Overexpression of GmWRKY172 enhances cadmium tolerance in plants and reduces cadmium accumulation in soybean seeds

Metal transport proteins and transcription factor networks in plant responses to cadmium stress

Cadmium (Cd) contamination poses a significant threat to agriculture and human health due to its high soil mobility and toxicity. This review synthesizes current knowledge on Cd uptake, transport, detoxification, and transcriptional regulation in plants, emphasizing the roles of metal transport proteins and transcription factors (TFs). We explore transporter families like NRAMP, HMA, ZIP, ABC, and YSL in facilitating Cd movement within plant tissues, identifying potential targets for reducing Cd accumulation in crops. Additionally, regulatory TF families, including WRKY, MYB, bHLH, and ERF, are highlighted for their roles in modulating gene expression to counteract Cd toxicity. This review consolidates the existing literature on plant-Cd interactions, providing insights into established mechanisms and identifying gaps for future research. Understanding these mechanisms is crucial for developing strategies to enhance plant tolerance, ensure food safety, and promote sustainable agriculture amidst increasing heavy-metal pollution.

Integrative study of transcriptome and microbiome to reveal the response of Rhododendron decorum to cadmium stress

The anomalies of cadmium (Cd) in karst region pose a severe threat to plant growth and development. In this study, the responses of Rhododendron decorum to Cd stress were investigated at physiological, molecular, and endophytic microbial levels, and the potential correlation among these responses was assessed. The Cd stress impeded R. decorum growth and led to an increase in malondialdehyde (MDA) and hydrogen peroxide (H2O2) levels, as well as enhanced superoxide dismutase (SOD) and catalase (CAT) activities. Meanwhile, Cd stress increased the Cd (up to 80 times compared to the control), sodium (Na), aluminum (Al), and zinc (Zn) contents, while decreased the magnesium (Mg) and manganese (Mn) contents in R. decorum leaves. Transcriptome suggested that Cd significantly regulated the pathways including "protein repair", "hormone-mediated signaling pathway", and "ATP-binding cassette (ABC) transporters". Additionally, q-PCR analysis showed that Cd stress significantly up-regulated the expressions of ABCB19-like and pleiotropic drug resistance, while down-regulated the expressions of indole-3-acetic acid-amido synthetase and cytokinin dehydrogenase. The Cd stress influenced the composition of endophytic microbial communities in R. decorum leaves and enhanced the interspecific bacterial associations. Furthermore, the bacterial genera Achromobacter, Aureimonas and fungal genus Vishniacozyma exhibited a high degree of connectivity with other nodes in networks constructed by the metal element contents, differentially expressed genes (DEGs), and microbial communities, respectively. These findings provide a comprehensive insight into the response of R. decorum to Cd-induced stress, which might facilitate the breeding of the Cd-tolerant R. decorum.

WRKY Transcription Factor Responses and Tolerance to Abiotic Stresses in Plants

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

A comprehensive analysis of the WRKY family in soybean and functional analysis of GmWRKY164-GmGSL7c in resistance to soybean mosaic virus

BACKGROUND

Soybean mosaic disease caused by soybean mosaic virus (SMV) is one of the most devastating and widespread diseases in soybean producing areas worldwide. The WRKY transcription factors (TFs) are widely involved in plant development and stress responses. However, the roles of the GmWRKY TFs in resistance to SMV are largely unclear.

RESULTS

Here, 185 GmWRKYs were characterized in soybean (Glycine max), among which 60 GmWRKY genes were differentially expressed during SMV infection according to the transcriptome data. The transcriptome data and RT-qPCR results showed that the expression of GmWRKY164 decreased after imidazole treatment and had higher expression levels in the incompatible combination between soybean cultivar variety Jidou 7 and SMV strain N3. Remarkably, the silencing of GmWRKY164 reduced callose deposition and enhanced virus spread during SMV infection. In addition, the transcript levels of the GmGSL7c were dramatically lower upon the silencing of GmWRKY164. Furthermore, EMSA and ChIP-qPCR revealed that GmWRKY164 can directly bind to the promoter of GmGSL7c, which contains the W-box element.

CONCLUSION

Our findings suggest that GmWRKY164 plays a positive role in resistance to SMV infection by regulating the expression of GmGSL7c, resulting in the deposition of callose and the inhibition of viral movement, which provides guidance for future studies in understanding virus-resistance mechanisms in soybean.

Transcription factors involved in plant responses to cadmium-induced oxidative stress

Cadmium (Cd) is a heavy metal highly toxic to living organisms. Cd pollution of soils has become a serious problem worldwide, posing a severe threat to crop production and human health. When plants are poisoned by Cd, their growth and development are inhibited, chloroplasts are severely damaged, and respiration and photosynthesis are negatively affected. Therefore, elucidating the molecular mechanisms that underlie Cd tolerance in plants is important. Transcription factors can bind to specific plant cis-acting genes. Transcription factors are frequently reported to be involved in various signaling pathways involved in plant growth and development. Their role in the resistance to environmental stress factors, particularly Cd, should not be underestimated. The roles of several transcription factor families in the regulation of plant resistance to Cd stress have been widely demonstrated. In this review, we summarize the mechanisms of five major transcription factor families-WRKY, ERF, MYB, bHLH, and bZIP-in plant resistance to Cd stress to provide useful information for using molecular techniques to solve Cd pollution problems in the future.

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.

The Uptake, Transfer, and Detoxification of Cadmium in Plants and Its Exogenous Effects

Cadmium (Cd) exerts a toxic influence on numerous crucial growth and development processes in plants, notably affecting seed germination rate, transpiration rate, chlorophyll content, and biomass. While considerable advances in Cd uptake and detoxification of plants have been made, the mechanisms by which plants adapt to and tolerate Cd toxicity remain elusive. This review focuses on the relationship between Cd and plants and the prospects for phytoremediation of Cd pollution. We highlight the following issues: (1) the present state of Cd pollution and its associated hazards, encompassing the sources and distribution of Cd and the risks posed to human health; (2) the mechanisms underlying the uptake and transport of Cd, including the physiological processes associated with the uptake, translocation, and detoxification of Cd, as well as the pertinent gene families implicated in these processes; (3) the detrimental effects of Cd on plants and the mechanisms of detoxification, such as the activation of resistance genes, root chelation, vacuolar compartmentalization, the activation of antioxidant systems and the generation of non-enzymatic antioxidants; (4) the practical application of phytoremediation and the impact of incorporating exogenous substances on the Cd tolerance of plants.

Unveiling Innovative Approaches to Mitigate Metals/Metalloids Toxicity for Sustainable Agriculture

Due to anthropogenic activities, environmental pollution of heavy metals/metalloids (HMs) has increased and received growing attention in recent decades. Plants growing in HM-contaminated soils have slower growth and development, resulting in lower agricultural yield. Exposure to HMs leads to the generation of free radicals (oxidative stress), which alters plant morpho-physiological and biochemical pathways at the cellular and tissue levels. Plants have evolved complex defense mechanisms to avoid or tolerate the toxic effects of HMs, including HMs absorption and accumulation in cell organelles, immobilization by forming complexes with organic chelates, extraction via numerous transporters, ion channels, signaling cascades, and transcription elements, among others. Nonetheless, these internal defensive mechanisms are insufficient to overcome HMs toxicity. Therefore, unveiling HMs adaptation and tolerance mechanisms is necessary for sustainable agriculture. Recent breakthroughs in cutting-edge approaches such as phytohormone and gasotransmitters application, nanotechnology, omics, and genetic engineering tools have identified molecular regulators linked to HMs tolerance, which may be applied to generate HMs-tolerant future plants. This review summarizes numerous systems that plants have adapted to resist HMs toxicity, such as physiological, biochemical, and molecular responses. Diverse adaptation strategies have also been comprehensively presented to advance plant resilience to HMs toxicity that could enable sustainable agricultural production.

Transcriptome analysis reveals cadmium exposure enhanced the isoquinoline alkaloid biosynthesis and disease resistance in Coptis chinensis

Coptis chinensis Franch is a perennial herb from the Ranunculaceae family with a long history of medicinal use. As the medicinal part, the rhizome of coptis often accumulates excessive cadmium (Cd) even at low concentrations in the soil, which not only compromises its medicinal safety but also raises concerns about adverse effects on human health. Therefore, effective strategies are needed to mitigate this accumulation and ensure its safe use in traditional medicine. This study utilized transcriptome profiling and physiological analysis to explore molecular mechanisms associated with ecological significance and the active accumulation of Cd in C. chinensis. The response to Cd in C. chinensis was assessed through RNA sequencing, Cd determination and isoquinoline alkaloid measurement using its roots, stems, and leaves. The transcriptome revealed, a total of 2667, 2998, or 2815 up-regulated deferentially expressed genes in roots, stems or leaves in response to Cd exposure. Furthermore, we identified phenylpropanoid and isoquinoline alkaloid biosynthesis as the key pathways response to Cd exposure, which suggests that C. chinensis may improve its tolerance to Cd through regulating the phenylpropanoid biosynthesis pathway. Under Cd exposure, plant-pathogen interaction in leaves was identified as the key pathway, which indicates that upregulation of genes involved in plant-pathogen interaction could enhance disease resistance in C. chinensis. WGCNA analysis identified WRKY8 (Cluster-55763.31419) and WRKY47 (Cluster-55763.221590) as potential regulators of secondary metabolic synthesis and plant-pathogen interaction pathway in C. chinensis triggered by Cd. The measurement of berberine, coptisine, palmatine, and epiberberine also demonstrated that Cd simulated the four isoquinoline alkaloids in roots. Therefore, our study not only presented a transcriptome expression profiles that revealed significant upregulation of genes involved in metal transport and detoxification pathways but also suggested a possible mechanism to cope with Cd accumulation. This knowledge provides a new insight into gene manipulation for controlling Cd accumulation, enhancing resistance and promoting synthesis of secondary metabolites with potential medicinal properties in other medicinal plant species.

A WRKY transcription factor, PyWRKY71, increased the activities of antioxidant enzymes and promoted the accumulation of cadmium in poplar

Cadmium (Cd) pollution poses significant threats to the ecological environment and human health. Currently, phytoremediation is recognized as an environmentally friendly approach for mitigating Cd pollution, with increasing attention on the utilization of transgenic plants in Cd-contaminated soil remediation. In this study, we isolated and cloned PyWRKY71 from Populus yunnanensis and conducted a pot experiment to validate its enhanced functionality in conferring Cd tolerance to woody plants (poplar). During the experiment, the increase in plant height of the OE-87 line (overexpression poplar) was 1.46 times than that of the wild type (WT). Moreover, PyWRKY71 significantly promoted the accumulation of Cd in poplar, especially in the roots, where the Cd content in the OE-45 and OE-87 lines was 1.42 times than that in the WT. The chlorophyll content of transgenic poplar leaves was higher than that of the WT, reflecting a protective mechanism of PyWRKY71. Additionally, the activities of other antioxidants, including POD, SOD, CAT, and MDA, were elevated in transgenic poplars, bolstering their tolerance to Cd stress. In summary, PyWRKY71 exhibits substantial potential in regulating plant tolerance to Cd stress. This study not only provides a solid scientific foundation but also introduces a novel modified poplar variety for the remediation of Cd pollution.

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.

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.

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.