Expression profiles of the Arabidopsis WRKY gene superfamily during plant defense response

Transcript profiling of plastid ferrochelatase two mutants reveals that chloroplast singlet oxygen signals lead to global changes in RNA profiles and are mediated by Plant U-Box 4

BACKGROUND

In response to environmental stresses, chloroplasts generate reactive oxygen species, including singlet oxygen (1O2), an excited state of oxygen that regulates chloroplast-to-nucleus (retrograde) signaling, chloroplast turnover, and programmed cell death (PCD). Yet, the central signaling mechanisms and downstream responses remain poorly understood. The Arabidopsis thaliana plastid ferrochelatase two (fc2) mutant conditionally accumulates 1O2, and Plant U-Box 4 (PUB4), a cytoplasmic E3 ubiquitin ligase, is involved in propagating 1O2 signals for chloroplast turnover and cellular degradation. Thus, the fc2 and fc2 pub4 mutants are useful genetic tools to elucidate these signaling pathways. Previous studies have focused on the role of 1O2 in promoting cellular degradation in fc2 mutants, but its impact on retrograde signaling from mature chloroplasts (the major site of 1O2 production) is poorly understood.

RESULTS

To gain mechanistic insights into 1O2 signaling pathways, we compared transcriptomes of adult wt, fc2, and fc2 pub4 plants. The accumulation of 1O2 in fc2 plants broadly repressed genes involved in chloroplast function and photosynthesis, while inducing genes and transcription factors involved in abiotic and biotic stress, the biosynthesis of jasmonic acid (JA) and salicylic acid (SA), microautophagy, and senescence. Elevated JA and SA levels were observed in 1O2-stressed fc2 plants. pub4 reversed most of this 1O2-induced gene expression and reduced the JA content in fc2 plants. The pub4 mutation also blocked JA-induced senescence pathways in the dark. However, fc2 pub4 plants maintained constitutively elevated levels of SA even in the absence of bulk 1O2 accumulation.

CONCLUSIONS

Together, this work demonstrates that in fc2 plants, 1O2 leads to a robust retrograde signal that may protect cells by downregulating photosynthesis and ROS production while simultaneously mounting a stress response involving SA and JA. The induction of microautophagy and senescence pathways indicate that 1O2-induced cellular degradation is a genetic response to this stress, and the bulk of this transcriptional response is modulated by the PUB4 protein. However, the effect of pub4 on hormone synthesis and signaling is complex and indicates that an intricate interplay of SA and JA are involved in promoting stress responses and programmed cell death during photo-oxidative damage.

Genome-Wide Characterization of WRKY Gene Family in Camellia chekiangoleosa Identifies Potential Regulatory Components in Pigment Biosynthesis Pathways

The WRKY gene family is essential for controlling a variety of plant physiological functions, yet the involvement of specific WRKY members in pigment biosynthesis and accumulation in Camellia chekiangoleosa remains unexplored, particularly in anthocyanins and carotenoids, which play crucial roles in the pigmentation of C. chekiangoleosa. This study systematically identified 87 WRKY genes across 15 chromosomes in C. chekiangoleosa through bioinformatic approaches. Further structural and phylogenetic analyses of these TFs enabled their classification into six different subgroups. WRKY family expansion was shown to be mostly driven by tandem duplication. W-box elements, which can be binding sites for WRKY transcription factors, were present in a number of biosynthetic genes in the pigment production pathway. Yeast one-hybrid assay confirmed that five WRKY transcription factors (CchWRKY15/24/33/47/76) directly bind to the promoter regions of two key biosynthetic genes, CchPSY1 and Cch4CL1. Intriguingly, among the five WRKYs tested, the expression levels of CchWRKY15, CchWRKY33, and CchWRKY47 showed the strongest positive associations with flavonoid accumulation (p < 0.05, Pearson correlation analysis).These findings provide novel insights into the evolutionary patterns, transcriptional regulation, and functional characteristics of CchWRKYs, while elucidating their possible regulatory mechanisms in the fruit coloration of C. chekiangoleosa.

Integrated analysis of Populus deltoides PR1 genes uncovered a PdePR1 as a defense marker against foliar rust

Pathogenesis-related protein 1 (PR1), a hallmark of plant disease resistance, plays pivotal roles in defense signaling. In this study, we identified 16 intronless PR1 genes in Populus deltoides, all classified within the CAP superfamily (cysteine-rich secretory protein, antigen 5, and pathogenesis-related 1) and characterized by conserved N-terminal signal peptides, caveolin-binding motifs, and CAP-derived peptides. Phylogenomic reconstruction of 231 PR1 homologs across 15 plant species traced their origin to Chara braunii, with lineage-specific expansions driven by gene duplication. Evolutionary analyses revealed strong purifying selection acting on ancestral PR1 paralogs to confer a selective advantage for disease resistance. Integrated transcriptomic profiling and quantitative RT-PCR analyses identified PdePR1_10 as a key marker gene for defense activation, exhibiting significant induction at two days post-inoculation in resistant poplars. Co-expression network analysis indicated that PdePR1_10 interacts with several defense-related genes, including NBS-LRR resistance genes, signaling kinases, and hormone biosynthesis enzymes. Specifically, the W-box cis-regulatory element in the PdePR1_10 promoter is hypothesized to interact with WRKY transcription factors, activating PdePR1_10 expression through a salicylic acid (SA)-dependent signaling pathway. Transgenic poplars overexpressing PdePR1_10 exhibited significantly enhanced rust resistance, confirming its critical in defense response. In summary, we thoroughly elucidated the biological functions and regulatory mechanisms of PR1 genes in rust resistance and provided a valuable transgenic poplar line for future studies.

Evolutional, expressional and functional analysis of WRKY gene family reveals that PbeWRKY16 and PbeWRKY31 contribute to the Valsa canker resistance in Pyrus betulifolia

The WRKY transcription factor family plays a crucial role in regulating plant growth and stress responses. However, there are few studies on the regulation of resistance to Valsa canker. In this study, a comprehensive analysis of WRKY genes across 19 plant species was conducted. The potential members of Valsa canker resistance regulation were identified via functional validation. A total of 1641 WRKY genes could be categorized into seven groups. WRKY family members show subfamily- and species-specific expansions. In Rosaceae, Group II-d and II-e were rapidly expanded, which mainly originated based from whole genome duplication (WGD). Cis-element analysis and protein interaction network prediction underscored that most WRKYs respond to stress signals. Based on expressional investigation and Weighted Gene Co-expression Network Analysis (WGCNA), 9 WRKY genes in Pyrus betulaefolia were screened as candidates for Valsa canker resistance regulation. Functional analysis further demonstrated that PbeWRKY16 and PbeWRKY31 regulate the expression of genes involved in salicylic acid (SA) biosynthesis and transport, thereby enhancing resistance to Valsa canker and activating immune responses. Our results provide a foundation for understanding the evolutionary mechanisms of the WRKY gene family and screened potential family members on Valsa canker resistance regulation.

Gibberellin Mediates VvmiR397a-VvLAC4 via VvSLR1-VvWRKY26 Cascade Signal to Repress the Seed-Stone Development During GA-Induced Grape Parthenocarpy

Exogenous gibberellin (GA) effectively inhibits the development of lignified seed-stone in grapes by inducing parthenocarpic seedless berries and significantly improving berry quality. However, the molecular mechanisms underlying this process remain elusive. Here, we uncovered the roles of miR397a in GA signalling-mediated grape seed-stone development through VvSLR1-VvWRKY26 cascade modulation in grapes, indicating 'VvSLR1-VvWRKY26-VvmiR397a-VvLAC4' is the key signalling regulatory module in lignin synthesis of seed-stone in GA-induced grape parthenocarpic berries. VvSLR1 inhibits VvmiR397a expression through interaction with VvWRKY26 and promotes the laccase-mediated lignin synthesis, while GA depresses lignin synthesis by overcoming VvSLR1-mediated multi-level cascade signals. We identified GA responsive cis-element of VvMIR397a promoter bound by VvWRKY26, which activated VvmiR397a expression, whereby inhibiting VvLAC4 level. The expression patterns and cleavage roles' variation of VvmiR397a-VvLAC4 during the seed stones of grape stone-hardening stage indicated that this pair is the one main regulatory module from VvLACs family in this process. Overexpression of VvMIR397a in tobacco and short tandem target mimic (STTM) assays of VvmiR397a/FvmiR397 in grape/strawberry highlighted the function of miR397a-LACs module during modulation of lignin synthesis. Our findings shed novel insights into the GA-responsive roles of VvmiR397a through multi-level cascade signals during modulation of grape seed-stone development, which has important implications for the molecular breeding of high-quality seedless grape berries.

Roles of WRKY Transcription Factors in Response to Sri Lankan Cassava Mosaic Virus Infection in Susceptible and Tolerant Cassava Cultivars

Cassava mosaic disease (CMD) is caused by viruses such as Sri Lankan cassava mosaic virus (SLCMV). It poses a significant threat to the cassava (Manihot esculenta) yield in Southeast Asia. Here, we investigated the expression of WRKY transcription factors (TFs) in SLCMV-infected cassava cultivars KU 50 (tolerant) and R 11 (susceptible) at 21, 32, and 67 days post-inoculation (dpi), representing the early, middle/recovery, and late infection stages, respectively. The 34 identified WRKYs were classified into the following six groups based on the functions of their homologs in the model plant Arabidopsis thaliana (AtWRKYs): plant defense; plant development; hormone signaling (abscisic, salicylic, and jasmonic acid); reactive oxygen species production; basal immune mechanisms; and other related hormones, metabolites, and abiotic stress responses. Regarding the protein interactions of the identified WRKYs, based on the interactions of their homologs (AtWRKYs), WRKYs increased reactive oxygen species production, leading to salicylic acid accumulation and systemic acquired resistance (SAR) against SLCMV. Additionally, some WRKYs were involved in defense-related mitogen-activated protein kinase signaling and abiotic stress responses. Furthermore, crosstalk among WRKYs reflected the robustly restricted viral multiplication in the tolerant cultivar, contributing to CMD recovery. This study highlights the crucial roles of WRKYs in transcriptional reprogramming, innate immunity, and responses to geminivirus infections in cassava, providing valuable insights to enhance disease resistance in cassava and, potentially, other crops.

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.

Genome-Wide Identification and Characterization of the WRKY Gene Family and Their Associated Regulatory Elements in Fortunella hindsii

Background

The WRKY gene family is identified as one of the most prominent transcription factor families in plants and is involved in various biological processes such as metabolism, growth and development, and response to biotic and abiotic stresses. In many plant species, the WRKY gene family was widely studied and analyzed but little to no information for Fortunella hindsii. However, the completion of the whole genome sequencing of Fortunella hindsii allowed us to investigate the genome-wide analysis of WRKY proteins.

Objective

The main objective of this study was to analyze and identify the WRKY gene family in Fortunella hindsii genome.

Methodology

Various bioinformatics approaches have been used to conduct this study.

Results

We constituted 46 members of the Fortunella hindsii WRKY gene family, which were unevenly distributed on all nine chromosomes. The phylogenetic relationship of predicted WRKY proteins of Fortunella hindsii with the WRKY proteins of Arabidopsis showed that 46 FhWRKY genes were divided into three main groups (G1, G2, G3) with five subgroups (2A, 2B, 2C, 2D, and 2E) of G2 group. Domain, conserved motif identification, and gene structure were conducted and the results found that these FhWRKY proteins have conserved identical characteristics within groups and maintain differences between groups. In silico subcellular localization, results showed that FhWRKY genes are located in the nucleus. The cis-regulatory element analysis identified several key CREs that are significantly associated with light, hormone responses, and stress. The gene ontology analysis of these predicted FhWRKY genes showed that these genes are significantly enriched in sequence-specific DNA binding, transcriptional activity, cellular biosynthesis, and metabolic processes.

Conclusion

Therefore, overall, our results provided an excellent foundation for further functional characterization of WRKY genes with an aim of Fortunella hindsii citrus crop improvement.

Genome-wide identification, characterization and expression analysis of WRKY transcription factors under abiotic stresses in Carthamus tinctorius L

BACKGROUND

WRKY transcription factors constitute one of the largest families of plant transcriptional regulators, playing pivotal roles in plant responses to biotic and abiotic stresses, as well as in hormonal signaling and secondary metabolism regulation. However, a comprehensive analysis of the WRKY family in Carthamus tinctorius (safflower) is lacking. This study aims to identify and characterize WRKY genes in safflower to enhance understanding of their roles in stress responses and metabolic regulation. Safflower, valued for its ornamental, medicinal, and culinary uses, exhibits significant resilience to salt, alkali, and drought. By elucidating the functions and expression patterns of WRKY genes, we aim to enhance breeding strategies for improved stress tolerance and metabolic traits in crops.

RESULTS

In this study, we identified 84 WRKY genes within the safflower genome, and classified them into three primary groups (Groups I, II, and III) based on molecular structure and phylogenetic relationships. Group II was further subdivided into five subgroups (II-a, II-b, II-c, II-d, and II-e). Gene structure, conserved domain, motif, cis-elements, and expression profiling were performed. Syntenic analysis revealed that there were 27 pairs of repetitive fragments. Expression profiles of CtWRKY genes were assessed across diverse tissues, colored cultivars, and abiotic stresses such as ABA, drought, and cold conditions. Several CtWRKY genes (e.g., CtWRKY44, CtWRKY63, CtWRKY65, CtWRKY70 and CtWRKY72) exhibited distinct expression patterns in response to cold stress and during different developmental stages. Additionally, CtWRKY13, CtWRKY69, CtWRKY29, CtWRKY56, and CtWRKY36 were upregulated across different flower colors. The expression patterns of CtWRKY48, CtWRKY58, and CtWRKY70 varied among safflower cultivars and flower colors. After exposure to drought stress, the expression levels of CtWRKY29 and CtWRKY58 were downregulated, while those of CtWRKY56 and CtWRKY62 were upregulated.

CONCLUSION

This study identified 84 WRKY genes in Carthamus tinctorius and classified them into three groups, with detailed analyses of their structure, conserved domains, motifs, and expression profiles under various stresses. Notably, several WRKY genes such as CtWRKY44, CtWRKY63, and CtWRKY72 displayed significant expression changes under cold stress, while CtWRKY56 and CtWRKY62 were responsive to drought stress. These findings highlight the critical roles of specific WRKY genes in abiotic stress tolerance and developmental regulation in safflower.

Identification of WRKY transcription factors in Ipomoea pes-caprae and functional role of IpWRKY16 in sweet potato salt stress response

BACKGROUND

WRKY transcription factors are plant-specific and play essential roles in growth, development, and stress responses, including reactions to salt, drought, and cold. Despite their significance, the WRKY genes in the wild sweet potato ancestor, Ipomoea pes-caprae, remain unexplored.

RESULTS

In this study, 65 WRKY genes were identified in the I. pes-caprae transcriptomic data. A phylogenetic tree incorporating Arabidopsis thaliana and Ipomoea batatas revealed seven major groups, each characterized by conserved gene structural features. Transcriptome data of I. pes-caprae under salt stress conditions identified 17 highly expressed WRKY genes, whose promoter regions contain cis-acting elements associated with plant growth, stress responses, and hormone signaling. Further analysis revealed that the 17 IpWRKY genes exhibited differential expression patterns under various abiotic stresses, suggesting their potential roles in specific stress responses. The gene IpWRKY16 was significantly up-expressed under salt stress, drought, salicylic acid (SA), and abscisic acid (ABA) treatments. Subcellular localization analysis confirmed that IpWRKY16 is located in the nucleus. Under salt stress, IpWRKY16 overexpressing roots showed high activity in superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and low content in malondialdehyde (MDA). Using non-invasive micro-test technology (NMT), a significant efflux of Na+ was observed in the elongation zones of sweet potato adventitious roots that overexpressed IpWRKY16. Quantitative reverse transcription PCR (qRT-PCR) revealed that several ion transporter genes were responsive to IpWRKY16 expression, with IbSOS3, IbAHA4-1, and IbAHA4-2 showing the highest expression levels. We hypothesize that IpWRKY16 responds to salt stress by forming a complex regulatory network involving these key genes.

CONCLUSIONS

This study provides a foundational understanding of WRKY transcription factors in I. pes-caprae, offering insights into their potential role in enhancing salt-tolerance in sweet potato. Our findings contribute valuable genetic knowledge that could aid in the molecular breeding of stress-resilient sweet potato varieties.

SlWRKY51 regulates proline content to enhance chilling tolerance in tomato

Chilling stress is a major environmental factor that significantly reduces crop production. To adapt to chilling stress, plants activate a series of cellular responses and accumulate an array of metabolites, particularly proline. Here, we report that the transcription factor SlWRKY51 increases proline contents in tomato (Solanum lycopersicum) under chilling stress. SlWRKY51 expression is induced under chilling stress. Knockdown or knockout of SlWRKY51 led to chilling-sensitive phenotypes, with lower photosynthetic capacity and more reactive oxygen species (ROS) accumulation than the wild type (WT). The proline contents were significantly reduced in SlWRKY51 knockdown and knockout lines under chilling stress, perhaps explaining the phenotypes of these lines. D-1-pyrroline-5-carboxylate synthetase (P5CS), which catalyses the rate-limiting step of proline biosynthesis, is encoded by two closely related P5CS genes (P5CS1 and P5CS2). We demonstrate that SlWRKY51 directly activates the expression of P5CS1 under chilling stress. In addition, the VQ (a class of plant-specific proteins containing the conserved motif FxxhVQxhTG) family member SlVQ10 physically interacts with SlWRKY51 to enhance its activation of P5CS1. Our study reveals that the chilling-induced transcription factor SlWRKY51 enhances chilling tolerance in tomato by promoting proline accumulation.

Transcript profiling of plastid ferrochelatase two mutants reveals that chloroplast singlet oxygen signals lead to global changes in RNA profiles and are mediated by Plant U-Box 4

Background

In response to environmental stresses, chloroplasts generate reactive oxygen species, including singlet oxygen (1O2), an excited state of oxygen that regulates chloroplast-to-nucleus (retrograde) signaling, chloroplast turnover, and programmed cell death (PCD). Yet, the central signaling mechanisms and downstream responses remain poorly understood. The Arabidopsis thaliana plastid ferrochelatase two (fc2) mutant conditionally accumulates 1O2 and Plant U-Box 4 (PUB4), a cytoplasmic E3 ubiquitin ligase, is involved in propagating 1O2 signals for chloroplast turnover and cellular degradation. Thus, the fc2 and fc2 pub4 mutants are useful genetic tools to elucidate these signaling pathways. Previous studies have focused on the role of 1O2 in promoting cellular degradation in fc2 mutants, but its impact on retrograde signaling from mature chloroplasts (the major site of 1O2 production) is poorly understood.

Results

To gain mechanistic insights into 1O2 signaling pathways, we compared transcriptomes of adult wt, fc2, and fc2 pub4 plants. The accumulation of 1O2 in fc2 plants broadly repressed genes involved in chloroplast function and photosynthesis, while inducing genes and transcription factors involved in abiotic and biotic stress, the biosynthesis of jasmonic acid (JA) and salicylic acid (SA), microautophagy, and senescence. Elevated JA and SA levels were observed in 1O2-stressed fc2 plants. pub4 reversed most of this 1O2-induced gene expression and reduced the JA content in fc2 plants. The pub4 mutation also blocked JA-induced senescence pathways in the dark. However, fc2 pub4 plants maintained constitutively elevated levels of SA even in the absence of bulk 1O2 accumulation.

Conclusions

Together, this work demonstrates that in fc2 plants, 1O2 leads to a robust retrograde signal that may protect cells by downregulating photosynthesis and ROS production while simultaneously mounting a stress response involving SA and JA. The induction of microautophagy and senescence pathways indicate that 1O2-induced cellular degradation is a genetic response to this stress, and the bulk of this transcriptional response is modulated by the PUB4 protein. However, the effect of pub4 on hormone synthesis and signaling is complex and indicates that an intricate interplay of SA and JA are involved in promoting stress responses and programmed cell death during photo-oxidative damage.

Ethyl acetate extract of Artemisia argyi improves the resistance of cotton to Verticillium dahliae by activating the immune response

Verticillium wilt, a significant pathogen affecting cotton, has historically been challenging to control, posing a substantial threat to the sustainable development of the cotton industry. This study demonstrates that resistance to Verticillium dahliae in cotton can be enhanced by treating the roots with an ethyl acetate extract (EAAA) extracted from Artemisia argyi. The mechanisms by which EAAA activates immunity in cotton were elucidated by examining the expression levels of resistance genes post-treatment, evaluating salicylic acid (SA) and jasmonic acid (JA) levels, analyzing transcriptome data, and employing virus-induced gene silencing (VIGS) technology. Additionally, pot experiments were conducted to validate the efficacy of EAAA in controlling Verticillium wilt. The flavonoid content in EAAA was qualitatively analyzed using Ultra-Performance Liquid Chromatography coupled with Tandem Mass Spectrometry (UPLC-MS/MS), identifying three specific flavonoids that were further screened to verify their roles in activating cotton immunity. Cotton plants treated with EAAA exhibited reduced leaf chlorosis and browning in the vascular bundles. Genes involved in SA and JA synthesis and signaling in the root system were highly expressed, resulting in increased levels of SA and JA. Transcriptome analysis revealed that most upregulated differentially expressed genes were primarily enriched in the Mitogen-Activated Protein Kinase (MAPK) signaling pathway. Two specific genes, RLK and MAPKKK18, were identified through VIGS technology as key regulators of the immune pathway in cotton. The flavonoid monomer activation experiment demonstrated that eupatilin, hispidulin, jaceosidin, and a mixture of these three could induce the expression of cotton-related resistance genes. Collectively, these findings provide a research basis for the development of EAAA as a natural plant immune-inducing agent against cotton Verticillium wilt.

Transcription factor gene TaWRKY76 confers plants improved drought and salt tolerance through modulating stress defensive-associated processes in Triticum aestivum L

WRKY transcription factor (TF) family acts as essential regulators in plant growth and abiotic stress responses. This study reported the function of TaWRKY76, a member of WRKY TF family in Triticum aestivum L., in regulating plant osmotic stress tolerance. TaWRKY76 transcripts were significantly upregulated upon drought and salt signaling, with dose extent- and stress temporal-dependent manners. Plant GUS activity assays suggested that stress responsive cis-acting elements, such as DRE and ABRE, exert essential roles in defining gene transcription under osmotic stress conditions. The TaWRKY76 protein targeted onto nucleus and possessed ability interacting with TaMYC2, a MYC TF member of wheat. TaWRKY76 and TaMYC2 positively regulated plant drought and salt adaptation by modulating osmotic stress-related physiological indices, including osmolyte contents, stomata movement, root morphology, and reactive oxygen species (ROS) homeostasis. Yeast one-hybrid assay indicated the binding ability of TaWRKY76 with promoters of TaDREB1;1, TaNCEB3, and TaCOR15;4. ChIP-PCR analysis confirmed that the osmotic stress genes are transcriptionally regulated by TaWRKY76. Moreover, the transgenic lines with knockdown of these stress-response genes displayed lowered plant biomass together with worsened root growth traits, decreased proline contents, and elevated ROS amounts. These results suggested that these stress defensive genes contributed to TaWRKY76-modulated osmotic stress tolerance. Highly positive correlations were observed between yield and the transcripts of TaWRKY76 in a wheat variety panel under field drought condition. A major haplotype TaWRKY76 Hap1 conferred improved drought tolerance. Our results suggested that TaWRKY76 is essential in plant drought and salt adaptation and a valuable target for molecular breeding stress-tolerant cultivars in Triticum aestivum L..

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.

Transcriptome, hormonal, and secondary metabolite changes in leaves of DEFENSE NO DEATH 1 (DND1) silenced potato plants

DEFENSE NO DEATH 1 (DND1) is a cyclic nucleotide-gated ion channel protein. Earlier, it was shown that the silencing of DND1 in the potato (Solanum tuberosum L.) leads to resistance to late blight, powdery mildew, and gray mold diseases. At the same time, however, it can reduce plant growth and cause leaf necrosis. To obtain knowledge of the molecular events behind the pleiotropic effect of DND1 downregulation in the potato, metabolite and transcriptome analyses were performed on three DND1 silenced lines of the cultivar 'Désirée.' A massive increase in the salicylic acid content of leaves was detected. Concentrations of jasmonic acid and chlorogenic acid and their derivatives were also elevated. Expression of 1866 genes was altered in the same way in all three DND1 silenced lines, including those related to the synthesis of secondary metabolites. The activation of several alleles of leaf rust, late blight, and other disease resistance genes, as well as the induction of pathogenesis-related genes, was detected. WRKY and NAC transcription factor families were upregulated, whereas bHLHs were downregulated, indicating their central role in transcriptome changes. These results suggest that the maintenance of the constitutive defense state leads to the reduced growth of DND1 silenced potato plants.

Functional characterization of AcWRKY94 in response to Pseudomonas syringae pv. actinidiae in kiwifruit

WRKY transcription factors are essential for coping with various biotic stresses. Pseudomonas syringae pv. actinidiae (Psa)-induced kiwifruit canker is a major problem restricting kiwifruit yield. Nevertheless, it's unclear how the kiwifruit WRKY genes respond to Psa. Through genome-wide identification, 112 WRKY members were found in 'Hongyang' genome in this work. Promoter analysis revealed that there were many cis-acting elements associated with stress responses in the AcWRKY gene's promoter region. According to transcriptomic analysis, 90 of the AcWRKY genes were differently expressed following Psa, salicylic acid (SA), or methyl jasmonate (MeJA) treatments. Almost all group III WRKYs were responsive to at least one of these treatments, with tissue-specific expression patterns. Quantitative RT-PCR study provided more evidence that Psa and SA treatments significantly induced the expression of the group III WRKY gene AcWRKY94, whereas MeJA treatment repressed it. AcWRKY94 was a transcriptionally active protein localized in the nucleus. Transient overexpression of AcWRKY94 in the leaves of 'Hongyang' enhanced the resistance of kiwifruit to Psa. Overexpression of AcWRKY94 in kiwifruit callus remarkably promoted the expression of PR and JAZ genes associated with SA and JA signals, respectively. These data imply that AcWRKY94 controls the signaling pathway dependent on SA and JA, thereby enhancing resistance to Psa. Taken together, this study establishes the basis for functional research on WRKY genes and provides important information for elucidating the resistance mechanism of kiwifruit canker disease.

Streamlined spatial and environmental expression signatures characterize the minimalist duckweed Wolffia australiana

Single-cell genomics permits a new resolution in the examination of molecular and cellular dynamics, allowing global, parallel assessments of cell types and cellular behaviors through development and in response to environmental circumstances, such as interaction with water and the light-dark cycle of the Earth. Here, we leverage the smallest, and possibly most structurally reduced, plant, the semiaquatic Wolffia australiana, to understand dynamics of cell expression in these contexts at the whole-plant level. We examined single-cell-resolution RNA-sequencing data and found Wolffia cells divide into four principal clusters representing the above- and below-water-situated parenchyma and epidermis. Although these tissues share transcriptomic similarity with model plants, they display distinct adaptations that Wolffia has made for the aquatic environment. Within this broad classification, discrete subspecializations are evident, with select cells showing unique transcriptomic signatures associated with developmental maturation and specialized physiologies. Assessing this simplified biological system temporally at two key time-of-day (TOD) transitions, we identify additional TOD-responsive genes previously overlooked in whole-plant transcriptomic approaches and demonstrate that the core circadian clock machinery and its downstream responses can vary in cell-specific manners, even in this simplified system. Distinctions between cell types and their responses to submergence and/or TOD are driven by expression changes of unexpectedly few genes, characterizing Wolffia as a highly streamlined organism with the majority of genes dedicated to fundamental cellular processes. Wolffia provides a unique opportunity to apply reductionist biology to elucidate signaling functions at the organismal level, for which this work provides a powerful resource.

Identification and Analysis of WRKY Transcription Factors in Response to Cowpea Fusarium Wilt in Cowpea

In plants, WRKY transcription factors play a crucial role in plant growth, development, and response to abiotic and biotic stress. Cowpea (Vigna unguiculata) is an important legume crop. However, cowpea Fusarium wilt (CFW), caused by Fusarium oxysporum f. sp. tracheiphilum (Fot), poses a serious threat to its production. In this study, we systematically identified members of the cowpea WRKY (VuWRKY) gene family and analyzed their expression patterns under CFW stress. A total of 91 WRKY transcription factors were identified in the cowpea genome. Phylogenetic and synteny analyses indicated that the expansion of VuWRKY genes in cowpea is primarily due to recent duplication events. Transcriptome analysis of cowpea inoculated with Fo revealed 31 differentially expressed VuWRKY genes, underscoring their role in the response to CFW infection. Four differentially expressed WRKY genes were selected for validation. Subcellular localization and Western blot assays showed their nuclear localization and normal expression in N. benthamiana. Additionally, yeast one-hybrid assays demonstrated that VuWRKY2 can bind to the promoter region of the Catalase (CAT) gene, indicating its potential role in transcriptional regulation. This study establishes a foundation for further exploration of the role and regulatory mechanisms of VuWRKY genes in response to CFW stress.

Stress responsive ZmWRKY53 gene increases cold tolerance in rice

Plant WRKY transcription factors are responsible for biotic and abiotic stresses and play an important role in enhancing their adaptability. The AtWRKY33 is a gene that functions in response to abiotic stresses such as low temperature, drought, salinity, etc. In this study, a recombinant vector YG8198-ZmWRKY53 carrying the ZmWRKY53, an interspecific homolog of the dicotyledonous AtWRKY33, was transferred to rice plants by Agrobacterium mediated transformation. The ectopic expression of the ZmWRKY53 in transgenic rice plants conferred cold tolerance with a higher accumulation of free proline and water-soluble sugars, an increase in chlorophyll content, a decrease in electrolyte leakage rate and MDA levels compared to control plants. This result suggests that ZmWRKY53 may confer cold tolerance in rice.

Ubiquitin ligase VvPUB26 in grapevine promotes proanthocyanidin synthesis and resistance to powdery mildew

Proanthocyanidins (PAs) are an important group of flavonoids that contribute to astringency, color, and flavor in grapes (Vitis vinifera) and wines. They also play a crucial role in enhancing plant resistance to various stresses. However, the underlying regulatory mechanism governing PAs biosynthesis, particularly in relation to conferring resistance to powdery mildew, has not been extensively explored. This study focused on identifying a key player in PAs biosynthesis, namely the plant U-box (PUB) E3 ubiquitin ligase VvPUB26. We discovered that overexpression of VvPUB26 in grapes leads to a significant increase in PAs content, whereas interfering with VvPUB26 has the opposite effect. Additionally, our findings demonstrated that overexpression of VvPUB26 in transgenic grapevines enhances defense against powdery mildew while interfering with VvPUB26 results in increased susceptibility to the pathogen. Interestingly, we observed that VvPUB26 interacts with the WRKY transcription factor VvWRKY24, thereby facilitating ubiquitination and degradation processes. Through RNA-Seq analysis, we found that VvWRKY24 primarily participates in secondary metabolites biosynthesis, metabolic pathways, and plant-pathogen interaction. Notably, VvWRKY24 directly interacts with the promoters of dihydroflavonol-4-reductase (DFR) and leucoanthocyanidin reductase (LAR) to inhibit PAs biosynthesis. Meanwhile, VvWRKY24 also influences the expression of MYB transcription factor genes related to PAs synthesis. In conclusion, our results unveil a regulatory module involving VvPUB26-VvWRKY24-VvDFR/VvLAR that plays a fundamental role in governing PAs biosynthesis in grapevines. These findings enhance our understanding of the relationship between PAs biosynthesis and defense mechanisms against powdery mildew.

CaWRKY22b Plays a Positive Role in the Regulation of Pepper Resistance to Ralstonia solanacearum in a Manner Associated with Jasmonic Acid Signaling

As important transcription factors, WRKYs play a vital role in the defense response of plants against the invasion of multiple pathogens. Though some WRKY members have been reported to participate in pepper immunity in response to Ralstonia solanacearum infection, the functions of the majority of WRKY members are still unknown. Herein, CaWRKY22b was cloned from the pepper genome and its function against R. solanacearum was analyzed. The transcript abundance of CaWRKY22b was significantly increased in response to the infection of R. solanacearum and the application of exogenous methyl jasmonate (MeJA). Subcellular localization assay in the leaves of Nicotiana benthamiana showed that CaWRKY22b protein was targeted to the nuclei. Agrobacterium-mediated transient expression in pepper leaves indicated that CaWRKY22b overexpression triggered intensive hypersensitive response-like cell death, H2O2 accumulation, and the up-regulation of defense- and JA-responsive genes, including CaHIR1, CaPO2, CaBPR1, and CaDEF1. Virus-induced gene silencing assay revealed that knock-down of CaWRKY22b attenuated pepper's resistance against R. solanacearum and the up-regulation of the tested defense- and jasmonic acid (JA)-responsive genes. We further assessed the role of CaWRKY22b in modulating the expression of JA-responsive CaDEF1, and the result demonstrated that CaWRKY22b trans-activated CaDEF1 expression by directly binding to its upstream promoter. Collectively, our results suggest that CaWRKY22b positively regulated pepper immunity against R. solanacearum in a manner associated with JA signaling, probably by modulating the expression of JA-responsive CaDEF1.

TaWRKY50-TaSARK7 module-mediated cysteine-rich protein phosphorylation suppresses the programmed cell death response to Chinese wheat mosaic virus infection

WRKY transcription factors are widely involved in plant responses to biotic and abiotic stresses. However, there is currently a limited understanding of the regulation of viral infection by WRKY transcription factors in wheat (Triticum aestivum). The WRKY transcription factor TaWRKY50 in group IIb wheat exhibited a significant response to Chinese wheat mosaic virus infection. TaWRKY50 is localized in the nucleus and is an activating transcription factor. Interestingly, we found that silencing TaWRKY50 induces cell death following inoculation with CWMV. The protein kinase TaSAPK7 is specific to plants, whereas NbSRK is a closely related kinase with high homology to TaSAPK7. The transcriptional activities of both TaSAPK7 and NbSRK can be enhanced by TaWRKY50 binding to their promoters. CRP is an RNA silencing suppressor. Furthermore, TaWRKY50 may regulate CWMV infection by regulating the expression of TaSAPK7 and NbSRK to increase CRP phosphorylation and reduce the amount of programmed cell death (PCD).

Genome-wide identification, expression analysis of WRKY transcription factors in Citrus ichangensis and functional validation of CiWRKY31 in response to cold stress

BACKGROUND

Ichang papeda (Citrus ichangensis), a wild perennial plant of the Rutaceae family, is a cold-hardy plant. WRKY transcription factors are crucial regulators of plant growth and development as well as abiotic stress responses. However, the WRKY genes in C. ichangensis (CiWRKY) and their expression patterns under cold stress have not been thoroughly investigated, hindering our understanding of their role in cold tolerance.

RESULTS

In this study, a total of 52 CiWRKY genes identified in the genome of C. ichangensis were classified into three main groups and five subgroups based on phylogenetic analysis. Comprehensive analyses of motif features, conserved domains, and gene structures were performed. Segmental duplication plays a significant role in the CiWRKY gene family expansion. Cis-acting element analysis revealed the presence of various stress-responsive elements in the promoters of the majority of CiWRKYs. Gene ontology (GO) analysis and protein-protein interaction predictions indicate that the CiWRKYs exhibit crucial roles in regulation of both development and stress response. Expression profiling analysis demonstrates that 14 CiWRKYs were substantially induced under cold stress. Virus-induced gene silencing (VIGS) assay confirmed that CiWRKY31, one of the cold-induced WRKYs, functions positively in regulation of cold tolerance.

CONCLUSION

Sequence and protein properties of CiWRKYs were systematically analyzed. Among the 52 CiWRKY genes 14 members exhibited cold-responsive expression patterns, and CiWRKY31 was verified to be a positive regulator of cold tolerance. These findings pave way for future investigations to understand the molecular functions of CiWRKYs in cold tolerance and contribute to unravelling WRKYs that may be used for engineering cold tolerance in citrus.

Genome-wide profiling of WRKY genes involved in flavonoid biosynthesis in Erigeron breviscapus

The transcription factors of WRKY genes play essential roles in plant growth, stress responses, and metabolite biosynthesis. Erigeron breviscapus, a traditional Chinese herb, is abundant in flavonoids and has been used for centuries to treat cardiovascular and cerebrovascular diseases. However, the WRKY transcription factors that regulate flavonoid biosynthesis in E. breviscapus remain unknown. In this study, a total of 75 EbWRKY transcription factors were predicted through comprehensive genome-wide characterization of E. breviscapus and the chromosomal localization of each EbWRKY gene was investigated. RNA sequencing revealed transient responses of 74 predicted EbWRKY genes to exogenous abscisic acid (ABA), salicylic acid (SA), and gibberellin 3 (GA3) after 4 h of treatment. In contrast, the expression of key structural genes involved in flavonoid biosynthesis increased after 4 h in GA3 treatment. However, the content of flavonoid metabolites in leaves significantly increased at 12 h. The qRT-PCR results showed that the expression patterns of EbWRKY11, EbWRKY30, EbWRKY31, EbWRKY36, and EbWRKY44 transcription factors exhibited a high degree of similarity to the 11 structural genes involved in flavonoid biosynthesis. Protein-DNA interactions were performed between the key genes involved in scutellarin biosynthesis and candidate WRKYs. The result showed that F7GAT interacts with EbWRKY11, EbWRKY36, and EbWRKY44, while EbF6H has a self-activation function. This study provides comprehensive information on the regulatory control network of flavonoid accumulation mechanisms, offering valuable insights for breeding E. breviscapus varieties with enhanced scutellarin content.

Changes in secondary metabolites contents and stress responses in Salvia miltiorrhiza via ScWRKY35 overexpression: Insights from a wild relative Salvia castanea

Salvia castanea Diels, a close wild relative to the medicinal plant, Salvia miltiorrhiza Bunge, primarily grows in high-altitude regions. While the two species share similar active compounds, their content varies significantly. WRKY transcription factors are key proteins, which regulate plant growth, stress response, and secondary metabolism. We identified 46 ScWRKY genes in S. castanea and found that ScWRKY35 was a highly expressed gene associated with secondary metabolites accumulation. This study aimed to explore the role of ScWRKY35 gene in regulating the accumulation of secondary metabolites and its response to UV and cadmium (Cd) exposure in S. miltiorrhiza. It was found that transgenic S. miltiorrhiza hairy roots overexpressing ScWRKY35 displayed upregulated expression of genes related to phenolic acid synthesis, resulting in increased salvianolic acid B (SAB) and rosmarinic acid (RA) contents. Conversely, tanshinone pathway gene expression decreased, leading to lower tanshinone levels. Further, overexpression of ScWRKY35 upregulated Cd transport protein HMA3 in root tissues inducing Cd sequestration. In contrast, the Cd uptake gene NRAMP1 was downregulated, reducing Cd absorption. In response to UV radiation, ScWRKY35 overexpression led to an increase in the accumulation of phenolic acid and tanshinone contents, including upregulation of genes associated with salicylic acid (SA) and jasmonic acid (JA) synthesis. Altogether, these findings highlight the role of ScWRKY35 in enhancing secondary metabolites accumulation, as well as in Cd and UV stress modulation in S. miltiorrhiza, which offers a novel insight into its phytochemistry and provides a new option for the genetic improvement of the plants.

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.

Molecular basis for the interference of the Arabidopsis WRKY54-mediated immune response by two sequence-unrelated bacterial effectors

Arabidopsis thaliana WRKY proteins are potential targets of pathogen-secreted effectors. RESISTANT TO RALSTONIA SOLANACEARUM 1 (RRS1; AtWRKY52) is a well-studied Arabidopsis nucleotide-binding and leucine-rich repeat (NLR) immune receptor carrying a C-terminal WRKY domain that functions as an integrated decoy. RRS1-R recognizes the effectors AvrRps4 from Pseudomonas syringae pv. pisi and PopP2 from Ralstonia pseudosolanacearum by direct interaction through its WRKY domain. AvrRps4 and PopP2 were previously shown to interact with several AtWRKYs. However, how these effectors selectively interact with their virulence targets remains unknown. Here, we show that several members of subgroup IIIb of the AtWRKY family are targeted by AvrRps4 and PopP2. We demonstrate that several AtWRKYs induce cell death when transiently expressed in Nicotiana benthamiana, indicating the activation of immune responses. AtWRKY54 was the only cell death-inducing AtWRKY that interacted with both AvrRps4 and PopP2. We found that AvrRps4 and PopP2 specifically suppress AtWRKY54-induced cell death. We also demonstrate that the amino acid residues required for the avirulence function of AvrRps4 and PopP2 are critical for suppressing AtWRKY54-induced cell death. AtWRKY54 residues predicted to form a binding interface with AvrRps4 were predominantly located in the DNA binding domain and necessary for inducing cell death. Notably, one AtWRKY54 residue, E164, contributes to affinity with AvrRps4 and is exclusively present among subgroup IIIb AtWRKYs, yet is located outside of the DNA-binding domain. Surprisingly, AtWRKY54 mutated at E164 evaded AvrRps4-mediated cell death suppression. Taking our observations together, we propose that AvrRp4 and PopP2 specifically target AtWRKY54 to suppress plant immune responses.

Genomic overview of INA-induced NPR1 targeting and transcriptional cascades in Arabidopsis

The phytohormone salicylic acid (SA) triggers transcriptional reprogramming that leads to SA-induced immunity in plants. NPR1 is an SA receptor and master transcriptional regulator in SA-triggered transcriptional reprogramming. Despite the indispensable role of NPR1, genome-wide direct targets of NPR1 specific to SA signaling have not been identified. Here, we report INA (functional SA analog)-specific genome-wide targets of Arabidopsis NPR1 in plants expressing GFP-fused NPR1 under its native promoter. Analyses of NPR1-dependently expressed direct NPR1 targets revealed that NPR1 primarily activates genes encoding transcription factors upon INA treatment, triggering transcriptional cascades required for INA-induced transcriptional reprogramming and immunity. We identified genome-wide targets of a histone acetyltransferase, HAC1, including hundreds of co-targets shared with NPR1, and showed that NPR1 and HAC1 regulate INA-induced histone acetylation and expression of a subset of the co-targets. Genomic NPR1 targeting was principally mediated by TGACG-motif binding protein (TGA) transcription factors. Furthermore, a group of NPR1 targets mostly encoding transcriptional regulators was already bound to NPR1 in the basal state and showed more rapid and robust induction than other NPR1 targets upon SA signaling. Thus, our study unveils genome-wide NPR1 targeting, its role in transcriptional reprogramming, and the cooperativity between NPR1, HAC1, and TGAs in INA-induced immunity.

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.

Overexpression of the potato VQ31 enhances salt tolerance in Arabidopsis

Plant-specific VQ proteins have crucial functions in the regulation of plant growth and development, as well as in plant abiotic stress responses. Their roles have been well established in the model plant Arabidopsis thaliana; however, the functions of the potato VQ proteins have not been adequately investigated. The VQ protein core region contains a short FxxhVQxhTG amino acid motif sequence. In this study, the VQ31 protein from potato was cloned and functionally characterized. The complete open reading frame (ORF) size of StVQ31 is 672 bp, encoding 223 amino acids. Subcellular localization analysis revealed that StVQ31 is located in the nucleus. Transgenic Arabidopsis plants overexpressing StVQ31 exhibited enhanced salt tolerance compared to wild-type (WT) plants, as evidenced by increased root length, germination rate, and chlorophyll content under salinity stress. The increased tolerance of transgenic plants was associated with increased osmotic potential (proline and soluble sugars), decreased MDA accumulation, decreased total protein content, and improved membrane integrity. These results implied that StVQ31 overexpression enhanced the osmotic potential of the plants to maintain normal cell growth. Compared to the WT, the transgenic plants exhibited a notable increase in antioxidant enzyme activities, reducing cell membrane damage. Furthermore, the real-time fluorescence quantitative PCR analysis demonstrated that StVQ31 regulated the expression of genes associated with the response to salt stress, including ERD, LEA4-5, At2g38905, and AtNCED3. These findings suggest that StVQ31 significantly impacts osmotic and antioxidant cellular homeostasis, thereby enhancing salt tolerance.

MdWRKY71 promotes the susceptibility of apple to Glomerella leaf spot by controlling salicylic acid degradation

Glomerella leaf spot (GLS), a fungal disease caused by Colletotrichum fructicola, severely affects apple (Malus domestica) quality and yield. In this study, we found that the transcription factor MdWRKY71 was significantly induced by C. fructicola infection in the GLS-susceptible apple cultivar Royal Gala. The overexpression of MdWRKY71 in apple leaves resulted in increased susceptibility to C. fructicola, whereas RNA interference of MdWRKY71 in leaves showed the opposite phenotypes. These findings suggest that MdWRKY71 functions as a susceptibility factor for the apple-C. fructicola interaction. Furthermore, MdWRKY71 directly bound to the promoter of the salicylic acid (SA) degradation gene Downy Mildew Resistant 6 (DMR6)-Like Oxygenase 1 (DLO1) and promoted its expression, resulting in a reduced SA level. The sensitivity of 35S:MdWRKY71 leaves to C. fructicola can be effectively alleviated by knocking down MdDLO1 expression, confirming the critical role of MdWRKY71-mediated SA degradation via regulating MdDLO1 expression in GLS susceptibility. In summary, we identified a GLS susceptibility factor, MdWRKY71, that targets the apple SA degradation pathway to promote fungal infection.

Defense signaling pathways in resistance to plant viruses: Crosstalk and finger pointing

Resistance to infection by plant viruses involves proteins encoded by plant resistance (R) genes, viz., nucleotide-binding leucine-rich repeats (NLRs), immune receptors. These sensor NLRs are activated either directly or indirectly by viral protein effectors, in effector-triggered immunity, leading to induction of defense signaling pathways, resulting in the synthesis of numerous downstream plant effector molecules that inhibit different stages of the infection cycle, as well as the induction of cell death responses mediated by helper NLRs. Early events in this process involve recognition of the activation of the R gene response by various chaperones and the transport of these complexes to the sites of subsequent events. These events include activation of several kinase cascade pathways, and the syntheses of two master transcriptional regulators, EDS1 and NPR1, as well as the phytohormones salicylic acid, jasmonic acid, and ethylene. The phytohormones, which transit from a primed, resting states to active states, regulate the remainder of the defense signaling pathways, both directly and by crosstalk with each other. This regulation results in the turnover of various suppressors of downstream events and the synthesis of various transcription factors that cooperate and/or compete to induce or suppress transcription of either other regulatory proteins, or plant effector molecules. This network of interactions results in the production of defense effectors acting alone or together with cell death in the infected region, with or without the further activation of non-specific, long-distance resistance. Here, we review the current state of knowledge regarding these processes and the components of the local responses, their interactions, regulation, and crosstalk.

Identification of Clubroot (Plasmodiophora brassicae) Resistance Loci in Chinese Cabbage (Brassica rapa ssp. pekinensis) with Recessive Character

The soil-borne pathogen Plasmodiophora brassicae is the causal agent of clubroot, a major disease in Chinese cabbage (Brassica rapa ssp. pekinensis). The host's resistance genes often confer immunity to only specific pathotypes and may be rapidly overcome. Identification of novel clubroot resistance (CR) from germplasm sources is necessary. In this study, Bap246 was tested by being crossed with different highly susceptible B. rapa materials and showed recessive resistance to clubroot. An F2 population derived from Bap246 × Bac1344 was used to locate the resistance Quantitative Trait Loci (QTL) by Bulk Segregant Analysis Sequencing (BSA-Seq) and QTL mapping methods. Two QTL on chromosomes A01 (4.67-6.06 Mb) and A08 (10.42-11.43 Mb) were found and named Cr4Ba1.1 and Cr4Ba8.1, respectively. Fifteen and eleven SNP/InDel markers were used to narrow the target regions in the larger F2 population to 4.67-5.17 Mb (A01) and 10.70-10.84 Mb (A08), with 85 and 19 candidate genes, respectively. The phenotypic variation explained (PVE) of the two QTL were 30.97% and 8.65%, respectively. Combined with gene annotation, mutation site analysis, and real-time quantitative polymerase chain reaction (qRT-PCR) analysis, one candidate gene in A08 was identified, namely Bra020861. And an insertion and deletion (InDel) marker (co-segregated) named Crr1-196 was developed based on the gene sequence. Bra013275, Bra013299, Bra013336, Bra013339, Bra013341, and Bra013357 in A01 were the candidate genes that may confer clubroot resistance in Chinese cabbage. The resistance resource and the developed marker will be helpful in Brassica breeding programs.

Genetic Analysis of Partially Resistant and Susceptible Chickpea Cultivars in Response to Ascochyta rabiei Infection

The molecular mechanism involved in chickpea (Cicer arietinum L.) resistance to the necrotrophic fungal pathogen Ascochyta rabiei is not well documented. A. rabiei infection can cause severe damage in chickpea, resulting in significant economic losses. Understanding the resistance mechanism against ascochyta blight can help to define strategies to develop resistant cultivars. In this study, differentially expressed genes from two partially resistant cultivars (CDC Corinne and CDC Luna) and a susceptible cultivar (ICCV 96029) to ascochyta blight were identified in the early stages (24, 48 and 72 h) of A. rabiei infection using RNA-seq. Altogether, 3073 genes were differentially expressed in response to A. rabiei infection across different time points and cultivars. A larger number of differentially expressed genes (DEGs) were found in CDC Corinne and CDC Luna than in ICCV 96029. Various transcription factors including ERF, WRKY, bHLH and MYB were differentially expressed in response to A. rabiei infection. Genes involved in pathogen detection and immune signalings such as receptor-like kinases (RLKs), Leucine-Rich Repeat (LRR)-RLKs, and genes associated with the post-infection defence response were differentially expressed among the cultivars. GO functional enrichment and pathway analysis of the DEGs suggested that the biological processes such as metabolic process, response to stimulus and catalytic activity were overrepresented in both resistant and susceptible chickpea cultivars. The expression patterns of eight randomly selected genes revealed by RNA-seq were confirmed by quantitative PCR (qPCR) analysis. The results provide insights into the complex molecular mechanism of the chickpea defence in response to the A. rabiei infection.

Transcriptomic Analysis Reveals Candidate Genes in Response to Sorghum Mosaic Virus and Salicylic Acid in Sugarcane

Sorghum mosaic virus (SrMV) is one of the most prevalent viruses deteriorating sugarcane production. Salicylic acid (SA) plays an essential role in the defense mechanism of plants and its exogenous application has been observed to induce the resistance against biotic and abiotic stressors. In this study, we set out to investigate the mechanism by which sorghum mosaic virus (SrMV) infected sugarcane responds to SA treatment in two sugarcane cultivars, i.e., ROC22 and Xuezhe. Notably, significantly low viral populations were observed at different time points (except for 28 d in ROC22) in response to post-SA application in both cultivars as compared to control based on qPCR data. Furthermore, the lowest number of population size in Xuezhe (20 copies/µL) and ROC22 (95 copies/µL) was observed in response to 1 mM exogenous SA application. A total of 2999 DEGs were identified, of which 731 and 2268 DEGs were up- and down-regulated, respectively. Moreover, a total of 806 DEGs were annotated to GO enrichment categories: 348 biological processes, 280 molecular functions, and 178 cellular components. GO functional categorization revealed that DEGs were mainly enriched in metabolic processes, extracellular regions, and glucosyltransferase activity, while KEGG annotation revealed that DEGs were mainly concentrated in phenylpropanoid biosynthesis and plant-pathogen interaction suggesting the involvement of these pathways in SA-induced disease resistance of sugarcane in response to SrMV infection. The RNA-seq dataset and qRT-PCR assay showed that the transcript levels of PR1a, PR1b, PR1c, NPR1a, NPR1b, PAL, ICS, and ABA were significantly up-regulated in response to SA treatment under SrMV infection, indicating their positive involvement in stress endorsement. Overall, this research characterized sugarcane transcriptome during SrMV infection and shed light on further interaction of plant-pathogen under exogenous application of SA treatment.

TaWRKY31, a novel WRKY transcription factor in wheat, participates in regulation of plant drought stress tolerance

BACKGROUND

Wheat, a crucial food crop in China, is highly vulnerable to drought stress throughout its growth and development. WRKY transcription factors (TFs), being one of the largest families of TFs, play a vital role in responding to various abiotic stresses in plants.

RESULTS

Here, we cloned and characterized the TF TaWRKY31 isolated from wheat. This TF, belonging to the WRKY II family, contains a WRKYGQK amino acid sequence and a C2H2-type zinc finger structure. TaWRKY31 exhibits tissue-specific expression and demonstrates responsiveness to abiotic stresses in wheat. TaWRKY31 protein is localized in the nucleus and can function as a TF with transcription activating activity at the N-terminus. Results showed that the wheat plants with silenced strains (BSMV:TaWRKY31-1as and BSMV:TaWRKY31-2as) exhibited poor growth status and low relative water content when subjected to drought treatment. Moreover, the levels of O2·-, H2O2, and malondialdehyde (MDA) in the BSMV:TaWRKY31-induced wheat plants increased, while the activities of antioxidant enzymes (superoxide dismutase, peroxidase, and catalase) decreased. Compared to control plants, BSMV:TaWRKY31-induced wheat plants exhibited lower expression levels of TaSOD (Fe), TaPOD, TaCAT, TaDREB1, TaP5CS, TaNCED1, TaSnRK2, TaPP2C, and TaPYL5.Under stress or drought treatment conditions, the overexpression of TaWRKY31 in Arabidopsis resulted in decreased levels of H2O2 and MDA, as well as reduced stomatal opening and water loss. Furthermore, an increase in resistance oxidase activity, germination rate, and root length in the TaWRKY31 transgenic Arabidopsis was observed. Lastly, overexpression of TaWRKY31 in Arabidopsis resulted in higher the expression levels of AtNCED3, AtABA2, AtSnRK2.2, AtABI1, AtABF3, AtP5CS1, AtSOD (Cu/Zn), AtPOD, AtCAT, AtRD29A, AtRD29B, and AtDREB2A than in control plants.

CONCLUSIONS

Our findings indicate that TaWRKY31 enhances drought resistance in plants by promoting the scavenging of reactive oxygen species, reducing stomatal opening, and increasing the expression levels of stress-related genes.

Molecular switches in plant stress adaptation

Climate change poses a significant threat to the global ecosystem, prompting plants to use various adaptive mechanisms via molecular switches to combat biotic and abiotic stress factors. These switches activate stress-induced pathways by altering their configuration between stable states. In this review, we investigated the regulation of molecular switches in different plant species in response to stress, including the stress-regulated response of multiple switches in Arabidopsis thaliana. We also discussed techniques for developing stress-resilient crops using molecular switches through advanced biotechnological tools. The literature search, conducted using databases such as PubMed, Google Scholar, Web of Science, and SCOPUS, utilized keywords such as molecular switch, plant adaptation, biotic and abiotic stresses, transcription factors, Arabidopsis thaliana, and crop improvement. Recent studies have shown that a single molecular switch can regulate multiple stress networks, and multiple switches can regulate a single stress condition. This multifactorial understanding provides clarity to the switch regulatory network and highlights the interrelationships of different molecular switches. Advanced breeding techniques, along with genomic and biotechnological tools, have paved the way for further research on molecular switches in crop improvement. The use of synthetic biology in molecular switches will lead to a better understanding of plant stress biology and potentially bring forth a new era of stress-resilient, climate-smart crops worldwide.

Unraveling the involvement of WRKY TFs in regulating plant disease defense signaling

MAIN CONCLUSION

This review article explores the intricate role, regulation, and signaling mechanisms of WRKY TFs in response to biotic stress, particularly emphasizing their pivotal role in the trophism of plant-pathogen interactions. Transcription factors (TFs) play a vital role in governing both plant defense and development by controlling the expression of various downstream target genes. Early studies have shown the differential expression of certain WRKY transcription factors by microbial infections. Several transcriptome-wide studies later demonstrated that diverse sets of WRKYs are significantly activated in the early stages of viral, bacterial, and fungal infections. Furthermore, functional investigations indicated that overexpression or silencing of certain WRKY genes in plants can drastically alter disease symptoms as well as pathogen multiplication rates. Hence the new aspects of pathogen-triggered WRKY TFs mediated regulation of plant defense can be explored. The already recognized roles of WRKYs include transcriptional regulation of defense-related genes, modulation of hormonal signaling, and participation in signal transduction pathways. Some WRKYs have been shown to directly bind to pathogen effectors, acting as decoys or resistance proteins. Notably, the signaling molecules like salicylic acid, jasmonic acid, and ethylene which are associated with plant defense significantly increase the expression of several WRKYs. Moreover, induction of WRKY genes or heightened WRKY activities is also observed during ISR triggered by the beneficial microbes which protect the plants from subsequent pathogen infection. To understand the contribution of WRKY TFs towards disease resistance and their exact metabolic functions in infected plants, further studies are required. This review article explores the intrinsic transcriptional regulation, signaling mechanisms, and hormonal crosstalk governed by WRKY TFs in plant disease defense response, particularly emphasizing their specific role against different biotrophic, hemibiotrophic, and necrotrophic pathogen infections.

The expression of the NPR1-dependent defense response pathway genes in Persea americana (Mill.) following infection with Phytophthora cinnamomi

A plant's defense against pathogens involves an extensive set of phytohormone regulated defense signaling pathways. The salicylic acid (SA)-signaling pathway is one of the most well-studied in plant defense. The bulk of SA-related defense gene expression and the subsequent establishment of systemic acquired resistance (SAR) is dependent on the nonexpressor of pathogenesis-related genes 1 (NPR1). Therefore, understanding the NPR1 pathway and all its associations has the potential to provide valuable insights into defense against pathogens. The causal agent of Phytophthora root rot (PRR), Phytophthora cinnamomi, is of particular importance to the avocado (Persea americana) industry, which encounters considerable economic losses on account of this pathogen each year. Furthermore, P. cinnamomi is a hemibiotrophic pathogen, suggesting that the SA-signaling pathway plays an essential role in the initial defense response. Therefore, the NPR1 pathway which regulates downstream SA-induced gene expression would be instrumental in defense against P. cinnamomi. Thus, we identified 92 NPR1 pathway-associated orthologs from the P. americana West Indian pure accession genome and interrogated their expression following P. cinnamomi inoculation, using RNA-sequencing data. In total, 64 and 51 NPR1 pathway-associated genes were temporally regulated in the partially resistant (Dusa®) and susceptible (R0.12) P. americana rootstocks, respectively. Furthermore, 42 NPR1 pathway-associated genes were differentially regulated when comparing Dusa® to R0.12. Although this study suggests that SAR was established successfully in both rootstocks, the evidence presented indicated that Dusa® suppressed SA-signaling more effectively following the induction of SAR. Additionally, contrary to Dusa®, data from R0.12 suggested a substantial lack of SA- and NPR1-related defense gene expression during some of the earliest time-points following P. cinnamomi inoculation. This study represents the most comprehensive investigation of the SA-induced, NPR1-dependent pathway in P. americana to date. Lastly, this work provides novel insights into the likely mechanisms governing P. cinnamomi resistance in P. americana.

Salicylic acid accelerates carbon starvation-induced leaf senescence in Arabidopsis thaliana by inhibiting autophagy through Nonexpressor of pathogenesis-related genes 1

In plants, leaf senescence is regulated by several factors, including age and carbon starvation. The molecular mechanism of age-regulated developmental leaf senescence differs from that of carbon starvation-induced senescence. Salicylic acid (SA) and Nonexpressor of pathogenesis-related genes 1 (NPR1) play important roles in promoting developmental leaf senescence. However, the relationship between SA signaling and carbon starvation-induced leaf senescence is not currently well understood. Here, we used Arabidopsis thaliana as material and found that carbon starvation-induced leaf senescence was accelerated in the SA dihydroxylase mutants s3hs5h compared to the Columbia ecotype (Col). Exogenous SA treatment significantly promoted carbon starvation-induced leaf senescence, especially in NPR1-GFP. Increasing the endogenous SA and overexpression of NPR1 inhibited carbon starvation-induced autophagy. However, mutation of NPR1 delayed carbon starvation-induced leaf senescence, increased autophagosome production and accelerated autophagic degradation of the Neighbor of BRCA1 gene 1 (NBR1). In conclusion, SA promotes carbon starvation-induced leaf senescence by inhibiting autophagy via NPR1.

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.

Arabidopsis transcription factor WRKY45 confers cadmium tolerance via activating PCS1 and PCS2 expression

Cadmium (Cd) has long been recognized as toxic pollutant to crops worldwide. The biosynthesis of glutathione-dependent phytochelatin (PC) plays crucial roles in the detoxification of Cd in plants. However, its regulatory mechanism remains elusive. Here, we revealed that Arabidopsis transcription factor WRKY45 confers Cd tolerance via promoting the expression of PC synthesis-related genes PCS1 and PCS2, respectively. Firstly, we found that Cd stress induces the transcript levels of WRKY45 and its protein abundance. Accordingly, in contrast to wild type Col-0, the increased sensitivity to Cd is observed in wrky45 mutant, while overexpressing WRKY45 plants are more tolerant to Cd. Secondly, quantitative real-time PCR revealed that the expression of AtPCS1 and AtPCS2 is stimulated in overexpressing WRKY45 plants, but decreased in wrky45 mutant. Thirdly, WRKY45 promotes the expression of PCS1 and PCS2, electrophoresis mobility shift assay analysis uncovered that WRKY45 directly binds to the W-box cis-element of PCS2 promoter. Lastly, the overexpression of WRKY45 in Col-0 leads to more accumulation of PCs in Arabidopsis, and the overexpression of PCS1 or PCS2 in wrky45 mutant plants rescues the phenotypes induced by Cd stress. In conclusion, our results show that AtWRKY45 positively regulates Cd tolerance in Arabidopsis via activating PCS1 and PCS2 expression.

A Common Molecular Signature Indicates the Pre-Meristematic State of Plant Calli

In response to different degrees of mechanical injury, certain plant cells re-enter the division cycle to provide cells for tissue replenishment, tissue rejoining, de novo organ formation, and/or wound healing. The intermediate tissue formed by the dividing cells is called a callus. Callus formation can also be induced artificially in vitro by wounding and/or hormone (auxin and cytokinin) treatments. The callus tissue can be maintained in culture, providing starting material for de novo organ or embryo regeneration and thus serving as the basis for many plant biotechnology applications. Due to the biotechnological importance of callus cultures and the scientific interest in the developmental flexibility of somatic plant cells, the initial molecular steps of callus formation have been studied in detail. It was revealed that callus initiation can follow various ways, depending on the organ from which it develops and the inducer, but they converge on a seemingly identical tissue. It is not known, however, if callus is indeed a special tissue with a defined gene expression signature, whether it is a malformed meristem, or a mass of so-called "undifferentiated" cells, as is mostly believed. In this paper, I review the various mechanisms of plant regeneration that may converge on callus initiation. I discuss the role of plant hormones in the detour of callus formation from normal development. Finally, I compare various Arabidopsis gene expression datasets obtained a few days, two weeks, or several years after callus induction and identify 21 genes, including genes of key transcription factors controlling cell division and differentiation in meristematic regions, which were upregulated in all investigated callus samples. I summarize the information available on all 21 genes that point to the pre-meristematic nature of callus tissues underlying their wide regeneration potential.

Loss-of-function mutations in WRKY22 and WRKY25 impair stomatal-mediated immunity and PTI and ETI responses against Pseudomonas syringae pv. tomato

Plants defend themselves against pathogens using a two-layered immune system. The first response, pattern-triggered immunity (PTI), is activated upon recognition of microbe-associated molecular patterns (MAMPs). Virulent bacteria such as Pseudomonas syringae pv. tomato (Pst), deliver effector proteins into the plant cell to promote susceptibility. However, some plants possess resistance (R) proteins that recognize specific effectors leading to the activation of the second response, effector-triggered immunity (ETI). Resistant tomatoes such as Río Grande-PtoR recognize two Pst effectors (AvrPto and AvrPtoB) through the host Pto/Prf complex and activate ETI. We previously showed that the transcription factors (TF) WRKY22 and WRKY25 are positive regulators of plant immunity against bacterial and potentially non-bacterial pathogens in Nicotiana benthamiana. Here, the CRISPR-Cas9 technique was used to develop three knockout tomato lines for either one or both TFs. The single and double mutants were all compromised in Pto/Prf-mediated ETI and had a weaker PTI response. The stomata apertures in all of the mutant lines did not respond to darkness or challenge with Pst DC3000. The WRKY22 and WRKY25 proteins both localize in the nucleus, but we found no evidence of a physical interaction between them. The WRKY22 TF was found to be involved in the transcriptional regulation of WRKY25, supporting the idea that they are not functionally redundant. Together, our results indicate that both WRKY TFs play a role in modulating stomata and are positive regulators of plant immunity in tomato.

The Transcription Factors WRKY41 and WRKY53 Mediate Early Flowering Induced by the Novel Plant Growth Regulator Guvermectin in Arabidopsis thaliana

Flowering is a crucial stage for plant reproductive success; therefore, the regulation of plant flowering has been widely researched. Although multiple well-defined endogenous and exogenous flowering regulators have been reported, new ones are constantly being discovered. Here, we confirm that a novel plant growth regulator guvermectin (GV) induces early flowering in Arabidopsis. Interestingly, our genetic experiments newly demonstrated that WRKY41 and its homolog WRKY53 were involved in GV-accelerated flowering as positive flowering regulators. Overexpression of WRKY41 or WRKY53 resulted in an early flowering phenotype compared to the wild type (WT). In contrast, the w41/w53 double mutants showed a delay in GV-accelerated flowering. Gene expression analysis showed that flowering regulatory genes SOC1 and LFY were upregulated in GV-treated WT, 35S:WRKY41, and 35S:WRKY53 plants, but both declined in w41/w53 mutants with or without GV treatment. Meanwhile, biochemical assays confirmed that SOC1 and LFY were both direct targets of WRKY41 and WRKY53. Furthermore, the early flowering phenotype of 35S:WRKY41 lines was abolished in the soc1 or lfy background. Together, our results suggest that GV plays a function in promoting flowering, which was co-mediated by WRKY41 and WRKY53 acting as new flowering regulators by directly activating the transcription of SOC1 and LFY in Arabidopsis.

GhWRKY41 forms a positive feedback regulation loop and increases cotton defence response against Verticillium dahliae by regulating phenylpropanoid metabolism

Despite the established significance of WRKY proteins and phenylpropanoid metabolism in plant immunity, how WRKY proteins modulate aspects of the phenylpropanoid pathway remains undetermined. To understand better the role of WRKY proteins in plant defence, we identified a cotton (Gossypium hirsutum) protein, GhWRKY41, that is, universally and rapidly induced in three disease-resistant cotton cultivars following inoculation with the plant pathogenic fungus, Verticillium dahliae. We show that overexpression of GhWRKY41 in transgenic cotton and Arabidopsis enhances resistance to V. dahliae, while knock-down increases cotton more susceptibility to the fungus. GhWRKY41 physically interacts with itself and directly activates its own transcription. A genome-wide chromatin immunoprecipitation and high-throughput sequencing (ChIP-seq), in combination with RNA sequencing (RNA-seq) analyses, revealed that 43.1% of GhWRKY41-binding genes were up-regulated in cotton upon inoculation with V. dahliae, including several phenylpropanoid metabolism master switches, receptor kinases, and disease resistance-related proteins. We also show that GhWRKY41 homodimer directly activates the expression of GhC4H and Gh4CL, thereby modulating the accumulation of lignin and flavonoids. This finding expands our understanding of WRKY-WRKY protein interactions and provides important insights into the regulation of the phenylpropanoid pathway in plant immune responses by a WRKY protein.

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.

Overexpression of a WRKY transcription factor McWRKY57-like from Mentha canadensis L. enhances drought tolerance in transgenic Arabidopsis

BACKGROUND

Drought has become a major environmental problem affecting crop production. Members of the WRKY family play important roles in plant development and stress responses. However, their roles in mint have been barely explored.

RESULTS

In this study, we isolated a drought-inducible gene McWRKY57-like from mint and investigated its function. The gene encodes a group IIc WRKY transcription factor, McWRKY57-like, which is a nuclear protein with a highly conserved WRKY domain and a C2H2 zinc-finger structure, and has transcription factor activity. Its expression levels were examined in different tissues of mint and under the treatment of mannitol, NaCl, abscisic acid, and methyl jasmonate. We found that McWRKY57-like overexpression in Arabidopsis significantly increased drought tolerance. Further studies showed that under drought stress, McWRKY57-like-overexpressing plants had higher chlorophyll, soluble sugar, soluble protein, and proline contents but lower water loss rate and malondialdehyde content than wild-type plants. Moreover, the activities of antioxidant enzymes catalase, superoxide dismutase, and peroxidase were enhanced in McWRKY57-like transgenic plants. Furthermore, qRT-PCR analysis revealed that the drought-related genes AtRD29A, AtRD29B, AtRD20, AtRAB18, AtCOR15A, AtCOR15B, AtKIN2, and AtDREB1A were upregulated in McWRKY57-like transgenic plants than in wild-type Arabidopsis under simulated drought conditions.

CONCLUSION

These data demonstrated that McWRKY57-like conferred drought tolerance in transgenic Arabidopsis by regulating plant growth, osmolyte accumulation and antioxidant enzyme activities, and the expression of stress-related genes. The study indicates that McWRKY57-like plays a positive role in drought response in plants.

Progress in the understanding of WRKY transcription factors in woody plants

The WRKY transcription factor (TF) family, named for its iconic WRKY domain, is among the largest and most functionally diverse TF families in higher plants. WRKY TFs typically interact with the W-box of the target gene promoter to activate or inhibit the expression of downstream genes; these TFs are involved in the regulation of various physiological responses. Analyses of WRKY TFs in numerous woody plant species have revealed that WRKY family members are broadly involved in plant growth and development, as well as responses to biotic and abiotic stresses. Here, we review the origin, distribution, structure, and classification of WRKY TFs, along with their mechanisms of action, the regulatory networks in which they are involved, and their biological functions in woody plants. We consider methods currently used to investigate WRKY TFs in woody plants, discuss outstanding problems, and propose several new research directions. Our objective is to understand the current progress in this field and provide new perspectives to accelerate the pace of research that enable greater exploration of the biological functions of WRKY TFs.