Type 1 metallothionein (ZjMT) is responsible for heavy metal tolerance in Ziziphus jujuba

Abstract

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.

Phytoremediation of Cadmium: Physiological, Biochemical, and Molecular Mechanisms

“…However, the role of different types of MTs as metal chelators has been identified, which can lead to the tolerance and accumulation of heavy metals in plants [238]. MTs have a great tendency to bind to heavy metals containing Cd, Zn, Cu, and As, and can eliminate them even at a low amount; nevertheless, in terms of the importance as a Cd chelator, MT is considered after PCs [242]. Generally, MTs play multiple roles in plants, such as tolerance and maintenance of the cellular ion balance by detoxification of heavy metals, ROS scavenging, damaged DNA repair, and as well as various physiological processes, including seed germination and fruit ripening in plants [240,243].…”

“…It has been established that MT2, in Coptis japonica, has 14 Cys-residues in its C-and N-terminal that can bind to four Cd(II) ions [239]. Li et al [242], proved that in Ziziphus jujuba 24 h after Cd exposure, ZjMTs levels elevated and caused increased Cd tolerance and detoxification. This MTs also has six Cys residues in the C-and N-terminal structure and belongs to the MT-Type1 group [242].…”

“…Li et al [242], proved that in Ziziphus jujuba 24 h after Cd exposure, ZjMTs levels elevated and caused increased Cd tolerance and detoxification. This MTs also has six Cys residues in the C-and N-terminal structure and belongs to the MT-Type1 group [242]. It was found that the expression of a gene of CsMTL2 screened from cucumber fruit was regulated by induction of metal stress, especially Cd in the transformed cells of Escherichia.…”

Cloning and functional characterization of a novel metallothionein gene in Antarctic sea‐ice yeast (Rhodotorula mucilaginosa)

“…In this study, the bioaccumulation properties of RmMT were assessed using transformed E. coli BL21, and the results indicated that the recombinant protein RmMT could chelate multiple heavy metals in the following order of preference: Cu 2+ > Pb 2+ > Zn 2+ > Cd 2+ > Ag + (Figure ). It was observed that ZjMT gene from plant Ziziphus jujube displayed higher bioaccumulation ability of essential and nonessential metal ions compared with control cells in E. coli . These results prove that the functional contribution of MTs to metal detoxification and homeostasis was most likely through their ability to bind different metal ions .…”

“…Many studies have reported that MT genes could enhance metal accumulation capacity in different organisms . Zhang et al transferred SaMT2 gene (from plant Sedum alfredii Hance) into yeast and tobacco and found that the expression of the MT gene enhanced Cd and Zn accumulation in the transgenic organisms.…”