Analysis of BnMTL, a novel metallothionein‐like protein in the bast fiber crop Ramie (Boehmeria nivea)

Abstract

Ramie ( Boehmeria nivea ) is a perennial herb that is highly tolerant of heavy metals. In the present study, we cloned a novel metallothionein‐like gene from ramie; this gene, termed Bn MTL , encodes a putative 46 amino acid protein with a molecular mass of 4.38 kD a. Analysis using quantitative RT ‐ PCR revealed that cadmium (Cd 2+ ) treatment results in elevated expression of Bn MTL in the roots. We heterologously overexpressed Bn MTL in Escherichia coli cells to examine its binding to Cd 2+ and its possible role in homeostasis. Recombinant E. coli cells expressing Bn MTL exhibited a high tolerance of Cd 2+ stress up to a concentration of 1 m m , and the observed accumulation of Cd 2+ was almost eight‐fold higher than the control. These results demonstrate that Bn MTL (i) is highly expressed in the root following exposure to Cd 2+ and (ii) encodes a typical metallothionein‐like protein with high cadmium‐binding activity.