Abstract
Phytoremediation is a promising means of ameliorating heavy metal pollution through the use of transgenic plants as artificial hyperaccumulators. A novel Streptococcus thermophilus γ-glutamylcysteine synthetase-glutathione synthetase (StGCS-GS) that synthesizes glutathione (GSH) with limited feedback inhibition was overexpressed in sugar beet (Beta vulgaris L.), yielding three transgenic lines (s2, s4 and s5) with enhanced tolerance to different concentrations of cadmium, zinc and copper, as indicated by their increased biomass, root length and relative growth compared with wild-type plants. Transgenic sugar beets accumulated more Cd, Zn and Cu ions in shoots than wild-type, as well as higher GSH and phytochelatin (PC) levels under different heavy metal stresses. This enhanced heavy metal tolerance and increased accumulation were likely due to the increased expression of StGCS-GS and consequent overproduction of both GSH and PC. Furthermore, when multiple heavy metal ions were present at the same time, transgenic sugar beets overexpressing StGCS-GS resisted two or three of the metal combinations (50 μM Cd-Zn, Cd-Cu, Zn-Cu and Cd-Zn-Cu), with greater absorption in shoots. Additionally, there was no obvious competition between metals. Overall, the results demonstrate the explicit role of StGCS-GS in enhancing Cd, Zn and Cu tolerance and accumulation in transgenic sugar beet, which may represent a highly promising new tool for phytoremediation.
Highlights
Cadmium, zinc and copper ions are toxic at certain concentrations and can pose threats to plants and the environment
Overexpressing GSH1 and AsPCS1 increased the tolerance to and accumulation of cadmium and arsenic in Arabidopsis thaliana, while at the same time, the GSH and PC contents increased [13]. These findings suggest that the increased demand for GSH is an essential component of plant tolerance to and accumulation of various heavy metals, and they provide support for the development of transgenic plants overexpressing genes involved in GSH synthesis, which exhibit increased heavy metal resistance and uptake, for phytoremediation purposes
Transgenic sugar beet seedlings overexpressing StGCS-GS were generated by introducing the StGCS-GS cassette from pGWB2-StGCS-GS
Summary
Zinc and copper ions are toxic at certain concentrations and can pose threats to plants and the environment. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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