Sulfur-responsive promoter of sulfate transporter gene is potentially useful to detect and quantify selenate and chromate

Abstract

Heavy metals are highly toxic for living organisms when excess amounts exist in the environment (Salt et al. 1998;Kovalchuk et al. 2001). Soils and water contaminated with heavy metals cause major environmental and human health problems. During the last few decades, phytoremediation and plant-based assays for cleanup and monitoring of these contaminated environments have been developed (Salt et al. 1998;Kovalchuk et al. 2001;Krizek et al. 2003;Pilon-Smits 2005). These methods take advantage of the sedentary nature of plants, providing inexpensive and nontechnical means of environmental analysis and restoration (Kovalchuk et al. 2001;Krizek et al. 2003).Among heavy metals, selenium and chromium function as toxic analogs of sulfur, and they exist in nature mainly as selenate (SeO 4 2Ϫ) and chromate (CrO 4 2Ϫ ) anions at ϩ6 oxidation states. Because of their structural similarities to sulfate (SO 4 2Ϫ ), selenate and chromate are readily imported into plant cells through the activities of sulfate transporters. In fact, selenate competitively inhibits the influx of sulfate, and after incorporation into the cells, it is subsequently assimilated into selenocysteine and seleno-methionine by sharing the pathways of sulfur metabolism; ultimately, these seleniumcontaining amino acids are incorporated into proteins (Terry et al. 2000;Ellis and Salt 2003). Chromate also has an inhibitory effect on sulfate uptake, but is mainly reduced to ϩ3 oxidation states, Cr 3ϩ or Cr 2 O 3 , presumably by using reducing cofactors. Accordingly, excess amounts of selenate and chromate taken up from the environment can affect the cellular function of living organisms and sometimes have lethal effects. Indeed, several mutants lacking sulfate transporter genes have been isolated from yeast and plants by using the toxic effects of selenate and chromate as sulfate analogs (Smith et al. 1995a, b;Cherest et al. 1997;Shibagaki et al. 2002).In Arabidopsis, two high-affinity sulfate transporters, SULTR1;1 and SULTR1;2, facilitate the initial uptake of sulfate into the roots (Takahashi et al. 2000;Vidmar et al. 2000;Shibagaki et al. 2002; Yoshimoto et al. 2002). These transporters are expressed in the epidermis and cortex of roots, and their transcripts can accumulate through sulfur depletion to maximize sulfate uptake for efficiently using limited amounts of sulfur in the soil environment (Takahashi et al. 2000;Vidmar et al. 2000;Shibagaki et al. 2002; Yoshimoto et al. 2002). The expression of these SULTRs depends on the promoter activities of their 5Ј-regions controlled by sulfur deficiency (Maruyama-Nakashita et al. 2004a, b, 2005. The presence of a specific sulfur-responsive cis-element in the SULTR1;1 promoter region further elaborates the Abstract Plant-based assays for monitoring contaminated environments provide inexpensive and nontechnical means of environmental analysis. Here we report a model system for monitoring selenium and chromium, which are highly toxic heavy metals for living organisms. The major forms of selenium and chromium ...

Combinatorial use of sulfur-responsive regions of sulfate transporters provides a highly sensitive plant-based system for detecting selenate and chromate in the environment

“…3). It is possible that chromate affects plant viability more severely than selenate does, causing a distortion in the expression of the GFP reporter gene in transgenic plants at relatively high concentrations, as also suggested in previous studies (Maruyama-Nakashita et al 2007;Schiavon et al 2007).…”

“…P SULTR1;2 -GFP transgenic plants express GFP under the control of SULTR1;2 promoter, and GFP is accumulated in association with the increasing levels of SULTR1;2 mRNA (Maruyama-Nakashita et al 2004). Selenate and chromate can be detected by measuring GFP accumulation in P SULTR1;2 -GFP plants at concentrations of 10 μmol L −1 or higher, while selenate concentration can be roughly measured in a range of 1-30 μmol L −1 , enabling the estimation of external selenate concentration (Maruyama-Nakashita et al 2007). However, the detection limit of 10 μmol L −1 is 10 times higher than the environmental standard recommended by the World Health Organization (WHO 2011).…”

Transcriptome profiling of genes differentially modulated by sulfur and chromium identifies potential targets for phytoremediation and reveals a complex S–Cr interplay on sulfate transport regulation in B. juncea

“…Therefore, higher plants likely do not possess specific mechanisms to acquire this element [6]. Studies concerning the uptake of Cr from soil by different plant species have shown that Cr(III) is taken up passively, while Cr(VI) transport over plasma membranes is active and seems to be mediated by transporters of essential anions, such as sulfate [7][8][9][10][11][12][13].…”