Heavy Metal ATPase Research Articles

Genome wide analysis of HMA gene family in Hydrangea macrophylla and characterization of HmHMA2 in response to aluminum stress

Aluminum toxicity poses a significant threat to plant growth, especially in acidic soils. Heavy metal ATPases (HMAs) are crucial for transporting heavy metal ions across plant cell membranes, yet their role in Al3+ transport remains unexplored. This study identified eight HmHMA genes in the genome of Hydrangea macrophylla, categorizing them into two major clades based on phylogenetic relationships. These genes were found unevenly distributed across six chromosomes. Detailed analysis of their physicochemical properties, collinearity, and gene structure was conducted. RNA-seq and qRT-PCR analyses revealed that specific HmHMA genes, notably HmHMA2, were predominantly expressed in roots and flowers under Al3+ stress, indicating their potential role in Al3+ tolerance. HmHMA2 showed significant expression in roots, especially under Al3+ stress conditions, and when expressed in yeast cells, it conferred resistance to aluminum and zinc but increased sensitivity to cadmium. Overexpression of HmHMA2 in hydrangea leaf discs significantly improved Al3+ tolerance, reduced oxidative stress markers like hydrogen peroxide and malondialdehyde, and enhanced antioxidant enzyme activity such as SOD, POD and CAT compared to controls. These findings shed lights on the potential role of HmHMAs in Al transport and tolerance in H. macrophylla.

Responses of Brassica napus to soil cadmium under elevated CO2 concentration based on rhizosphere microbiome, root transcriptome and metabolome

Rising atmospheric carbon dioxide (CO2) and soil heavy metal pollution affect crop safety and production. Exposure to elevated CO2 (ECO2) increases cadmium (Cd) uptake in some crops like wheat and rice, however, it remains unclear how ECO2 affects Cd uptake by Brassica napus. Here, we investigated the responses of B. napus seedlings exposed to ECO2 and Cd through analyses of physiology, transcriptome, metabolome, and rhizosphere microbes. Compared with Cd-stress alone (Cd50_ACO2), ECO2 boosted the uptake of Cd by B. napus roots by 38.78% under coupled stresses (Cd50_ECO2). The biomass and leaf chlorophyll a content increased by 38.49% and 79.66% respectively in Cd50_ECO2 relative to Cd50_ACO2. Activities of superoxide dismutase (SOD) and peroxidase (POD) enhanced by 8.42% and 185.01%, respectively, while glutathione (GSH) and ascorbic acid (AsA) contents increased by 16.44% and 52.48%, and abundances of rhizosphere microbes changed significantly under coupled stresses (Cd50_ECO2) relative to Cd-stress alone (Cd50_ACO2). Also, the upregulation of glutathione, glutathione transferase genes, and heavy metal ATPase expression promoted the detoxification effect of rapeseed on Cd. Changes in the expression of transcription factors like MAPK, WRKY, BAK1 and PR1, as well as changes in metabolic pathways like β-alanine, may be involved in the regulatory mechanism of stress response. These findings provide new insights for studying the regulatory mechanism of rapeseed under ECO2 on soil Cd stress, and also provide a basis for further research on Cd tolerant rapeseed varieties in the future climate context.

Root Zn sequestration transporter heavy metal ATPase 3 from Odontarrhena chalcidica enhance Cd tolerance and accumulation in Arabidopsis thaliana

The Ni hyperaccumulator Odontarrhena chalcidica (formerly Alyssum murale), exhibits a significant capacity to accumulate Zn in the roots. However, the molecular mechanisms underlying the variation in Ni and Zn accumulation are poorly understood. Here, we isolated a homolog of heavy metal ATPase 3 from O. chalcidica (OcHMA3) and characterized its functions using heterologous systems. Phylogenetic analysis revealed that OcHMA3 protein shares 87.6 % identity with AtHMA3, with similar metal binding sites to other HMA3 proteins. Heterologous expression of OcHMA3 in yeast increased sensitivity to Cd, Ni and Zn, suggesting it functions as a broad-specificity transporter. Further investigation showed OcHMA3 is constitutively expressed in the roots and localized to the tonoplast. Overexpression of OcHMA3 in A. thaliana shoots increased its roots Zn concentrations by 41.9 % – 74.1 %. However, overexpression of OcHMA3 in roots enhanced its tolerance to Cd and increased roots Cd concentrations by 50.9 % – 90.6 %. Our findings indicated OcHMA3 is responsible for Zn sequestration in root vacuoles, likely leading to Zn retention in roots and subsequent Ni hyperaccumulation in shoots. This study elucidates the molecular mechanism of Ni and Zn accumulation in O. chalcidica, and identifies OcHMA3 as a potential gene for developing Zn-rich plants and for phytoextraction in Cd-contaminated soils.

Genome-wide association study of trace elements in maize kernels

Maize (Zea mays L.), a staple food and significant economic crop, is enriched with riboflavin, micronutrients and other compounds that are beneficial for human health. As emphasis on the nutritional quality of crops increases maize research has expanded to focus on both yield and quality. This study exploreed the genetic factors influencing micronutrient levels in maize kernels through a comprehensive genome-wide association study (GWAS). We utilized a diverse panel of 244 inbred maize lines and approximately 3 million single nucleotide polymorphisms (SNPs) to investigate the accumulation of essential and trace elements including cadmium (Cd), cobalt (Co), copper (Cu), nickel (Ni), selenium (Se) and zinc (Zn). Our analysis identified 842 quantitative trait loci (QTLs), with 12 QTLs shared across multiple elements and pinpointed 524 potential genes within a 100 kb radius of these QTLs. Notably ZmHMA3 has emerged as a key candidate gene previously reported to influence the Cd accumulation. We highlighted ten pivotal genes associated with trace element transport including those encoding heavy metal ATPases, MYB transcription factors, ABC transporters and other crucial proteins involved in metal handling. Additionally, haplotype analysis revealed that eight inbred linesaccumulated relatively high levels of beneficial elements while harmful elements were minimized. These findings elucidate the genetic mechanisms underlying trace element accumulation in maize kernels and provide a foundation for the breeding of nutritionally enhanced maize varieties.

Differential reduction in cadmium accumulation in barley under cadmium-salt co-exposure involves specific HMA genes and antioxidative responses

Salinity and heavy metal accumulation adversely affect agricultural productivity and environmental sustainability. Little information exists about the combinatory effect of various stresses on plants, but it is assumed that stress interaction may trigger a specific response. Here, we assessed the combinatory effect of salinity and cadmium on various physiological and molecular traits in two cultivated barley genotypes with contrasting salinity tolerance; Rihane (RH, salt tolerant) and Lemsi (LM, salt sensitive). Studied genotypes were hydroponically exposed to CdCl2 (30 µM), NaCl (300 mM) or the combined Cd-NaCl stresses for 15 days. Salinity and to a lesser degree Cd-NaCl stress significantly reduced growth, leaf water content, chlorophyll pigments, and K uptake, and increased Na and Cl contents for both genotypes, with LM being more affected than RH. Cd content in roots was higher than in shoots for both genotypes either under Cd alone or when combined with NaCl. Interestingly, NaCl addition reduced Cd accumulation in both roots and shoots of the two barley genotypes, suggesting that the interaction of NaCl and Cd on their uptake and accumulation is antagonistic. The tolerant genotype (RH) accumulated lower Cd levels in shoots and roots than the salt-sensitive one (LM). Cd-NaCl stress significantly lowered H2O2 and MDA contents relative to NaCl treatment alone. The activity of several antioxidant enzymes was essentially higher in RH than in LM, under the different stresses. These responses were in concomitant with an enhanced expression of specific Heavy Metal ATPases (HvHMA) genes, mainly in RH, which can partially, explain the reduced Cd accumulation in this genotype. Overall, these findings suggest the possibility of cultivating salt-tolerant barley genotypes in saline soils slightly contaminated with Cd, whereas barley sensitive genotypes could be assessed for phytoremediation purposes.

Genome-wide identification of heavy-metal ATPases genes in Areca catechu: investigating their functionality under heavy metal exposure

Heavy-metal ATPases (HMAs) play a vital role in plants, helping to transport heavy metal ions across cell membranes.However, insufficient data exists concerning HMAs genes within the Arecaceae family.In this study, 12 AcHMA genes were identified within the genome of Areca catechu, grouped into two main clusters based on their phylogenetic relationships.Genomic distribution analysis reveals that the AcHMA genes were unevenly distributed across six chromosomes. We further analyzed their physicochemical properties, collinearity, and gene structure.Furthermore, RNA-seq data analysis exhibited varied expressions in different tissues of A. catechu and found that AcHMA1, AcHMA2, and AcHMA7 were highly expressed in roots, leaves, pericarp, and male/female flowers. A total of six AcHMA candidate genes were selected based on gene expression patterns, and their expression in the roots and leaves was determined using RT-qPCR under heavy metal stress. Results showed that the expression levels of AcHMA1 and AcHMA3 genes were significantly up-regulated under Cd2 + and Zn2 + stress. Similarly, in response to Cu2+, the AcHMA5 and AcHMA8 revealed the highest expression in roots and leaves, respectively. In conclusion, this study will offer a foundation for exploring the role of the HMAs gene family in dealing with heavy metal stress conditions in A. catechu.

Cadmium and zinc accumulation and tolerance in two Egyptian cultivars (S53 and V120) of Helianthus annuus L. as potential phytoremediator

One of the most important oil crops in the world, sunflower (Helianthus annuus L.), is recognized to help in soil phytoremediation. Heavy metal (HM) contamination is one of the most abiotic challenges that may affect the growth and productivity of such an important crop plant. We studied the influence of HM-contaminated soils on metal homeostasis and the potential hypertolerance mechanisms in two sunflower Egyptian cultivars (V120 and S53). Both cultivars accumulated significantly higher cadmium concentrations in their roots compared to their shoots during Cd and Zn/Cd treatments. Higher root concentrations of 121 mg g−1 dry weight (DW) and 125 mg g−1 DW were measured in V120 plants compared to relatively lower values of 111 mg g−1 DW and 105 mg g−1 DW in the roots of S53 plants, respectively. Cadmium contamination significantly upregulated the expression of heavy metal ATPases (HaHMA4) in the shoots of V120 plants. On the other hand, their roots displayed a notable expression of HaHMA3. This study indicates that V120 plants accumulated and sequestered Cd in their roots. Therefore, it is advised to cultivate the V120 cultivar in areas contaminated with heavy metals as it is a promising Cd phytoremediator.

Knockout of OsHMA3 in an indica rice increases cadmium sensitivity and inhibits plant growth

Cadmium (Cd) is a heavy metal that poses harm to both plants and humans. OsHMA3, a member of the heavy metal ATPase (HMA) family, plays a crucial role in sequestering Cd into the vacuoles of roots, thereby limiting its accumulation in rice grains. However, the response of rice plants to Cd under complete loss-of-function of OsHMA3 remains unclear. In this study, we successfully generated OsHMA3 null mutants in an indica variety 93 − 11 using CRISPR/Cas9 technology. A Cd resistance experiment revealed that the Oshma3 mutants exhibited increased sensitivity to Cd compared to the wild-type at a tested concentration of 10 µM CdCl2. Furthermore, the seedlings of Oshma3 mutant lines displayed inhibited plant growth in the presence of 1 µM Cd, specifically suppressing aboveground growth. As expected, knockout lines of OsHMA3 showed lower Cd accumulation in roots but higher concentrations in shoots compared to wild-type plants, highlighting the role of OsHMA3 in root-to-shoot Cd translocation. We further performed RNA sequencing analysis on wild-type and Oshma3 plants under control and Cd treatment conditions and found that differentially expressed genes were mainly enriched in metal ion binding, integral component of the membranes, and biosynthesis pathways for secondary metabolites triggered by exposure to Cd. When grown in a paddy field, the Oshma3 mutants exhibited shorter plant height, lower seed setting rate, and higher Cd accumulation in grains compared to wild-type plants. Our results indicate that knockout of OsHMA3 in the 93 − 11 variety increases sensitivity to Cd and inhibits plant growth.

Melatonin reduces cadmium accumulation through cell wall fraction fixation capacity in cotton seedlings

Melatonin (MT) participates in plants' responses in plants’ response to cadmium (Cd) tolerance, although its work model remains elusive. Here, the function of MT in adjusting Cd accumulation in Gossypium hirsutum (CCRI12) was investigated. In this research we observed that exogenous 50 μM MT significantly reduced the Cd accumulation under 100 μМ Cd stress for 7 days of treatment in cotton seedlings. Cd markedly induced the ROS (H2O2, O2-) accumulation and elevated the expression of transporters for Cd uptake and translocation. After application of MT reduced ROS and MDA accumulation in response to high induction of antioxidant defense system; the genes encoding superoxide dismutase (GhSOD), catalase (GhCAT), and peroxidase (GhPOD), ascorbate peroxidase (GhAPX), and glutathione S-transferase (GhGST) were significantly upregulated accompanied by their level of content. Furthermore, MT down-regulated transporters for Cd uptake include Natural Resistance-Associated Macrophage Protein 1 (GhNRAMP3), Zinc/Iron-regulated transporter-like protein (GhZIP1/4/6), Heavy Metal ATPase gene (GhHMA2), and ATP-binding Cassette sub family C (GhABCC3/2). Exogenous application of MT raised the hemicelluloses, cellulose and pectin content accompanied by their expression levels, xyloglucan endotransglucosylase/hydrolase (GhXTH28/6/9/B), cellulose synthase like (GhCSLG1/2) and COBRA-like (GhCOBL4), pectin acetylesterases (GhPAE8/7), pectin methylesterases (GhPME31) which in turn increased the cell wall's binding capacity to Cd.

Brassinosteroid decreases cadmium accumulation via regulating gibberellic acid accumulation and Cd fixation capacity of root cell wall in rice (Oryza sativa)

The precise mechanism behind the association between plants' reactions to cadmium (Cd) stress and brassinosteroid (BR) remains unclear. In the current investigation, Cd stress quickly increased the endogenous BR concentration in the rice roots. Exogenous BR also increased the hemicellulose level in the root cell wall, which in turn increased its capacity to bind Cd. Simultaneously, the transcription level of genes responsible for root Cd absorption was decreased, including Natural Resistance-Associated Macrophage Protein 1/5 (OsNRAMP1/5) and a major facilitator superfamily gene called OsCd1. Ultimately, the increased expression of Heavy Metal ATPase 3 (OsHMA3) and the decreased expression of OsHMA2, which was in charge of separating Cd into vacuoles and translocating Cd to the shoots, respectively, led to a decrease in the amount of Cd that accumulated in the rice shoots. In contrast, transgenic rice lines overexpressing OsGSK2 (a negative regulator in BR signaling) accumulated more Cd, while OsGSK2 RNA interference (RNAi) rice line accumulated less Cd. Furthermore, BR increased endogenous Gibberellic acid (GA) level, and applying GA could replicate its alleviative effect. Taken together, BR decreased Cd accumulation in rice by mediating the cell wall’s fixation capacity to Cd, which might relied on the buildup of the GA.

Genome-Wide Identification and Expression Profiling of Heavy Metal ATPase (HMA) Genes in Peanut: Potential Roles in Heavy Metal Transport.

The heavy metal ATPase (HMA) family belongs to the P-type ATPase superfamily and plays an essential role in the regulation of metal homeostasis in plants. However, the gene family has not been fully investigated in peanut. Here, a genome-wide identification and bioinformatics analysis was performed on AhHMA genes in peanut, and the expression of 12 AhHMA genes in response to Cu, Zn, and Cd was evaluated in two peanut cultivars (Silihong and Fenghua 1) differing in Cd accumulation. A total of 21 AhHMA genes were identified in the peanut genome, including ten paralogous gene pairs derived from whole-genome duplication, and an additional gene resulting from tandem duplication. AhHMA proteins could be divided into six groups (I-VI), belonging to two clades (Zn/Co/Cd/Pb-ATPases and Cu/Ag-ATPases). Most AhHMA proteins within the same clade or group generally have a similar structure. However, significant divergence exists in the exon/intron organization even between duplicated gene pairs. RNA-seq data showed that most AhHMA genes are preferentially expressed in roots, shoots, and reproductive tissues. qRT-PCR results revealed that AhHMA1.1/1.2, AhHMA3.1/3.2, AhHMA7.1/7.4, and AhHMA8.1 might be involved in Zn transport in peanut plants, while AhHMA3.2 and AhHMA7.5 might be involved in Cd transport. Our findings provide clues to further characterize the functions of AhHMA genes in metal uptake and translocation in peanut plants.

Investigating the growth characteristics, oxidative stress, and metal absorption of chickpea (Cicer arietinum L.) under cadmium stress and in silico features of HMAs proteins

Heavy metal contamination can have a strong effect on the morphological and physiological characteristics of plants. In the present study, Cicer arietinum L. (chickpea) was exposed to different concentrations of cadmium (control, 2, 4, 8 μg Cd g-1 perlite) and the effect on plant growth and antioxidant enzymes were evaluated. The observed morphological changes in chickpea plant included stunted growth, reduced root system development and plant color change. A significant increase in enzyme activity of peroxidase, superoxide dismutase, catalase, and ascorbate peroxidase was observed at 4 μg Cd g-1 perlite, with a subsequent decrease when concentration was increased to 8 μg Cd g-1 perlite in the leaves of the plants. The highest cadmium levels were determined at a concentration of 8 μg Cd g-1 perlite. With the addition of 2 μg Cd g-1 perlite, manganese uptake in the aboveground part of the plant increased significantly, but then decrease at higher cadmium concentrations. In addition, zinc and copper levels decrease in the presence of cadmium. These results indicate that chickpea has a relatively high adsorption capacity for cadmium in aboveground tissues and special precautions should be taken when growing chickpea. In silico analysis led to the identification of 13 heavy metal ATPases (HMAs) in chickpea. These proteins contain 130 to 1032 amino acids with 3 to 18 exons. They are involved in the transfer of cadmium and zinc and help in heavy metal detoxification of plants. Bioinformatics studies have been conducted to better understand the mechanism by which the plant is able to combat heavy metal stress.

Auxin is involved in cadmium accumulation in rice through controlling nitric oxide production and the ability of cell walls to bind cadmium

Although auxin has been linked to plants' responses to cadmium (Cd) stress, the exact mechanism is yet elusive. The objective of the current investigation was to determine the role and the mechanism of auxin in controlling rice's Cd accumulation. Rice roots with Cd stress have higher endogenous auxin levels, and exogenous auxin combined Cd treatment could reduce root cell wall's hemicellulose content when compared with Cd treatment alone, which in turn reduced its fixation of Cd, as well as decreased the expression of OsCd1 (a major facilitator superfamily gene), OsNRAMP1/5 (Natural Resistance-Associated Macrophage Protein 1/5), OsZIP5/9 (Zinc Transporter 5/9), and OsHMA2 (Heavy Metal ATPase 2) that participated in Cd uptake and root to shoot translocation. Furthermore, less Cd accumulated in the shoots as a result of auxin's impact in increasing the expression of OsCAL1 (Cadmium accumulation in Leaf 1), OsABCG36/OsPDR9 (G-type ATP-binding cassette transporter/Pleiotropic drug resistance 9), and OsHMA3, which were in charge of Cd efflux and sequestering into vacuoles, respectively. Additionally, auxin decreased endogenous nitric oxide (NO) levels and antioxidant enzyme activity, while treatment of a NO scavenger-cPTIO-reduced auxin's alleviatory effects. In conclusion, the rice's ability to tolerate Cd toxicity was likely increased by the auxin-accelerated cell wall Cd exclusion mechanism, a pathway that controlled by the buildup of NO.

Salylic acid minimize cadmium accumulation in rice through regulating the fixation capacity of the cell wall to cadmium

Although salylic acid (SA) has been linked to how plants react to cadmium (Cd) stress, the exact mechanism is still unknown. The endogenous SA concentration in the rice (Oryza sativa L.) roots was enhanced by Cd stress in the current investigation, and exogenous SA reduced the hemicellulose content in root cell wall, which in turn inhibited its Cd binding capacity. What's more, exogenous SA also decreased the transcription level of genes such as Natural Resistance-Associated Macrophage Protein 5 (OsNRAMP5) and a major facilitator superfamily gene-OsCd1 that responsible for root Cd absorption. Finally, less Cd was accumulated in the rice as a result of the higher expression of Heavy Metal ATPase 3 (OsHMA3), Cation/Ca exchanger 2 (OsCCX2) and Pleiotropic Drug Resistance 9 (OsPDR9/OsABCG36) that were responsible for separating Cd into vacuole and getting Cd out of cells, respectively. In contrast, mutant with low SA level accumulated more Cd. Additionally, SA enhanced endogenous nitric oxide (NO) levels, and its alleviatory effects were mimicked by a NO donor, sodium nitroprusside (SNP). In conclusion, SA enhanced rice’s Cd resistance through regulating the binding capacity of the cell wall to Cd, a pathway that might dependent on the NO accumulation.

EcAGL enhances cadmium tolerance in transgenic Arabidopsis thaliana through inhibits cadmium transport and ethylene synthesis pathway

Cadmium (Cd) is a highly toxic heavy metal with severe impacts on plant growth and development. Although a multitude of plants have acquired strong tolerance to Cd stress, the underlying molecular mechanism has not been fully elucidated. Here, we identified a Agamous-like MADS-box gene (EcAGL) from Erigeron canadensis. The expression of EcAGL was obviously raised under Cd stress and subcellular localization indicated EcAGL was localized in the nucleus. Overexpression of EcAGL in Arabidopsis thaliana showed marked alleviation of the Cd-induced reduction; Compared to wild-type lines, the antioxidant enzymes activities were increased in EcAGL overexpressing lines under Cd stress. The roots Cd content of transgenic lines was not different with the control plants, whereas significant reduction in shoots Cd content was detected in the transgenic lines, indicating that this gene can enhance Cd tolerance by reducing Cd accumulation in Arabidopsis. Moreover, the expression levels of heavy metal ATPase (AtHMA2 and AtHMA3) and natural resistance-associated macrophage protein (AtNRAMP5) genes in the root of transgenic lines decreased under Cd stress, indicating that EcAGL likely hampered the Cd transport pathway. Gene expression profiles in shoot showed that EcAGL likely modulates the expression of 1-aminocyclopropane-1-carboxylic acid synthase gene (AtACS2), which is involved in the ethylene synthesis pathway, to strengthen the tolerance to Cd. Collectively, these results indicate that EcAGL plays a significant role in regulating Cd tolerance in E. canadensis by alleviating oxidative stress, Cd transport and affecting the ethylene biosynthesis pathway, providing new insight into the molecular mechanism underlying plant tolerance to Cd stress.

Genome-wide analysis of heavy metal ATPases (HMAs) in Poaceae species and their potential role against copper stress in Triticum aestivum

Plants require copper for normal growth and development and have evolved an efficient system for copper management based on transport proteins such as P1B-ATPases, also known as heavy metal ATPases (HMAs). Here, we report HMAs in eleven different Poaceae species, including wheat. Furthermore, the possible role of wheat HMAs in copper stress was investigated. BlastP searches identified 27 HMAs in wheat, and phylogenetic analysis based on the Maximum Likelihood method demonstrated a separation into four distinct clades. Conserved motif analysis, domain identification, gene structure, and transmembrane helices number were also identified for wheat HMAs using computational tools. Wheat seedlings grown hydroponically were subjected to elevated copper and demonstrated toxicity symptoms with effects on fresh weight and changes in expression of selected HMAs TaHMA7, TaHMA8, and TaHMA9 were upregulated in response to elevated copper, suggesting a role in wheat copper homeostasis. Further investigations on these heavy metal pumps can provide insight into strategies for enhancing crop heavy metal tolerance in the face of heavy metal pollution.

The Effect of Cadmium on Plants in Terms of the Response of Gene Expression Level and Activity.

Cadmium (Cd) is a heavy metal that can cause damage to living organisms at different levels. Even at low concentrations, Cd can be toxic to plants, causing harm at multiple levels. As they are unable to move away from areas contaminated by Cd, plants have developed various defence mechanisms to protect themselves. Hyperaccumulators, which can accumulate and detoxify heavy metals more efficiently, are highly valued by scientists studying plant accumulation and detoxification mechanisms, as they provide a promising source of genes for developing plants suitable for phytoremediation techniques. So far, several genes have been identified as being upregulated when plants are exposed to Cd. These genes include genes encoding transcription factors such as iron-regulated transporter-like protein (ZIP), natural resistance associated macrophage protein (NRAMP) gene family, genes encoding phytochelatin synthases (PCs), superoxide dismutase (SOD) genes, heavy metal ATPase (HMA), cation diffusion facilitator gene family (CDF), Cd resistance gene family (PCR), ATP-binding cassette transporter gene family (ABC), the precursor 1-aminocyclopropane-1-carboxylic acid synthase (ACS) and precursor 1-aminocyclopropane-1-carboxylic acid oxidase (ACO) multigene family are also influenced. Thanks to advances in omics sciences and transcriptome analysis, we are gaining more insights into the genes involved in Cd stress response. Recent studies have also shown that Cd can affect the expression of genes related to antioxidant enzymes, hormonal pathways, and energy metabolism.

Ectopic Expression of PvHMA2.1 Enhances Cadmium Tolerance in Arabidopsis thaliana

Cadmium (Cd) in soil inhibits plant growth and development and even harms human health through food chain transmission. Switchgrass (Panicum virgatum L.), a perennial C4 biofuel crop, is considered an ideal plant for phytoremediation due to its high efficiency in removing Cd and other heavy metals from contaminated soil. The key to understanding the mechanisms of switchgrass Cd tolerance is to identify the genes involved in Cd transport. Heavy-metal ATPases (HMAs) play pivotal roles in heavy metal transport, including Cd, in Arabidopsis thaliana and Oryza sativa, but little is known about the functions of their orthologs in switchgrass. Therefore, we identified 22 HMAs in switchgrass, which were distributed on 12 chromosomes and divided into 4 groups using a phylogenetic analysis. Then, we focused on PvHMA2.1, which is one of the orthologs of the rice Cd transporter OsHMA2. We found that PvHMA2.1 was widely expressed in roots, internodes, leaves, spikelets, and inflorescences, and was significantly induced in the shoots of switchgrass under Cd treatment. Moreover, PvHMA2.1 was found to have seven transmembrane domains and localized at the cell plasma membrane, indicating that it is a potential transporter. The ectopic expression of PvHMA2.1 alleviated the reduction in primary root length and the loss of fresh weight of Arabidopsis seedlings under Cd treatment, suggesting that PvHMA2.1 enhanced Cd tolerance in Arabidopsis. The higher levels of relative water content and chlorophyll content of the transgenic lines under Cd treatment reflected that PvHMA2.1 maintained water retention capacity and alleviated photosynthesis inhibition under Cd stress in Arabidopsis. The roots of the PvHMA2.1 ectopically expressed lines accumulated less Cd compared to the WT, while no significant differences were found in the Cd contents of the shoots between the transgenic lines and the WT under Cd treatment, suggesting that PvHMA2.1 reduced Cd absorption from the environment through the roots in Arabidopsis. Taken together, our results showed that PvHMA2.1 enhanced Cd tolerance in Arabidopsis, providing a promising target that could be engineered in switchgrass to repair Cd-contaminated soil.

Expression of heavy metal ATPases (HMA1 and HMA3) in Brassica nigra and B. juncea grown at different Cu levels

Metal pollution is a major environmental problem which affects agriculture and human health. Turkey has significant Cu mining areas in Diyarbak?r and its surrounding areas (Southeast Anatolia). Several crop plants cultivated in these areas are irrigated with water from the Tigris, and most agricultural lands are contaminated with Cu. Brassica nigra and B. juncea are well-known metal accumulator plant species which can hyperaccumulate metals, including copper, in their shoots. The purpose of this study is to evaluate their potential for the phytoremediation of Cu from these contaminated areas as an environmentally friendly and cost-effective means of reducing Cu-contamination. In this research, B. nigra and B. juncea plants were grown in soil at different Cu concentrations (0 to 1000 ?M) and showed no toxicity symptoms while accumulating a significant amount of metal in their leaves. In the leaves of both species, the Cu content increased significantly with the increase in the Cu level in the media. HMA1 (Heavy Metal ATPase 1) in the leaves of both plant species gradually increased with increased Cu levels until 50 ?M, then its expression slowly decreased with the further increase in Cu levels. The expression of HMA3 also increased with an increase in Cu in the leaves of both plant species. However, its expression pattern differed from that of HMA1. Our data showed that an increase in Cu levels in the leaves triggers the expression of both genes, suggesting that they play an active role in Cu detoxification. We propose that these plant species could be used for the decontamination of Cu from polluted soils. These data also indicate that Cu accumulation and tolerance in both plant species is probably a multi-genetic response, possibly involving several other transporter genes in the stress signal pathway. Hence, we also explored the expression of the other metal transporters, such as other HMAs (HMAs 5-8), Nramps (e.g., Nramp3), COPT proteins, and some Cu chaperons in these plant species.

RNA Sequencing indicates gene expression changes in Silene sendtneri seeds after seed priming with silicic acid

To improve our understanding of the molecular mechanisms underlaying seed priming, RNA transcriptome analysis was performed using primed and non-primed seeds of Silene sendtneri. Seed priming was performed by submergence in 1% silicic acid for 24h at 4°C, followed by rinsing with sterilised water and desiccation to original moisture content. Silene sendtneri is a species with no sequenced genome and annotation of de novo assembly of transcriptome was done against several species. Gene ontology (GO) analysis indicated that genes related to heavy metal transporters and heat shock proteins are differentially expressed after priming with silicic acid. Within these gene categories, genes such as heavy metal-associated isoprenylated plant protein 26-like (log2fold -8.79) were downregulated, while others such as heavy metal ATPase 5 (log2fold 6.46), heat shock factor protein HSF30-like isoform X1 (log2fold 5.98) were upregulated.