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  • Title: Cloning and transcript analysis of type 2 metallothionein gene (SbMT-2) from extreme halophyte Salicornia brachiata and its heterologous expression in E. coli.
    Author: Chaturvedi AK, Mishra A, Tiwari V, Jha B.
    Journal: Gene; 2012 May 15; 499(2):280-7. PubMed ID: 22441126.
    Abstract:
    Salicornia brachiata is an extreme halophyte growing luxuriantly in the coastal marshes and frequently exposed to various abiotic stresses including heavy metals. A full length type 2 metallothionein (SbMT-2) gene was isolated using RACE and its copy number was confirmed by southern blot analysis. Transcript expression of SbMT-2 gene was analyzed by semi-quantitative Rt-PCR and real time quantitative (qRT) PCR. Expression of SbMT-2 gene was up-regulated concurrently with zinc, copper, salt, heat and drought stress, down regulated by cold stress while unaffected under cadmium stress. Heterologous expression of SbMT-2 gene enhances metal accumulation and tolerance in E. coli. Metal-binding characteristics of SbMT-2 protein show its possible role in homeostasis and/or detoxification of heavy metals. Significant tolerance was observed by E. coli cells expressing recombinant SbMT-2 for Zn(++), Cu(++) and Cd(++) compared to cells expressing GST only. Sequestration of zinc was 4-fold higher compared to copper and in contrast SbMT-2 inhibits the relative accumulation of cadmium by 1.23-fold compared to GST protein. Fusion protein SbMT-2 showed utmost affinity to zinc (approx. 2.5 fold to Cu(++) and Cd(++)) followed by copper and cadmium ions with same affinity. Halophyte S. brachiata has inherent resilience of varying abiotic tolerance therefore SbMT-2 gene could be a potential candidate to be used for enhanced metal tolerance and heavy metal phytoremediation.
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