWRKY33 in the nucleus. Additionally, CkWRKY33 was overexpressed in Arabidopsis thaliana. A phenotypic investigation revealed that compared with wild-type plants, CkWRKY33-overexpressing transgenic plants had higher survival rates, as well as relative soluble sugar, proline and peroxidase contents, but lower malondialdehyde contents, following a drought stress treatment.

Conclusions

This suggested that the overexpression of CkWRKY33 led to an enhanced drought-stress tolerance in transgenic A. thaliana. Thus, CkWRKY33 may act as a positive regulator involved in the drought-stress responses in Caragana korshinskii.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12863-021-00965-4.

Identification and expression analysis of the WRKY gene family in Isatis indigotica

The WRKY proteins, which represent one of the largest families of transcriptional regulators in plants, play pivotal roles in regulating multiple processes of growth and development, particularly in diverse stress responses. Isatis indigotica is widely used in Traditional Chinese Medicine and is famous for its use as a dye for the color indigo. However, reports of the WRKY gene family in I. indigotica are limited. In this study, 64 IiWRKY genes encoding proteins with the complete WRKY domain were identified from genome of I. indigotica. Based on their structure and phylogenetic relationships of this gene family in I. indigotica, the IiWRKY genes were classified into three groups: Group I (n = 13), Group II (n = 35) and Group III (n = 16). Sequence alignment revealed that IiWRKY proteins harbored two variants, WRKYRQK and WRKYGKK, of the highly conserved WRKYGQK motif. The number of exons in IiWRKY genes varied from two to 14, with most of IiWRKY genes containing three exons. Investigation of gene duplication demonstrated that 10 and 14 IiWRKY genes were incorporated in tandem and segmental duplication events, respectively. Finally, the expression profiles derived from transcriptome data and quantitative real-time PCR analysis showed distinct expression patterns of these IiWRKY gene in five different organs or in response to four abiotic stresses. Taken together, our results will contribute to functional analysis of IiWRKY genes, and also provide a basis for further clarification of the molecular mechanism of stress responses in this important herb.

Comprehensive evaluation of candidate reference genes for quantitative real-time PCR-based analysis in Caucasian clover

The forage species Caucasian clover (Trifolium ambiguum M. Bieb.), a groundcover plant, is resistant to both cold and drought. However, reference genes for qRT-PCR-based analysis of Caucasian clover are lacking. In this study, 12 reference genes were selected on the basis of transcriptomic data. These genes were used to determine the most stably expressed genes in various organs of Caucasian clover under cold, salt and drought stress for qRT-PCR-based analysis. Reference gene stability was analyzed by geNorm, NormFinder, BestKeeper, the ∆Ct method and RefFinder. Under salt stress, RCD1 and PPIL3 were the most stable reference genes in the leaves, and NLI1 and RCD1 were the most stable references genes in the roots. Under low-temperature stress, APA and EFTu-GTP were the most stable reference genes in the leaves, and the RCD1 and NLI2 genes were highly stable in the roots. Under 10% PEG-6000 stress, NLI1 and NLI2 were highly stable in the leaves, and RCD1 and PPIL3 were the most stable in the roots. Overall, RCD1 and NLI2 were the most stable reference genes in organs under normal conditions and across all samples. The most and least stable reference genes were validated by assessing their appropriateness for normalization via WRKY genes.

Genome-Wide Characterization of HSP90 Gene Family in Cucumber and Their Potential Roles in Response to Abiotic and Biotic Stresses

Heat shock protein 90 (HSP90) possesses critical functions in plant developmental control and defense reactions. The HSP90 gene family has been studied in various plant species. However, the HSP90 gene family in cucumber has not been characterized in detail. In this study, a total of six HSP90 genes were identified from the cucumber genome, which were distributed to five chromosomes. Phylogenetic analysis divided the cucumber HSP90 genes into two groups. The structural characteristics of cucumber HSP90 members in the same group were similar but varied among different groups. Synteny analysis showed that only one cucumber HSP90 gene, Csa1G569290, was conservative, which was not collinear with any HSP90 gene in Arabidopsis and rice. The other five cucumber HSP90 genes were collinear with five Arabidopsis HSP90 genes and six rice HSP90 genes. Only one pair of paralogous genes in the cucumber HSP90 gene family, namely one pair of tandem duplication genes (Csa1G569270/Csa1G569290), was detected. The promoter analysis showed that the promoters of cucumber HSP90 genes contained hormone, stress, and development-related cis-elements. Tissue-specific expression analysis revealed that only one cucumber HSP90 gene Csa3G183950 was highly expressed in tendril but low or not expressed in other tissues, while the other five HSP90 genes were expressed in all tissues. Furthermore, the expression levels of cucumber HSP90 genes were differentially induced by temperature and photoperiod, gibberellin (GA), downy mildew, and powdery mildew stimuli. Two cucumber HSP90 genes, Csa1G569270 and Csa1G569290, were both differentially expressed in response to abiotic and biotic stresses, which means that these two HSP90 genes play important roles in the process of cucumber growth and development. These findings improve our understanding of cucumber HSP90 family genes and provide preliminary information for further studies of cucumber HSP90 gene functions in plant growth and development.

Genomic Characterization of WRKY Transcription Factors Related to Andrographolide Biosynthesis in Andrographis paniculata

Andrographolide, which is enriched in the leaves of Andrographis paniculata, has been known as “natural antibiotic” due to its pharmacological activities such as anti-inflammatory, antimicrobial and antioxidant effects. Several key enzymes in andrographolide biosynthetic pathway have been studied since the genome sequences were released, but its regulatory mechanism remains unknown. WRKY transcription factors proteins have been reported to regulate plant secondary metabolism, development as well as biotic and abiotic stresses. Here, WRKY transcription factors related to andrographolide biosynthesis were systematically identified, including sequences alignment, phylogenetic analysis, chromosomal distribution, gene structure, conserved motifs, synteny, alternative splicing event and Gene ontology (GO) annotation. A total of 58 WRKYs were identified in Chuanxinlian genome and phylogenetically classified into three groups. Moreover, nine WRKY genes underwent alternative splicing events. Furthermore, the combination of binding site prediction, gene-specific expression patterns, and phylogenetic analysis suggested that 7 WRKYs (ApWRKY01, ApWRKY08, ApWRKY12, ApWRKY14, ApWRKY19, ApWRKY20, and ApWRKY50) might regulate andrographolide biosynthesis. This study laid a foundation for understanding the regulatory mechanism of andrographolide biosynthesis and the improvement and breeding of Andrographis paniculata varieties.

Transcriptome-wide identification of WRKY family genes and their expression profiling toward salicylic acid in Camellia japonica

The ornamental plant Camellia japonica is widely distributed worldwide and is susceptible to various environmental stresses. The WRKY transcription factor (TF) is an important node of plant tolerance. However, WRKY TFs from C. japonica have not been reported yet. In this study, 48 CjWRKYs, namely, CjWRKY1 to CjWRKY48, were identified. Protein structure analysis revealed that CjWRKY proteins contain a highly conserved motif (WRKYGQK) and two variant motifs (WRKYGKK and WRKYGRK). Phylogenetic analysis indicated that the 48 CjWRKYs can be divided into three groups, which are further classified into six subgroups, namely, I-C, II-a, II-b, II-c, II-e, and III, which contain 10, 6, 8, 13, 7, and 4 members, respectively. The expression patterns of 15 CjWRKYs under salicylic acid (SA) treatment were investigated by real-time quantitative PCR (qRT-PCR). Results showed that the 15 CjWRKYs could be induced by SA treatment. This study is the first to screen CjWRKYs and identify the expression profile of CjWRKYs under SA treatment and provides a theoretical basis for analyzing the function of CjWRKY genes to SA stress tolerance in C. japonica.

A conserved double-W box in the promoter of CaWRKY40 mediates autoregulation during response to pathogen attack and heat stress in pepper

CaWRKY40 was previously found to be transcriptionally up-regulated by Ralstonia solanacearum inoculation (RSI) or heat stress (HS), but the underlying mechanism remains unknown. Herein, we report that a double-W box-element (DWE) in the promoter of CaWRKY40 is critical for these responses. The upstream W box unit WI of this composite element is crucial for preferential binding by CaWRKY40 and responsiveness to RSI or HS. DWE-driven CaWRKY40 can be transcriptionally and nonspecifically regulated by itself and by CaWRKY58 and CaWRKY27. The DWE was also found in the promoters of CaWRKY40 orthologs, including AtWRKY40, VvWRKY40, GmWRKY40, CplWRKY40, SaWRKY40, SpWRKY40, NtWRKY40, and NaWRKY40. DWE^AtWRKY40 was analogous to DWE^CaWRKY40 by responding to RSI or HS and AtWRKY40 expression. These data suggest that a conserved response of plants to pathogen infection or HS is probably mediated by binding of the DWE by WRKY40.