We have developed a genetics-based phytoremediation strategy for arsenic in which the oxyanion arsenate is transported aboveground, reduced to arsenite, and sequestered in thiol-peptide complexes. The Escherichia coli arsC gene encodes arsenate reductase (ArsC), which catalyzes the glutathione (GSH)-coupled electrochemical reduction of arsenate to the more toxic arsenite. Arabidopsis thaliana plants transformed with the arsC gene expressed from a light-induced soybean rubisco promoter (SRS1p) strongly express ArsC protein in leaves, but not roots, and were consequently hypersensitive to arsenate. Arabidopsis plants expressing the E. coli gene encoding gamma-glutamylcysteine synthetase (gamma-ECS) from a strong constitutive actin promoter (ACT2p) were moderately tolerant to arsenic compared with wild type. However, plants expressing SRS1p/ArsC and ACT2p/gamma-ECS together showed substantially greater arsenic tolerance than gamma-ECS or wild-type plants. When grown on arsenic, these plants accumulated 4- to 17-fold greater fresh shoot weight and accumulated 2- to 3-fold more arsenic per gram of tissue than wild type or plants expressing gamma-ECS or ArsC alone. This arsenic remediation strategy should be applicable to a wide variety of plant species.

The potential risks from metal-based nanoparticles (NPs) in the environment have increased with the rapidly rising demand for and use of nanoenabled consumer products. Plant's central roles in ecosystem function and food chain integrity ensure intimate contact with water and soil systems, both of which are considered sinks for NPs accumulation. In this review, we document phytotoxicity caused by metal-based NPs exposure at physiological, biochemical, and molecular levels. Although the exact mechanisms of plant defense against nanotoxicity are unclear, several relevant studies have been recently published. Possible detoxification pathways that might enable plant resistance to oxidative stress and facilitate NPs detoxification are reviewed herein. Given the importance of understanding the effects and implications of metal-based NPs on plants, future research should focus on the following: (1) addressing key knowledge gaps in understanding molecular and biochemical responses of plants to NPs stress through global transcriptome, proteome, and metablome assays; (2) designing long-term experiments under field conditions at realistic exposure concentrations to investigate the impact of metal-based NPs on edible crops and the resulting implications to the food chain and to human health; and (3) establishing an impact assessment to evaluate the effects of metal-based NPs on plants with regard to ecosystem structure and function.

Endogenous plant arsenate reductase (ACR) activity converts arsenate to arsenite in roots, immobilizing arsenic below ground. By blocking this activity, we hoped to construct plants that would mobilize more arsenate aboveground. We have identified a single gene in the Arabidopsis thaliana genome, ACR2, with moderate sequence homology to yeast arsenate reductase. Expression of ACR2 cDNA in Escherichia coli complemented the arsenate-resistant and arsenate-sensitive phenotypes of various bacterial ars operon mutants. RNA interference reduced ACR2 protein expression in Arabidopsis to as low as 2% of wild-type levels. The various knockdown plant lines were more sensitive to high concentrations of arsenate, but not arsenite, than wild type. The knockdown lines accumulated 10-to 16-fold more arsenic in shoots (350 -500 ppm) and retained less arsenic in roots than wild type, when grown on arsenate medium with <8 ppm arsenic. Reducing expression of ACR2 homologs in tree, shrub, and grass species should play a vital role in the phytoremediation of environmental arsenic contamination.Escherichia coli ArsC ͉ drinking water ͉ CDC25 ͉ toxicant ͉ arsenic pollution E nvironmental arsenic pollution is widely recognized as a global health problem (1) (www.epa.gov͞ogwdw͞ars͞arsenic.html). High levels of arsenic in soil and drinking water have been reported around the world, but the situation is worst in India and Bangladesh, where Ͼ400 million people are at risk of arsenic poisoning (2). The World Health Organization predicts that long-term exposure to arsenic could reach epidemic proportions, estimating that 1 in 10 people in the most contaminated areas may ultimately die from diseases related to arsenic poisoning (3). The high financial cost associated with repairing the environmental damage by using physical remediation methods such as excavation and reburial make these technologies unacceptable for cleaning up the vast areas of the planet that need arsenic remediation. As a result, the overwhelming majority of arsenic-contaminated sites are not being cleaned up.Phytoremediation is the use of plants to clean up environmental pollutants and is considered an important alternative to physical methods for cleaning up arsenic (4). Our objective is to develop a genetics-based arsenic phytoremediation strategy that can be used in any plant species. Plants that hyperaccumulate arsenic to high levels aboveground would be harvested and the arsenic further concentrated by incineration. In previous studies, we engineered model plants expressing a bacterial arsenate reductase (ArsC; EC 1.20.4.1) aboveground and constitutively expressing ␥-glutamylcysteine synthetase (5). By reducing arsenate to arsenite in leaves and trapping arsenite in thiol-peptide complexes, these plants accumulate 3-fold more arsenic aboveground than wild type and are also highly tolerant to toxic levels of arsenic. The research described herein extends these observations and attacks a particular problem limiting the engineered phytoremediation of arsenic: its transpor...

Food security and the protection of the environment are urgent issues for global society, particularly with the uncertainties of climate change. Changing climate is predicted to have a wide range of negative impacts on plant physiology metabolism, soil fertility and carbon sequestration, microbial activity and diversity that will limit plant growth and productivity, and ultimately food production. Ensuring global food security and food safety will require an intensive research effort across the food chain, starting with crop production and the nutritional quality of the food products. Much uncertainty remains concerning the resilience of plants, soils, and associated microbes to climate change. Intensive efforts are currently underway to improve crop yields with lower input requirements and enhance the sustainability of yield through improved biotic and abiotic stress tolerance traits. In addition, significant efforts are focused on gaining a better understanding of the root/soil interface and associated microbiomes, as well as enhancing soil properties.

There has been great interest in the use of carbon nano-materials (CNMs) in agriculture. However, the existing literature reveals mixed effects from CNM exposure on plants, ranging from enhanced crop yield to acute cytotoxicity and genetic alteration. These seemingly inconsistent research-outcomes, taken with the current technological limitations for in situ CNM detection, present significant hurdles to the wide scale use of CNMs in agriculture. The objective of this review is to evaluate the current literature, including studies with both positive and negative effects of different CNMs (e.g., carbon nano-tubes, fullerenes, carbon nanoparticles, and carbon nano-horns, among others) on terrestrial plants and associated soil-dwelling microbes. The effects of CNMs on the uptake of various co-contaminants will also be discussed. Last, we highlight critical knowledge gaps, including the need for more soil-based investigations under environmentally relevant conditions. In addition, efforts need to be focused on better understanding of the underlying mechanism of CNM-plant interactions.

In agriculture, loss of crop yield to pathogen damage seriously threatens efforts to achieve global food security. In the present work, “organic” elemental sulfur nanoparticles (SNPs) were investigated for management of the fungal pathogen Fusarium oxysporum f. sp. lycopersici on tomatoes. Foliar application and seed treatment with SNPs (30–100 mg/L, 30 and 100 nm) suppressed pathogen infection in tomatoes, in a concentration- and size-dependent fashion in a greenhouse experiment. Foliar application with 1 mg/plant of 30 nm SNPs (30-SNPs) exhibited the best performance for disease suppression, significantly decreasing disease incidence by 47.6% and increasing tomato shoot biomass by 55.6% after 10 weeks application. Importantly, the disease control efficacy with 30-SNPs was 1.43-fold greater than the commercially available fungicide hymexazol. Mechanistically, 30-SNPs activated the salicylic acid-dependent systemic acquired resistance pathway in tomato shoots and roots, with subsequent upregulation of the expression of pathogenesis-related and antioxidase-related genes (upregulated by 11–352%) and enhancement of the activity and content of disease-related biomolecules (enhanced by 5–49%). In addition, transmission electron microscopy imaging shows that SNPs were distributed in the tomato stem and directly inactivated in vivo pathogens. The oxidative stress in tomato shoots and roots, the root plasma membrane damage, and the growth of the pathogen in stem were all significantly decreased by SNPs. The findings highlight the significant potential of SNPs as an eco-friendly and sustainable crop protection strategy.

Global mechanization, urbanization, and various natural processes have led to the increased release of toxic compounds into the biosphere. These hazardous toxic pollutants include a variety of organic and inorganic compounds, which pose a serious threat to the ecosystem. The contamination of soil and water are the major environmental concerns in the present scenario. This leads to a greater need for remediation of contaminated soils and water with suitable approaches and mechanisms. The conventional remediation of contaminated sites commonly involves the physical removal of contaminants, and their disposition. Physical remediation strategies are expensive, non-specific and often make the soil unsuitable for agriculture and other uses by disturbing the microenvironment. Owing to these concerns, there has been increased interest in eco-friendly and sustainable approaches such as bioremediation, phytoremediation and rhizoremediation for the cleanup of contaminated sites. This review lays particular emphasis on biotechnological approaches and strategies for heavy metal and metalloid containment removal from the environment, highlighting the advances and implications of bioremediation and phytoremediation as well as their utilization in cleaning-up toxic pollutants from contaminated environments.

The effects of cerium oxide (CeO 2 ) and indium oxide (In 2 O 3 ) nanoparticles (NPs) exposure on Arabidopsis thaliana (L.) Heynh. were investigated. After inoculation in half strength MS medium amended with 0−2000 ppm CeO 2 and In 2 O 3 NPs for 25 days, both physiological and molecular responses were evaluated. Exposure at 250 ppm CeO 2 NPs significantly increased plant biomass, but at 500−2000 ppm, plant growth was decreased by up to 85% in a dose-dependent fashion. At 1000 and 2000 ppm CeO 2 NPs, chlorophyll production was reduced by nearly 60% and 85%, respectively, and anthocyanin production was increased 3−5-fold. Malondialdehyde (MDA) production, a measure of lipid peroxidation, was unaffected by exposure to 250−500 ppm CeO 2 NPs, but at 1000 ppm, MDA formation was increased by 2.5-fold. Exposure to 25−2000 ppm In 2 O 3 NPs had no effect on A. thaliana biomass and only minor effects (15%) on root elongation. Total chlorophyll and MDA production were unaffected by In 2 O 3 NPs exposure. Molecular response to NP exposure as measured by qPCR showed that both types of elements altered the expression of genes central to the stress response such as the sulfur assimilation and glutathione (GSH) biosynthesis pathway, a series of genes known to be significant in the detoxification of metal toxicity in plants. Interestingly, In 2 O 3 NPs exposure resulted in a 3.8−4.6-fold increase in glutathione synthase (GS) transcript production, whereas CeO 2 NPs yielded only a 2-fold increase. It seems likely that the significantly greater gene regulation response upon In 2 O 3 NPs exposure was directly related to the decreased phytotoxicity relative to CeO 2 treatment. The use of NP rare earth oxide elements has increased dramatically, yet knowledge on fate and toxicity has lagged behind. To our knowledge, this is the first report evaluating both physiological and molecular plant response from exposure to these important nanoparticles. KEYWORDS: Arabidopsis thaliana, CeO 2 and In 2 O 3 NPs, Stress response, Gene expression, Anthocyanin, Lipid peroxidation, Sulfur assimilation pathway coli, Bacillus subtilis, and Pseudomonas f luorescens), 5,6 plants (Cucurbita pepo L., Solanum lycopersicum L., and Zea mays L.) 7−9 and animals (Zebrafish: Danio rerio). 10,11 Moreover, the potential hazards of nanoparticles to human health have been discussed in assays using human cells. 4,12 Given these findings, it is clear that a full and mechanistic understanding of the risks Special Issue: Sustainable Nanotechnology