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Type 1 Metallothionein (ZjMT) Is Responsible for Heavy Metal Tolerance in Ziziphus jujuba

Lan-Song Li1,2, Yu-Ping Meng2, Qiu-Fen Cao2,3*, Yong-Zhen Yang3, Fan Wang2, Hu-Sheng Jia3, Shu-Biao Wu2,4*, and Xu-Guang Liu1,3*

1College of Chemistry and Chemical Engineering, Taiyuan University of Technology, 030024 Taiyuan, China; fax: +86-351-6014138; E-mail: liuxuguang@tyut.edu.cn

2Biotechnology Research Center, Shanxi Academy of Agricultural Sciences, 030031 Taiyuan, China; fax: +86-354-6215341; E-mail: qiufengcao@163.com

3Taiyuan University of Technology, Key Laboratory of Interface Science and Engineering in Advanced Materials, Ministry of Education, 030024 Taiyuan, China

4University of New England, School of Environmental and Rural Science, NSW 2351 Armidale, Australia; fax: +61-2-6773-3922; E-mail: shubiao.wu@une.edu.au

* To whom correspondence should be addressed.

Received November 16, 2015; Revision received February 3, 2016
Metallothioneins (MTs) are a family of low molecular weight, cysteine-rich, metal-binding proteins that are able to make cells to uptake heavy metals from the environment. Molecular and functional characterization of this gene family improves understanding of the mechanisms underlying heavy metal tolerance in higher organisms. In this study, a cDNA clone, encoding 74-a.a. metallothionein type 1 protein (ZjMT), was isolated from the cDNA library of Ziziphus jujuba. At the N- and C-terminals of the deduced amino acid sequence of ZjMT, six cysteine residues were arranged in a CXCXXXCXCXXXCXC and CXCXXXCXCXXCXC structure, respectively, indicating that ZjMT is a type 1 MT. Quantitative PCR analysis of plants subjected to cadmium stress showed enhanced expression of ZjMT gene in Z. jujuba within 24 h upon Cd exposure. Escherichia coli cells expressing ZjMT exhibited enhanced metal tolerance and higher accumulation of metal ions compared with control cells. The results indicate that ZjMT contributes to the detoxification of metal ions and provides marked tolerance against metal stresses. Therefore, ZjMT may be a potential candidate for tolerance enhancement in vulnerable plants to heavy metal stress and E. coli cells containing the ZjMT gene may be applied to adsorb heavy metals in polluted wastewater.
KEY WORDS: Z. jujuba Mill., metallothionein, heavy metal tolerance, heavy metal hyperaccumulation

DOI: 10.1134/S000629791606002X