摘要
The excess amounts of heavy metals are toxic to various physiological processes in plants.Plant metallothioneins(MTs)are low molecular weight,cysteine-rich metal-binding proteins that play important roles in the detoxification of heavy metal ions.In this study,we characterized Cs MT4,a plant type 4 MT gene identified in a complementary DNA(cDNA)library prepared from young cucumber(Cucumis sativus)fruit.Cs MT4encodes a 90 amino acid protein with a predicted molecular mass of 9.028 kD.CsMT4 contains 17 cysteine residues in three highly conserved cysteine-rich domains.In contrast to the structures of other MTs,the highly conserved amino acid pattern CxCxxxCxCxxCxC is present in the middle of CsMT4.Furthermore,CsMT4 was markedly induced in various tissues by various concentrations of Cd^(2+)and Zn^(2+)(>1.0 mmol·L^(-1)).Similar to AtMT4b function,heterologous expression of Cs MT4 in E.coli could also improved its tolerance to Cd^(2+)and led to increased uptake of Cd^(2+),and the rate of Cd^(2+)uptake was the highest in cells expressing a phytochelatin-like peptide.Our findings demonstrate that CsMT4 might be obviously induced by the metal stress in cucumber,and improves tolerance to Cd ions but not Zn ions when heterologously expressed in E.coli,and suggest that the composition and arrangement of N-terminal Cys-residues in MT4 are associated with their binding capacity and preference for different metal ions.
The excess amounts of heavy metals are toxic to various physiological processes in plants.Plant metallothioneins(MTs)are low molecular weight,cysteine-rich metal-binding proteins that play important roles in the detoxification of heavy metal ions.In this study,we characterized Cs MT4,a plant type 4 MT gene identified in a complementary DNA(cDNA)library prepared from young cucumber(Cucumis sativus)fruit.Cs MT4encodes a 90 amino acid protein with a predicted molecular mass of 9.028 kD.CsMT4 contains 17 cysteine residues in three highly conserved cysteine-rich domains.In contrast to the structures of other MTs,the highly conserved amino acid pattern CxCxxxCxCxxCxC is present in the middle of CsMT4.Furthermore,CsMT4 was markedly induced in various tissues by various concentrations of Cd^(2+)and Zn^(2+)(>1.0 mmol·L^(-1)).Similar to AtMT4b function,heterologous expression of Cs MT4 in E.coli could also improved its tolerance to Cd^(2+)and led to increased uptake of Cd^(2+),and the rate of Cd^(2+)uptake was the highest in cells expressing a phytochelatin-like peptide.Our findings demonstrate that CsMT4 might be obviously induced by the metal stress in cucumber,and improves tolerance to Cd ions but not Zn ions when heterologously expressed in E.coli,and suggest that the composition and arrangement of N-terminal Cys-residues in MT4 are associated with their binding capacity and preference for different metal ions.
基金
supported by the National Natural Science Foundation of China (NSFC) [31471885,31772320]
Fundamental Research Funds for the Central Universities [XDJK2016A005]
the Research Innovation Program for College Graduates of Chongqing [CYS18092]
