Abstract
Phytochelatins (PCs) catalyzed by phytochelatin synthases (PCS) are important for the detoxification of metals in plants and other living organisms. In this study, we isolated a PCS gene (VsPCS1) from Vicia sativa and investigated its role in regulating cadmium (Cd) tolerance. Expression of VsPCS1 was induced in roots of V. sativa under Cd stress. Analysis of subcellular localization showed that VsPCS1 was localized in the cytoplasm of mesophyll protoplasts of V. sativa. Overexpression of VsPCS1 (35S::VsPCS1, in wild-type background) in Arabidopsis thaliana could complement the defects of Cd tolerance of AtPCS1-deficent mutant (atpcs1). Compared with atpcs1 mutants, 35S::VsPCS1/atpcs1 (in AtPCS1-deficent mutant background) transgenic plants significantly lowered Cd-fluorescence intensity in mesophyll cytoplasm, accompanied with enhanced Cd-fluorescence intensity in the vacuoles, demonstrating that the increased Cd tolerance may be attributed to the increased PC-based sequestration of Cd into the vacuole. Furthermore, overexpressing VsPCS1 could enhance the Cd tolerance in 35S::VsPCS1, but have no effect on Cd accumulation and distribution, showing the same level of Cd-fluorescence intensity between 35S::VsPCS1 and wild-type (WT) plants. Further analysis indicated this increased tolerance in 35S::VsPCS1 was possibly due to the increased PCs-chelated Cd in cytosol. Taken together, a functional PCS1 homolog from V. sativa was identified, which hold a strong catalyzed property for the synthesis of high-order PCs that retained Cd in the cytosol rather the vacuole. These findings enrich the original model of Cd detoxification mediated by PCS in higher plants.
Highlights
Heavy metal contamination is a predominant environmental issue in the world
Seven Cys residues are conserved in plant kingdom, and one Cys specific residue is in VsPCS1 (Supplementary Figure 1)
25 and 50 μM Cd, 35S::VsPCS1 (#2 and #5) had a longer root length and more fresh weight than WT (Figures 4B,C). These results demonstrate that overexpression of VsPCS1 increase Cd tolerance in 35S::VsPCS1
Summary
Cadmium (Cd) is one of highly toxic metals for all organisms and is of particular concern to human health since Cd can readily uptake by plant roots from polluted soils and transported to shoots (Wagner, 1993). This element enters the environment mainly through mining operations, smelting of metals, electroplating, municipal wastes, and phosphate fertilizers. PC is a family of peptides with the general structure (Glu-Cys)n-Gly, where n is in the range of 2–11 (Cobbett and Goldsbrough, 2002) They form stable metal complexes and are subsequently sequestrate from the cytosol into vacuoles. Some studies showed that increased PCs production is not the primary tolerance mechanism to Cd (De Knecht et al, 1992; Wójcik et al, 2015), indicating a complicated mechanism underlying the PCs involved Cd tolerance
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