The walnut JrVHAG1 gene is involved in cadmium stress response through ABA-signal pathway and MYB transcription regulation

Comprehensive transcriptome, physiological and biochemical analyses reveal that key role of transcription factor WRKY and plant hormone in responding cadmium stress

Cadmium (Cd) is readily absorbed by tobacco and accumulates in the human body through smoke inhalation, posing threat to human health. While there have been many studies on the negative impact of cadmium in tobacco on human health, the specific adaptive mechanism of tobacco roots to cadmium stress is not well understood. In order to comprehensively investigate the effects of Cd stress on the root system of tobacco, the combination of transcriptomic, biochemical, and physiological methods was utilized. In this study, tobacco growth was significantly inhibited by 50 μM of Cd, which was mainly attributed to the destruction of root cellular structure. By comparing the transcriptome between CK and Cd treatment, there were 3232 up-regulated deferentially expressed genes (DEGs) and 3278 down-regulated DEGs. The obvious differential expression of genes related to the nitrogen metabolism, metal transporters and the transcription factors families. In order to mitigate the harmful effects of Cd, the root system enhances Cd accumulation in the cell wall, thereby reducing the Cd content in the cytoplasm. This result may be mediated by plant hormones and transcription factor (TF). Correlational statistical analysis revealed significant negative correlations between IAA and GA with cadmium accumulation, indicated by correlation coefficients of -0.91 and -0.93, respectively. Conversely, ABA exhibited a positive correlation with a coefficient of 0.96. In addition, it was anticipated that 3 WRKY TFs would lead to a reduction in Cd accumulation. Our research provides a theoretical basis for the systematic study of the specific physiological processes of plant roots under Cd stress.

Heavy metal stress and mitogen activated kinase transcription factors in plants: Exploring heavy metal-ROS influences on plant signalling pathways

Due to their stationary nature, plants are exposed to a diverse range of biotic and abiotic stresses, of which heavy metal (HM) stress poses one of the most detrimental abiotic stresses, targeting diverse plant processes. HMs instigate the overproduction of reactive oxygen species (ROS), and to mitigate the adverse effects of ROS, plants induce multiple defence mechanisms. Besides the negative implications of overproduction of ROS, these molecules play a multitude of signalling roles in plants, acting as a central player in the complex signalling network of cells. One of the ROS-associated signalling mechanisms is the mitogen-activated protein kinase (MAPK) cascade, a signalling pathway which transduces extracellular stimuli into intracellular responses. Plant MAPKs have been implicated in signalling involved in stress response, phytohormone regulation, and cell cycle cues. However, the influence of various HMs on MAPK activation has not been well documented. In this review, we address and summarise several aspects related to various HM-induced ROS signalling. Additionally, we touch on how these signals activate the MAPK cascade and the downstream transcription factors that influence plant responses to HMs. Moreover, we propose a workflow that could characterise genes associated with MAPKs and their roles during plant HM stress responses.

The A subunit of vacuolar H+-ATPase gene (CmVHA-A) plays opposite roles in plant growth and drought tolerance of chrysanthemum under different growing conditions

As the most prominent proton pumps in plants, vacuolar H+-ATPases (VHAs) comprise multiple subunits that are important for physiological processes and stress tolerance in plants. However, few studies on the roles of subunit genes of VHAs in chrysanthemum have been reported to date. In this study, the gene of A subunit of V-ATPase in chrysanthemum (CmVHA-A) was cloned and identified. CmVHA-A was conserved with VHA-A proteins from other plants. Expression analysis showed that CmVHA-A was highly expressed in most tissues of chrysanthemum except for the flower bud, and was readily induced by polyethylene glycol (PEG) treatment. Functional analysis demonstrated that CmVHA-A exerted a negative influence on the growth and development of shoot and root of chrysanthemum under normal conditions. RNA-sequencing (RNA-seq) analysis revealed the possible explanations for phenotypic differences between transgenic and wild-type (WT) plants. Under drought conditions, CmVHA-A positively affected the drought tolerance of chrysanthemum by enhancing antioxidase activity and alleviating photosynthetic disruption. Overall, CmVHA-A plays opposite roles in plant growth and drought tolerance of chrysanthemums under different growing conditions.

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.

The Physiological Response Mechanism of Peanut Leaves under Al Stress

Aluminum (Al) toxicity in acidic soils can significantly reduce peanut yield. The physiological response of peanut leaves to Al poisoning stress still has not been fully explored. This research examined the influences of Al toxicity on peanut leaves by observing the leaf phenotype, scanning the leaf area and perimeter, and by measuring photosynthetic pigment content, physiological response indices, leaf hormone levels, and mineral element accumulation. Fluorescence quantitative RT-PCR (qPCR) was utilized to determine the relative transcript level of specific genes. The results indicated that Al toxicity hindered peanut leaf development, reducing their biomass, surface area, and perimeter, although the decrease in photosynthetic pigment content was minimal. Al toxicity notably affected the activity of antioxidative enzymes, proline content, and MDA (malondialdehyde) levels in the leaves. Additionally, Al poisoning resulted in the increased accumulation of iron (Fe), potassium (K), and Al in peanut leaves but reduced the levels of calcium (Ca), manganese (Mn), copper (Cu), zinc (Zn), and magnesium (Mg). There were significant changes in the content of hormones and the expression level of genes connected with hormones in peanut leaves. High Al concentrations may activate cellular defense mechanisms, enhancing antioxidative activity to mitigate excess reactive oxygen species (ROS) and affecting hormone-related gene expression, which may impede leaf biomass and development. This research aimed to elucidate the physiological response mechanisms of peanut leaves to Al poisoning stress, providing insights for breeding new varieties resistant to Al poisoning.

Impacts of polypropylene microplastics on lipid profiles of mouse liver uncovered by lipidomics analysis and Raman spectroscopy

Microplastics (MPs) are emerging contaminants, and there are only limited studies reporting the impacts of some MPs on liver lipid metabolism in animals. In this study, we investigated the accumulation of polypropylene-MPs in mouse liver and unraveled the change in lipid metabolic profiles by both lipidomics and Raman spectroscopy. Polypropylene-MP exposure did not cause obvious health symptoms, but hematoxylin-eosin staining showed pathological changes that polypropylene-MPs induced lipid droplet accumulation in liver. Lipidomics results showed a significant change in lipid metabolic profiles and the most influenced categories were triglycerides, fatty acids, free fatty acids and lysophosphatidylcholine, implying the effects of polypropylene-MPs on the hemostasis of lipid droplet biogenesis and catabolism. Most altered lipids contained unsaturated bonds and polyunsaturated phospholipids, possibly affecting the fluidity and curvature of membrane surfaces. Raman spectroscopy confirmed that the major spectral alterations of liver tissues were related to lipids, evidencing the altered lipid metabolism and cell membrane components in the presence of polypropylene-MPs. Our findings firstly disclosed the impacts of polypropylene-MPs on lipid metabolisms in mouse liver and hinted at their detrimental disturbance on membrane properties, cellular lipid storage and oxidation regulation, helping our deeper understanding on the toxicities and corresponding risks of polypropylene-MPs to mammals.

Arabidopsis Protein Phosphatase PIA1 Impairs Plant Drought Tolerance by Serving as a Common Negative Regulator in ABA Signaling Pathway

Reversible phosphorylation of proteins is a ubiquitous regulatory mechanism in vivo that can respond to external changes, and plays an extremely important role in cell signal transduction. Protein phosphatase 2C is the largest protein phosphatase family in higher plants. Recently, it has been found that some clade A members can negatively regulate ABA signaling pathways. However, the functions of several subgroups of Arabidopsis PP2C other than clade A have not been reported, and whether other members of the PP2C family also participate in the regulation of ABA signaling pathways remains to be studied. In this study, based on the previous screening and identification work of PP2C involved in the ABA pathway, the clade F member PIA1 encoding a gene of the PP2C family, which was down-regulated after ABA treatment during the screening, was selected as the target. Overexpression of PIA1 significantly down-regulated the expression of ABA marker gene RD29A in Arabidopsis protoplasts, and ABA-responsive elements have been found in the cis-regulatory elements of PIA1 by promoter analysis. When compared to Col-0, transgenic plants overexpressing PIA1 were less sensitive to ABA, whereas pia1 showed the opposite trait in seed germination, root growth, and stomatal opening experiments. Under drought stress, SOD, POD, CAT, and APX activities of PIA1 overexpression lines were lower than Col-0 and pia1, while the content of H₂O₂ was higher, leading to its lowest survival rate in test plants, which were consistent with the significant inhibition of the expression of ABA-dependent stress-responsive genes RD29B, ABI5, ABF3, and ABF4 in the PIA1 transgenic background after ABA treatment. Using yeast two-hybrid and luciferase complementation assays, PIA1 was found to interact with multiple ABA key signaling elements, including 2 RCARs and 6 SnRK2s. Our results indicate that PIA1 may reduce plant drought tolerance by functioning as a common negative regulator involved in ABA signaling pathway.

Genome wide association studies and candidate gene mining for understanding the genetic basis of straw silica content in a set of Oryza nivara (Sharma et Shastry) accessions

Rice is a high-silica (SiO₂·nH₂O) accumulator. Silicon (Si) is designated as a beneficial element associated with multiple positive effects on crops. However, the presence of high silica content is detrimental to rice straw management, hampering its use as animal feed and as raw material in multiple industries. Rice straw management is a serious concern in north-western India, and it is eventually burned in situ by farmers, contributing to air pollution. A practical solution could lie in reducing the silica content in rice while also attaining sound plant growth. A set of 258 Oryza nivara accessions along with 25 cultivated varieties of Oryza sativa was used to assess the variation in straw silica content using the molybdenum blue colorimetry method. A large continuous variation was observed for straw silica content in O. nivara accessions, ranging from 5.08% to 16%, while it varied from 6.18% to 15.81% in the cultivated varieties. The O. nivara accessions containing 43%-54% lower straw silica content than the currently prominent cultivated varieties in the region were identified. A set of 22,528 high-quality single nucleotide polymorphisms (SNPs) among 258 O. nivara accessions was used for estimating population structure and genome-wide association studies (GWAS). A weak population structure with 59% admixtures was identified among O. nivara accessions. Further, multi-locus GWAS revealed the presence of 14 marker-trait associations (MTAs) for straw silica content, with six of them co-localizing with previously reported quantitative trait loci (QTL). Twelve out of 14 MTAs showed statistically significant allelic differences. Thorough candidate gene analyses revealed the presence of promising candidate genes, including those encoding the ATP-binding cassette (ABC) transporter, Casparian thickening, multi-drug and toxin extrusion (MATE) protein, F-box, and MYB-transcription factors. Besides, ortho-QTLs among rice and maize genomes were identified, which could open ways for further genetic analysis of this trait. The findings of the study could aid in further understanding and characterizing genes for Si transport and regulation in the plant body. The donors carrying the alleles for lower straw silica content can be used in further marker-assisted breeding programs to develop rice varieties with lower silica content and higher yield potential.

Physiological dynamics as indicators of plant response to manganese binary effect

Introduction

Heavy metals negatively affect plant physiology. However, plants can reduce their toxicity through physiological responses. Broussonetia papyrifera is a suitable candidate tree for carrying out the phytoremediation of manganese (Mn)-contaminated soil.

Methods

Considering that Mn stress typically exerts a binary effect on plants, to reveal the dynamic characteristics of the physiological indexes of B. papyrifera to Mn stress, we conducted pot experiments with six different Mn concentrations (0, 0.25, 0.5, 1, 2, and 5 mmol/L) for 60 days. In addition to the chlorophyll content, malondialdehyde (MDA), proline (PRO), soluble sugar, superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), the absorption and transfer characteristics of Mn, and root structure were also measured.

Results

Phytoremedial potential parameters such as the bioconcentration factor (BCF) and translocation factor (TF) displayed an increasing trend with the increase of Mn concentration. At lower Mn concentrations (<0.5 mmol/L), the TF value was <1 but crossed 1 when the Mn concentration exceeded 100 mmol/L. The Mn distribution in various tissues was in the following order: leaf > stem > root. The root structure analysis revealed that low-level concentrations of Mn (1 mmol/L) promoted root development. Mn concentration and stress duration had significant effects on all measured physiological indexes, and except soluble sugar, Mn concentration and stress time displayed a significant interaction on the physiological indexes.

Discussion

Our study demonstrates that the physiological indexes of B. papyrifera display dynamic characteristics under Mn stress. Thus, during the monitoring process of Mn stress, it appears to be necessary to appropriately select sampling parts according to Mn concentration.

Abscisic-Acid-Regulated Responses to Alleviate Cadmium Toxicity in Plants

High levels of cadmium (Cd) in soil can cause crop yield reduction or death. Cadmium accumulation in crops affects human and animal health as it passes through the food chain. Therefore, a strategy is needed to enhance the tolerance of crops to this heavy metal or reduce its accumulation in crops. Abscisic acid (ABA) plays an active role in plants' response to abiotic stress. The application of exogenous ABA can reduce Cd accumulation in shoots of some plants and enhance the tolerance of plants to Cd; therefore, ABA may have good application prospects. In this paper, we reviewed the synthesis and decomposition of ABA, ABA-mediated signal transduction, and ABA-mediated regulation of Cd-responsive genes in plants. We also introduced physiological mechanism underlying Cd tolerance because of ABA. Specifically, ABA affects metal ion uptake and transport by influencing transpiration and antioxidant systems, as well as by affecting the expression of metal transporter and metal chelator protein genes. This study may provide a reference for further research on the physiological mechanism of heavy metal tolerance in plants.

Abscisic acid: Metabolism, transport, crosstalk with other plant growth regulators, and its role in heavy metal stress mitigation

Heavy metal (HM) stress is threatening agricultural crops, ecological systems, and human health worldwide. HM toxicity adversely affects plant growth, physiological processes, and crop productivity by disturbing cellular ionic balance, metabolic balance, cell membrane integrity, and protein and enzyme activities. Plants under HM stress intrinsically develop mechanisms to counter the adversities of HM but not prevent them. However, the exogenous application of abscisic acid (ABA) is a strategy for boosting the tolerance capacity of plants against HM toxicity by improving osmolyte accumulation and antioxidant machinery. ABA is an essential plant growth regulator that modulates various plant growth and metabolic processes, including seed development and germination, vegetative growth, stomatal regulation, flowering, and leaf senescence under diverse environmental conditions. This review summarizes ABA biosynthesis, signaling, transport, and catabolism in plant tissues and the adverse effects of HM stress on crop plants. Moreover, we describe the role of ABA in mitigating HM stress and elucidating the interplay of ABA with other plant growth regulators.

Transcriptome-wide identification of walnut PP2C family genes in response to external stimulus

Walnut is an important economic tree species while confronting with global environmental stress, resulting in decline in quality and yield. Therefore, it is urgent to elucidate the molecular mechanism for the regulation of walnut response to adversity. The protein phosphatase 2C (PP2C) gene family participates in cellular processes in eukaryotes through reversible phosphorylation of proteins and signal transduction regulation. However, the stress response function of PP2C genes was far to be clarified. Therefore, to understand the stress response mechanism of walnut tree, in this study, a total of 41 PP2C genes with complete ORFs were identified from Juglans regia, whose basic bio-information and expression patterns in response to multiple stresses and ABA were confirmed. The results showed that the ORFs of JrPP2Cs were 495 ~ 3231 bp in length, the predicted JrPP2C proteins contained 164 to 1076 amino acids and the molecular weights were 18,581.96 ~ 118,853.34 Da, the pI was 4.55 ~ 9.58. These JrPP2C genes were unevenly distributed on 14 chromosomes, among which Chr11 and Chr13 contained the most genes. Phylogenetic analysis found that these JrPP2C proteins were classed into 9 subfamilies, among which group F covered most JrPP2Cs. The JrPP2Cs in the same subfamily exhibited similarities in the composition of conserved domains, amino acid sequences of motifs and exon/intron organization in DNA sequences. Each JrPP2C includes 4 ~ 10 motifs and each motif contained 15 ~ 37 amino acids. Among the motifs, motif1, motif2, motif3 and motif8 were most abundant. Most of the JrPP2C genes diversely response to osmotic, cadmium, and Colletotrichum gloeosporioide stress as well as ABA treatments, among which JrPP2C28, JrPP2C17, JrPP2C09, JrPP2C36 were more obvious and deserves further attention. All these results indicated that JrPP2C genes play potential vital roles in plant response to multiple stimulus, and are possibly involved in ABA-dependent signaling pathway.

A novel microRNA IamiR-4-3p from water spinach (Ipomoea aquatica Forsk.) increased Cd uptake and translocation in Arabidopsis thaliana

MicroRNAs (miRNAs) play important roles in plant response to Cd stress. In our previous study, we observed significant differences in the expression levels of IamiR-4-3p between high-Cd and low-Cd cultivars of water spinach. The function of IamiR-4-3p was investigated by using wild type Arabidopsis (WT), Arabidopsis transfected with empty vector pCambia1302 (CK), and Arabidopsis transfected with IamiR-4-3p + vector pCambia1302 (p35S::miR-4-3p) in this study. In p35S::miR-4-3p Arabidopsis, the expression levels of GST3 and AWPM19-like were reduced by 20% and 24%. Under Cd treatment, higher root and shoot Cd concentrations were detected in the transgenic p35S::miR-4-3p Arabidopsis. MDA and H₂O₂ concentrations were positively correlated with the Cd concentrations in all Arabidopsis. The elevated GSH pool in p35S::miR-4-3p Arabidopsis should compensate for its restricted GST3 expression in response to Cd-induced oxidative stress. Lower F1 (cell wall) and higher F2 (organelle) and F3 (soluble fraction) Cd concentrations were observed along with the reduced ABA level in p35S::miR-4-3p Arabidopsis, which could induce a weakened apoplastic barrier and higher Cd accumulation and translocation in roots. It is suggested that IamiR-4-3p is able to reduce the expression levels of GST3 and AWPM19-like, resulting in higher Cd uptake and translocation in Arabidopsis.

MAPK Cascades and Transcriptional Factors: Regulation of Heavy Metal Tolerance in Plants

In nature, heavy metal (HM) stress is one of the most destructive abiotic stresses for plants. Heavy metals produce toxicity by targeting key molecules and important processes in plant cells. The mitogen-activated protein kinase (MAPK) cascade transfers the signals perceived by cell membrane surface receptors to cells through phosphorylation and dephosphorylation and targets various effector proteins or transcriptional factors so as to result in the stress response. Signal molecules such as plant hormones, reactive oxygen species (ROS), and nitric oxide (NO) can activate the MAPK cascade through differentially expressed genes, the activation of the antioxidant system and synergistic crosstalk between different signal molecules in order to regulate plant responses to HMs. Transcriptional factors, located downstream of MAPK, are key factors in regulating plant responses to heavy metals and improving plant heavy metal tolerance and accumulation. Thus, understanding how HMs activate the expression of the genes related to the MAPK cascade pathway and then phosphorylate those transcriptional factors may allow us to develop a regulation network to increase our knowledge of HMs tolerance and accumulation. This review highlighted MAPK pathway activation and responses under HMs and mainly focused on the specificity of MAPK activation mediated by ROS, NO and plant hormones. Here, we also described the signaling pathways and their interactions under heavy metal stresses. Moreover, the process of MAPK phosphorylation and the response of downstream transcriptional factors exhibited the importance of regulating targets. It was conducive to analyzing the molecular mechanisms underlying heavy metal accumulation and tolerance.

Genome-wide identification and genetic characterization of the CaMYB family and its response to five types of heavy metal stress in hot pepper (Capsicum annuum cv. CM334)

MYB proteins play a crucial role in plant growth and development and stress responses. In this study, 160 members of the MYB gene family from the pepper genome database were used to analyze gene structures, chromosome localization, collinearity, genetic affinity and expression in response to heavy metals. The results identified R2R3-MYB members and further phylogenetically classified them into 35 subgroups based on highly conserved gene structures and motifs. Collinearity analysis showed that segmental duplication events played a crucial role in the functional expansion of the CaMYB gene family by intraspecific collinearity, and at least 12 pairs of CaMYB genes existed between species prior to the differentiation between monocots and dicots. Moreover, the upstream CaMYB genes were mainly localized to the phytohormone elements ABRE and transcription factor elements MYB and MYC. Further analysis revealed that MYB transcription factors were closely associated with a variety of abiotic stress-related proteins (e.g., MAC-complex and SKIP). Under the stress of five metal ions, Cd²⁺, Cu²⁺, Pb²⁺, Zn²⁺, and Fe³⁺, the expression levels of some CaMYB family genes were upregulated. Of these genes, pairing homologous 1 (PH-1), PH-13, and PH-15 in the roots of Capsicum annuum were upregulated to the greatest extent, indicating that these three MYB family members are particularly sensitive to these five metals. This study provides a theoretical reference for the analysis of the molecular regulatory mechanism of MYB family genes in mediating the response to heavy metals in plants. This study reveals the mode of interaction between MYB and a variety of abiotic stress proteins and clarifies the biological functions of CaMYB family members in the regulation of heavy metal stress.

Knockout of FER decreases cadmium concentration in roots of Arabidopsis thaliana by inhibiting the pathway related to iron uptake

Identifying the genes that affect cadmium (Cd) accumulation in plants is a prerequisite for minimizing dietary Cd uptake from contaminated edible parts of plants by genetic engineering. This study showed that Cd stress inhibited the expression of FERONIA (FER) gene in the roots of wild-type Arabidopsis. Knockout of FER in fer-4 mutants downregulated the Cd-induced expression of several genes related to iron (Fe) uptake, including IRT1, bHLH38, NRAMP1, NRAMP3, FRO2 andFIT. In addition, the Cd concentration in fer-4 mutant roots reduced to approximately half of that in the wild-type seedlings. As a result, the Cd tolerance of fer-4 was higher. Furthermore, increased Fe supplementation had little effect on the Cd tolerance of fer-4 mutants, but clearly improved the Cd tolerance of wild-type seedlings, showing that the alleviation of Cd toxicity by Fe depends on the action of FER. Taken together, the findings demonstrate that the knockout of FER might provide a strategy to reduce Cd contamination and improve the Cd tolerance in plants by regulating the pathways related to Fe uptake.

Regulating role of abscisic acid on cadmium enrichment in ramie (Boehmeria nivea L.)

Abscisic acid (ABA) is known as an important hormone regulating plant stress resistance, such as salt, drought and heavy metal resistance. However, the relationship between ABA and cadmium (Cd) enrichment in ramie (Boehmeria nivea L.) is still unclear to date. This study aimed to reveal the effect of ABA on Cd enrichment in ramie, and we received the following results: (1) Under Cd treatment, the Cd uptake of ramie increased with the increase of Cd concentration, but the chlorophyll content decreased. Under Cd treatment, the ABA content was highest in roots of ramie, followed by that in old leaves, and lowest in new leaves. Long-time treatment of high Cd concentration reduced the ability of endogenous ABA biosynthesis. (2) Spraying ABA on ramie plants (SORP) and adding ABA directly to the culture solution (ADCS) with low concentration can promote the growth of ramie and increase the amount of Cd uptake, and the effect of SORP is better. (3) The molecular reason for the decrease of chlorophyll content due to Cd stress, may be resulted from the down-regulated expression of the chlorophyll synthesis genes (BnPAO and BnNYC1) and the up-regulated expression of the chlorophyll degradation genes (BnCHLH, BnCHLG, BnHAP3A and BnPPR1). The elevated ABA content in ramie plants may due to the up-regulated expression of the ABA synthesis related genes (BnABA1, BnNCED3, and BnNCED5) and the genes (BnABCG40, BnNFXL2, BnPYL9, BnGCR2, BnGTG1, BnBGLU1, BnUTG1, BnVHAG1 and BnABI5) that encoding ABA transport and response proteins, which was consistent with the enhance the Cd uptake in ramie. Our study revealed the relationship between ABA and Cd uptake in ramie, which provided a reference for improving the enrichment of Cd in ramie.

Comparative physiological and transcriptomic analyses illuminate common mechanisms by which silicon alleviates cadmium and arsenic toxicity in rice seedlings

The inessential heavy metal/loids cadmium (Cd) and arsenic (As), which often co-occur in polluted paddy soils, are toxic to rice. Silicon (Si) treatment is known to reduce Cd and As toxicity in rice plants. To better understand the shared mechanisms by which Si alleviates Cd and As stress, rice seedlings were hydroponically exposed to Cd or As, then treated with Si. The addition of Si significantly ameliorated the inhibitory effects of Cd and As on rice seedling growth. Si supplementation decreased Cd and As translocation from roots to shoots, and significantly reduced Cd- and As-induced reactive oxygen species generation in rice seedlings. Transcriptomics analyses were conducted to elucidate molecular mechanisms underlying the Si-mediated response to Cd or As stress in rice. The expression patterns of the differentially expressed genes in Cd- or As-stressed rice roots with and without Si application were compared. The transcriptomes of the Cd- and As-stressed rice roots were similarly and profoundly reshaped by Si application, suggesting that Si may play a fundamental, active role in plant defense against heavy metal/loid stresses by modulating whole genome expression. We also identified two novel genes, Os01g0524500 and Os06g0514800, encoding a myeloblastosis (MYB) transcription factor and a thionin, respectively, which may be candidate targets for Si to alleviate Cd and As stress in rice, as well as for the generation of Cd- and/or As-resistant plants. This study provides valuable resources for further clarification of the shared molecular mechanisms underlying the Si-mediated alleviation of Cd and As toxicity in rice.

Walnut ethylene response factor JrERF2-2 interact with JrWRKY7 to regulate the GSTs in plant drought tolerance

Juglans regia is a world-famous woody oil plant, whose yield and quality are affected by drought stress. Ethylene-responsive factors (ERFs) play vital role in plant stress response. In current study, to comprehend the walnut molecular mechanism of drought stress response, an ERF transcription factor was clarified from J. regia (JrERF2-2) and its potential function mechanism to drought was clarified. The results showed that JrERF2-2 could be induced significantly by drought. The transgenic Arabidopsis over-expression of JrERF2-2 displayed enhanced growth, antioxidant enzyme vitalities, reactive oxygen species scavenging and proline produce under drought stress. Especial the glutathione-S-transferase (GST) activity and most GST genes' transcription were elevated obviously. Yeast one-hybrid (Y1H) and co-transient expression (CTE) methods revealed that JrERF2-2 could recognize JrGST4, JrGST6, JrGST7, JrGST8, and JrGSTF8 by binding to GCC-box, and recognize JrGST11, JrGST12, and JrGSTN2 by binding to DRE motif. Meanwhile, the binding activity was strengthened by drought stress. Moreover, JrERF2-2 could interact with JrWRKY7 to promote plant drought tolerance; JrWRKY7 could also distinguish JrGST4, JrGST7, JrGST8, JrGST11, JrGST12, and JrGSTF8 via binding to W-Box motif. These results suggested that JrERF2-2 could effectively improve plant drought tolerance through interacting with JrWRKY7 to control the expression of GSTs. JrERF2-2 is a useful plant representative gene for drought response in molecular breeding.

Identification and characterization of 5 walnut MYB genes in response to drought stress involved in ABA signaling

Walnut is a popular nut tree species and usually suffers from drought stress. However, little information is available on the mechanism of walnut responding to drought stress, resulting in lack of basic understanding for its resistance. In order to excavate more functional genes that can respond to stressors, and enrich the theoretical basis for walnut resistance, in this study, 5 MYB genes with complete ORFs were identified from J. regia and the basic bio-information as well as expression patterns in different tissues and response to drought and ABA stresses were confirmed using qRT-PCR assay. The results showed that 2 JrMYB genes belong to R1-MYB subfamily and 3 JrMYBs belong to R2R3-MYB, encoding the proteins from 212 to 362 aa in length. The phylogenetic analysis categorized proteins of 5 JrMYBs and 40 Arabidopsis AtMYBs into 10 subgroups. JrMYBs in the same subgroup exhibited significant similarities in the composition of conserved domains and motifs in amino acid sequences and exon/intron organization in DNA sequences. The results of qRT-PCR analysis revealed that JrMYB genes diversely expressed in various tissues. Moreover, the expression values of JrMYBs were upregulated or downregulated significantly under drought and ABA stresses. Most attractively, in contrast with suffering from drought stress alone, the treatments with drought and additional ABA greatly enhanced the transcript levels of JrMYBs. All these results suggested that JrMYB genes play a vital role in plant biological processes and drought as well as ABA stress response, and possibly perform as ABA-dependent drought response transcription factors in plant.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-021-01008-z.

Effects of Maternal Environment on Seed Germination and Seedling Vigor of Petunia × hybrida under Different Abiotic Stresses

Seed germination and seedling vigor can be affected by environmental cues experienced by the mother plant. However, information about how the maternal environment affects seed quality is scarce in ornamental plants. This study aimed to investigate the effects of two different maternal environments on the seed germination and seedling vigor of Petunia × hybrida under a variety of abiotic stresses. Petunia mother plants were grown in either a greenhouse during the summer months or an indoor controlled-temperature-and-light environment. Collected seeds were subjected to external stressors, including polyethylene glycol (PEG), sodium chloride (NaCl), high temperature, and abscisic acid (ABA), to determine seed germination percentage and seedling vigor. Results indicated that seeds harvested from the mother plants grown in a controlled environment germinated better than seeds harvested from the mother plants grown in the greenhouse when suboptimal germination conditions were applied. Additionally, the seedlings from the controlled maternal environment performed better in both ABA and salinity stress tests than the greenhouse seedlings. Interestingly, the greenhouse seedlings displayed less reactive oxygen species (ROS) damage and lower electrolyte leakage than the controlled environment seedlings under dehydration stress. The difference in germination and seedling vigor of seeds from the two different maternal environments might be due to the epigenetic memory inherited from the mother plants. This study highlighted the strong impact of the maternal environment on seed germination and seedling vigor in Petunia and may assist in high-quality seed production in ornamental plants.

Genome-Wide Identification of the Vacuolar H+-ATPase Gene Family in Five Rosaceae Species and Expression Analysis in Pear (Pyrus bretschneideri)

Vacuolar H⁺-ATPases (V-ATPase) are multi-subunit complexes that function as ATP hydrolysis-driven proton pumps. They play pivotal roles in physiological processes, such as development, metabolism, stress, and growth. However, there have been very few studies on the characterisation of V-ATPase (VHA) genes in Rosaceae species. Therefore, in the present study, we performed a genome-wide analysis and identified VHA gene family members in five Rosaceae species (Pyrus bretschneideri, Malus domestica, Prunus persica, Fragaria vesca, and Prunus mume). A total of 159 VHA genes were identified, and were classified into 13 subfamilies according to the phylogenetic analysis. The structure of VHA proteins revealed high similarity among different VHA genes within the same subgroup. Gene duplication event analysis revealed that whole-genome duplications represented the major pathway for expansion of the Pyrus bretschneideri VHA genes (PbrVHA genes). The tissue-specific expression analysis of the pear showed that 36 PbrVHA genes were expressed in major tissues. Seven PbrVHA genes were significantly downregulated when the pollen tube growth stopped. Moreover, many PbrVHA genes were differentially expressed during fruit development and storage, suggesting that VHA genes play specific roles in development and senescence. The present study provides fundamental information for further elucidating the potential roles of VHA genes during development and senescence.

Transcription Factor GmWRKY142 Confers Cadmium Resistance by Up-Regulating the Cadmium Tolerance 1-Like Genes

Cadmium (Cd) is a widespread pollutant that is toxic to living organisms. Previous studies have identified certain WRKY transcription factors, which confer Cd tolerance in different plant species. In the present study, we have identified 29 Cd-responsive WRKY genes in Soybean [Glycine max (L.) Merr.], and confirmed that 26 of those GmWRKY genes were up-regulated, while 3 were down-regulated. We have also cloned the novel, positively regulated GmWRKY142 gene from soybean and investigated its regulatory mechanism in Cd tolerance. GmWRKY142 was highly expressed in the root, drastically up-regulated by Cd, localized in the nucleus, and displayed transcriptional activity. The overexpression of GmWRKY142 in Arabidopsis thaliana and soybean hairy roots significantly enhanced Cd tolerance and lead to extensive transcriptional reprogramming of stress-responsive genes. ATCDT1, GmCDT1-1, and GmCDT1-2 encoding cadmium tolerance 1 were induced in overexpression lines. Further analysis showed that GmWRKY142 activated the transcription of ATCDT1, GmCDT1-1, and GmCDT1-2 by directly binding to the W-box element in their promoters. In addition, the functions of GmCDT1-1 and GmCDT1-2, responsible for decreasing Cd uptake, were validated by heterologous expression in A. thaliana. Our combined results have determined GmWRKYs to be newly discovered participants in response to Cd stress, and have confirmed that GmWRKY142 directly targets ATCDT1, GmCDT1-1, and GmCDT1-2 to decrease Cd uptake and positively regulate Cd tolerance. The GmWRKY142-GmCDT1-1/2 cascade module provides a potential strategy to lower Cd accumulation in soybean.

Genome-wide association study of soybean seed germination under drought stress

Drought stress, which is increasing with climate change, is a serious threat to agricultural sustainability worldwide. Seed germination is an essential growth phase that ensures the successful establishment and productivity of soybean, which can lose substantial productivity in soils with water deficits. However, only limited genetic information is available about how germinating soybean seeds may exert drought tolerance. In this study, we examined the germinating seed drought-tolerance phenotypes and genotypes of a panel of 259 released Chinese soybean cultivars panel. Based on 4616 Single-Nucleotide Polymorphisms (SNPs), we conducted a mixed-linear model GWAS that identified a total of 15 SNPs associated with at least one drought-tolerance index. Notably, three of these SNPs were commonly associated with two drought-tolerance indices. Two of these SNPs are positioned upstream of genes, and 11 of them are located in or near regions where QTLs have been previously mapped by linkage analysis, five of which are drought-related. The SNPs detected in this study can both drive hypothesis-driven research to deepen our understanding of genetic basis of soybean drought tolerance at the germination stage and provide useful genetic resources that can facilitate the selection of drought stress traits via genomic-assisted selection.

Transcriptome analysis reveals comprehensive responses to cadmium stress in maize inoculated with arbuscular mycorrhizal fungi

Biological strategy of utilization of plants-microbe's interactions to remediate cadmium (Cd) contaminated soils is effective and practical. However, limited evidence at transcriptome level is available about how microbes work with host plants to alleviate Cd stress. In the present study, comparative transcriptomic analysis was performed between maize seedlings inoculated with arbuscular mycorrhizal (AM) fungi and non-AM fungi inoculation under distinct concentrations of CdCl₂ (0, 25, and 50 mg per kg soil). Significantly higher levels of Cd were found in root tissues of maize colonized by AM fungi, whereas, Cd content was reduced as much as 50% in leaf tissues when compared to non-AM seedlings, indicating that symbiosis between AM fungi and maize seedlings can significantly block translocation of Cd from roots to leaf tissues. Moreover, a total of 5827 differentially expressed genes (DEG) were determined and approximately 68.54% DEGs were downregulated when roots were exposed to high Cd stress. In contrast, 67.16% (595) DEGs were significantly up-regulated when seedlings were colonized by AM fungi under 0 mg CdCl₂. Based on hierarchical clustering analysis, global expression profiles were split into eight distinct clusters. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that hundreds of genes functioning in plant hormone signal transduction, mitogen-activated protein kinase (MAPK) signaling pathway and glutathione metabolism were enriched. Furthermore, MapMan pathway analysis indicated a more comprehensive overview response, including hormone metabolism, especially in JA, glutathione metabolism, transcription factors and secondary metabolites, to Cd stress in mycorrhizal maize seedlings. These results provide an overview, at the transcriptome level, of how inoculation of maize seedlings by AM fungi could facilitate the relief of Cd stress.

MicroRNA-mRNA expression profiles and their potential role in cadmium stress response in Brassica napus

BACKGROUND

Oilseed rape is an excellent candidate for phytoremediation of cadmium (Cd) contaminated soils given its advantages of high biomass, fast growth, moderate metal accumulation, ease of harvesting, and metal tolerance, but the cadmium response pathways in this species (Brassica napus) have yet to be fully elucidated. A combined analysis of miRNA and mRNA expression to infer Cd-induced regulation has not been reported in B. napus.

RESULTS

We characterized concurrent changes in miRNA and mRNA profiles in the roots and shoots of B. napus seedlings after 10 days of 10 mg/L Cd²⁺ treatment. Cd treatment significantly affected the expression of 22 miRNAs belonging to 11 families in the root and 29 miRNAs belonging to 14 miRNA families in the shoot. Five miRNA families (MIR395, MIR397, MIR398, MIR408 and MIR858) and three novel miRNAs were differentially expressed in both tissues. A total of 399 differentially expressed genes (DEGs) in the root and 389 DEGs in the shoot were identified, with very little overlap between tissue types. Eight anti-regulation miRNA-mRNA interaction pairs in the root and eight in the shoot were identified in response to Cd and were involved in key plant stress response pathways: for example, four genes targeted by miR398 were involved in a pathway for detoxification of superoxide radicals. Cd stress significantly impacted the photosynthetic pathway. Transcription factor activation, antioxidant response pathways and secondary metabolic processes such as glutathione (GSH) and phenylpropanoid metabolism were identified as major components for Cd-induced response in both roots and shoots.

CONCLUSIONS

Combined miRNA and mRNA profiling revealed miRNAs, genes and pathways involved in Cd response which are potentially critical for adaptation to Cd stress in B. napus. Close crosstalk between several Cd-induced miRNAs and mRNAs was identified, shedding light on possible mechanisms for response to Cd stress in underground and aboveground tissues in B. napus. The pathways, genes, and miRNAs identified here will be valuable targets for future improvement of cadmium tolerance in B. napus.

Multiple transcriptional regulation of walnut JrGSTTau1 gene in response to osmotic stress

Glutathione S-transferases (GSTs) are important plant proteins involved in biotic and abiotic stress responses. A gene from Juglans regia, JrGSTTau1 was previously cloned and functionally characterized as an enzyme involved in improving cold tolerance in plants. To clarify the functional mechanism of JrGSTTau1 and its role in stress response, here, the JrGSTTau1 promoter including the up-stream regulators was examined using yeast one-hybrid together with transient expression assays, and the osmotic stress response ability was confirmed by comparing with wild-type plants. The 1500 bp JrGSTTau1 promoter displayed high GUS expression activity and was enhanced by mannitol stress. The promoter is composed of abundant cis-elements, some of which were osmotic stress response-related motifs, such as ABRE, DRE and MYB, indicating that the expression of JrGSTTau1 is regulated by potential up-stream regulators under abiotic stress. The transcription factors (TFs) of JrDREB2A, JrMYC2, JrMYB44, JrDof1 and JrWRKY7 were identified, which shared a similar response with JrGSTTau1 when exposed to PEG₆₀₀₀ in walnut leaf and root. These results implied that JrDREB2A, JrMYC2, JrMYB44, JrDof1 and JrWRKY7 may act as up-stream regulators of JrGSTTau1 to regulate or combine functionality with JrGSTTau1 in osmotic stress response. Furthermore, compared with the WT plants, the transgenic tobacco plants that overexpress JrGSTTau1 showed improved tolerance to drought induced by osmotic stress, in which antioxidant enzymes, proline and reactive oxygen species (ROS) are involved. Our results demonstrated the positive role played by JrGSTTau1 in osmotic tolerance, which is regulated by multiple up-stream regulators.

New insight into the molecular basis of cadmium stress responses of wild paper mulberry plant by transcriptome analysis

BACKGROUND

Heavy metal contamination is becoming a limitation to the utilization of soil and the distribution of vegetation. In particular, cadmium (Cd) pollution has had a serious impact on the food chain. Broussonetia papyrifera is a widely distributed pioneer tree species of heavy metal contaminated areas with important economic value. However, little is known about the genomic background of the Cd-tolerance mechanism in B. papyrifera.

RESULTS

The CdCl₂ responsive physiology was evaluated and proved to be involved in antioxidase activity and active oxygen species (ROS) accumulation. The leaf and root transcriptomes derived from B. papyrifera grown under normal and CdCl₂ stress conditions were systematically investigated using the Illumina HiSeq method. A total of 180,678,660 bp (27.1 GB) clean reads were assembled into 589,487 high-quality unigenes, of which 256,025 (43.43% of the total) and 250,251 (42.45% of the total) were aligned in Gene Ontology (GO) and Protein family (Pfam), respectively. A total of 24,414 differentially expressed genes (DEGs) were GO-annotated into 53, 23, 55, and 60 terms from the transcriptomes of root and leaf tissues under Cd stress and control conditions. A total of 117,547 Kyoto Encyclopedia of Genes and Genomes (KEGG) Orthology (KO)-annotated DEGs were enriched in at least 47 KEGG pathway terms among the four comparisons. Many genes encoding important transcription factors (e.g., auxin/indole-3-acetic acid (AUX/IAA), basic helix-loop-helix (bHLH), DNA-binding one zinc finger (Dof), and MYB) and proteins involved in plant-pathogen interactions, phenylpropanoid biosynthesis, plant hormone signal transduction, oxidative phosphorylation, carbon fixation, peroxisomes, flavonoid biosynthesis, and glutathione metabolism, among others, were substantially upregulated under CdCl₂ stress.

CONCLUSIONS

These genes represent important candidates for studying Cd-response mechanisms and molecular biology of B. papyrifera and related species. Our findings provide a genomic sequence resource for functional genetic assignments in B. papyrifera, which will help elucidate the molecular mechanisms of its Cd-stress responses and facilitate the bioremediation of heavy metal contaminated areas via breeding of new stress-tolerant cultivars.

Overexpression of RsMYB1 Enhances Anthocyanin Accumulation and Heavy Metal Stress Tolerance in Transgenic Petunia

The RsMYB1 transcription factor (TF) controls the regulation of anthocyanin in radishes (Raphanus sativus), and its overexpression in tobacco and petunias strongly enhances anthocyanin production. However, there are no data on the involvement of RsMYB1 in the mechanisms underlying abiotic stress tolerance, despite strong sequence similarity with other MYBs that confer such tolerance. In this study, we used the anthocyanin-enriched transgenic petunia lines PM6 and PM2, which overexpress RsMYB1. The tolerance of these lines to heavy metal stress was investigated by examining several physiological and biochemical factors, and the transcript levels of genes related to metal detoxification and antioxidant activity were quantified. Under normal conditions (control conditions), transgenic petunia plants (T2-PM6 and T2-PM2) expressing RsMYB1, as well as wild-type (WT) plants, were able to thrive by producing well-developed broad leaves and regular roots. In contrast, a reduction in plant growth was observed when these plants were exposed to heavy metals (CuSO4, ZnSO4, MnSO4, or K2Cr2O7). However, T2-PM6 and T2-PM2 were found to be more stress tolerant than the WT plants, as indicated by superior results in all analyzed parameters. In addition, RsMYB1 overexpression enhanced the expression of genes related to metal detoxification [glutathione S-transferase (GST) and phytochelatin synthase (PCS)] and antioxidant activity [superoxide dismutase (SOD), catalase (CAT), and peroxidase (POX)]. These results suggest that enhanced expression levels of the above genes can improve metal detoxification activities and antioxidant activity, which are the main components of defense mechanism included in abiotic stress tolerance of petunia. Our findings demonstrate that RsMYB1 has potential as a dual-function gene that can have an impact on the improvement of anthocyanin production and heavy metal stress tolerance in horticultural crops.