Overexpression of a Novel Arabidopsis Gene Related to Putative Zinc-Transporter Genes from Animals Can Lead to Enhanced Zinc Resistance and Accumulation

Abstract

We describe the isolation of an Arabidopsis gene that is closely related to the animal ZnT genes (Zn transporter)Several heavy metals are essential during plant growth and development, but their excess can easily lead to toxic effects. Contamination of soils with heavy metals, either by natural causes or due to pollution, often has pronounced effects on the vegetation, resulting in the appearance of metallophytes, heavy-metal-tolerant plants. The precise mechanisms of uptake, transport, and accumulation of heavy metals in plants are poorly understood, but several genes likely to be involved in these processes have been described. Recently, a family of ZIP genes that are expressed in roots upon Zn deficiency was isolated from Arabidopsis (Grotz et al., 1998). The proteins encoded by the ZIP genes have eight predicted TM regions and a high degree of similarity to the ZRT genes from yeast that are involved in Zn uptake. Expression of the ZIP genes in yeast conferred Zn-uptake activities to these cells, demonstrating that they are probably functional homologs of the yeast ZRT genes (Grotz et al., 1998). The only other metaltransporting protein recently identified in plants belongs to the large family of cation-transporting P-type ATPases (Tabata et al., 1997), but these proteins are structurally very different from the metal-transporting proteins mentioned above.Recent data have provided more insight into the mechanisms of heavy-metal tolerance. Metallophytes often exhibit tolerance to several different heavy metals, but all of these metals need not be present at toxic levels in their habitat (Schat and ten Bookum, 1992a; Schat and Vooijs, 1997, and refs. therein;Schat and Verkleij, 1998). Although such a feature is suggestive of a general mechanism of heavy-metal tolerance, recent genetic evidence has shown that a number of different mechanisms must exist, each with its own metal specificity (Schat and Vooijs, 1997). In Arabidopsis, a plant species with a typical level of tolerance to heavy metals, it has been demonstrated that the Cd-sensitive mutants cad1 and cad2 are defective in the synthesis of the metal-binding compound phytochelatin (Howden et al., 1995). cad1 plants were only slightly more sensitive to Cu and Zn, indicating that phytochelatinmediated detoxification is not sufficient for Cu and Zn detoxification (Howden et al., 1995b). Metallothioneins appear to be of major importance for constitutive Cu tolerance in Arabidopsis (Zhou and Goldsbrough, 1994).Aside from complexation of heavy metals by heavymetal-binding proteins, there is evidence that transportmediated sequestration can contribute to heavy-metal tolerance. In the Zn-tolerant plant Silene vulgaris it was shown that Zn transport across the tonoplast was about 2.5 times higher than in Zn-sensitive plants of the same species (Verkleij et al

Common Functions or Only Phylogenetically Related? The Large Family of PLAC8 Motif-Containing/PCR Genes

“…CAXs and some MTP transporters catalyze the transport of heavy metals across the vacuolar membrane and are essential for vacuolar sequestration. Increasing the expression of the tonoplast-localized MTP1 can enhance Zn resistance (Blaudez et al, 2003;Gustin et al, 2009;van der Zaal et al, 1999). In yeast, ATP-binding cassette (ABC) transporters sequester heavy metals into vacuoles.…”

Quantitative detection of changes in the leaf‐mesophyll tonoplast proteome in dependency of a cadmium exposure of barley (Hordeum vulgare L.) plants

“…A detoxification strategy commonly found is the production of chelating compounds containing thiols, such as small proteins called metallothioneins [4], or peptides like glutathione and phytochelatins which strongly interact with Cd 2+ , reducing free Cd 2+ within the cytosol and hence limiting Cd 2+ toxicity [5][6][7]. In addition, several types of transport systems have been shown to contribute to heavy metal resistance, including P-type ATPases, ABC transporters or secondary energized heavy metal transporters [8][9][10]. They transport either free or conjugated heavy metals across biological membranes extruding them from the cytosol.…”

“…Indeed, Fe 2+ importers as well 4 as exporters have been identified. For Zn 2+ only the importer, MTP1, has been described [8,12,13]. It is interesting to note that Arabidopsis halleri, a typical Zn hyperaccumulator, has a constitutive high expression of a MTP1 homologue [14].…”

Elevated expression of metal transporter genes in three accessions of the metal hyperaccumulator Thlaspi caerulescens

“…The ZAT cDNA was isolated from Arabidopsis (Van der Zaal et al 1999) and is homologous to the mammalian Zn transporter genes ZnT2 (Palmiter, Cole & Findley 1996) and ZnT3 , which are involved in Zn vesicular sequestration, and ZnT4 (Huang & Gitschier 1997), which is involved in Zn transport into milk. Transgenic Arabidopsis which overexpressed the ZAT gene exhibited enhanced Zn resistance and an increased Zn content in roots under high Zn exposure suggesting that the ZAT protein is involved in the plant-internal compartmentation of this metal (Van der Zaal et al 1999).…”