The OsNRAMP1 iron transporter is involved in Cd accumulation in rice
TL;DR: The results suggest that OsNRAMP1 participates in cellular Cd uptake and Cd transport within plants, and the higher expression of Os NRAMP1 in the roots could lead to an increase in Cd accumulation in the shoots.
Abstract: Cadmium (Cd) is a heavy metal toxic to humans and the accumulation of Cd in the rice grain is a major agricultural problem, particularly in Asia. The role of the iron transporter OsNRAMP1 in Cd uptake and transport in rice was investigated here. An OsNRAMP1:GFP fusion protein was localized to the plasma membrane in onion epidermal cells. The growth of yeast expressing OsNRAMP1 was impaired in the presence of Cd compared with yeast transformed with an empty vector. Moreover, the Cd content of OsNRAMP1-expressing yeast exceeded that of the vector control. The expression of OsNRAMP1 in the roots was higher in a high Cd-accumulating cultivar (Habataki) than a low Cd-accumulating cultivar (Sasanishiki) regardless of the presence of Cd, and the amino acid sequence of OsNRAMP1 showed 100% identity between Sasanishiki and Habataki. Over-expression of OsNRAMP1 in rice increased Cd accumulation in the leaves. These results suggest that OsNRAMP1 participates in cellular Cd uptake and Cd transport within plants, and the higher expression of OsNRAMP1 in the roots could lead to an increase in Cd accumulation in the shoots. Our results indicated that OsNRAMP1 is an important protein in high-level Cd accumulation in rice.
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TL;DR: Key molecular components-including transporters, enzymes, and chelators-have been clarified for both strategies of reduction and chelation, and many of these components are now thought to also function inside the plant to facilitate internal iron transport.
Abstract: Iron is essential for the survival and proliferation of all plants. Higher plants have developed two distinct strategies to acquire iron, which is only slightly soluble, from the rhizosphere: the reduction strategy of nongraminaceous plants and the chelation strategy of graminaceous plants. Key molecular components—including transporters, enzymes, and chelators—have been clarified for both strategies, and many of these components are now thought to also function inside the plant to facilitate internal iron transport. Transporters for intracellular iron trafficking are also being clarified. A majority of genes encoding these components are transcriptionally regulated in response to iron availability. Recent research has uncovered central transcription factors, cis-acting elements, and molecular mechanisms regulating these genes. Manipulation of these molecular components has produced transgenic crops with enhanced tolerance to iron deficiency or with increased iron content in the edible parts.
907 citations
Cites background from "The OsNRAMP1 iron transporter is in..."
...IRT transporters generally localize to the plasma membrane, whereas NRAMP transporters localize to either intracellular vesicles or the plasma membrane depending on the species of the protein (8, 58, 126, 130)....
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TL;DR: In this article, a member of the Nramp (for the Natural Resistance-associated Macrophage Protein) family (Nramp5) was found to be involved in Mn uptake and subsequently the accumulation of high concentrations of Mn in rice.
Abstract: Paddy rice (Oryza sativa) is able to accumulate high concentrations of Mn without showing toxicity; however, the molecular mechanisms underlying Mn uptake are unknown. Here, we report that a member of the Nramp (for the Natural Resistance-Associated Macrophage Protein) family, Nramp5, is involved in Mn uptake and subsequently the accumulation of high concentrations of Mn in rice. Nramp5 was constitutively expressed in the roots and encodes a plasma membrane–localized protein. Nramp5 was polarly localized at the distal side of both exodermis and endodermis cells. Knockout of Nramp5 resulted in a significant reduction in growth and grain yield, especially when grown at low Mn concentrations. This growth reduction could be partially rescued by supplying high concentrations of Mn but not by the addition of Fe. Mineral analysis showed that the concentration of Mn and Cd in both the roots and shoots was lower in the knockout line than in wild-type rice. A short-term uptake experiment revealed that the knockout line lost the ability to take up Mn and Cd. Taken together, Nramp5 is a major transporter of Mn and Cd and is responsible for the transport of Mn and Cd from the external solution to root cells.
829 citations
Cites background from "The OsNRAMP1 iron transporter is in..."
...Nramp1 showed transport activity for Fe and Cd in yeast but not Mn (Curie et al., 2000; Takahashi et al., 2011)....
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...The expression of this gene was also low in the presence of Fe, but greatly induced by Fe deficiency (Takahashi et al., 2011)....
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...Overexpression of Nramp1 resulted in a slight increase in Cd in the leaves (Takahashi et al., 2011)....
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...Recently, a homolog of Os Nramp5, Os Nramp1, was reported to be involved in Cd uptake (Takahashi et al., 2011), based on a slight increase in Cd in the shoot of the Os Nramp1–overexpressing line....
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TL;DR: Recent studies on rice (Oryza sativa) and Cd-hyperaccumulating plants that have led to important insights into the processes controlling the passage of Cd from the soil to edible plant organs are reviewed.
775 citations
TL;DR: Proteins mediating the uptake of arsenic and cadmium have been identified, and the speciation and biotransformations of arsenic are now understood, and factors controlling the efficiency of root-to-shoot translocation and the partitioning of toxic elements through the rice node have also been identified.
Abstract: Arsenic, cadmium, lead, and mercury are toxic elements that are almost ubiquitously present at low levels in the environment because of anthropogenic influences. Dietary intake of plant-derived food represents a major fraction of potentially health-threatening human exposure, especially to arsenic and cadmium. In the interest of better food safety, it is important to reduce toxic element accumulation in crops. A molecular understanding of the pathways responsible for this accumulation can enable the development of crop varieties with strongly reduced concentrations of toxic elements in their edible parts. Such understanding is rapidly progressing for arsenic and cadmium but is in its infancy for lead and mercury. Basic discoveries have been made in Arabidopsis, rice, and other models, and most advances in crops have been made in rice. Proteins mediating the uptake of arsenic and cadmium have been identified, and the speciation and biotransformations of arsenic are now understood. Factors controlling the efficiency of root-to-shoot translocation and the partitioning of toxic elements through the rice node have also been identified.
745 citations
Cites background from "The OsNRAMP1 iron transporter is in..."
...(118) reported similar but much less pronounced effects in rice plants overexpressing OsNramp1....
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TL;DR: To eliminate the long-term risk of Cd entering the food chain, soils contaminated by Cd should be cleaned up when cost-effective remediation measures are available.
491 citations
References
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TL;DR: The GATEWAY conversion technology has provided a fast and reliable alternative to the cloning of sequences into large acceptor plasmids for transformation of a wide range of plant species.
3,473 citations
"The OsNRAMP1 iron transporter is in..." refers methods in this paper
...The OsNRAMP1 ORF without the stop codon was cloned into the plant transient expression vector pH7FWG2 (Karimi et al., 2002) using the Gateway system (Invitrogen) to generate a fusion construct with green fluorescent protein (GFP) as an additional Cterminal domain under the control of the CaMV 35S promoter....
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...The OsNRAMP1 ORF without the stop codon was cloned into the plant transient expression vector pH7FWG2 (Karimi et al., 2002) using the Gateway system (Invitrogen) to generate a fusion construct with green fluorescent protein (GFP) as an additional Cterminal domain under the control of the CaMV 35S…...
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TL;DR: This work focuses on recent progress in transcriptional, post-transcriptional and post- translational regulation of gene expression that is critical for cold acclimation in temperate plants.
1,569 citations
"The OsNRAMP1 iron transporter is in..." refers background in this paper
...Some MYB proteins act as negative regulators of gene expression (Chinnusamy et al., 2007; Matsui et al., 2008), and some MYB genes have been reported to be responsive to Cd (Chen et al., 2006)....
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...Some MYB proteins act as negative regulators of gene expression (Chinnusamy et al., 2007; Matsui et al., 2008), and some MYB genes have been reported to be responsive to Cd (Chen et al....
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TL;DR: This analysis indicated that the expression for most of the Arabidopsis MYB genes were responsive to one or multiple types of hormone and stress treatments, and may help elucidate the possible biological roles of the MyB genes in various aspects of flowering plants.
Abstract: MYB proteins are a superfamily of transcription factors that play regulatory roles in developmental processes and defense responses in plants. We identified 198 genes in the MYB superfamily from an analysis of the complete Arabidopsis genome sequence, among them, 126 are R2R3-MYB, 5 are R1R2R3-MYB, 64 are MYB-related, and 3 atypical MYB genes. Here we report the expression profiles of 163 genes in the Arabidopsis MYB superfamily whose full-length open reading frames have been isolated. This analysis indicated that the expression for most of the Arabidopsis MYB genes were responsive to one or multiple types of hormone and stress treatments. A phylogenetic comparison of the members of this superfamily in Arabidopsis and rice suggested that the Arabidopsis MYB superfamily underwent a rapid expansion after its divergence from monocots but before its divergence from other dicots. It is likely that the MYB-related family was more ancient than the R2R3-MYB gene family, or had evolved more rapidly. Therefore, the MYB gene superfamily represents an excellent system for investigating the evolution of large and complex gene families in higher plants. Our comprehensive analysis of this largest transcription factor superfamily of Arabidopsis and rice may help elucidate the possible biological roles of the MYB genes in various aspects of flowering plants.
856 citations
"The OsNRAMP1 iron transporter is in..." refers background in this paper
...Some MYB proteins act as negative regulators of gene expression (Chinnusamy et al., 2007; Matsui et al., 2008), and some MYB genes have been reported to be responsive to Cd (Chen et al., 2006)....
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..., 2008), and some MYB genes have been reported to be responsive to Cd (Chen et al., 2006)....
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TL;DR: The results show that Nramp genes in plants encode metal transporters and that AtNramps transport both the metal nutrient Fe and the toxic metal cadmium.
Abstract: Metal cation homeostasis is essential for plant nutrition and resistance to toxic heavy metals. Many plant metal transporters remain to be identified at the molecular level. In the present study, we have isolated AtNramp cDNAs from Arabidopsis and show that these genes complement the phenotype of a metal uptake deficient yeast strain, smf1. AtNramps show homology to the Nramp gene family in bacteria, yeast, plants, and animals. Expression of AtNramp cDNAs increases Cd2+ sensitivity and Cd2+ accumulation in yeast. Furthermore, AtNramp3 and AtNramp4 complement an iron uptake mutant in yeast. This suggests possible roles in iron transport in plants and reveals heterogeneity in the functional properties of Nramp transporters. In Arabidopsis, AtNramps are expressed in both roots and aerial parts under metal replete conditions. Interestingly, AtNramp3 and AtNramp4 are induced by iron starvation. Disruption of the AtNramp3 gene leads to slightly enhanced cadmium resistance of root growth. Furthermore, overexpression of AtNramp3 results in cadmium hypersensitivity of Arabidopsis root growth and increased accumulation of Fe, on Cd2+ treatment. Our results show that Nramp genes in plants encode metal transporters and that AtNramps transport both the metal nutrient Fe and the toxic metal cadmium.
833 citations
"The OsNRAMP1 iron transporter is in..." refers background in this paper
...AtNRAMP3 and AtNRAMP4 are also induced by Fe starvation and mobilize vacuolar Fe (Thomine et al., 2000, 2003; Lanquar et al., 2005)....
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...Yeast expressing AtNRAMP1, AtNRAMP3, AtNRAMP4, and AtNRAMP6 showed increased sensitivity to Cd, and the over-expression of AtNRAMP3, AtNRAMP4, and At NRAMP6 in Arabidopsis conferred hypersensitivity to Cd (Thomine et al., 2000; Lanquar et al., 2004; Cailliatte et al., 2009)....
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TL;DR: The results suggest that the expression of IRT1 is controlled by two distinct mechanisms that provide an effective means of regulating metal transport in response to changing environmental conditions.
Abstract: Iron, an essential nutrient, is not readily available to plants because of its low solubility. In addition, iron is toxic in excess, catalyzing the formation of hydroxyl radicals that can damage cellular constituents. Consequently, plants must carefully regulate iron uptake so that iron homeostasis is maintained. The Arabidopsis IRT1 gene is the major transporter responsible for high-affinity iron uptake from the soil. Here, we show that the steady state level of IRT1 mRNA was induced within 24 h after transfer of plants to iron-deficient conditions, with protein levels peaking 72 h after transfer. IRT1 mRNA and protein were undetectable 12 h after plants were shifted back to iron-sufficient conditions. Overexpression of IRT1 did not confer dominant gain-of-function enhancement of metal uptake. Analysis of 35S-IRT1 transgenic plants revealed that although IRT1 mRNA was expressed constitutively in these plants, IRT1 protein was present only in the roots when iron is limiting. Under these conditions, plants that overexpressed IRT1 accumulated higher levels of cadmium and zinc than wild-type plants, indicating that IRT1 is responsible for the uptake of these metals and that IRT1 protein levels are indeed increased in these plants. Our results suggest that the expression of IRT1 is controlled by two distinct mechanisms that provide an effective means of regulating metal transport in response to changing environmental conditions.
692 citations
"The OsNRAMP1 iron transporter is in..." refers background in this paper
...Arabidopsis over-expressing AtIRT1 and AtIRT2 also showed increased Cd accumulation (Connolly et al., 2002; Vert et al., 2009)....
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