Differential transcriptome modulation leads to variation in arsenic stress response in Arabidopsis thaliana accessions

Mechanism of flavonols on detoxification, migration and transformation of indium in rhizosphere system

Soil contamination by toxic heavy metal induces serious environmental hazards. In recent years, the use of indium (In) in semiconductor products has increased considerably and the release of In is inevitable, which will pose great risk to the ecosystem. The interaction between metal and plants which are the fundamental components of all ecosystems are an indispensable aspect of indium assessment and remediation. The role of flavonols, which is essential to plant resistance to In stress, remains largely unknown. FLS1 related lines of A. thaliana (Col, fls1-3 and OE) were exposed to In stress in soil and flavonols as root exudates were analyzed in exogenous application test. The accumulation and release of flavonols could be induced by In stress. However, flavonols exhibited different function in vivo and in vitro of plant. The basic function of flavonols was to affect root morphology via regulating auxin, but being intervened by In stress. The synthesis and accumulation of flavonols in vivo could activate the antioxidant system and the metal detoxification system to alleviate the toxic effects of In on plant. In addition, plants could make phone calls to rhizosphere microbes for help when exposed to In. Flavonols in vitro might act as the information transmission. Combination of endogenous and exogenous flavonols could affect the migration and transformation of In in soil-plant system via metal complexation and transportation pathway.

Physiological and transcriptomic response reveals new insight into manganese tolerance of Celosia argentea Linn

Celosia argentea is a manganese (Mn) hyperaccumulator with high ornamental value and strong stress resistance. It is important to understand the molecular mechanism of tolerance to heavy metals of hyperaccumulators to improve the efficiency of phytoremediation. In this study, the effects of different Mn concentrations (0, 0.8, 3, and 10 mM) on physiological characteristics and molecular changes were determined. Low concentrations of Mn increased the growth of C. argentea, while high concentrations of Mn suppressed its growth, A concentration up to 3 mM did not affect the growth of C. argentea, and the highest transfer factor (TF) was 6.16. Oxidative damage of different Mn level treatments in C. argentea was verified through relative water content, electrolyte leakage, MDA content, H2O2 content and superoxide contents. With an increase in Mn concentration, the contents of chlorophyll a, chlorophyll b, and carotenoids decreased. Our results indicated that low-concentration manganese treatment can reduce the reactive oxygen burst and MDA, soluble sugar and proline, making C. argentea have strong abiotic stress tolerance. The molecular mechanism of C. argentea after 10 mM Mn treatment was analysed through transcriptome analysis, and differentially expressed genes (DEGs) in these pathways were further verified by qRTPCR. Plantpathogen interactions, plant hormone signal transduction, the MAPK signalling pathway and the phenylpropanoid biosynthesis pathway were important in the response to Mn stress, and the heavy metal-associated isoprenylated plant protein, metal transporter Nramp, and zinc transporter play key roles in the strong ability of C. argentea to tolerate heavy metals. These results suggest that C. argentea exhibits strong manganese tolerance and provide new insight into the molecular mechanisms of plant responses to heavy metal stress.

N-acetyl-cysteine mitigates arsenic stress in lettuce: Molecular, biochemical, and physiological perspective

Agricultural land contaminated with heavy metals such as non-biodegradable arsenic (As) has become a serious global problem as it adversely affects agricultural productivity, food security and human health. Therefore, in this study, we investigated how the administration of N-acetyl-cysteine (NAC), regulates the physio-biochemical and gene expression level to reduce As toxicity in lettuce. According to our results, different NAC levels (125, 250 and 500 μM) significantly alleviated the growth inhibition and toxicity induced by As stress (20 mg/L). Shoot fresh weight, root fresh weight, shoot dry weight and root dry weight (33.05%, 55.34%, 17.97% and 46.20%, respectively) were decreased in plants grown in As-contaminated soils compared to lettuce plants grown in soils without the addition of As. However, NAC applications together with As stress increased these growth parameters. While the highest increase in shoot fresh and dry weight (58.31% and 37.85%, respectively) was observed in 250 μM NAC application, the highest increase in root fresh and dry weight (75.97% and 63.07%, respectively) was observed in 125 μM NAC application in plants grown in As-polluted soils. NAC application decreased the amount of ROS, MDA and H2O2 that increased with As stress, and decreased oxidative damage by regulating hormone levels, antioxidant and enzymes involved in nitrogen metabolism. According to gene expression profiles, LsHIPP28 and LsABC3 genes have shown important roles in reducing As toxicity in leaves. This study will provide insight for future studies on how NAC applications develop resistance to As stress in lettuce.

Depolymerized carrageenan expresses elicitor-like activity on Mentha arvensis L. under arsenic stress: Insights into arsenic resilience and monoterpene synthesis

Heavy metals contaminate agricultural land by limiting the productivity of crops and making them or their products unfit for consumption. Arsenic (As) is a potentially hazardous metalloid that severely impacts plants' survival. Menthol mint (Mentha arvensis L.) bears volatile compounds that are harshly exaggerated by diverse environmental factors like drought, salinity, heavy metal, temperature, photoperiod, and luminosity stresses. In this study, the phytotoxicity of As was examined in M. arvensis L. and its alleviation through the supplementation of oligomers of carrageenan. Noticeably, scanty information is available regarding the effect of irradiated carrageenan (ICA) on As-stressed plants. In order to observe the same in the case of M. arvensis L., the effect of ICA on As-treated plants was explored. The ICA concentration (foliar-applied) selected for the study was 80 mg L-1, 100 mg L-1 and 120 mg L-1, and that of As (soil-applied) was 80 mg kg-1 soil. Excess accumulation of As resulted in reduced growth, enzymatic activities, and yield and quality parameters of M. arvensis L. under As toxicity. However, the foliage application of ICA strengthens the antioxidant machinery and other physiological and oxidative stress biomarkers of the plant by facilitating the activity of superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), and proline, and, therefore aids in alleviating the toxicity generated by As. Nevertheless, ICA supplementation proves beneficial in enhancing the monoterpene synthesis (essential oil production and its active constituents) of M. arvensis L. by maintaining a steady-state equilibrium between reactive oxygen species (ROS) production and its scavenging process.

Transcriptomic analysis revealing the molecular response to arsenic stress in desert Eremostachys moluccelloides Bunge

The saline, alkaline environment of arid soils is conducive to the diffusion of the metalloid arsenic (As). Desert plants in this area are of great ecological importance and practical value. However, there are few studies on the mechanism of arsenic action in desert plants. Therefore, in this study, Eremostachys moluccelloides Bunge was treated with different concentrations of As2O5 [As(V)] to analyze the physiological, biochemical, and transcriptomic changes of its roots and leaves and to explore the molecular mechanism of its response to As(Ⅴ) stress. The activities of catalase, superoxidase, peroxidase, and the contents of malondialdehyde and proline in roots and leaves first increased and then decreased under the As(Ⅴ) stress of different concentrations. The content of As was higher in roots than in leaves, and the As content was positively correlated with As(Ⅴ) stress concentration. In the differentially expressed gene analysis, the key enzymes of the oxidative stress response in roots and leaves were significantly enriched in the GO classification. In the KEGG pathway, genes related to the abscisic acid signal transduction pathway were co-enriched and up-regulated in roots and leaves. The related genes in the phenylpropanoid biosynthesis pathway were significantly enriched and down-regulated only in roots. In addition, the transcription factors NAC, HB-HD-ZIP, and NF-Y were up-regulated in roots and leaves. These results suggest that the higher the As(V) stress concentration, the more As is taken up by roots and leaves of E. molucelloides Bunge. In addition to causing greater oxidative damage, this may interfere with the production of secondary metabolites. Moreover, it may improve As(V) tolerance by regulating abscisic acid and transcription factors. The results will deepen our understanding of the molecular mechanism of As(Ⅴ) response in E. moluccelloides Bunge, lay the foundation for developing and applying desert plants, and provide new ideas for the phytoremediation of As pollution in arid areas.

Transcriptomic analysis reveals the molecular mechanisms of Boehmeria nivea L. in response to antimonite and antimonate stresses

Soil antimony (Sb) pollution is a global concern that threatens food security and human health. Boehmeria nivea L. (ramie) is a promising phytoremediation plant exhibiting high tolerance and enrichment capacity for Sb. To reveal the molecular mechanisms and thus enhance the ramie uptake, transport, and detoxification of Sb with practical strategies, a hydroponic experiment was conducted to compare the physiological and transcriptomic responses of ramie towards antimonite (Sb(Ⅲ)) and antimonate (Sb(Ⅴ)). Phenotypic results showed that Sb(Ⅲ) had a stronger inhibitory effect on the growth of ramie. Root Sb content under Sb(Ⅲ) was 2.43 times higher than that in Sb(Ⅴ) treatment. Based on the ribonucleic acid sequencing (RNA-Seq) technique, 3915 and 999 significant differentially expressed genes (DEGs) were identified under Sb(Ⅲ) and Sb(Ⅴ), respectively. Transcriptomic analysis revealed that ramie showed different adaptation strategies to Sb(Ⅲ) and Sb(V). Key DEGs and their involved pathways such as catalytic activity, carbohydrate metabolisms, phenylpropanoid biosynthesis, and cell wall modification were identified to perform crucial roles in Sb tolerance and detoxification. Two heavy metal-associated domain-type genes, six heavy metal-associated isoprenylated plant proteins, and nine ABC transporters showed possible roles in the transport and detoxification of Sb. The significant upregulation of NRAMP5 and three NIPs suggested their roles in the transport of Sb(V). This study is the basis for future research to identify the exact genes and biological processes that can effectively enhance Sb accumulation or improve plant tolerance to Sb, thereby promoting the phytoremediation of Sb-polluted soils.

Physiological and transcriptomic study reveal SeNPs-mediated AsIII stress detoxification mechanisms involved modulation of antioxidants, metal transporters, and transcription factors in Glycine max L. (Merr.) roots

Physiological changes and genome-wide alteration in gene expression were performed in soybean (Glycine max [L.] Merr.) roots exposed to AsⅢ (25 μmol/L) alone and supplemented with selenium nanoparticles (SeNPs) at the concentration of 10 and 25 μmol/L at the V2 growth stage. Excessive arsenic in the root zone poses a potential threat to soybean yield, particularly to roots, due to the limited translocation of AsIII from root to shoot in the case of soybean. We hypothesized that SeNPs can relieve AsⅢ toxicity to soybean root by reducing the AsⅢ uptake and regulating the internal tolerance mechanism of the plants. Results accomplished that SeNPs had positive impact on soybean dry weight and roots parameters under AsⅢ stress. Then, we further evaluated physiological indexes, whole genome transcriptomic analysis and quantitative real-time PCR to elucidate the underlying mechanism of AsⅢ tolerance under SeNPs supplementation. Under the condition of AsⅢ-stress, SeNPs exposure significantly reduced the electrolyte leakage, O₂^-•, H₂O₂ and MDA accumulation while increasing the antioxidants level. The RNA-seq dataset revealed total of 5819 up and 7231 down expressed DEGs across all libraries. The number of exclusively regulated genes were higher under As + SeNP10 (4909) treatment than in the AsⅢ-alone (4830) and As + SeNP25 (3311) treatments. The KEGG and GO analyses revealed that stress responsive DEGs such as glutathione S-transferase, glutathione peroxidase, ascorbate, glutaredoxin, thioredoxin, and phytochelatins synthase are responsible for AsⅢ tolerance under the SeNPs supplementation. Similarly, sulfate transporter, and ABC transporters (ATP-binding cassettes) expression were induced, and aquaporin channels related DEGs expression were reduced under SeNPs application in AsⅢ exposure condition. Furthermore, the expression of molecular chaperones (HSP) and transcription factors (MYB, bZIP, bHLH, and HSFs) were increased in SeNPs treatment groups. These results provide vital information of AsⅢ tolerance mechanism in response to SeNPs in soybean. We suggest that functional characterization of these genes will help us learn more about the SeNPs responsive arsenic tolerance mechanism in soybean.

Identification of arsenic-tolerant varieties and candidate genes of tolerance in spring wheat (Triticum aestivum L.)

Despite the growing concerns about arsenic toxicity, information on tolerance and responsible genetic factors in wheat remains elusive. To address that, the present study aimed to screen the wheat varieties against arsenic based on growth parameters, yield, grain accumulation, and associated genes. A total of 110 wheat varieties were grown in arsenic-contaminated regions to record physio-morphological traits. The wheat 90K Infinium iSelect SNP array was used for the genome-wide association model to identify genomic regions. Wheat varieties such as Punjab-81, AARI-11, and Daman showed arsenic concentrations >45 μg/kg in similar conditions as well as the impact on grain yield, chlorophyll, Thousand Kernel Weight, and plant height. Contrastingly, varieties like Kohistan-97, As-2002, Barani-70, and Pari-73 showed grain concentrations <5 μg/kg grown under highly contaminated conditions. Three significant loci associated with arsenic accumulation in grain were identified on chromosomes 6A (qASG1-6A) and 6B (qASG3-6B and qASG4-6B). Annotation at these loci identified 39 wheat genes among which several were important for growth and tolerance against stress. The candidate gene (TraesCS6B02G429400) responsible for Glutathione-S-transferase was identified in the present study and must be investigated further using a transcriptomic approach. The present study provided background information for breeding prospects to improve wheat yield and tolerance against arsenic.

State-of-the-art OMICS strategies against toxic effects of heavy metals in plants: A review

Environmental pollution of heavy metals (HMs), mainly due to anthropogenic activities, has received growing attention in recent decades. HMs, especially the non-essential carcinogenic ones, including chromium (Cr), cadmium (Cd), mercury (Hg), aluminum (Al), lead (Pb), and arsenic (As), have appeared as the most significant air, water, and soil pollutants, which adversely affect the quantity, quality, and security of plant-based food all over the world. Plants exposed to HMs could experience significant decline in growth and yield. To avoid or tolerate the toxic effects of HMs, plants have developed complicated defense mechanisms, including absorption and accumulation of HMs in cell organelles, immobilization by forming complexes with organic chelates, extraction by using numerous transporters, ion channels, signalling cascades, and transcription elements, among others. OMICS strategies have developed significantly to understand the mechanisms of plant transcriptomics, genomics, proteomics, metabolomics, and ionomics to counter HM-mediated stress stimuli. These strategies have been considered to be reliable and feasible for investigating the roles of genomics (genomes), transcriptomic (coding), mRNA transcripts (non-coding), metabolomics (metabolites), and ionomics (metal ions) to enhance stress resistance or tolerance in plants. The recent developments in the mechanistic understandings of the HMs-plant interaction in terms of their absorption, translocation, and toxicity invasions at the molecular and cellular levels, as well as plants' response and adaptation strategies against these stressors, are summarized in the present review. Transcriptomics, genomics, metabolomics, proteomics, and ionomics for plants against HMs toxicities are reviewed, while challenges and future recommendations are also discussed.

Antioxidants as modulators of arsenic-induced oxidative stress tolerance in plants: An overview

Arsenic (As) is a highly toxic contaminant in the environment. Although both inorganic and organic types of arsenic exist in the environment, the most common inorganic forms of As that adversely affect plants are arsenite (As III) and arsenate (As V). Despite no evidence for As being essential for plant growth, exposure of roots to this element can cause its uptake primarily via transporters responsible for the transport of essential mineral nutrients. Arsenic exposure even at low concentrations disturbs the plant normal functioning via excessive generation of reactive oxygen species, a condition known as oxidative stress leading to an imbalance in the redox system of the plant. This is associated with considerable damage to the cell components thereby impairing normal cellular functions and activation of several cell survival and cell death pathways. To counteract this oxidative disorder, plants possess natural defense mechanisms such as chemical species and enzymatic antioxidants. This review considers how different types of antioxidants participate in the oxidative defense mechanism to alleviate As stress in plants. Since the underlying phenomena of oxidative stress tolerance are not yet fully elucidated, the potential for "Omics" technologies to uncover molecular mechanisms are discussed. Various strategies to improve As-induced oxidative tolerance in plants such as exogenous supplementation of effective growth regulators, protectant chemicals, transgenic approaches, and genome editing are also discussed thoroughly in this review.

Influence of arsenate imposition on modulation of antioxidative defense network and its implication on thiol metabolism in some contrasting rice (Oryza sativa L.) cultivars

Globally, many people have been suffering from arsenic poisoning. Arsenate (AsV) exposure to twelve rice cultivars caused growth retardation, triggered production of As-chelatin biopeptides and altered activities of antioxidants along with increase in ascorbate (AsA)-glutathione (GSH) contents as a protective measure. The effects were more conspicuous in cvs. Swarnadhan, Tulaipanji, Pusa basmati, Badshabhog, Tulsibhog and IR-20 to attenuate oxidative-overload mediated adversities. Contrastingly, in cvs. Bhutmuri, Kumargore, Binni, Vijaya, TN-1 and IR-64, effects were less conspicuous in terms of alterations in the said variables due to reduced generation of oxidative stress. Under As(V) imposition, the protective role of phytochelatins (PCs) were recorded where peaks height and levels of PCs (PC2, PC3 and PC4) were elevated significantly in the test seedlings with an endeavour to detoxify cells by sequestering arsenic-phytochelatin (As-PC) complex into vacuole that resulted in reprogramming of antioxidants network. Additionally, scatter plot correlation matrices, color-coded heat map analysis and regression slopes demonstrated varied adaptive responses of test cultivars, where cvs. Bhutmuri, Kumargore, Binni, Vijaya, TN-1 and IR-64 found tolerant against As(V) toxicity. Results were further justified by hierarchical clustering. These findings could help to grow identified tolerant rice cultivars in As-prone soil with sustainable growth and productivity after proper agricultural execution.

Molecular insight into arsenic uptake, transport, phytotoxicity, and defense responses in plants: a critical review

A critical investigation into arsenic uptake and transportation, its phytotoxic effects, and defense strategies including complex signaling cascades and regulatory networks in plants. The metalloid arsenic (As) is a leading pollutant of soil and water. It easily finds its way into the food chain through plants, more precisely crops, a common diet source for humans resulting in serious health risks. Prolonged As exposure causes detrimental effects in plants and is diaphanously observed through numerous physiological, biochemical, and molecular attributes. Different inorganic and organic As species enter into the plant system via a variety of transporters e.g., phosphate transporters, aquaporins, etc. Therefore, plants tend to accumulate elevated levels of As which leads to severe phytotoxic damages including anomalies in biomolecules like protein, lipid, and DNA. To combat this, plants employ quite a few mitigation strategies such as efficient As efflux from the cell, iron plaque formation, regulation of As transporters, and intracellular chelation with an array of thiol-rich molecules such as phytochelatin, glutathione, and metallothionein followed by vacuolar compartmentalization of As through various vacuolar transporters. Moreover, the antioxidant machinery is also implicated to nullify the perilous outcomes of the metalloid. The stress ascribed by the metalloid also marks the commencement of multiple signaling cascades. This whole complicated system is indeed controlled by several transcription factors and microRNAs. This review aims to understand, in general, the plant-soil-arsenic interaction, effects of As in plants, As uptake mechanisms and its dynamics, and multifarious As detoxification mechanisms in plants. A major portion of this article is also devoted to understanding and deciphering the nexus between As stress-responsive mechanisms and its underlying complex interconnected regulatory networks.

Advances in "Omics" Approaches for Improving Toxic Metals/Metalloids Tolerance in Plants

Food safety has emerged as a high-urgency matter for sustainable agricultural production. Toxic metal contamination of soil and water significantly affects agricultural productivity, which is further aggravated by extreme anthropogenic activities and modern agricultural practices, leaving food safety and human health at risk. In addition to reducing crop production, increased metals/metalloids toxicity also disturbs plants' demand and supply equilibrium. Counterbalancing toxic metals/metalloids toxicity demands a better understanding of the complex mechanisms at physiological, biochemical, molecular, cellular, and plant level that may result in increased crop productivity. Consequently, plants have established different internal defense mechanisms to cope with the adverse effects of toxic metals/metalloids. Nevertheless, these internal defense mechanisms are not adequate to overwhelm the metals/metalloids toxicity. Plants produce several secondary messengers to trigger cell signaling, activating the numerous transcriptional responses correlated with plant defense. Therefore, the recent advances in omics approaches such as genomics, transcriptomics, proteomics, metabolomics, ionomics, miRNAomics, and phenomics have enabled the characterization of molecular regulators associated with toxic metal tolerance, which can be deployed for developing toxic metal tolerant plants. This review highlights various response strategies adopted by plants to tolerate toxic metals/metalloids toxicity, including physiological, biochemical, and molecular responses. A seven-(omics)-based design is summarized with scientific clues to reveal the stress-responsive genes, proteins, metabolites, miRNAs, trace elements, stress-inducible phenotypes, and metabolic pathways that could potentially help plants to cope up with metals/metalloids toxicity in the face of fluctuating environmental conditions. Finally, some bottlenecks and future directions have also been highlighted, which could enable sustainable agricultural production.

Arsenic acquisition, toxicity and tolerance in plants - From physiology to remediation: A review

Globally, environmental contamination by potentially noxious metalloids like arsenic is becoming a critical concern to the living organisms. Arsenic is a non-essential metalloid for plants and can be acclimatised in plants to toxic levels. Arsenic acquisition by plants poses serious health risks in human due to its entry in the food chain. High arsenic regimes disturb plant water relations, promote the generation of reactive oxygen species (ROS) and induce oxidative outburst in plants. This review evidences a conceivable tie-up among arsenic levels, speciation, its availability, uptake, acquisition, transport, phytotoxicity and arsenic detoxification in plants. The role of different antioxidant enzymes to confer plant tolerance towards the enhanced arsenic distress has also been summed up. Additionally, the mechanisms involved in the modulation of different genes coupled with arsenic tolerance have been thoroughly discussed. This review is intended to present an overview to rationalise the contemporary progressions on the recent advances in phytoremediation approaches to overcome ecosystem contamination by arsenic.

Role of Jasmonates, Calcium, and Glutathione in Plants to Combat Abiotic Stresses Through Precise Signaling Cascade

Plant growth regulators have an important role in various developmental processes during the life cycle of plants. They are involved in abiotic stress responses and tolerance. They have very well-developed capabilities to sense the changes in their external milieu and initiate an appropriate signaling cascade that leads to the activation of plant defense mechanisms. The plant defense system activation causes build-up of plant defense hormones like jasmonic acid (JA) and antioxidant systems like glutathione (GSH). Moreover, calcium (Ca2+) transients are also seen during abiotic stress conditions depicting the role of Ca2+ in alleviating abiotic stress as well. Therefore, these growth regulators tend to control plant growth under varying abiotic stresses by regulating its oxidative defense and detoxification system. This review highlights the role of Jasmonates, Calcium, and glutathione in abiotic stress tolerance and activation of possible novel interlinked signaling cascade between them. Further, phyto-hormone crosstalk with jasmonates, calcium and glutathione under abiotic stress conditions followed by brief insights on omics approaches is also elucidated.

Influence of agricultural amendments on arsenic biogeochemistry and phytotoxicity in a soil polluted by the destruction of arsenic-containing shells

Agricultural soils can contain high arsenic (As) concentrations due to specific geological contexts or pollution. Fertilizer amendments could influence As speciation and mobility thus increasing its transfer to crops and its toxicity. In the present study, field-relevant amounts of fertilizers were applied to soils from a cultivated field that was a former ammunition-burning site. Potassium phosphate (KP), ammonium sulfate and organic matter (OM) were applied to these soils in laboratory experiments to assess their impact on As leaching, bioavailability to Lactuca sativa and microbial parameters. None of the fertilizers markedly influenced As speciation and mobility, although trends showed an increase of mobility with KP and a decrease of mobility with ammonium sulfate. Moreover, KP induced a small increase of As in Lactuca sativa, and the polluted soil amended with ammonium sulfate was significantly less phytotoxic than the un-amended soil. Most probable numbers of AsIII-oxidizing microbes and AsIII-oxidizing activity were strongly linked to As levels in water and soils. Ammonium sulfate negatively affected AsIII-oxidizing activity in the un-polluted soil. Whereas no significant effect on As speciation in water could be detected, amendments may have an impact in the long term.

An amiRNA screen uncovers redundant CBF and ERF34/35 transcription factors that differentially regulate arsenite and cadmium responses

Arsenic stress causes rapid transcriptional responses in plants. However, transcriptional regulators of arsenic-induced gene expression in plants remain less well known. To date, forward genetic screens have proven limited for dissecting arsenic response mechanisms. We hypothesized that this may be due to the extensive genetic redundancy present in plant genomes. To overcome this limitation, we pursued a forward genetic screen for arsenite tolerance using a randomized library of plants expressing >2,000 artificial microRNAs (amiRNAs). This library was designed to knock-down diverse combinations of homologous gene family members within sub-clades of transcription factor and transporter gene families. We identified six transformant lines showing an altered response to arsenite in root growth assays. Further characterization of an amiRNA line targeting closely homologous CBF and ERF transcription factors show that the CBF1,2 and 3 transcription factors negatively regulate arsenite sensitivity. Furthermore, the ERF34 and ERF35 transcription factors are required for cadmium resistance. Generation of CRISPR lines, higher-order T-DNA mutants and gene expression analyses, further support our findings. These ERF transcription factors differentially regulate arsenite sensitivity and cadmium tolerance.

Arsenic Stress-Related F-Box (ASRF) gene regulates arsenic stress tolerance in Arabidopsis thaliana

Arsenic (As), a non-biodegradable contaminant, is extremely toxic to plants and animals in its inorganic form. As negatively affects plant growth and development, primarily by inducing oxidative stress through redox imbalance. Here we characterized the Arabidopsis F-box protein gene AT2G16220 (Arsenic Stress-Related F-box (ASRF)) that we identified in the genome-wide association study. The asrf mutant seedlings showed high sensitivity to arsenate (As^V) stress. As^V significantly affected asrf seedling growth when germinated on or exposed to As^V-supplemented growth regimes. As^V stress significantly induced production of reactive oxygen species and proline accumulation in asrf, so the asrf maintained high proline content, possibly for cellular protection and redox homeostasis. Heterozygous seedlings (Col-0 x asrf, F1 progeny) were relatively less affected by As^V stress than asrf mutant but showed slightly reduced growth compared with the Col-0 wild type, which suggests that the homozygous ASRF locus is important for As^V stress resistance. Transcriptome analysis involving the mutant and wild type revealed altered phosphate homeostasis in asrf seedlings, which implies that ASRF is required for maintaining phosphate and cellular- homeostasis under excess As^V. Our findings confirm the roles of ASRF in As stress tolerance in plants, for a novel way to mitigate arsenic stress.

Expressing Phosphate Transporter PvPht2;1 Enhances P Transport to the Chloroplasts and Increases Arsenic Tolerance in Arabidopsis thaliana

Arsenic (As) contamination in soils is of great concerns due to its toxicity to plants. As an analogue, phosphorus plays an important role in protecting plants from As toxicity. In this study, we identified a new phosphate transporter 2 (PHT2), PvPht2;1, from As-hyperaccumulator Pteris vittata and analyzed its functions in As and P transport in a yeast mutant, and model plant Arabidopsis thalian. PvPht2;1 contained 12 transmembrane domains, sharing high identity with PHT2 genes in diverse plants. Further, independent of external P or As levels, PvPht2;1 was mainly expressed in P. vittata fronds with the expression being 3-4 folds higher than that in the roots and rhizomes. Localized to the chloroplasts based on GFP-fused PvPht2;1 in model plant tobacco, PvPht2;1 functioned as a low-affinity P transporter. Under As exposure, PvPht2;1 yeast transformants showed comparable growth with the control while high-affinity P transporter PvPht1;3 transformants showed better growth, suggesting that PvPht2;1 transported P but slower than PvPht1;3 transporter. Expressing PvPht2;1 in A. thaliana increased its shoot P concentration without influencing its As accumulation. Further, the chloroplasts' P content in transgenic A. thaliana increased by 37-59% than wild-type (WT) plants. Under As exposure, the photosynthesis of PvPht2;1-expressing A. thaliana remained stable but that of WT plants decreased. The data indicate that, under As stress, expressing PvPht2;1 in A. thaliana enhanced its P transport to the chloroplasts and protected its photosynthesis. In short, highly expressed in the fronds and not impacted by As exposure, chloroplast-located PvPht2;1 may have protected As-hyperaccumulator P. vittata from As toxicity by efficiently transporting only P to its chloroplasts.

An Overview of Morpho-Physiological, Biochemical, and Molecular Responses of Sorghum Towards Heavy Metal Stress

Heavy metal (HM) contamination is a serious global environmental crisis. Over the past decade, industrial effluents, modern agricultural practices, and other anthropogenic activities have significantly depleted the soil environment. In plants, metal toxicity leads to compromised growth, development, productivity, and yield. Also, HMs negatively affect human health due to food chain contamination. Thus, it is imperative to reduce metal accumulation and toxicity. In nature, certain plant species exhibit an inherent capacity of amassing large amounts of HMs with remarkable tolerance. These plants with unique characteristics can be employed for the remediation of contaminated soil and water. Among different plant species, Sorghum bicolor has the potential of accumulating huge amounts of HMs, thus could be regarded as a hyperaccumulator. This means that it is a metal tolerant, high biomass producing energy crop, and thus can be utilized for phytoremediation. However, high concentrations of HMs hamper plant height, root hair density, shoot biomass, number of leaves, chlorophyll, carotenoid, and carbohydrate content. Thus, understanding the response of Sorghum towards different HMs holds considerable importance. Considering this, we have uncovered the basic information about the metal uptake, translocation, and accumulation in Sorghum. Plants respond to different HMs via sensing, signaling, and modulations in physico-chemical processes. Therefore, in this review, a glimpse of HM toxicity and the response of Sorghum at the morphological, physiological, biochemical, and molecular levels has been provided. The review highlights the future research needs and emphasizes the extensive molecular dissection of Sorghum to explore its genetic adaptability towards different abiotic stresses that can be exploited to develop resilient crop varieties.

CATALASE2 plays a crucial role in long-term heat tolerance of Arabidopsis thaliana

Plants are often exposed not only to short-term (S-) heat stress but also to diurnal long-term (L-) heat stress over several consecutive days; nevertheless, most previous studies of heat tolerance have used S-heat stress, such as 42 °C for 30-60 min, for evaluation. Yet the mechanisms underlying L-heat tolerance remain poorly understood. Here we found that hydrogen peroxide (H₂O₂) in Arabidopsis thaliana plants increased time-dependently under L-heat stress (37 °C, 5 days) but not under S-heat stress (42 °C, 40 min). To reveal the contribution of reactive oxygen species (ROS) scavenging to heat tolerance, we evaluated the heat tolerance of ROS mutants. Only cat2 mutants, in which catalase (CAT) activity is defective, were hypersensitive to L-heat stress, but they were S-heat tolerant. We further revealed that (1) CAT2 was induced by L-heat stress but not by S-heat stress; (2) H₂O₂ accumulated highly in cat2 under L-heat stress, but not in cat1, cat3, or wild type; and (3) CAT activity was significantly reduced in cat2 under both normal and L-heat conditions. These results suggest that ROS scavenging is responsible for L-heat tolerance, and CAT2 plays a crucial role. On the other hand, since overexpression of CAT2 in wild-type plants did not enhance L-heat tolerance, CAT2 activity is necessary but insufficient for increasing L-heat tolerance.

Transcriptome -wide modulation combined with morpho-physiological analyses of Typha orientalis roots in response to lead challenge

Lead (Pb) is a common pollutant in many environments, including in the soil, water, and/or air. Typha orientalis Presl, a large emergent aquatic plant, has been reported to function as a Pb-tolerant and Pb-accumulating plant; however, very little molecular information regarding the tolerance of T. orientalis towards Pb is known. In this study, Pb accumulation and key factors involved in the Pb stress response at different Pb concentrations were investigated. Pb was primarily accumulated in the roots and was mainly located in the cell wall and membrane systems. Differentially expressed genes (DEGs) were identified in T. orientalis roots after Pb exposure via RNA-seq analyses. In the 0.10 mM and 0.25 mM Pb²⁺-treated groups, a total of 3275 DEGs were detected relative to the control. Many of these genes were associated with oxidation-reduction processes, metal transport, protein kinase/phosphorylation, and DNA binding transcription factors, which were shown to be Pb-responsive DEGs. Mapping Kyoto Encyclopedia of Genes and Genomes (KEGG) database, "phenylpropanoid biosynthesis" was analyzed as the major pathway of the important modules of overlapping DEGs of 0.10 mM and 0.25 mM Pb²⁺ treatments. Furthermore, a lead response gene named ToLR1 with unknown function was of particular interest. The full-length of ToLR1 sequence was cloned using rapid amplification of cDNA ends (RACE) and overexpressed in Arabidopsis thaliana, which resulted in enhanced resistance to Pb stress. This is the first report providing genomic information detailing Pb responsive genes in T. orientalis. Moreover, this study provides novel insights into the molecular mechanisms underlying the response of T. orientalis and other accumulators towards Pb stress. The key genes identified in this study may serve as potential targets for genetic engineering targeting phytoremediation.

24-Epibrassinolide promotes arsenic tolerance in Arabidopsis thaliana L. by altering stress responses at biochemical and molecular level

In this study, the effect of 24-Epibrassinolide (EBL) on antioxidant system in Arabidopsis thaliana were investigated under arsenate [As(V)] stress. The enzyme activity of superoxide dismutase (SOD) and catalase (CAT), total antioxidant status, malondialdehyde (MDA) level and free proline content, as well as the expression levels of SOD isoforms (Cu-ZnSODs, FeSODs and MnSOD), CAT isoforms (CAT1, CAT2 and CAT3), some heat shock proteins (Hsp70-4 and Hsp90-1) and proline biosynthesis (P5CS1 and P5CS2) genes were determined in rosette leaves of eight-week old plants under exposure of 100 and 200 μM As(V) and/or 1 μM EBL treatments for 24 h. Total SOD and CAT enzyme activities increased as a result of 100 μM As(V) + EBL treatments compared to 100 μM As(V) treatment. Total antioxidant and proline levels increased in plants subjected to As(V), and the treatment of EBL together with stress caused further increase. As the MDA level increased in As-treated plants, 100 μM As(V) + EBL treatment decreased MDA level. Transcript levels of CSD1, CSD2, FSD1, FSD2, MSD1 and CAT2 genes increased as a result of combined treatment of EBL and As(V) compared to control and alone stress treatments (except CSD1 gene). Expression level of CSD3, CAT1 and CAT3 genes were downregulated in response to As(V) and/or EBL treatments. EBL application alone and in combination with As(V) elevated the expression level of P5CS1 gene dramatically. Treatment with 100 μM As(V) and EBL increased the transcript level of Hsp70-4 and Hsp90-1 genes in leaves compared to 100 μM As(V) treatment. To our best knowledge, this is the first detailed study to evaluate the improving effect of EBL on antioxidant defense system at biochemical and transcriptional level in A. thaliana plants under As(V) stress.

Glutathione S-Transferases: Role in Combating Abiotic Stresses Including Arsenic Detoxification in Plants

Arsenic (As), naturally occurring metalloid and a potential hazardous material, is found in low concentrations in the environment and emerges from natural sources and anthropogenic activities. The presence of As in ground water, which is used for irrigation, is a matter of great concern since it affects crop productivity and contaminates food chain. In plants, As alters various metabolic pathways in cells including the interaction of substrates/enzymes with the sulfhydryl groups of proteins and the replacement of phosphate in ATP for energy. In addition, As stimulates the generation of free radicals and reactive oxygen species (ROS), resulting in oxidative stress. Glutathione S-transferases (GSTs) quench reactive molecules with the addition of glutathione (GSH) and protect the cell from oxidative damage. GSTs are a multigene family of isozymes, known to catalyze the conjugation of GSH to miscellany of electrophilic and hydrophobic substrates. GSTs have been reported to be associated with plant developmental processes and are responsive to multitude of stressors. In past, several studies suggested involvement of plant GST gene family in As response due to the requirement of sulfur and GSH in the detoxification of this toxic metalloid. This review provides updated information about the role of GSTs in abiotic and biotic stresses with an emphasis on As uptake, metabolism, and detoxification in plants. Further, the genetic manipulations that helped in enhancing the understanding of the function of GSTs in abiotic stress response and heavy metal detoxification has been reviewed.