CaWRKY01-10 and CaWRKY08-4 Confer Pepper's Resistance to Phytophthora capsici Infection by Directly Activating a Cluster of Defense-Related Genes

Phytophthora blight of pepper, which is caused by the notorious oomycete pathogen Phytophthora capsici, is a serious disease in global pepper production regions. Our previous study had identified two WRKY transcription factors (TFs), CaWRKY01-10 and CaWRKY08-4, which are prominent modulators in the resistant pepper line CM334 against P. capsici infection. However, their functional mechanisms and underlying signaling networks remain unknown. Herein, we determined that CaWRKY01-10 and CaWRKY08-4 are localized in plant nuclei. Transient overexpression assays indicated that both CaWRKY01-10 and CaWRKY08-4 act as positive regulators in pepper resistance to P. capsici. Besides, the stable overexpression of CaWRKY01-10 and CaWRKY08-4 in transgenic Nicotiana benthamiana plants also significantly enhanced the resistance to P. capsici. Using comprehensive approaches including RNA-seq, CUT&RUN-qPCR, and dual-luciferase reporter assays, we revealed that overexpression of CaWRKY01-10 and CaWRKY08-4 can activate the expressions of the same four Capsicum annuum defense-related genes (one PR1, two PR4, and one pathogen-related gene) by directly binding to their promoters. However, we did not observe protein-protein interactions and transcriptional amplification/inhibition effects of their shared target genes when coexpressing these two WRKY TFs. In conclusion, these data suggest that both of the resistant line specific upregulated WRKY TFs (CaWRKY01-10 and CaWRKY08-4) can confer pepper's resistance to P. capsici infection by directly activating a cluster of defense-related genes and are potentially useful for genetic improvement against Phytophthora blight of pepper and other crops.

Enhancing plant defensins in a desert shrub: Exploring a regulatory pathway of AnWRKY29

A distinct family of plant-specific WRKY transcription factors plays a crucial role in modulating responses to biotic and abiotic stresses. In this investigation, we unveiled a signaling pathway activated in the desert shrub Ammopiptanthus nanus during feeding by the moth Spodoptera exigua. The process involves a Ca2+ flux that facilitates interaction between the protein kinase AnCIPK12 and AnWRKY29. AnWRKY29 directly interacts with the promoters of two key genes encoding AnPDF1 and AnHsfB1, involved in the biosynthesis of plant defensins. Consequently, AnWRKY29 exerts its transcriptional regulatory function, influencing plant defensins biosynthesis. This discovery implies that A. nanus can bolster resistance against herbivorous insects like S. exigua by utilizing this signaling pathway, providing an effective natural defense mechanism that supports its survival and reproductive success.

WRKY transcription factors modulate flowering time and response to environmental changes

WRKY transcription factors (TFs), originating in green algae, regulate flowering time and responses to environmental changes in plants. However, the molecular mechanisms underlying the role of WRKY TFs in the correlation between flowering time and environmental changes remain unclear. Therefore, this review summarizes the association of WRKY TFs with flowering pathways to accelerate or delay flowering. WRKY TFs are implicated in phytohormone pathways, such as ethylene, auxin, and abscisic acid pathways, to modulate flowering time. WRKY TFs can modulate salt tolerance by regulating flowering time. WRKY TFs exhibit functional divergence in modulating environmental changes and flowering time. In summary, WRKY TFs are involved in complex pathways and modulate response to environmental changes, thus regulating flowering time.

NaWRKY70 is a key regulator of Nicotiana attenuata resistance to Alternaria alternata through regulation of phytohormones and phytoalexins biosynthesis

Jasmonate (JA) and abscisic acid (ABA) are two major phytohormones involved in pathogen resistance. However, how their biosynthesis is regulated is not well understood. We silenced NaWRKY70 in wild tobacco Nicotiana attenuata and determined its role in regulating genes involved in the production of JA, ABA and the phytoalexin capsidiol in response to the fungal pathogen Alternaria alternata using techniques including electrophoretic mobility shift, chromatin immunoprecipitation, transient overexpression and virus-induced gene silencing. Silencing NaWRKY70 dramatically reduced both basal and A. alternata-induced jasmonoyl-isoleucine (JA-Ile) and ABA. Further evidence showed that NaWRKY70 directly binds to the W-boxes of the promoters of NaAOS and NaJAR4 (JA biosynthesis), NaNCED1 and NaXD1-like (ABA biosynthesis), and NaMPK4 (ABA signaling) to activate their expression, while binding but repressing the expression of NaCYP707A4-like3 (ABA degradation). Additionally, NaWRKY70 regulates capsidiol production through its key enzyme genes NaEASs and NaEAHs, and interacts with its regulator NaERF2-like to enhance their expression, whereas ABA negatively regulates capsidiol biosynthesis. Our results highlight the key role of NaWRKY70 in controlling both JA-Ile and ABA production, as well as capsidiol production, thus providing new insight into the defense mechanism of plant resistance to A. alternata.

The MdVQ37-MdWRKY100 complex regulates salicylic acid content and MdRPM1 expression to modulate resistance to Glomerella leaf spot in apples

Glomerella leaf spot (GLS), caused by the fungus Colletotrichum fructicola, is considered one of the most destructive diseases affecting apples. The VQ-WRKY complex plays a crucial role in the response of plants to biotic stresses. However, our understanding of the defensive role of the VQ-WRKY complex on woody plants, particularly apples, under biotic stress, remains limited. In this study, we elucidated the molecular mechanisms underlying the defensive role of the apple MdVQ37-MdWRKY100 module in response to GLS infection. The overexpression of MdWRKY100 enhanced resistance to C. fructicola, whereas MdWRKY100 RNA interference in apple plants reduced resistance to C. fructicola by affecting salicylic acid (SA) content and the expression level of the CC-NBS-LRR resistance gene MdRPM1. DAP-seq, Y1H, EMSA, and RT-qPCR assays indicated that MdWRKY100 inhibited the expression of MdWRKY17, a positive regulatory factor gene of SA degradation, upregulated the expression of MdPAL1, a key enzyme gene of SA biosynthesis, and promoted MdRPM1 expression by directly binding to their promotors. Transient overexpression and silencing experiments showed that MdPAL1 and MdRPM1 positively regulated GLS resistance in apples. Furthermore, the overexpression of MdVQ37 increased the susceptibility to C. fructicola by reducing the SA content and expression level of MdRPM1. Additionally, MdVQ37 interacted with MdWRKY100, which repressed the transcriptional activity of MdWRKY100. In summary, these results revealed the molecular mechanism through which the apple MdVQ37-MdWRKY100 module responds to GLS infection by regulating SA content and MdRPM1 expression, providing novel insights into the involvement of the VQ-WRKY complex in plant pathogen defence responses.

Dissection of the IDA promoter identifies WRKY transcription factors as abscission regulators in Arabidopsis

Plants shed organs such as leaves, petals, or fruits through the process of abscission. Monitoring cues such as age, resource availability, and biotic and abiotic stresses allow plants to abscise organs in a timely manner. How these signals are integrated into the molecular pathways that drive abscission is largely unknown. The INFLORESCENCE DEFICIENT IN ABSCISSION (IDA) gene is one of the main drivers of floral organ abscission in Arabidopsis and is known to transcriptionally respond to most abscission-regulating cues. By interrogating the IDA promoter in silico and in vitro, we identified transcription factors that could potentially modulate IDA expression. We probed the importance of ERF- and WRKY-binding sites for IDA expression during floral organ abscission, with WRKYs being of special relevance to mediate IDA up-regulation in response to biotic stress in tissues destined for separation. We further characterized WRKY57 as a positive regulator of IDA and IDA-like gene expression in abscission zones. Our findings highlight the promise of promoter element-targeted approaches to modulate the responsiveness of the IDA signaling pathway to harness controlled abscission timing for improved crop productivity.

Genome-Wide Analysis of the WRKY Transcription Factor Family in Roses and Their Putative Role in Defence Signalling in the Rose-Blackspot Interaction

WRKY transcription factors are important players in plant regulatory networks, where they control and integrate various physiological processes and responses to biotic and abiotic stresses. Here, we analysed six rose genomes of 5 different species (Rosa chinensis, R. multiflora, R. roxburghii, R. sterilis, and R. rugosa) and extracted a set of 68 putative WRKY genes, extending a previously published set of 58 WRKY sequences based on the R. chinensis genome. Analysis of the promoter regions revealed numerous motifs related to induction by abiotic and, in some cases, biotic stressors. Transcriptomic data from leaves of two rose genotypes inoculated with the hemibiotrophic rose black spot fungus Diplocarpon rosae revealed the upregulation of 18 and downregulation of 9 of these WRKY genes after contact with the fungus. Notably, the resistant genotype exhibited the regulation of 25 of these genes (16 upregulated and 9 downregulated), while the susceptible genotype exhibited the regulation of 20 genes (15 upregulated and 5 downregulated). A detailed RT-qPCR analysis of RcWRKY37, an orthologue of AtWRKY75 and FaWRKY1, revealed induction patterns similar to those of the pathogenesis-related (PR) genes induced in salicylic acid (SA)-dependent defence pathways in black spot inoculation experiments. However, the overexpression of RcWRKY37 in rose petals did not induce the expression of any of the PR genes upon contact with black spot. However, wounding significantly induced the expression of RcWRKY37, while heat, cold, or drought did not have a significant effect. This study provides the first evidence for the role of RcWRKY37 in rose signalling cascades and highlights the differences between RcWRKY37 and AtWRKY75. These results improve our understanding of the regulatory function of WRKY transcription factors in plant responses to stress factors. Additionally, they provide foundational data for further studies.

Genome-Wide Identification of the WRKY Gene Family and Functional Characterization of CpWRKY5 in Cucurbita pepo

The WRKY gene family is crucial for regulating plant growth and development. However, the WRKY gene is rarely studied in naked kernel formation in hull-less Cucurbita pepo L. (HLCP), a natural mutant that lacks the seed coat. In this research, 76 WRKY genes were identified through bioinformatics-based methods in C. pepo, and their phylogenetics, conserved motifs, synteny, collinearity, and temporal expression during seed coat development were analyzed. The results showed that 76 CpWRKYs were identified and categorized into three main groups (I-III), with Group II further divided into five subgroups (IIa-IIe). Moreover, 31 segmental duplication events were identified in 49 CpWRKY genes. A synteny analysis revealed that C. pepo shared more collinear regions with cucumber than with melon. Furthermore, quantitative RT-PCR (qRT-PCR) results indicated the differential expression of CpWRKYs across different varieties, with notable variations in seed coat development between HLCP and CP being attributed to differences in CpWRKY5 expression. To investigate this further, CpWRKY5-overexpression tobacco plants were generated, resulting in increased lignin content and an upregulation of related genes, as confirmed by qRT-PCR. This study offers valuable insights for future functional investigations of CpWRKY genes and presents novel information for understanding the regulation mechanism of lignin synthesis.

A transcriptional regulation of ERF15 contributes to ABA-mediated cold tolerance in tomato

Cold stress is a major meteorological threat to crop growth and yield. Abscisic acid (ABA) plays important roles in plant cold tolerance by activating the expression of cold-responsive genes; however, the underlying transcriptional regulatory module remains unknown. Here, we demonstrated that the cold- and ABA-responsive transcription factor ETHYLENE RESPONSE FACTOR 15 (ERF15) positively regulates ABA-mediated cold tolerance in tomato. Exogenous ABA treatment significantly enhanced cold tolerance in wild-type tomato plants but failed to rescue erf15 mutants from cold stress. Transcriptome analysis showed that ERF15 was associated with the expression of cold-responsive transcription factors such as CBF1 and WRKY6. Further RT-qPCR assays confirmed that the ABA-induced increased in CBF1 and WRKY6 transcripts was suppressed in erf15 mutants when the plants were subjected to cold treatment. Moreover, yeast one-hybrid assays, dual-luciferase assays and electrophoretic mobility shift assays demonstrated that ERF15 activated the transcription of CBF1 and WRKY6 by binding their promoters. Silencing CBF1 or WRKY6 significantly decreased cold tolerance. Overall, our study identified the role of ERF15 in conferring ABA-mediated cold tolerance in tomato plants by activating CBF1 and WRKY6 expression. This study not only broadens our knowledge of the mechanism of ABA-mediated cold tolerance in plants but also highlights ERF15 as an ideal target gene for cold-tolerant crop breeding.

Comparative transcriptional analysis of Persea americana MYB, WRKY and AP2/ERF transcription factors following Phytophthora cinnamomi infection

Plant cells undergo extensive transcriptional reprogramming following pathogen infection, with these reprogramming patterns becoming more complex when pathogens, such as hemibiotrophs, exhibit different lifestyles. These transcriptional changes are often orchestrated by MYB, WRKY and AP2/ERF transcription factors (TFs), which modulate both growth and defence-related gene expression. Transcriptional analysis of defence-related genes in avocado (Persea americana) infected with Phytophthora cinnamomi indicated differential immune response activation when comparing a partially resistant and susceptible rootstock. This study identified 226 MYB, 82 WRKY, and 174 AP2/ERF TF-encoding genes in avocado, using a genome-wide approach. Phylogenetic analysis revealed substantial sequence conservation within TF groups underscoring their functional significance. RNA-sequencing analysis in a partially resistant and susceptible avocado rootstock infected with P. cinnamomi was indicative of an immune response switch occurring in either rootstock after 24 and 6 h post-inoculation, respectively. Different clusters of co-expressed TF genes were observed at these times, suggesting the activation of necrotroph-related immune responses at varying intervals between the two rootstocks. This study aids our understanding of avocado immune response activation following P. cinnamomi infection, and the role of the TFs therein, elucidating the transcriptional reprogramming disparities between partially resistant and susceptible rootstocks.

Tobacco Transcription Factor NtWRKY70b Facilitates Leaf Senescence via Inducing ROS Accumulation and Impairing Hydrogen Sulfide Biosynthesis

Leaf senescence is the terminal stage of leaf development, and its initiation and progression are closely controlled by the integration of a myriad of endogenous signals and environmental stimuli. It has been documented that WRKY transcription factors (TFs) play essential roles in regulating leaf senescence, yet the molecular mechanism of WRKY-mediated leaf senescence still lacks detailed elucidation in crop plants. In this study, we cloned and identified a tobacco WRKY TF gene, designated NtWRKY70b, acting as a positive regulator of natural leaf senescence. The expression profile analysis showed that NtWRKY70b transcript levels were induced by aging and hydrogen peroxide (H2O2) and downregulated upon hydrogen sulfide (H2S) treatment. The physiological and biochemical assays revealed that overexpression of NtWRKY70b (OE) clearly promoted leaf senescence, triggering increased levels of reactive oxygen species (ROS) and decreased H2S content, while disruption of NtWRKY70b by chimeric repressor silencing technology (SRDX) significantly delayed the onset of leaf senescence, leading to a decreased accumulation of ROS and elevated concentration of H2S. The quantitative real-time PCR analysis showed that the expression levels of various senescence-associated genes and ROS biosynthesis-related genes (NtRbohD and NtRbohE) were upregulated in OE lines, while the expression of H2S biosynthesis-related genes (NtDCD and NtCYSC1) were inhibited in OE lines. Furthermore, the Yeast one-hybrid analysis (Y1H) and dual luciferase assays showed that NtWRKY70b could directly upregulate the expression of an ROS biosynthesis-related gene (NtRbohD) and a chlorophyll degradation-related gene (NtPPH) by binding to their promoter sequences. Accordingly, these results indicated that NtWYKY70b directly activated the transcript levels of NtRbohD and NtPPH and repressed the expression of NtDCD and NtCYCS1, thereby promoting ROS accumulation and impairing the endogenous H2S production, and subsequently accelerating leaf aging. These observations improve our knowledge of the regulatory mechanisms of WRKY TFs controlling leaf senescence and provide a novel method for ensuring high agricultural crop productivity via genetic manipulation of leaf senescence in crops.

Genome-wide identification of WRKY transcription factor family members in Miscanthus sinensis (Miscanthus sinensis Anderss)

Miscanthus is an emerging sustainable bioenergy crop whose growing environment is subject to many abiotic and biological stresses. WRKY transcription factors play an important role in stress response and growth of biotic and abiotic. To clarify the distribution and expression of the WRKY genes in Miscanthus, it is necessary to classify and phylogenetically analyze the WRKY genes in Miscanthus. The v7.1 genome assembly of Miscanthus was analyzed by constructing an evolutionary tree. In Miscanthus, there are 179 WRKY genes were identified. The 179 MsWRKYs were classified into three groups with conserved gene structure and motif composition. The tissue expression profile of the WRKY genes showed that MsWRKY genes played an essential role in all growth stages of plants. At the early stage of plant development, the MsWRKY gene is mainly expressed in the rhizome of plants. In the middle stage, it is mainly expressed in the leaf. At the end stage, mainly in the stem. According to the results, it showed significant differences in the expression of the MsWRKY in different stages of Miscanthus sinensis. The results of the study contribute to a better understanding of the role of the MsWRKY gene in the growth and development of Miscanthus.

WRKY48 negatively regulates plant acclimation to a combination of high light and heat stress

Plants growing under natural conditions experience high light (HL) intensities that are often accompanied by elevated temperatures. These conditions could affect photosynthesis, reduce yield, and negatively impact agricultural productivity. The combination of different abiotic challenges creates a new type of stress for plants by generating complex environmental conditions that often exceed the impact of their individual parts. Transcription factors (TFs) play a key role in integrating the different molecular signals generated by multiple stress conditions, orchestrating the acclimation response of plants to stress. In this study, we show that the TF WRKY48 negatively controls the acclimation of Arabidopsis thaliana plants to a combination of HL and heat stress (HL + HS), and its expression is attenuated by jasmonic acid under HL + HS conditions. Using comparative physiological and transcriptomic analyses between wild-type and wrky48 mutants, we further demonstrate that under control conditions, WRKY48 represses the expression of a set of transcripts that are specifically required for the acclimation of plants to HL + HS, hence its suppression during the HL + HS stress combination contributes to plant survival under these conditions. Accordingly, mutants that lack WRKY48 are more resistant to HL + HS, and transgenic plants that overexpress WRKY48 are more sensitive to it. Taken together, our findings reveal that WRKY48 is a negative regulator of the transcriptomic response of Arabidopsis to HL + HS and provide new insights into the complex regulatory networks of plant acclimation to stress combination.

Transcription factors RhbZIP17 and RhWRKY30 enhance resistance to Botrytis cinerea by increasing lignin content in rose petals

The petals of ornamental plants such as roses (Rosa spp.) are the most economically important organs. This delicate, short-lived plant tissue is highly susceptible to pathogens, in large part because the walls of petal cells are typically thinner and more flexible compared with leaf cells, allowing the petals to fold and bend without breaking. The cell wall is a dynamic structure that rapidly alters its composition in response to pathogen infection, thereby reinforcing its stability and boosting plant resistance against diseases. However, little is known about how dynamic changes in the cell wall contribute to resistance to Botrytis cinerea in rose petals. Here, we show that the B. cinerea-induced transcription factor RhbZIP17 is required for the defense response of rose petals. RhbZIP17 is associated with phenylpropanoid biosynthesis and binds to the promoter of the lignin biosynthesis gene RhCAD1, activating its expression. Lignin content showed a significant increase under gray mold infection compared with the control. RhCAD1 functions in the metabolic regulation of lignin production and, consequently, disease resistance, as revealed by transient silencing and overexpression in rose petals. The WRKY transcription factor RhWRKY30 is also required to activate RhCAD1 expression and enhance resistance against B. cinerea. We propose that RhbZIP17 and RhWRKY30 increase lignin biosynthesis, improve the resistance of rose petals to B. cinerea, and regulate RhCAD1 expression.

Synergistic induction of phytoalexins in Nicotiana attenuata by jasmonate and ethylene signaling mediated by NaWRKY70

Production of the phytoalexins scopoletin and scopolin is regulated by jasmonate (JA) and ethylene signaling in Nicotiana species in response to Alternaria alternata, the necrotrophic fungal pathogen that causes brown spot disease. However, how these two signaling pathways are coordinated to control this process remains unclear. In this study, we found that the levels of these two phytoalexins and transcripts of their key enzyme gene, feruloyl-CoA 6'-hydroxylase 1 (NaF6'H1), were synergistically induced in Nicotiana attenuata by co-treatment with methyl jasmonate (MeJA) and ethephon. By combination of RNA sequencing and virus-induced gene silencing, we identified a WRKY transcription factor, NaWRKY70, which had a similar expression pattern to NaF6'H1 and was responsible for A. alternata-induced NaF6'H1 expression. Further evidence from stable transformed plants with RNA interference, knock out and overexpression of NaWRKY70 demonstrated that it is a key player in the synergistic induction of phytoalexins and plant resistance to A. alternata. Electrophoretic mobility shift, chromatin immunoprecipitation-quantitative PCR, and dual-luciferase assays revealed that NaWRKY70 can bind directly to the NaF6'H1 promoter and activate its expression. Furthermore, the key regulator of the ethylene pathway, NaEIN3-like1, can directly bind to the NaWRKY70 promoter and activate its expression. Meanwhile, NaMYC2s, important JA pathway transcription factors, also indirectly regulate the expression of NaWRKY70 and NaF6'H1 to control scopoletin and scopolin production. Our data reveal that these phytoalexins are synergistically induced by JA and ethylene signaling during A. alternata infection, which is largely mediated by NaWRKY70, thus providing new insights into the defense responses against A. alternata in Nicotiana species.

Review: Structural-functional relationship of WRKY transcription factors: Unfolding the role of WRKY in plants

WRKY as the name suggests, are the transcription factors (TFs) that contain the signature WRKY domains, hence named after it. Since their discovery in 1994, they have been well studied in plants with exploration of approximately 74 WRKY genes in the model plant, Arabidopsis alone. However, the study of these transcription factors (TFs) is not just limited to model plant now. They have been studied widely in crop plants as well, because of their tremendous contribution in stress as well as in growth and development. Here, in this review, we describe the story of WRKY TFs from their identification to their origin, the binding mechanisms, structure and their contribution in regulating plant development and stress physiology. High throughput transcriptomics-based data also opened a doorway to understand the comprehensive and detailed functioning of WRKY TFs in plants. Indeed, the detailed functional role of each and every WRKY member in regulating the gene expression is required to pave the path to develop holistic understanding of their role in stress physiology and developmental processes in plants.

Identification and expression analysis of miR396 and its target genes in Jerusalem artichoke under temperature stress

The highly conserved miR396 plays a pivotal role in the growth, development, and responses to abiotic and biotic stresses in plants. However, research on miR396 and its targets in Jerusalem artichoke remains largely unexplored. In this study, we employed bioinformatics and experimental techniques, such as cloning and qRT-PCR, to investigate the regulatory role of miR396 on its targets, leveraging our lab's transcriptomic and degradomic data of Jerusalem artichoke. Specifically, we initially cloned and characterized the precursors (htu-MIR396a/b/c) and mature sequences (htu-miR396a/b/c) of three miR396 isoforms. Subsequently, we identified nine target genes, including seven Growth-Regulating Factors (GRFs) (HtGRF3/4/6/9/10/12/13), one WRKY transcription factor (HtWRKY40), and one Scarecrow-like (SCL) transcription factor (HtSCL33). Finally, we conducted an analysis of their expression patterns across various tissues and their responses to temperature stress. Notably, htu-MIR396s exhibited high expression in seedling stems, while htu-miR396s predominantly expressed in seedling leaves. Moreover, HtWRKY40 and HtSCL33 displayed higher expression levels than HtGRFs in most tissues, except leaves. Remarkably, HtGRF4/6/10/12/13 exhibited higher expression in leaves than in roots and stems during seedling growth. Furthermore, during tuber development, HtGRF4/6/10, HtWRKY40, and HtSCL33 were highly expressed, while HtGRF3/9/12/13 showed relatively lower expression levels. Under heat stress (42℃), htu-MIR396 expression was up-regulated, and htu-miR396 showed dynamic expression patterns in seedlings, resulting in the induction of HtGRF4/6/10/12/13 in leaves and HtSCL33 in roots, while HtWRKY40 in leaves was repressed. Conversely, under cold stress (4℃), htu-MIR396s showed fluctuating expression levels, and htu-miR396s were up-regulated in seedlings. Notably, HtGRF4/13 and HtSCL33 in seedlings were reduced, whereas HtGRF6 in roots and HtWRKY40 in leaves were enhanced. These findings offer valuable insights into the functional roles of miR396-target interactions under abiotic stress in Jerusalem artichoke.

Genome-wide analysis of the Tritipyrum NAC gene family and the response of TtNAC477 in salt tolerance

NAC transcription factors are widely distributed in the plant kingdom and play an important role in the response to various abiotic stresses in plant species. Tritipyrum, an octoploid derived from hybridization of Triticum aestivum (AABBDD) and Thinopyrum elongatum (EE), is an important genetic resource for integrating the desirable traits of Th. elongatum into wheat. In this study, we investigated the tissue distribution and expression of Tritipyrum NAC genes in the whole genomes of T. aestivum and Th. elongatum after obtaining their complete genome sequences. Based on phylogenetic relationships, conserved motifs, gene synthesis, evolutionary analysis, and expression patterns, we identified and characterized 732 Tritipyrum NAC genes. These genes were divided into six main groups (A, B, C, D, E, and G) based on phylogenetic relationships and evolutionary studies, with members of these groups sharing the same motif composition. The 732 TtNAC genes are widely distributed across 28 chromosomes and include 110 duplicated genes. Gene synthesis analysis indicated that the NAC gene family may have a common ancestor. Transcriptome data and quantitative polymerase chain reaction (qPCR) expression profiles showed 68 TtNAC genes to be highly expressed in response to various salt stress and recovery treatments. Tel3E01T644900 (TtNAC477) was particularly sensitive to salt stress and belongs to the same clade as the salt tolerance genes ANAC019 and ANAC055 in Arabidopsis. Pearson correlation analysis identified 751 genes that correlated positively with expression of TtNAC477, and these genes are enriched in metabolic activities, cellular processes, stimulus responses, and biological regulation. TtNAC477 was found to be highly expressed in roots, stems, and leaves in response to salt stress, as confirmed by real-time PCR. These findings suggest that TtNAC477 is associated with salt tolerance in plants and might serve as a valuable exogenous gene for enhancing salt tolerance in wheat.

ZmB12D, a target of transcription factor ZmWRKY70, enhances the tolerance of Arabidopsis to submergence

Submergence stress represents a serious threat to the yield and quality of maize because it can lead to oxygen deficiency and the accumulation of toxic metabolites. However, the mechanisms by which maize resists the adverse effects of submergence stress have yet to be fully elucidated. Here, we cloned a gene from maize Balem (Barley aleurone and embryo), ZmB12D, which was expressed at significant levels in seed embryos during imbibition and in leaves under submergence stress. Subcellular localization analysis indicated that the ZmB12D protein was localized in the mitochondria. The overexpression of ZmB12D in increased the tolerance of Arabidopsis to submergence stress, probably due to a reduction in the levels of malonaldehyde (MDA), the increased activity of antioxidant enzymes (SOD, POD and CAT), enhanced electron transport by coordinating the expression of non-symbiotic hemoglobin-2 (AHb2) and Fe transport-related (AtNAS3) genes (mediating Fe and oxygen availability) and also modulated the anaerobic respiration rates through upregulated the AtPDC1, AtADH1, AtSUS4 genes under submergence. Yeast one-hybrid (Y1H) and transient transactivation assays demonstrated that ZmWRKY70 bound to the ZmB12D promoter and activated ZmB12D. Collectively, out findings indicate that ZmB12D plays an important role in the tolerance of maize to submergence stress. This research provides new insights into the genetic improvement of maize with regards to submergence tolerance.

Genome-wide identification and expression analysis of WRKY gene family members in red clover (Trifolium pratense L.)

Trifolium pratense is an important legume forage grass and a key component of sustainable livestock development. Serving as an essential component, the WRKY gene family, a crucial group of regulatory transcription factors in plants, holds significant importance in their response to abiotic stresses. However, there has been no systematic analysis conducted on the WRKY gene family in Trifolium pratense. This study conducted a comprehensive genomic characterization of the WRKY gene family in Trifolium pratense, utilizing the latest genomic data, resulting in the identification of 59 TpWRKY genes. Based on their structural features, phylogenetic characteristics, and conserved motif composition, the WRKY proteins were classified into three groups, with group II further subdivided into five subgroups (II-a, II-b, II-c, II-d, and II-e). The majority of the TpWRKYs in a group share a similar structure and motif composition. Intra-group syntenic analysis revealed eight pairs of duplicate segments. The expression patterns of 59 TpWRKY genes in roots, stems, leaves, and flowers were examined by analyzing RNA-seq data. The expression of 12 TpWRKY genes under drought, low-temperature (4°C), methyl jasmonate (MeJA) and abscisic acid (ABA) stresses was analyzed by RT-qPCR. The findings indicated that TpWRKY46 was highly induced by drought stress, and TpWRKY26 and TpWRKY41 were significantly induced by low temperature stress. In addition, TpWRKY29 and TpWRKY36 were greatly induced by MeJA stress treatment, and TpWRKY17 was significantly upregulated by ABA stress treatment. In this research, we identified and comprehensively analyzed the structural features of the WRKY gene family in T.pratense, along with determined the possible roles of WRKY candidate genes in abiotic stress. These discoveries deepen our understandings of how WRKY transcription factors contribute to species evolution and functional divergence, laying a solid molecular foundation for future exploration and study of stress resistance mechanisms in T.pratense.

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.

Cloning and functional characterization of FtWRKY29, a low phosphorus stress-inducible transcription factor in Tartary buckwheat

The regulation of the expression of genes related to abiotic stress in plants is significantly influenced by the binding of the transcription factor (TF) WRKY to the W-box elements in their promoters. The findings of this study have confirmed that the ability of Tartary buckwheat (Fagopyrum tataricum Gaertn.) to tolerate phosphorus (P) deficiency is regulated by FtWRKY29, which is classified as a member of group II of the WRKY family. The roots predominantly exhibited an enhanced expression of FtWRKY29, which was significantly upregulated in response to low-P-induced stress. The W-box motif was bound to by FtWRKY29 which enhanced the transcription of genes and was localized to the nucleus. The overexpression of FtWRKY29 in Arabidopsis thaliana produced transgenic lines that exhibited phenotypes typical of diminished sensitivity to low-P-induced stress by promoting root growth, increasing P-uptake, and regulating the accumulation of anthocyanin. The low-P-responsive genes, PHT1;1, PHT1;4, and PHO1 were significantly up-regulated in these lines. In addition, the overexpression of FtWRKY29 restored the P-absorption ability of the wrky75 mutant to a certain extent. Moreover, the binding of FtWRKY29 to the promoter of PHT1;1 activated its expression in tobacco. It was also observed that FtWRKY29 interacts with AtMPK3, AtMPK6, FtMPK3, and FtMPK7. This study provides preliminary evidence that FtWRKY29 improved the tolerance of transgenic A. thaliana plants to low-P-induced stress and deepened the understanding of the regulatory mechanism behind the same in Tartary buckwheat.

AaWRKY6 contributes to artemisinin accumulation during growth in Artemisia annua

Artemisinin, which is extracted from the plant Artemisia annua L., is a crucial drug for curing malaria and has potential applications for treating cancer, diabetes, pulmonary tuberculosis, and other conditions. Demand for artemisinin is therefore high, and enhancing its yield is important. Artemisinin dynamics change during the growth cycle of A. annua; however, the regulatory networks underlying these changes are poorly understood. Here, we collected A. annua leaves at different growth stages and identified target genes from transcriptome data. We determined that WRKY6 binds to the promoters of the artemisinin biosynthesis gene artemisinic aldehyde Δ11(13) reductase (DBR2). In agreement, overexpression of WRKY6 in A. annua resulted in higher expression levels of genes in the artemisinin biosynthesis pathway and greater artemisinin contents than in the wild type. When expression of WRKY6 was down-regulated, artemisinin biosynthesis pathway genes were also down-regulated and the content of artemisinin was lower. WRKY6 mediates the transcriptional activation of artemisinin biosynthesis by binding to the promoter of DBR2, making it a key regulator for modulating the dynamics of artemisinin changes during the A. annua growth cycle.

The transcription factor BnaA9.WRKY47 coordinates leaf senescence and nitrogen remobilization in Brassica napus

Nitrogen (N) is an essential macronutrient for plants, and its remobilization is key for adaptation to deficiency stress. However, there is limited understanding of the regulatory mechanisms of N remobilization in the important crop species Brassica napus (oilseed rape). Here, we report the identification of a transcription factor, BnaA9.WRKY47, that is induced by N starvation in a canola variety. At the seedling stage, BnaA9.WRKY47-overexpressing (OE) lines displayed earlier senescence of older leaves and preferential growth of juvenile leaves compared to the wild type under N starvation. At the field scale, the seed yield was significantly increased in the BnaA9.WRKY47-OE lines compared with the wild type when grown under N deficiency conditions and, conversely, it was reduced in BnaA9.WRKY47-knockout mutants. Biochemical analyses demonstrated that BnaA9.WRKY47 directly activates BnaC7.SGR1 to accelerate senescence of older leaves. In line with leaf senescence, the concentration of amino acids in the older leaves of the OE lines was elevated, and the proportion of plant N that they contained was reduced. This was associated with BnaA9.WRKY47 activating the amino acid permease BnaA9.AAP1 and the nitrate transporter BnaA2.NRT1.7. Thus, the expression of BnaA9.WRKY47 efficiently facilitated N remobilization from older to younger leaves or to seeds. Taken together, our results demonstrate that BnaA9.WRKY47 up-regulates the expression of BnaC7.SGR1, BnaA2.NRT1.7, and BnaA9AAP1, thus promoting the remobilization of N in B. napus under starvation conditions.

An NLR integrated domain toolkit to identify plant pathogen effector targets

Plant immune receptors, known as NOD-like receptors (NLRs), possess unique integrated decoy domains that enable plants to attract pathogen effectors and initiate a specific immune response. The present study aimed to create a library of these integrated domains (IDs) and screen them with pathogen effectors to identify targets for effector virulence and NLR-effector interactions. This works compiles IDs found in NLRs from seven different plant species and produced a library of 78 plasmid clones containing a total of 104 IDs, representing 43 distinct InterPro domains. A yeast two-hybrid assay was conducted, followed by an in planta interaction test, using 32 conserved effectors from Ralstonia pseudosolanacearum type III. Through these screenings, three interactions involving different IDs (kinase, DUF3542, WRKY) were discovered interacting with two unrelated type III effectors (RipAE and PopP2). Of particular interest was the interaction between PopP2 and ID#85, an atypical WRKY domain integrated into a soybean NLR gene (GmNLR-ID#85). Using a Förster resonance energy transfer-fluorescence lifetime imaging microscopy technique to detect protein-protein interactions in living plant cells, PopP2 was demonstrated to physically associate with ID#85 in the nucleus. However, unlike the known WRKY-containing Arabidopsis RRS1-R NLR receptor, GmNLR-ID#85 could not be acetylated by PopP2 and failed to activate RPS4-dependent immunity when introduced into the RRS1-R immune receptor. The generated library of 78 plasmid clones, encompassing these screenable IDs, is publicly available through Addgene. This resource is expected to be valuable for the scientific community with respect to discovering targets for effectors and potentially engineering plant immune receptors.

Co-Expression Networks in Sunflower: Harnessing the Power of Multi-Study Transcriptomic Public Data to Identify and Categorize Candidate Genes for Fungal Resistance

Fungal plant diseases are a major threat to food security worldwide. Current efforts to identify and list loci involved in different biological processes are more complicated than originally thought, even when complete genome assemblies are available. Despite numerous experimental and computational efforts to characterize gene functions in plants, about ~40% of protein-coding genes in the model plant Arabidopsis thaliana L. are still not categorized in the Gene Ontology (GO) Biological Process (BP) annotation. In non-model organisms, such as sunflower (Helianthus annuus L.), the number of BP term annotations is far fewer, ~22%. In the current study, we performed gene co-expression network analysis using eight terabytes of public transcriptome datasets and expression-based functional prediction to categorize and identify loci involved in the response to fungal pathogens. We were able to construct a reference gene network of healthy green tissue (GreenGCN) and a gene network of healthy and stressed root tissues (RootGCN). Both networks achieved robust, high-quality scores on the metrics of guilt-by-association and selective constraints versus gene connectivity. We were able to identify eight modules enriched in defense functions, of which two out of the three modules in the RootGCN were also conserved in the GreenGCN, suggesting similar defense-related expression patterns. We identified 16 WRKY genes involved in defense related functions and 65 previously uncharacterized loci now linked to defense response. In addition, we identified and classified 122 loci previously identified within QTLs or near candidate loci reported in GWAS studies of disease resistance in sunflower linked to defense response. All in all, we have implemented a valuable strategy to better describe genes within specific biological processes.

CdWRKY2 transcription factor modulates salt oversensitivity in bermudagrass [Cynodon dactylon (L.) Pers.]

Common bermudagrass [Cynodon dactylon (L.) Pers.] has higher utilization potential on saline soil due to its high yield potential and excellent stress tolerance. However, key functional genes have not been well studied partly due to its hard transformation. Here, bermudagrass "Wrangler" successfully overexpressing CdWRKY2 exhibited significantly enhanced salt and ABA sensitivity with severe inhibition of shoot and root growth compared to the transgenic negative line. The reduced auxin accumulation and higher ABA sensitivity of the lateral roots (LR) under salt stress were observed in CdWRKY2 overexpression Arabidopsis lines. IAA application could rescue or partially rescue the salt hypersensitivity of root growth inhibition in CdWRKY2-overexpressing Arabidopsis and bermudagrass, respectively. Subsequent experiments in Arabidopsis indicated that CdWRKY2 could directly bind to the promoter region of AtWRKY46 and downregulated its expression to further upregulate the expression of ABA and auxin pathway-related genes. Moreover, CdWRKY2 overexpression in mapk3 background Arabidopsis could partly rescue the salt-inhibited LR growth caused by CdWRKY2 overexpression. These results indicated that CdWRKY2 could negatively regulate LR growth under salt stress via the regulation of ABA signaling and auxin homeostasis, which partly rely on AtMAPK3 function. CdWRKY2 and its homologue genes could also be useful targets for genetic engineering of salinity-tolerance plants.

Genome-wide analysis of the WRKY genes and their important roles during cold stress in white clover

Background

White clover (Trifolium repens L) is a high-quality forage grass with a high protein content, but it is vulnerable to cold stress, which can negatively affect its growth and development. WRKY transcription factor is a family of plant transcription factors found mainly in higher plants and plays an important role in plant growth, development, and stress response. Although WRKY transcription factors have been studied extensively in other plants, it has been less studied in white clover.

Methods and Results

In the present research, we have performed a genome-wide analysis of the WRKY gene family of white clover, in total, there were 145 members of WRKY transcription factors identified in white clover. The characterization of the TrWRKY genes was detailed, including conserved motif analysis, phylogenetic analysis, and gene duplication analysis, which have provided a better understanding of the structure and evolution of the TrWRKY genes in white clover. Meanwhile, the genetic regulation network (GRN) containing TrWRKY genes was reconstructed, and Gene Ontology (GO) annotation analysis of these function genes showed they contributed to regulation of transcription process, response to wounding, and phosphorylay signal transduction system, all of which were important processes in response to abiotic stress. To determine the TrWRKY genes function under cold stress, the RNA-seq dataset was analyzed; most of TrWRKY genes were highly upregulated in response to cold stress, particularly in the early stages of cold stress. These results were validated by qRT-PCR experiment, implying they are involved in various gene regulation pathways in response to cold stress.

Conclusion

The results of this study provide insights that will be useful for further functional analyses of TrWRKY genes in response to biotic or abiotic stresses in white clover. These findings are likely to be useful for further research on the functions of TrWRKY genes and their role in response to cold stress, which is important to understand the molecular mechanism of cold tolerance in white clover and improve its cold tolerance.

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.

Identification of the Regulatory Role of SlWRKYs in Tomato Defense against Meloidogyne incognita

Root-knot nematode (RKN) infections are among the most serious soil-borne diseases in the world, and tomato is a common host of RKNs. WRKY transcription factors are involved in complex, diverse biological processes in plants. In a previous study, a resistant variety, LA3858 (Mi-3/Mi-3), was treated at different soil temperatures before RNA-seq, and six differentially expressed genes (DEGs) encoding WRKY proteins were screened. In this study, cloning and sequencing were used to identify six target DEGs encoding SlWRKY1, SlWRKY13, SlWRKY30, SlWRKY41, SlWRKY46, and SlWRKY80. Conserved domain identification and phylogenetic tree analysis showed that SlWRKY1, SlWRKY13, and SlWRKY46 have similar functions and are mainly involved in plant growth and development and abiotic stress responses. SlWRKY30 and SlWRKY41 share high homology, while AtWRKY46 and AtWRKY70, which are highly homologous to SlWRKY80, play an important role in the disease resistance of A. thaliana. Considering these findings combined with the high level of SlWRKY80 expression observed in the roots and leaves of the resistant variety Motelle (Mi-1/Mi-1) and the continuous upregulation of SlWRKY80 expression in the roots after inoculation of Motelle with M. incognita, it is speculated that SlWRKY80 plays an important role in the Mi-1-mediated disease resistance pathway. Further study revealed that SlWRKY80 is a typical nuclear-localized protein, and a virus-induced gene silencing (VIGS) assay verified that SlWRKY80 is involved in tomato resistance to RKNs as a positive regulator. SA and JA signals play an important role in Mi-1-mediated resistance to RKNs. SlWRKY80 was able to respond rapidly to treatment with both plant hormones, which indicated that SlWRKY80 might be involved in disease resistance regulation through various immune pathways.

Two Sweet Sorghum (Sorghum bicolor L.) WRKY Transcription Factors Promote Aluminum Tolerance via the Reduction in Callose Deposition

Aluminum (Al) toxicity is a primary limiting factor for crop production in acidic soils. The WRKY transcription factors play important roles in regulating plant growth and stress resistance. In this study, we identified and characterized two WRKY transcription factors, SbWRKY22 and SbWRKY65, in sweet sorghum (Sorghum bicolor L.). Al induced the transcription of SbWRKY22 and SbWRKY65 in the root apices of sweet sorghum. These two WRKY proteins were localized in the nucleus and exhibited transcriptional activity. SbWRKY22 showed the significant transcriptional regulation of SbMATE, SbGlu1, SbSTAR1, SbSTAR2a, and SbSTAR2b, which are major known Al tolerance genes in sorghum. Interestingly, SbWRKY65 had almost no effect on the aforementioned genes, but it significantly regulated the transcription of SbWRKY22. Therefore, it is speculated that SbWRKY65 might indirectly regulate Al-tolerance genes mediated by SbWRKY22. The heterologous expression of SbWRKY22 and SbWRKY65 greatly improved the Al tolerance of transgenic plants. The enhanced Al tolerance phenotype of transgenic plants is associated with reduced callose deposition in their roots. These findings suggest the existence of SbWRKY22- and SbWRKY65-mediated Al tolerance regulation pathways in sweet sorghum. This study extends our understanding of the complex regulatory mechanisms of WRKY transcription factors in response to Al toxicity.

Potential pathways and genes expressed in Chrysanthemum in response to early fusarium oxysporum infection

BACKGROUND

Chrysanthemum Fusarium wilt is a common fungal disease caused by Fusarium oxysporum, which causes continuous cropping obstacles and huge losses to the chrysanthemum industry. The defense mechanism of chrysanthemum against F. oxysporum remains unclear, especially during the early stages of the disease. Therefore, in the present study, we analyzed chrysanthemum 'Jinba' samples inoculated with F. oxysporum at 0, 3, and 72 h using RNA-seq.

RESULTS

The results revealed that 7985 differentially expressed genes (DEGs) were co-expressed at 3 and 72 h after F. oxysporum infection. We analyzed the identified DEGs using Kyoto Encyclopedia of Genes and Genomes and Gene Ontology. The DEGs were primarily enriched in "Plant pathogen interaction", "MAPK signaling pathway", "Starch and sucrose metabolism", and "Biosynthesis of secondary metabolites". Genes related to the synthesis of secondary metabolites were upregulated in chrysanthemum early during the inoculation period. Furthermore, peroxidase, polyphenol oxidase, and phenylalanine ammonia-lyase enzymes were consistently produced to accumulate large amounts of phenolic compounds to resist F. oxysporum infection. Additionally, genes related to the proline metabolic pathway were upregulated, and proline levels accumulated within 72 h, regulating osmotic balance in chrysanthemum. Notably, the soluble sugar content in chrysanthemum decreased early during the inoculation period; we speculate that this is a self-protective mechanism of chrysanthemums for inhibiting fungal reproduction by reducing the sugar content in vivo. In the meantime, we screened for transcription factors that respond to F. oxysporum at an early stage and analyzed the relationship between WRKY and DEGs in the "Plant-pathogen interaction" pathway. We screened a key WRKY as a research target for subsequent experiments.

CONCLUSION

This study revealed the relevant physiological responses and gene expression changes in chrysanthemum in response to F. oxysporum infection, and provided a relevant candidate gene pool for subsequent studies on chrysanthemum Fusarium wilt.

Dioscorea composita WRKY5 positively regulates AtSOD1 and AtABF2 to enhance drought and salt tolerances

KEY MESSAGE

DcWRKY5 increases the antioxidant enzyme activity and proline accumulation, oppositely, reduces the accumulation of ROS and MDA, through directly activating the genes expression, finally enhances the salt and drought tolerance. Drought and salinity are two main environmental factors that limit the large-scale cultivation of the medicinal plant Dioscorea composita (D. composita). WRKY transcription factors (TFs) play vital roles in regulating drought and salt tolerance in plants. Nevertheless, the molecular mechanism of WRKY TF mediates drought and salt resistance of D. composita remains largely unknown. Here, we isolated and characterized a WRKY TF from D. composita, namely DcWRKY5, which was localized to the nucleus and bound to the W-box cis-acting elements. Expression pattern analysis showed that it was highly expressed in root and significantly up-regulated in the presence of salt, polyethylene glycol-6000 (PEG-6000) and abscisic acid (ABA). Heterologous expression of DcWRKY5 increased salt and drought tolerance in Arabidopsis, but was insensitive to ABA. In addition, compared with the wild type, the DcWRKY5 overexpressing transgenic lines had more proline, higher antioxidant enzyme (POD, SOD, and CAT) activities, less reactive oxygen species (ROS) and malondialdehyde (MDA). Correspondingly, the overexpression of DcWRKY5 modulated the expression of genes related to salt and drought stresses, such as AtSS1, AtP5CS1, AtCAT, AtSOD1, AtRD22, and AtABF2. Dual luciferase assay and Y1H were further confirmed that DcWRKY5 activate the promoter of AtSOD1 and AtABF2 through directly binding to the enrichment region of the W-box cis-acting elements. These results suggest that DcWRKY5 is a positive regulator of the drought and salt tolerance in D. composita and has potential applications in transgenic breeding.

Genome-Wide Analysis of WRKY Transcription Factors Involved in Abiotic Stress and ABA Response in Caragana korshinskii

The WRKY transcription factor family plays a vital role in plant development and environmental response. However, the information of WRKY genes at the genome-wide level is rarely reported in Caragana korshinskii. In this study, we identified and renamed 86 CkWRKY genes, which were further classified into three groups through phylogenetic analysis. Most of these WRKY genes were clustered and distributed on eight chromosomes. Multiple sequence alignment revealed that the conserved domain (WRKYGQK) of the CkWRKYs was basically consistent, but there were also six variation types (WRKYGKK, GRKYGQK, WRMYGQK, WRKYGHK, WKKYEEK and RRKYGQK) that appeared. The motif composition of the CkWRKYs was quite conservative in each group. In general, the number of WRKY genes gradually increased from lower to higher plant species in the evolutionary analysis of 28 species, with some exceptions. Transcriptomics data and RT-qPCR analysis showed that the CkWRKYs in different groups were involved in abiotic stresses and ABA response. Our results provided a basis for the functional characterization of the CkWRKYs involved in stress resistance in C. korshinskii.

rubrum

The WRKY gene family plays important roles in plant growth and development, as well as in the responses to biotic and abiotic stresses. Loropetalum chinense var. rubrum has high ornamental and medicinal value. However, few WRKY genes have been reported in this plant, and their functions remain unknown. To explore the roles that the WRKY genes play in L. chinense var. rubrum, we identified and characterized 79 LcWRKYs through BLAST homology analysis and renamed them (as LcWRKY1-79) based on their distribution on the chromosomes of L. chinense var. rubrum. In this way, according to their structural characteristics and phylogenetic analysis, they were divided into three groups containing 16 (Group I), 52 (Group II), and 11 (Group III) WRKYs, respectively. LcWRKYs in the same group have similar motifs and gene structures; for instance, Motifs 1, 2, 3, 4, and 10 constitute the WRKY domain and zinc-finger structure. The LcWRKY promoter region contains light response elements (ACE, G-box), stress response elements (TC-rich repeats), hormone response elements (TATC-box, TCA-element), and MYB binding sites (MBS, MBSI). Synteny analysis of LcWRKYs allowed us to establish orthologous relationships among the WRKY gene families of Arabidopsis thaliana, Oryza sativa, Solanum lycopersicum L., Vitis vinifera L., Oryza sativa L., and Zea mays L.; furthermore, analysis of the transcriptomes of mature leaves and flowers from different cultivars demonstrated the cultivar-specific LcWRKY gene expression. The expression levels of certain LcWRKY genes also presented responsive changes from young to mature leaves, based on an analysis of the transcriptome in leaves at different developmental stages. White light treatment led to a significant decrease in the expression of LcWRKY6, 18, 24, 34, 36, 44, 48, 61, 62, and 77 and a significant increase in the expression of LcWRKY41, blue light treatment led to a significant decrease in the expression of LcWRKY18, 34, 50, and 77 and a significant increase in the expression of LcWRKY36 and 48. These results enable a better understanding of LcWRKYs, facilitating the further exploration of their genetic functions and the molecular breeding of L. chinense var. rubrum.

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.

Spatiotemporal, physiological and transcriptomic dynamics of wild jujube seedlings under saline conditions

Soil salinity is a major constraint limiting jujube production in China. Wild jujube (Ziziphus jujuba var. spinosa (Bunge) Hu ex H. F. Chow) is widely used as the rootstock of jujube (Z. jujuba) to overcome the saline conditions. To understand the adaptive mechanism in wild jujube under saline conditions, we combined spatiotemporal and physiological assessments with transcriptomic analysis on wild jujube seedlings undergoing various salt treatments. These salt treatments showed dose and duration effects on biomass, photosynthesis, (K+) and (Na+) accumulation. Salt treatments induced higher levels of salicylic acid in roots and leaves, whereas foliar abscisic acid was also elevated after 8 days. The number of differential expression genes increased with higher doses and also longer exposure of NaCl treatments, with concomitant changes in the enriched Gene Ontology terms that were indicative of altered physiological activities. Gene co-expression network analysis identified the core gene sets associated with salt-induced changes in leaves, stems and roots, respectively. The nitrogen transporters, potassium transporters and a few transcription factors belonging to WRKY/MYB/bHLH families were clustered as the hub genes responding to salt treatments, which were related to elevated nitrogen and K+/Na+. Ectopic overexpression of two WRKY transcription factor genes (ZjWRKY6 and ZjWRKY65) conferred stronger salt-tolerance in Arabidopsis thaliana transformants by enhancing the activities of antioxidant enzymes, decreasing malondialdehyde accumulation and maintaining K+/Na+ homeostasis. This study provided evidence about the spatiotemporal, physiological and transcriptomic dynamics of wild jujube during salt stress and identified potential genes for further research to improve salt tolerance in jujube.

Genome-wide identification and bioinformatics analysis of the WRKY transcription factors and screening of candidate genes for anthocyanin biosynthesis in azalea (Rhododendron simsii)

WRKY transcription factors have been demonstrated to influence the anthocyanin biosynthesis in many plant species. However, there is limited knowledge about the structure and function of WRKY genes in the major ornamental plant azalea (Rhododendron simsii). In this study, we identified 57 RsWRKY genes in the R. simsii genome and classified them into three main groups and several subgroups based on their structural and phylogenetic characteristics. Comparative genomic analysis suggested WRKY gene family has significantly expanded during plant evolution from lower to higher species. Gene duplication analysis indicated that the expansion of the RsWRKY gene family was primarily due to whole-genome duplication (WGD). Additionally, selective pressure analysis (Ka/Ks) suggested that all RsWRKY duplication gene pairs underwent purifying selection. Synteny analysis indicated that 63 and 24 pairs of RsWRKY genes were orthologous to Arabidopsis thaliana and Oryza sativa, respectively. Furthermore, RNA-seq data was used to investigate the expression patterns of RsWRKYs, revealing that 17 and 9 candidate genes may be associated with anthocyanin synthesis at the bud and full bloom stages, respectively. These findings provide valuable insights into the molecular mechanisms underlying anthocyanin biosynthesis in Rhododendron species and lay the foundation for future functional studies of WRKY genes.

The Role of Plant Transcription Factors in the Fight against Plant Viruses

Plants are vulnerable to the challenges of unstable environments and pathogen infections due to their immobility. Among various stress conditions, viral infection is a major threat that causes significant crop loss. In response to viral infection, plants undergo complex molecular and physiological changes, which trigger defense and morphogenic pathways. Transcription factors (TFs), and their interactions with cofactors and cis-regulatory genomic elements, are essential for plant defense mechanisms. The transcriptional regulation by TFs is crucial in establishing plant defense and associated activities during viral infections. Therefore, identifying and characterizing the critical genes involved in the responses of plants against virus stress is essential for the development of transgenic plants that exhibit enhanced tolerance or resistance. This article reviews the current understanding of the transcriptional control of plant defenses, with a special focus on NAC, MYB, WRKY, bZIP, and AP2/ERF TFs. The review provides an update on the latest advances in understanding how plant TFs regulate defense genes expression during viral infection.

Expansion and adaptive evolution of the WRKY transcription factor family in Avicennia mangrove trees

Mangroves are adapted to intertidal zones, which present extreme environmental conditions. WRKYs are among the most prominent transcription factors (TFs) in higher plants and act through various interconnected networks to regulate responses to multiple abiotic stressors. Here, based on omic data, we investigated the landscape and evolutionary patterns of WRKYs in the main mangrove genus Avicennia. We found that both the number and the proportion of TFs and WRKYs in Avicennia species exceeded their inland relatives, indicating a significant expansion of WRKYs in Avicennia. We identified 109 WRKY genes in the representative species Avicennia marina. Comparative genomic analysis showed that two recent whole-genome duplication (WGD) events played a critical role in the expansion of WRKYs, and 88% of Avicennia marina WRKYs (AmWRKYs) have been retained following these WGDs. Applying comparative transcriptomics on roots under experimental salt gradients, we inferred that there is high divergence in the expression of WGD-retained AmWRKYs. Moreover, we found that the expression of 16 AmWRKYs was stable between freshwater and moderately saline water but increased when the trees were exposed to high salinity. In particular, 14 duplicates were retained following the two recent WGD events, indicating potential neo- and sub-functionalization. We also found that WRKYs could interact with other upregulated genes involved in signalling pathways and natural antioxidant biosynthesis to enhance salt tolerance, contributing to the adaptation to intertidal zones. Our omic data of the WRKY family in A. marina broadens the understanding of how a TF family relates to the adaptive evolution of mangroves.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42995-023-00177-y.

Regulation of Nicotiana benthamiana cell death induced by citrus chlorotic dwarf-associated virus-RepA protein by WRKY 1

Citrus chlorotic dwarf-associated virus (CCDaV) is a Citlodavirus species in the Geminiviridae family that causes tremendous economic loss to the citrus industry in China. Some proteins encoded by geminiviruses are crucial for the interaction between the virus and its host plant. However, the exact functions of CCDaV-encoded proteins such as CCDaV-RepA have not been investigated. This study presents evidence that CCDaV-RepA elicits a hypersensitive response (HR)-like cell death in Nicotiana benthamiana that was accompanied by the production of H2O2 and ion leakage, which suggested that CCDaV-RepA is a potential recognition target for inducing host defense responses. Furthermore, the rolling-circle replication motifs of CCDaV-RepA are associated with triggering HR-like cell death in N. benthamiana. Confocal microscopy and deletion mutagenesis assays showed that CCDaV-RepA was located in the nucleus, while the first eight amino acids (aa) at the N terminus and two regions located between aa residues 122-263 and 220-264 of RepA were not associated with nuclear localization. Tobacco rattle virus-induced gene silencing of the key signaling cascade components revealed that HR-like cell death induced by RepA was inhibited in WRKY1-silenced N. benthamiana. Moreover, WRKY1 expression was upregulated in RepA-GFP infiltrated Overall, the results suggest that NbWRKY1 positively regulated CCDaV-RepA -induced cell death in N. benthamiana. These findings provide novel information for further research on the interactions between CCDaV and the host plant.

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.

Dioscorea composita WRKY12 is involved in the regulation of salt tolerance by directly activating the promoter of AtRCI2A

Dioscorea composita (D. composita) is an important medicinal plant worldwide with high economic value. However, its large-scale cultivation was limited by soil salinization. Identification of genes and their mechanisms of action in response to salt stress are critically important. In the present study, we isolated a classical WRKY transcription factor from D. composita, namely DcWRKY12, and analyzed its function in salt tolerance. Expression pattern analysis showed DcWRKY12 is mainly expressed in roots and significantly induced by NaCl, polyethylene glycol-6000 (PEG-6000), and abscisic acid (ABA). Phenotypic and physiological analyses revealed that heterologous expression of DcWRKY12 enhanced salt and osmotic stress tolerance by increasing antioxidant enzyme activity, osmoregulatory substance content, maintaining relative water content and ion homeostasis, decreasing reactive oxygen species and malondialdehyde content. Correspondingly, the overexpression of DcWRKY12 modulated the expression of salt stress-responsive and ion transport-related genes. Dual luciferase assay and Y1H were further confirmed that DcWRKY12 activates the promoter of AtRCI2A through directly binding to the specific W-box cis-acting elements. These results suggest that DcWRKY12 is a positive regulator of salt tolerance in D. composita and has potential applications in salt stress.

Identification and Functional Characterization of WRKY, PHD and MYB Three Salt Stress Responsive Gene Families in Mungbean (Vigna radiata L.)

WRKY-, PHD-, and MYB-like proteins are three important types of transcription factors in mungbeans, and play an important role in development and stress resistance. The genes' structures and characteristics were clearly reported and were shown to contain the conservative WRKYGQK heptapeptide sequence, Cys4-His-cys3 zinc binding motif, and HTH (helix) tryptophan cluster W structure, respectively. Knowledge on the response of these genes to salt stress is largely unknown. To address this issue, 83 VrWRKYs, 47 VrPHDs, and 149 VrMYBs were identified by using comparative genomics, transcriptomics, and molecular biology methods in mungbeans. An intraspecific synteny analysis revealed that the three gene families had strong co-linearity and an interspecies synteny analysis showed that mungbean and Arabidopsis were relatively close in genetic relationship. Moreover, 20, 10, and 20 genes showed significantly different expression levels after 15 days of salt treatment (p < 0.05; Log2 FC > 0.5), respectively. Additionally, in the qRT-PCR analysis, VrPHD14 had varying degrees of response to NaCl and PEG treatments after 12 h. VrWRKY49 was upregulated by ABA treatment, especially in the beginning (within 24 h). VrMYB96 was significantly upregulated in the early stages of ABA, NaCl, and PEG stress treatments (during the first 4 h). VrWRKY38 was significantly upregulated by ABA and NaCl treatments, but downregulated by PEG treatment. We also constructed a gene network centered on the seven DEGs under NaCl treatment; the results showed that VrWRKY38 was in the center of the PPI network and most of the homologous Arabidopsis genes of the interacted genes were reported to have response to biological stress. Candidate genes identified in this study provide abundant gene resources for the study of salt tolerance in mungbeans.

Overexpression of CmWRKY8-1-VP64 Fusion Protein Reduces Resistance in Response to Fusarium oxysporum by Modulating the Salicylic Acid Signaling Pathway in Chrysanthemum morifolium

Chrysanthemum Fusarium wilt, caused by the pathogenic fungus Fusarium oxysporum, severely reduces ornamental quality and yields. WRKY transcription factors are extensively involved in regulating disease resistance pathways in a variety of plants; however, it is unclear how members of this family regulate the defense against Fusarium wilt in chrysanthemums. In this study, we characterized the WRKY family gene CmWRKY8-1 from the chrysanthemum cultivar 'Jinba', which is localized to the nucleus and has no transcriptional activity. We obtained CmWRKY8-1 transgenic chrysanthemum lines overexpressing the CmWRKY8-1-VP64 fusion protein that showed less resistance to F. oxysporum. Compared to Wild Type (WT) lines, CmWRKY8-1 transgenic lines had lower endogenous salicylic acid (SA) content and expressed levels of SA-related genes. RNA-Seq analysis of the WT and CmWRKY8-1-VP64 transgenic lines revealed some differentially expressed genes (DEGs) involved in the SA signaling pathway, such as PAL, AIM1, NPR1, and EDS1. Based on Gene Ontology (GO) enrichment analysis, the SA-associated pathways were enriched. Our results showed that CmWRKY8-1-VP64 transgenic lines reduced the resistance to F. oxysporum by regulating the expression of genes related to the SA signaling pathway. This study demonstrated the role of CmWRKY8-1 in response to F. oxysporum, which provides a basis for revealing the molecular regulatory mechanism of the WRKY response to F. oxysporum infestation in chrysanthemum.

Tomato (Solanum lycopersicum) WRKY23 enhances salt and osmotic stress tolerance by modulating the ethylene and auxin pathways in transgenic Arabidopsis

Osmotic stress is one of the biggest problems in agriculture, which adversely affects crop productivity. Plants adopt several strategies to overcome osmotic stresses that include transcriptional reprogramming and activation of stress responses mediated by different transcription factors and phytohormones. We have identified a WRKY transcription factor from tomato, SlWRKY23, which is induced by mannitol and NaCl treatment. Over-expression of SlWRKY23 in transgenic Arabidopsis enhances osmotic stress tolerance to mannitol and NaCl and affects root growth and lateral root number. Transgenic Arabidopsis over-expressing SlWRKY23 showed reduced electrolyte leakage and higher relative water content than Col-0 plants upon mannitol and NaCl treatment. These lines also showed better membrane integrity with lower MDA content and higher proline content than Col-0. Responses to mannitol were governed by auxin as treatment with TIBA (auxin transport inhibitor) negatively affected the osmotic tolerance in transgenic lines by inhibiting lateral root growth. Similarly, responses to NaCl were controlled by ethylene as treatment with AgNO₃ (ethylene perception inhibitor) inhibited the stress response to NaCl by suppressing primary and lateral root growth. The study shows that SlWRKY23, a osmotic stress inducible gene in tomato, imparts tolerance to mannitol and NaCl stress through interaction of the auxin and ethylene pathways.

The wheat WRKY transcription factor TaWRKY1-2D confers drought resistance in transgenic Arabidopsis and wheat (Triticum aestivum L.)

The WRKY transcription factor family has been associated with a variety of plant biological processes, such as biotic and abiotic stress responses. In this study, 13 wheat TaWRKY DEGs in transcriptome data before and after drought stress, namely TaWRKY1 to TaWRKY8, including various copies, were identified and classified as Group I, II, or III. TaWRKY1-2D overexpression enhanced drought tolerance in transgenic Arabidopsis. Moreover, the AtRD29A, AtP5CS1, AtPOD1, AtCAT1, and AtSOD (Cu/Zn) genes, which are related to the stress response and antioxidant system, were significantly upregulated in TaWRKY1-2D transgenic Arabidopsis under drought stress. TaWRKY1-2 silencing in wheat increases the MDA content, reduces the contents of proline and chlorophyll and the activities of antioxidant enzymes, and inhibits the expression levels of antioxidant (TaPOD, TaCAT, and TaSOD (Fe))- and stress-related genes (TaP5CS) under drought stress. Yeast two-hybrid screening revealed TaDHN3 as an interaction partner of TaWRKY1-2D; their interaction was further confirmed using yeast two-hybrid and bimolecular fluorescence complementation. Furthermore, TaWRKY1-2D may play essential roles in wheat drought tolerance through posttranslational regulation of TaDHN3. Overall, these findings contribute to our knowledge of the WRKY family in wheat and identify TaWRKY1-2D as a promising candidate gene for improving wheat breeding to generate drought-tolerant wheat.

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.

Deciphering evolutionary dynamics of WRKY genes in Arachis species

BACKGROUND

Cultivated peanut (Arachis hypogaea), a progeny of the cross between A. duranensis and A. ipaensis, is an important oil and protein crop from South America. To date, at least six Arachis genomes have been sequenced. WRKY transcription factors (TFs) play crucial roles in plant growth, development, and response to abiotic and biotic stresses. WRKY TFs have been identified in A. duranensis, A. ipaensis, and A. hypogaea cv. Tifrunner; however, variations in their number and evolutionary patterns across various Arachis spp. remain unclear.

RESULTS

WRKY TFs were identified and compared across different Arachis species, including A. duranensis, A. ipaensis, A. monticola, A. hypogaea cultivars (cv.) Fuhuasheng, A. hypogaea cv. Shitouqi, and A. hypogaea cv. Tifrunner. The results showed that the WRKY TFs underwent dynamic equilibrium between diploid and tetraploid peanut species, characterized by the loss of old WRKY TFs and retention of the new ones. Notably, cultivated peanuts inherited more conserved WRKY orthologs from wild tetraploid peanuts than their wild diploid donors. Analysis of the W-box elements and protein-protein interactions revealed that different domestication processes affected WRKY evolution across cultivated peanut varieties. WRKY TFs of A. hypogaea cv. Fuhuasheng and Shitouqi exhibited a similar domestication process, while those of cv. Tifrunner of the same species underwent a different domestication process based on protein-protein interaction analysis.

CONCLUSIONS

This study provides new insights into the evolution of WRKY TFs in Arachis spp.

Global whole-genome comparison and analysis to classify subpopulations and identify resistance genes in weedy rice relevant for improving crops

Common weedy rice plants are important genetic resources for modern breeding programs because they are the closest relatives to rice cultivars and their genomes contain elite genes. Determining the utility and copy numbers of WRKY and nucleotide-binding site (NBS) resistance-related genes may help to clarify their variation patterns and lead to crop improvements. In this study, the weedy rice line LM8 was examined at the whole-genome level. To identify the Oryza sativa japonica subpopulation that LM8 belongs to, the single nucleotide polymorphisms (SNPs) of 180 cultivated and 23 weedy rice varieties were used to construct a phylogenetic tree and a principal component analysis and STRUCTURE analysis were performed. The results indicated that LM8 with admixture components from japonica (GJ) and indica (XI) belonged to GJ-admixture (GJ-adm), with more than 60% of its genetic background derived from XI-2 (22.98%), GJ-tropical (22.86%), and GJ-subtropical (17.76%). Less than 9% of its genetic background was introgressed from weedy rice. Our results also suggested LM8 may have originated in a subtropical or tropical geographic region. Moreover, the comparisons with Nipponbare (NIP) and Shuhui498 (R498) revealed many specific structure variations (SVs) in the LM8 genome and fewer SVs between LM8 and NIP than between LM8 and R498. Next, 96 WRKY and 464 NBS genes were identified and mapped on LM8 chromosomes to eliminate redundancies. Three WRKY genes (ORUFILM02g002693, ORUFILM05g002725, and ORUFILM05g001757) in group III and one RNL [including the resistance to powdery mildew 8 (RPW8) domain, NBS, and leucine rich repeats (LRRs)] type NBS gene (ORUFILM12g000772) were detected in LM8. Among the NBS genes, the RPW8 domain was detected only in ORUFILM12g000772. This gene may improve plant resistance to pathogens as previously reported. Its classification and potential utility imply LM8 should be considered as a germplasm resource relevant for rice breeding programs.