Transcription factor ZmWRKY20 interacts with ZmWRKY115 to repress expression of ZmbZIP111 for salt tolerance in maize

A GhLac1-centered transcriptional regulatory cascade mediates cotton resistance to Verticillium dahliae through the lignin biosynthesis pathway

The lignin biosynthesis pathway plays a crucial role in the defense response against V. dahliae in cotton, and it is essential to identify the key regulators in this pathway for disease-resistant breeding. In a previous study, the cotton laccase gene GhLac1 was identified as mediating plant broad-spectrum biotic stress tolerance by manipulating phenylpropanoid metabolism. However, the upstream master regulators and regulatory mechanism of lignin are still largely unknown. This study aims to identify the upstream regulators of GhLac1 and explore the molecular mechanism underlying cotton's disease resistance response to V. dahliae. Through the study, three WRKY, three MYB, and one APETALA2/ETHYLENE RESPONSIVE FACTOR (ERF) TFs were identified as differentially responding to V. dahliae infection in cotton. Among these TFs, GhWRKY30, GhWRKY41, GhMYB42, and GhTINY2 were found to directly bind to the GhLac1 promoter and activate its expression. Transient overexpression of these four TFs in cotton led to increased expression of GhLac1 and other the laccase family members, while knockdown of these TFs resulted in reduced lignin accumulation and increased susceptibility to V. dahliae. Additionally, GhWRKY30 and GhWRKY41 were observed to interact with themselves and each other, synergistically transactivating the GhLac1 promoter. This study reveals a GhLac1-centered transcriptional regulatory cascade of lignin synthesis that contributes to cotton's defense response by modulating lignin metabolism.

ZmWRKY30 modulates drought tolerance in maize by influencing myo-inositol and reactive oxygen species homeostasis

Maize (Zea mays L.) is an important food crop with a wide range of uses in both industry and agriculture. Drought stress during its growth cycle can greatly reduce maize crop yield and quality. However, the molecular mechanisms underlying maize responses to drought stress remain unclear. In this work, a WRKY transcription factor-encoding gene, ZmWRKY30, from drought-treated maize leaves was screened out and characterized. ZmWRKY30 gene expression was induced by dehydration treatments. The ZmWRKY30 protein localized to the nucleus and displayed transactivation activity in yeast. Compared with wild-type (WT) plants, Arabidopsis lines overexpressing ZmWRKY30 exhibited a significantly enhanced drought stress tolerance, as evidenced by the improved survival rate, increased antioxidant enzyme activity by superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), elevated proline content, and reduced lipid peroxidation recorded after drought stress treatment. In contrast, the mutator (Mu)-interrupted ZmWRKY30 homozygous mutant (zmwrky30) was more sensitive to drought stress than its null segregant (NS), characterized by the decreased survival rate, reduced antioxidant enzyme activity (SOD, POD, and CAT) and proline content, as well as increased malondialdehyde accumulation. RNA-Seq analysis further revealed that, under drought conditions, the knockout of the ZmWRKY30 gene in maize affected the expression of genes involved in reactive oxygen species (ROS), proline, and myo-inositol metabolism. Meanwhile, the zmwrky30 mutant exhibited significant downregulation of myo-inositol content in leaves under drought stress. Combined, our results suggest that ZmWRKY30 positively regulates maize responses to water scarcity. This work provides potential target genes for the breeding of drought-tolerant maize.

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.

PtWRKY2, a WRKY transcription factor from Pinellia ternata confers heat tolerance in Arabidopsis

High temperatures are a major stress factor that limit the growth of Pinellia ternata. WRKY proteins widely distribute in plants with the important roles in plant growth and stress responses. However, WRKY genes have not been identified in P. ternata thus far. In this study, five PtWRKYs with four functional subgroups were identified in P. ternata. One group III WRKY transcription factor, PtWRKY2, was strongly induced by high temperatures, whereas the other four PtWRKYs were suppressed. Analysis of transcription factor characteristics revealed that PtWRKY2 localized to the nucleus and specifically bound to W-box elements without transcriptional activation activity. Overexpression of PtWRKY2 increased the heat tolerance of Arabidopsis, as shown by the higher percentage of seed germination and survival rate, and the longer root length of transgenic lines under high temperatures compared to the wild-type. Moreover, PtWRKY2 overexpression significantly decreased reactive oxygen species accumulation by increasing the catalase, superoxide dismutase, and peroxidase activities. Furthermore, the selected heat shock-associated genes, including five transcription factors (HSFA1A, HSFA7A, bZIP28, DREB2A, and DREB2B), two heat shock proteins (HSP70 and HSP17.4), and three antioxidant enzymes (POD34, CAT1, and SOD1), were all upregulated in transgenic Arabidopsis. The study identifies that PtWRKY2 functions as a key transcriptional regulator in the heat tolerance of P. ternata, which might provide new insights into the genetic improvement of P. ternata.

Combining genome-wide association study and linkage mapping in the genetic dissection of amylose content in maize (Zea mays L.)

KEY MESSAGE

Integrated linkage and association analysis revealed genetic basis across multiple environments. The genes Zm00001d003102 and Zm00001d015905 were further verified to influence amylose content using gene-based association study. Maize kernel amylose is an important source of human food and industrial raw material. However, the genetic basis underlying maize amylose content is still obscure. Herein, we used an intermated B73 × Mo17 (IBM) Syn10 doubled haploid population composed of 222 lines and a germplasm set including 305 inbred lines to uncover the genetic control for amylose content under four environments. Linkage mapping detected 16 unique QTL, among which four were individually repeatedly identified across multiple environments. Genome-wide association study revealed 17 significant (P = 2.24E-06) single-nucleotide polymorphisms, of which two (SYN19568 and PZE-105090500) were located in the intervals of the mapped QTL (qAC2 and qAC5-3), respectively. According to the two population co-localized loci, 20 genes were confirmed as the candidate genes for amylose content. Gene-based association analysis indicated that the variants in Zm00001d003102 (Beta-16-galactosyltransferase GALT29A) and Zm00001d015905 (Sugar transporter 4a) affected amylose content across multi-environment. Tissue expression analysis showed that the two genes were specifically highly expressed in the ear and stem, respectively, suggesting that they might participate in sugar transport from source to sink organs. Our study provides valuable genetic information for breeding maize varieties with high amylose.

Genome-wide identification of WRKY transcription factors in Casuarina equisetifolia and the function analysis of CeqWRKY11 in response to NaCl/NaHCO3 stresses

BACKGROUND

Casuarina equisetifolia (C. equisetifolia) is a woody species with many excellent features. It has natural resistance against drought, salt and saline-alkali stresses. WRKY transcription factors (TFs) play significant roles in plant response to abiotic stresses, therefore, molecular characterization of WRKY gene family under abiotic stresses holds great significance for improvement of forest trees through molecular biological tools. At present, WRKY TFs from C. equisetifolia have not been thoroughly studied with respect to their role in salt and saline-alkali stresses response. The current study was conducted to bridge the same knowledge gap.

RESULTS

A total of 64 WRKYs were identified in C. equisetifolia and divided into three major groups i.e. group I, II and III, consisting of 10, 42 and 12 WRKY members, respectively. The WRKY members in group II were further divided into 5 subgroups according to their homology with Arabidopsis counterparts. WRKYs belonging to the same group exhibited higher similarities in gene structure and the presence of conserved motifs. Promoter analysis data showed the presence of various response elements, especially those related to hormone signaling and abiotic stresses, such as ABRE (ABA), TGACG (MeJA), W-box ((C/T) TGAC (T/C)) and TC-rich motif. Tissue specific expression data showed that CeqWRKYs were mainly expressed in root under normal growth conditions. Furthermore, most of the CeqWRKYs were up-regulated by NaCl and NaHCO3 stresses with few of WRKYs showing early responsiveness to both stresses while few others exhibiting late response. Although the expressions of CeqWRKYs were also induced by cold stress, the response was delayed compared with other stresses. Transgenic C. equisetifolia plants overexpressing CeqWRKY11 displayed lower electrolyte leakage, higher chlorophyll content, and enhanced tolerance to both stresses. The higher expression of abiotic stress related genes, especially CeqHKT1 and CeqPOD7, in overexpression lines points to the maintenance of optimum Na+/K+ ratio, and ROS scavenging as possible key molecular mechanisms underlying salt stress tolerance.

CONCLUSIONS

Our results show that CeqWRKYs might be key regulators of NaCl and NaHCO3 stresses response in C. equisetifolia. In addition, positive correlation of CeqWRKY11 expression with increased stress tolerance in C. equisetifolia encourages further research on other WRKY family members through functional genomic tools. The best candidates could be incorporated in other woody plant species for improving stress tolerance.

A novel maize F-bZIP member, ZmbZIP76, functions as a positive regulator in ABA-mediated abiotic stress tolerance by binding to ACGT-containing elements

The group F-bZIP transcription factors (TFs) in Arabidopsis are involved in nutrient deficiency or salt stress responses. Nevertheless, our learning about the functions of group F-bZIP genes in maize remains limited. Here, we cloned a new F-bZIP gene (ZmbZIP76) from maize inbred line He344. The expression of ZmbZIP76 in maize was dramatically induced by high salt, osmotic stress and abscisic acid. Accordingly, overexpression of ZmbZIP76 increased tolerance of transgenic plants to salt and osmotic stress. In addition, ZmbZIP76 functions as a nuclear transcription factor and upregulates the expression of a range of abiotic stress-responsive genes by binding to the ACGT-containing elements, leading to enhanced reactive oxygen species (ROS) scavenging capability, increased abscisic acid level, proline content, and ratio of K+/Na+, reduced water loss rate, and membrane damage. These physiological changes caused by ZmbZIP76 ultimately enhanced tolerance of transgenic plants to salt and osmotic stress.

Comprehensive in silico characterization of NAC transcription factor family of Pinellia ternata and functional analysis of PtNAC66 under high-temperature tolerance in transgenic Arabidopsis thaliana

Pinellia ternata, a valuable Chinese herb, suffers yield reduction due to "sprout tumble" under high temperatures. However, the mechanisms underlying its high-temperature stress remain poorly understood. NAM, ATAF1/2, and CUC2 (NAC) transcription factors regulate plant tissue growth and abiotic stress. Hence, there has been no comprehensive research conducted on NAC transcription factors in P. ternata. We identified 98 PtNAC genes unevenly distributed across 13 chromosomes, grouped into 15 families via phylogenetic analysis. Gene expression analysis revealed diverse expression patterns of PtNAC genes in different tissue types. Further studies revealed that PtNAC5/7/17/35/43/47/57/66/86 genes were highly expressed in various tissues of P. ternata and induced by heat stress, among which PtNAC66 was up-regulated at the highest folds induced by heat temperature. PtNAC66 is a nuclear protein that can selectively bind to the cis-responsive region NACRS but lacks the ability to activate transcription in yeast. For further research, PtNAC66 was cloned and transgenic Arabidopsis was obtained. PtNAC66 overexpression increased high-temperature tolerance compared to wild-type plants. Transcriptome profiling demonstrated that overexpression of PtNAC66 led to significant modification of genes responsible for regulating binding, catalytic activity, transcription regulator activity and transporter activity response genes. Additionally, PtNAC66 was found to bind the promoters of CYP707A3, MYB102 and NAC055, respectively, and inhibited their expression, affecting the high-temperature stress response in Arabidopsis. Our research established the foundation for functional studies of PtNAC genes in response to high-temperature forcing by characterizing the P. ternata NAC gene family and examining the biological role of PtNAC66 in plant high-temperature tolerance.

SlWRKY80-mediated jasmonic acid pathway positively regulates tomato resistance to saline-alkali stress by enhancing spermidine content and stabilizing Na+/K+ homeostasis

Saline-alkali is an important abiotic stressor influencing tomato production. Exogenous methyl jasmonate (MeJA) is well known to increase tomato resistance to a variety of stresses, although its exact mechanism is yet unknown. In this study we confirmed that 22.5 μmol/l MeJA could significantly improve the saline-alkali stress resistance of tomato. Saline-alkali (300 mM) stress increased the endogenous MeJA and jasmonic acid (JA) contents of tomato by 18.8 and 13.4%, respectively. Exogenous application of 22.5 μmol/l MeJA increased the endogenous MeJA and JA contents in tomato by 15.2 and 15.9%, respectively. Furthermore, we found an important transcription factor, SlWRKY80, which responded to MeJA, and constructed its overexpressing and knockout lines through genetic transformation. It was found that SlWRKY80 actively regulated tomato resistance to saline-alkali stress, and the spraying of exogenous MeJA (22.5 μmol/l) reduced the sensitivity of SlWRKY80 knockout lines to saline-alkali stress. The SlWRKY80 protein directly combines with the promoter of SlSPDS2 and SlNHX4 to positively regulate the transcription of SlSPDS2 and SlNHX4, thereby promoting the synthesis of spermidine and Na+/K+ homeostasis, actively regulating saline-alkali stress. The augmentation of JA content led to a notable reduction of 70.6% in the expression of SlJAZ1, and the release of the SlWRKY80 protein interacting with SlJAZ1. In conclusion, we revealed the mechanism of exogenous MeJA in tomato stress resistance through multiple metabolic pathways, elucidated that exogenous MeJA further promotes spermidine synthesis and Na+/K+ homeostasis by activating the expression of SlWRKY80, which provides a new theoretical basis for the study of the JA stress resistance mechanism and the production of tomato.

The WRKY transcription factor ZmWRKY92 binds to GA synthesis-related genes to regulate maize plant height

The plant height is a crucial agronomic trait in contemporary maize breeding. Appropriate plant height can improve crop lodging resistance, increase the planting density and harvest index of crops, and thus contribute to stable and increased yields. In this study, molecular characterization showed that ZmWRKY92 is a nuclear protein and has transcriptional activation in yeast. ZmWRKY92 can specifically bind to the W-box (TTGACC), which was confirmed by double LUC experiments and Yeast one-hybrid assays. Subsequently we screened wrky92 mutants from a library of ethyl methanesulfonate (EMS)-induced mutants. The mutation of a base in ZmWRKY92 leading to the formation of a truncated protein variant is responsible for the dwarfing phenotype of the mutant, which was further verified by allelic testing. Detailed phenotypic analysis revealed that wrky92 mutants have shorter internodes due to reduced internode cell size and lower levels of GA3 and IAA. Transcriptome analysis revealed that the ZmWRKY92 mutation caused significant changes in the expression of genes related to plant height in maize. Additionally, ZmWRKY92 was found to interact with the promoters of ZmGA20ox7 and ZmGID1L2, which are associated with GA synthesis. This study shows that ZmWRKY92 significantly affects the plants height in maize and is crucial in identifying new varieties suitable for growing in high-density conditions.

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.

WRKY transcription factors in passion fruit analysis reveals key PeWRKYs involved in abiotic stress and flavonoid biosynthesis

WRKY transcription factors (TFs) are a superfamily of regulators involved in plant responses to pathogens and abiotic stress. Passion fruit is famous for its unique flavor and nutrient-rich juice, but its growth is limited by environmental factors and pathogens. In this study, 55 WRKY genes were identified from the Passiflora edulis genome. The structure and evolutionary characteristics of PeWRKYs were analyzed using a bioinformatics approach. PeWRKYs were classified into seven subgroups (I, IIa, IIb, IIc, IId, IIe, III) according to their homologs in Arabidopsis thaliana. Group IIa PeWRKY48 gene was highly up-regulated under cold stress by RNA expression analysis, and transgenic PeWRKY48 in yeast and Arabidopsis showed resistance exposure to cold, salt, and drought stress. Metabolome and transcriptome co-expression analysis of two different disease resistance genotypes of P. edulis identified PeWRKY30 as a key TF co-expressed with flavonoid accumulation in yellow fruit P. edulis, which may contribute to biotic or abiotic resistance. The qRT-PCR verified the expression of key genes in different tissues of P. edulis and in different species of Passiflora. This study provides a set of WRKY candidate genes that will facilitate the genetic improvement of disease and abiotic tolerance in passion fruit.

BpGRP1 acts downstream of BpmiR396c/BpGRF3 to confer salt tolerance in Betula platyphylla

Glycine-rich RNA-binding proteins (GRPs) have been implicated in the responses of plants to environmental stresses, but the function of GRP genes involved in salt stress and the underlying mechanism remain unclear. In this study, we identified BpGRP1 (glycine-rich RNA-binding protein), a Betula platyphylla gene that is induced under salt stress. The physiological and molecular responses to salt tolerance were investigated in both BpGRP1-overexpressing and suppressed conditions. BpGRF3 (growth-regulating factor 3) was identified as a regulatory factor upstream of BpGRP1. We demonstrated that overexpression of BpGRF3 significantly increased the salt tolerance of birch, whereas the grf3-1 mutant exhibited the opposite effect. Further analysis revealed that BpGRF3 and its interaction partner, BpSHMT, function upstream of BpGRP1. We demonstrated that BpmiR396c, as an upstream regulator of BpGRF3, could negatively regulate salt tolerance in birch. Furthermore, we uncovered evidence showing that the BpmiR396c/BpGRF3 regulatory module functions in mediating the salt response by regulating the associated physiological pathways. Our results indicate that BpmiR396c regulates the expression of BpGRF3, which plays a role in salt tolerance by targeting BpGRP1.

Multifaceted roles of WRKY transcription factors in abiotic stress and flavonoid biosynthesis

Increasing biotic and abiotic stresses are seriously impeding the growth and yield of staple crops and threatening global food security. As one of the largest classes of regulators in vascular plants, WRKY transcription factors play critical roles governing flavonoid biosynthesis during stress responses. By binding major W-box cis-elements (TGACCA/T) in target promoters, WRKYs modulate diverse signaling pathways. In this review, we optimized existing WRKY phylogenetic trees by incorporating additional plant species with WRKY proteins implicated in stress tolerance and flavonoid regulation. Based on the improved frameworks and documented results, we aim to deduce unifying themes of distinct WRKY subfamilies governing specific stress responses and flavonoid metabolism. These analyses will generate experimentally testable hypotheses regarding the putative functions of uncharacterized WRKY homologs in tuning flavonoid accumulation to enhance stress resilience.

MsWRKY33 increases alfalfa (Medicago sativa L.) salt stress tolerance through altering the ROS scavenger via activating MsERF5 transcription

Alfalfa (Medicago sativa L.) is considered to be the most important forage crop on a global scale. Nevertheless, soil salinity significantly decreases productivity, seriously threatening food security worldwide. One viable strategy is to explore salt stress-responsive factors and elucidate their underlying molecular mechanism, and utilize them in further alfalfa breeding. In the present study, we designated MsWRKY33 as a representative salt stress-responsive factor preferentially expressed in alfalfa roots and leaves. Subsequently, it was demonstrated that MsWRKY33 was localized in the cell nucleus, and functioned as a transcriptional activator of the W-box element. Transgenic alfalfa overexpressing MsWRKY33 displayed enhanced salt stress tolerance and antioxidant activities with no significant difference in other agronomic traits. Transcriptome profiling of MsWRKY33 transgenic alfalfa under control and salt treatment unveiled significantly altered expression of reactive oxygen species (ROS) scavenger genes in transgenic alfalfa. Subsequent examination revealed that MsWRKY33 binded to the promoter of MsERF5, activating its expression and consequently fine-tuning the ROS-scavenging enzyme activity. Furthermore, MsWRKY33 interacted with the functional fragment of MsCaMBP25, which participates in Ca2+ signaling transduction. Collectively, this research offers new insight into the molecular mechanism of alfalfa salt stress tolerance and highlights the potential utility of MsWRKY33 in alfalfa breeding.

SmWRKY11 acts as a positive regulator in eggplant response to salt stress

Salt stress is one of the most threatening abiotic stresses to plants, which can seriously affect plant growth, development, reproduction, and yield. However, the mechanisms of plant against salt stress largely remain unclear. Herein, SmWRKY11, an assumed WRKY transcription factor, was functionally characterized in eggplant against salt stress. SmWRKY11 was significantly up-regulated by salt, dehydration stress, and ABA treatment. SmWRKY11 located in the nucleus, and the Plant_zn_clust conserved domain exhibited transcriptional activation activity. Silencing of SmWRKY11 enhanced the susceptibility of eggplant to salt stress, accompanied by significantly down-regulation of transcript expression levels of salt stress defense-related genes SmNCED1, SmGSTU10, and positive regulator of salt stress response SmERF1 as well as increase of hydrogen peroxide (H2O2) content and decrease of the enzyme activities of catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX). In addition, silencing of SmERF1 also could significantly down-regulate SmWRKY11 expression in eggplant response to salt stress. By luciferase reporter assay and chromatin immunoprecipitation PCR assay, SmERF1 expression was found to be indirectly activated by SmWRKY11. These data indicate that SmWRKY11 acts as a positive regulator by forming positive feedback loop with SmERF1 via an indirect regulatory manner in eggplant response to salt stress.

ZmWRKY70 activates the expression of hypoxic responsive genes in maize and enhances tolerance to submergence in Arabidopsis

Hypoxic stress due to submergence is a serious threat to the growth and development of maize. WRKY transcription factors are significant regulators of plant responses to various abiotic and biotic stresses. Nevertheless, their function and regulatory mechanisms in the resistance of maize to submergence stress remain unclear. Here we report the cloning of a maize WRKY transcription factor gene, ZmWRKY70, transcripts of which accumulate under submergence stress in maize seedlings. Subcellular localization analysis and yeast transcriptional activation assay indicated that ZmWRKY70 was localized in the nucleus and had transcriptional activation activity. Heterologous overexpression of ZmWRKY70 in Arabidopsis increased the tolerance of seeds and seedlings to submergence stress by upregulating the transcripts of several key genes involved in anaerobic respiration, such as group VII ethylene-responsive factor (ERFVII) (AtRAP2.2), alcohol dehydrogenase (AtADH1), pyruvate decarboxylase (AtPDC1/2), and sucrose synthase (AtSUS4), under submergence conditions. Moreover, the overexpression of ZmWRKY70 in maize mesophyll protoplasts enhanced the expression of ZmERFVII members (ZmERF148, ZmERF179, and ZmERF193), ZmADH1, ZmPDC2/3, and ZmSUS1. Yeast one-hybrid and dual-luciferase activity assays further confirmed that ZmWRKY70 enhanced the expression of ZmERF148 by binding to the W box motif located in the promoter region of ZmERF148. Together, these results indicate that ZmWRKY70 plays a significant role in tolerance of submergence stress. This work provides a theoretical basis, and suggests excellent genes, for biotechnological breeding to improve the tolerance of maize to submergence through the regulation of ZmWRKY genes.

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.

Transcriptome Profiling Reveals Differential Gene Expression during the Process of Microtuber Formation in Pinellia ternata

Using petiole material as explants and directly inducing the formation of microtubers without going through the callus stage is an essential way to rapidly expand scarce medical plants such as Pinellia ternata. However, the early molecular mechanism underlying the formation of the microtuber is largely elusive. Here, we conducted cytology and dynamic transcriptome analyses of inchoate microtubers in Pinellia explants and identified 1092 differentially expressed genes after their cultivation in vitro for 0, 5, and 15 days. Compared with 0 day, the number and size of the microtuber cells were larger at 5 and 15 days of culture. Detailed categorization revealed that the differentially expressed genes were mainly related to responses to stimulus, biological regulation, organelles, membranes, transcription factor activity, and protein binding. Further analysis revealed that the microtuber at different incubation days exhibited quite a difference in both hormone signaling pathway transduction and the regulation pattern of transcription factors. Therefore, this study contributes to a better understanding of the early molecular regulation during the formation of the microtuber and provides new insights for the study of the rapid expansion of P. ternata and other medical plants.

A Review of Potato Salt Tolerance

Potato is the world's fourth largest food crop. Due to limited arable land and an ever-increasing demand for food from a growing population, it is critical to increase crop yields on existing acreage. Soil salinization is an increasing problem that dramatically impacts crop yields and restricts the growing area of potato. One possible solution to this problem is the development of salt-tolerant transgenic potato cultivars. In this work, we review the current potato planting distribution and the ways in which it overlaps with salinized land, in addition to covering the development and utilization of potato salt-tolerant cultivars. We also provide an overview of the current progress toward identifying potato salt tolerance genes and how they may be deployed to overcome the current challenges facing potato growers.

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.

The UDP-glucuronic acid decarboxylase OsUXS3 regulates Na+ ion toxicity tolerance under salt stress by interacting with OsCATs in rice

Overly Na⁺ ion in soil caused by salt stress has a significant negative impact on the growth and production of crops, especially rice (Oryza sativa L.). Therefore, it is vital for us to clarify how salt stress tolerance in rice is caused by Na⁺ ion toxicity. The UDP-glucuronic acid decarboxylase (UXS) is a critical enzyme in the biosynthesis of UDP-xylose, which is the key substrate of cytoderm synthesis in plants. In this study, we found that OsUXS3, a rice UXS, is a positive regulator to regulate Na⁺ ion toxicity under salt stress by interacting with OsCATs (Oryza sativa catalase; OsCAT). The expression of OsUXS3 was significantly up-regulated under NaCl and NaHCO₃ treatments of rice seedlings. Meanwhile, by the genetic and biochemical evidence, knockout of OsUXS3 significantly increased reactive oxygen species (ROS) levels and decreased CAT activity under NaCl and NaHCO₃ treatments in tissue. Furthermore, knockout of OsUXS3 caused excessive accumulation of Na ⁺ ion and rapid loss of K⁺ ion and disrupts Na⁺/K⁺ homeostasis under NaCl and NaHCO₃ treatments. Based on the results above, we can conclude that OsUXS3 might regulate CAT activity by interacting with OsCATs, which is not only characterized for the first time but also regulating Na⁺/K⁺ homeostasis, positively regulating the Na⁺ ion toxicity tolerance under salt stress in rice.

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

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

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

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