Identification of drought responsive Elaeis guineensis WRKY transcription factors with sensitivity to other abiotic stresses and hormone treatments

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.

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

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

Genome-Wide Analysis of C-Repeat Binding Factor Gene Family in Capsicum baccatum and Functional Exploration in Low-Temperature Response

Capsicum baccatum is a close relative of edible chili peppers (Capsicum annuum) with high economic value. The CBF gene family plays an important role in plant stress resistance physiology. We detected a total of five CBF genes in the C. baccatum genome-wide sequencing data. These genes were scattered irregularly across four chromosomes. The genes were categorized into three groupings according to their evolutionary relationships, with genes in the same category showing comparable principles for motif composition. The 2000 bp upstream of CbCBF contains many resistance-responsive elements, hormone-responsive elements, and transcription factor binding sites. These findings emphasize the crucial functions of these genes in responding to challenging conditions and physiological regulation. Analysis of tissue-specific expression revealed that CbCBF3 exhibited the greatest level of expression among all tissues. Under conditions of low-temperature stress, all CbCBF genes exhibited different levels of responsiveness, with CbCBF3 showing a considerable up-regulation after 0.25 h of cold stress, indicating a high sensitivity to low-temperature response. The importance of the CbCBF3 gene in the cold response of C. baccatum was confirmed by the use of virus-induced gene silencing (VIGS) technology, as well as the prediction of its protein interaction network. To summarize, this study conducts a thorough bioinformatics investigation of the CbCBF gene family, showcases the practicality of employing VIGS technology in C. baccatum, and confirms the significance of the CbCBF3 gene in response to low temperatures. These findings provide significant references for future research on the adaptation of C. baccatum to low temperatures.

PoWRKY71 is involved in Paeonia ostii resistance to drought stress by directly regulating light-harvesting chlorophyll a/b-binding 151 gene

Although the functions of WRKY transcription factors in drought resistance are well known, their regulatory mechanisms in response to drought by stabilising photosynthesis remain unclear. Here, a differentially expressed PoWRKY71 gene that was highly expressed in drought-treated Paeonia ostii leaves was identified through transcriptome analysis. PoWRKY71 positively responded to drought stress with significantly enhanced expression patterns and overexpressing PoWRKY71 in tobacco greatly improved plant tolerance to drought stress, whereas silencing PoWRKY71 in P. ostii resulted in a drought-intolerant phenotype. Furthermore, lower chlorophyll contents, photosynthesis, and inhibited expression of photosynthesis-related light-harvesting chlorophyll a/b-binding 151 (CAB151) gene were found in PoWRKY71-silenced P. ostii. Meanwhile, a homologous system indicated that drought treatment increased PoCAB151 promoter activity. Interactive assays revealed that PoWRKY71 directly bound on the W-box element of PoCAB151 promoter and activated its transcription. In addition, PoCAB151 overexpressing plants demonstrated increased drought tolerance, together with significantly higher chlorophyll contents and photosynthesis, whereas these indices were dramatically lower in PoCAB151-silenced P. ostii. The above results indicated that PoWRKY71 activated the expression of PoCAB151, thus stabilising photosynthesis via regulating chloroplast homeostasis and chlorophyll content in P. ostii under drought stress. This study reveals a novel drought-resistance mechanism in plants and provides a feasible strategy for improving plant drought resistance via stabilising photosynthesis.

WRKY transcription factors in plant defense

Environmental stressors caused by climate change are fundamental barriers to agricultural sustainability. Enhancing the stress resilience of crops is a key strategy in achieving global food security. Plants perceive adverse environmental conditions and initiate signaling pathways to activate precise responses that contribute to their survival. WRKY transcription factors (TFs) are essential players in several signaling cascades and regulatory networks that have crucial implications for defense responses in plants. This review summarizes advances in research concerning how WRKY TFs mediate various signaling cascades and metabolic adjustments as well as how epigenetic modifications involved in environmental stress responses in plants can modulate WRKYs and/or their downstream genes. Emerging research shows that clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein (Cas)-mediated genome editing of WRKYs could be used to improve crop resilience.

Functional Study of Amorpha fruticosa WRKY20 Gene in Response to Drought Stress

The WRKY gene family in plants regulates the plant's response to drought through regulatory networks and hormone signaling. AfWRKY20 (MT859405) was cloned from Amorpha fruticosa (A. fruticosa) seedlings using RT-PCR. The binding properties of the AfWRKY20 protein and the W-box (a DNA cis-acting element) were verified both in vivo and in vitro using EMSA and Dual-Luciferase activity assays. RT-qPCR detected that the total expression level of AfWRKY20 in leaves and roots was 22 times higher in the 30% PEG6000 simulated drought treatment compared to the untreated group. Under the simulated drought stress treatments of sorbitol and abscisic acid (ABA), the transgenic tobacco with the AfWRKY20 gene showed enhanced drought resistance at the germination stage, with significantly increased germination rate, green leaf rate, fresh weight, and root length compared to the wild-type (WT) tobacco. In addition, the superoxide dismutase (SOD) activity, chlorophyll content, and Fv/Fm ratio of AfWRKY20 transgenic tobacco were significantly higher than those of the WT tobacco under natural drought stress, while the malondialdehyde (MDA) content and 3,3'-diaminobenzidine (DAB) and nitroblue tetrazolium (NBT) staining levels were lower. The expression levels of oxidation kinase genes (NbSOD, NbPOD, and NbCAT) in transgenic tobacco under drought stress were significantly higher than those in WT tobacco. This enhancement in gene expression improved the ability of transgenic tobacco to detoxify reactive oxygen species (ROS). The survival rate of transgenic tobacco after natural drought rehydration was four times higher than that of WT tobacco. In summary, this study revealed the regulatory mechanism of AfWRKY20 in response to drought stress-induced ABA signaling, particularly in relation to ROS. This finding provides a theoretical basis for understanding the pathways of WRKY20 involved in drought stress, and offers genetic resources for molecular plant breeding aimed at enhancing drought resistance.

Panax notoginseng transcription factor WRKY15 modulates resistance to Fusarium solani by up-regulating osmotin-like protein expression and inducing JA/SA signaling pathways

BACKGROUND

Panax notoginseng (Burk) F. H. Chen is a valuable traditional Chinese medicinal plant, but its commercial production is seriously affected by root rot caused by some pathogenic fungi, including Fusarium solani. Nevertheless, the genetic breeding for disease resistance of P. notoginseng remains limited. The WRKY transcription factors have been revealed to play important roles in plant defense responses, which might provide an inspiration for resistance improvement in P. notoginseng.

RESULTS

In this study, the regulatory mechanism of transcription factor PnWRKY15 on P. notoginseng resistance to F. solani infection was revealed. The suppressed expression of PnWRKY15 via RNA interference increased the sensitivity of P. notoginseng to F. solani and decreased the expression levels of some defense-related genes, including PnOLP1, which encodes an osmotin-like protein that confers resistance to F. solani. Ectopic expression of PnWRKY15 in the model plant tobacco significantly enhanced the resistance to F. solani. Moreover, the transcriptome sequencing analysis discovered that some pathogenesis-related genes were expressed at higher levels in the PnWRKY15-overexpressing tobacco than that in the wild-type tobacco. In addition, the jasmonic acid (JA) and salicylic acid (SA) signaling pathways were evidently induced by PnWRKY15-overexpression, that was evidenced by that the JA and SA contents were significantly higher in the PnWRKY15-overexpressing tobacco than that in the wild-type. Furthermore, PnWRKY15, which was localized in the nucleus, can trans-activate and up-regulate PnOLP1 expression according to the EMSA, yeast one-hybrid and co-expression assays.

CONCLUSIONS

PnWRKY15 contributes to P. notoginseng resistance to F. solani by up-regulating the expression of resistance-related gene PnOLP1 and activating JA/SA signaling pathways. These findings will help to further elucidate the transcriptional regulatory mechanism associated with the P. notoginseng defense response to F. solani.

Plants' Response to Abiotic Stress: Mechanisms and Strategies

Abiotic stress is the adverse effect of any abiotic factor on a plant in a given environment, impacting plants' growth and development. These stress factors, such as drought, salinity, and extreme temperatures, are often interrelated or in conjunction with each other. Plants have evolved mechanisms to sense these environmental challenges and make adjustments to their growth in order to survive and reproduce. In this review, we summarized recent studies on plant stress sensing and its regulatory mechanism, emphasizing signal transduction and regulation at multiple levels. Then we presented several strategies to improve plant growth under stress based on current progress. Finally, we discussed the implications of research on plant response to abiotic stresses for high-yielding crops and agricultural sustainability. Studying stress signaling and regulation is critical to understand abiotic stress responses in plants to generate stress-resistant crops and improve agricultural sustainability.

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.

Analyses of genes encoding the Glycogen Synthase Kinases in rice and Arabidopsis reveal mechanisms which regulate their expression during development and responses to abiotic stresses

Plant Glycogen Synthase Kinases (GSKs) enable a crosstalk among the brassinosteroid signaling and phytohormonal- and stress-response pathways to regulate various physiological processes. Initial information about regulation of the GSK proteins' activity was obtained, however, mechanisms that modulate expression of the GSK genes during plant development and stress responses remain largely unknown. Taking into account the importance of the GSK proteins, combined with the lack of in-depth knowledge about modulation of their expression, research in this area may provide a significant insight into mechanisms regulating these aspects of plant biology. In the current study, a detailed analysis of the GSK promoters in rice and Arabidopsis was performed, including identification of the CpG/CpNpG islands, tandem repeats, cis-acting regulatory elements, conserved motifs, and transcription factor-binding sites. Moreover, characterization of expression profiles of the GSK genes in different tissues, organs and under various abiotic stress conditions was perfomed. Additionally, protein-protein interactions between products of the GSK genes were predicted. Results of this study provided intriguing information about these aspects and insight into various regulatory mechanisms that influence non-redundant and diverse functions of the GSK genes during development and stress responses.Therefore, they may constitute a reference for future research in other plant species.

Advances in the Research on Plant WRKY Transcription Factors Responsive to External Stresses

The WRKY transcription factors are a class of transcriptional regulators that are ubiquitous in plants, wherein they play key roles in various physiological activities, including responses to stress. Specifically, WRKY transcription factors mediate plant responses to biotic and abiotic stresses through the binding of their conserved domain to the W-box element of the target gene promoter and the subsequent activation or inhibition of transcription (self-regulation or cross-regulation). In this review, the progress in the research on the regulatory effects of WRKY transcription factors on plant responses to external stresses is summarized, with a particular focus on the structural characteristics, classifications, biological functions, effects on plant secondary metabolism, regulatory networks, and other aspects of WRKY transcription factors. Future research and prospects in this field are also proposed.

Molecular Pathways of WRKY Genes in Regulating Plant Salinity Tolerance

Salinity is a natural and anthropogenic process that plants overcome using various responses. Salinity imposes a two-phase effect, simplified into the initial osmotic challenges and subsequent salinity-specific ion toxicities from continual exposure to sodium and chloride ions. Plant responses to salinity encompass a complex gene network involving osmotic balance, ion transport, antioxidant response, and hormone signaling pathways typically mediated by transcription factors. One particular transcription factor mega family, WRKY, is a principal regulator of salinity responses. Here, we categorize a collection of known salinity-responding WRKYs and summarize their molecular pathways. WRKYs collectively play a part in regulating osmotic balance, ion transport response, antioxidant response, and hormone signaling pathways in plants. Particular attention is given to the hormone signaling pathway to illuminate the relationship between WRKYs and abscisic acid signaling. Observed trends among WRKYs are highlighted, including group II WRKYs as major regulators of the salinity response. We recommend renaming existing WRKYs and adopting a naming system to a standardized format based on protein structure.

Optimized Method for the Identification of Candidate Genes and Molecular Maker Development Related to Drought Tolerance in Oil Palm (Elaeis guineensis Jacq.)

Drought is a major constraint in oil palm (Elaeis guineensis Jacq.) production. As oil palm breeding takes a long time, molecular markers of genes related to drought tolerance characteristics were developed for effective selection. Two methods of gene identification associated with drought, differential display reverse transcription polymerase chain reaction (DDRT-PCR) and pyrosequencing platform, were conducted before developing the EST-SSR marker. By DDRT-PCR, fourteen out of twenty-four primer combinations yielded the polymorphism in leaf as 77.66% and root as 96.09%, respectively. BLASTN and BLASTX revealed nucleotides from 8 out of 236 different banding similarities to genes associated with drought stress. Five out of eight genes gave a similarity with our pyrosequencing sequencing database. Furthermore, pyrosequencing analysis of two oil palm libraries, drought-tolerant, and drought sensitive, found 117 proteins associated with drought tolerance. Thirteen out of sixty EST-SSR primers could be distinguished in 119 oil palm parents in our breeding program. All of our found genes revealed an ability to develop as a molecular marker for drought tolerance. However, the function of the validated genes on drought response in oil palm must be evaluated.

In-Silico Study of Brassinosteroid Signaling Genes in Rice Provides Insight Into Mechanisms Which Regulate Their Expression

Brassinosteroids (BRs) regulate a diverse spectrum of processes during plant growth and development and modulate plant physiology in response to environmental fluctuations and stress factors. Thus, the BR signaling regulators have the potential to be targeted for gene editing to optimize the architecture of plants and make them more resilient to environmental stress. Our understanding of the BR signaling mechanism in monocot crop species is limited compared to our knowledge of this process accumulated in the model dicot species - Arabidopsis thaliana. A deeper understanding of the BR signaling and response during plant growth and adaptation to continually changing environmental conditions will provide insight into mechanisms that govern the coordinated expression of the BR signaling genes in rice (Oryza sativa) which is a model for cereal crops. Therefore, in this study a comprehensive and detailed in silico analysis of promoter sequences of rice BR signaling genes was performed. Moreover, expression profiles of these genes during various developmental stages and reactions to several stress conditions were analyzed. Additionally, a model of interactions between the encoded proteins was also established. The obtained results revealed that promoters of the 39 BR signaling genes are involved in various regulatory mechanisms and interdependent processes that influence growth, development, and stress response in rice. Different transcription factor-binding sites and cis-regulatory elements in the gene promoters were identified which are involved in regulation of the genes’ expression during plant development and reactions to stress conditions. The in-silico analysis of BR signaling genes in O. sativa provides information about mechanisms which regulate the coordinated expression of these genes during rice development and in response to other phytohormones and environmental factors. Since rice is both an important crop and the model species for other cereals, this information may be important for understanding the regulatory mechanisms that modulate the BR signaling in monocot species. It can also provide new ways for the plant genetic engineering technology by providing novel potential targets, either cis-elements or transcriptional factors, to create elite genotypes with desirable traits.

Genome-Wide Analysis of the WRKY Gene Family in Malus domestica and the Role of MdWRKY70L in Response to Drought and Salt Stresses

The WRKY transcription factors are unique regulatory proteins in plants, which are important in the stress responses of plants. In this study, 113 WRKY genes were identified from the apple genome GDDH13 and a comprehensive analysis was performed, including chromosome mapping, and phylogenetic, motif and collinearity analysis. MdWRKYs are expressed in different tissues, such as seeds, flowers, stems and leaves. We analyzed seven WRKY proteins in different groups and found that all of them were localized in the nucleus. Among the 113 MdWRKYs, MdWRKY70L was induced by both drought and salt stresses. Overexpression of it in transgenic tobacco plants conferred enhanced stress tolerance to drought and salt. The malondialdehyde content and relative electrolyte leakage values were lower, while the chlorophyll content was higher in transgenic plants than in the wild-type under stressed conditions. In conclusion, this study identified the WRKY members in the apple genome GDDH13, and revealed the function of MdWRKY70L in the response to drought and salt stresses.