Metallothionein 2 (SaMT2) from Sedum alfredii Hance confers increased Cd tolerance and accumulation in yeast and tobacco.

Jie Zhang,Min Zhang,Xiaoe Yang,M J I Shohag,Shengke Tian,Lingli Lu,Wagner L Araujo

doi:10.1371/journal.pone.0102750

Abstract

Metallothioneins are cysteine-rich metal-binding proteins. In the present study, SaMT2, a type 2 metallothionein gene, was isolated from Cd/Zn co-hyperaccumulator Sedum alfredii Hance. SaMT2 encodes a putative peptide of 79 amino acid residues including two cysteine-rich domains. The transcript level of SaMT2 was higher in shoots than in roots of S. alfredii, and was significantly induced by Cd and Zn treatments. Yeast expression assay showed SaMT2 significantly enhanced Cd tolerance and accumulation in yeast. Ectopic expression of SaMT2 in tobacco enhanced Cd and Zn tolerance and accumulation in both shoots and roots of the transgenic plants. The transgenic plants had higher antioxidant enzyme activities and accumulated less H2O2 than wild-type plants under Cd and Zn treatment. Thus, SaMT2 could significantly enhance Cd and Zn tolerance and accumulation in transgenic tobacco plants by chelating metals and improving antioxidant system.

Highlights

Heavy metals are known to cause toxic effects and inhibition of plant growth
Metallothioneins (MTs) are cysteine-rich proteins involved in metal tolerance of diverse living organisms
The MT gene cloned from S. alfredii encoded a protein with two Cys-rich regions, showing high identity with the N- and Cterminal regions of type 2 MTs of other plants; this MT gene was named as SaMT2

Summary

Introduction

Heavy metals are known to cause toxic effects and inhibition of plant growth. Rare plant species, which can accumulate and tolerate extremely high concentrations of heavy metals in their shoots without toxicity effects, have been defined as ‘‘hyperaccumulators’’ [1]. Higher plants have evolved various defense mechanisms to detoxify excess metals. These mechanisms contain compartmentalization in inactive tissues, chelation by metal ligands and detoxification by antioxidants [5]. Metal chelators such as organic acids, amino acids, phytochelatins and metallothioneins play important roles in metal detoxification [6]. There are some evidence indicating that plant MTs are involved in metal homeostasis, detoxification and reactive oxygen species (ROS) scavenging [8,9,10,11]

Methods

Results

Conclusion