Metallothionein 1 (CcMT1) of pigeonpea (Cajanus cajan, L.) confers enhanced tolerance to copper and cadmium in Escherichia coli and Arabidopsis thaliana

A cDNA clone, encoding 75-amino acids metallothionein type 1 protein (CcMT1), has been isolated from the cDNA library of pigeonpea. Northern blot analysis of pigeonpea plants subjected to heavy metal stress revealed increased levels of CcMT1 transcripts. Escherichia coli cells expressing CcMT1 exhibited enhanced metal tolerance and higher accumulation of metal ions than that of control cells. Over-expression of CcMT1 in transgenic Arabidopsis plants imparted increased copper and cadmium tolerance as evidenced by higher plant biomass and chlorophyll content besides profuse root growth when compared to the control plants. Transgenic plants expressing CcMT1 disclosed higher accumulations of Cu and Cd ions in roots as compared to the shoots. No worthwhile differences were observed in the expression levels of copper (AtZIP2) and cadmium (AtNRAMP) transporter genes of CcMT1-transgenics and control plants both under stressed and unstressed conditions. The overall results amply indicate that CcMT1 is contributing to the detoxification of metal ions, thereby providing marked tolerance against metal stresses. This study, first report of its kind, deals with the isolation, characterization and functional validation of CcMT1 in heterologous systems. As such, CcMT1 may be deployed as a potential candidate for enhancement of metal tolerance in diverse crop plants. (C) 2011 Elsevier B.V. All rights reserved.