Overexpression of Iris. lactea var. chinensis metallothionein IIMT2a enhances cadmium tolerance in Arabidopsis thaliana

Metallothioneins (MTs) are cysteine-rich, low molecular weight, heavy metal-binding protein molecules. Here, a full-length cDNA homologue of MT2a (type 2 metallothionein) was isolated from the cadmiumtolerant species Iris. lactea var. chinensis (I. lactea var. chinensis). Expression of IIMT2a in I. lactea var. chinensis roots and leaves was up-regulated in response to cadmium stress. When the gene was constitutively expressed in Arabidopsis thaliana (A. thaliana), root length of transgenic lines was longer than that of wild-type under 50 mu M or 100 mu M cadmium stress. However, there was no difference of cadmium absorption between wild-type and trangenic lines. Histochemical staining by 3,3-diamino-benzidine (DAB) and nitroblue tetrazoliu (NBT) clearly demonstrated that transgenic lines accumulated remarkably less H2O2 and O-2(center dot-) than wild-type. Together, IIMT2a may be a promising gene for the cadmium tolerance improvement. (C) 2014 Elsevier Inc. All rights reserved.