Yeast Metallothionein in Transgenic Tobacco Promotes Copper Uptake from Contaminated Soils

Abstract

Metallothioneins (MTs) are metal-binding proteins that confer heavy metal tolerance and accumulation in yeast. To augment higher plant metal sequestration, the yeast metallothionein (CUP 1) was introduced into tobacco plants. The CUP 1 gene expression and copper and cadmium phytoextraction were determined. To confirm transformation, selfed and kanamycin-resistant third generation plants were subjected to DNA blot and polymerase chain reaction (PCR) analysis. A 4 mM CuSO(4) stress for 7 days resulted in a decline in CUP 1 transcripts versus nonstress conditions. Despite low mRNA levels, CUP 1 transformants accumulated up to seven times more copper in older versus younger leaves during copper stress. Pooled leaves of transgenic plants grown in soils from copper stamp-sands contained two to three times the copper content as that of the control plants. Unlike some previous reports featuring MT overexpression in plants, CUP 1 seedlings did not significantly sequester or demonstrate tolerance to CdCl(2). Using this transgenic approach, yeast CUP 1 expression under nonstressed conditions contributed to copper metal phytoextraction during a subsequent copper challenge. This strategy could be incorporated into plants designed for enhanced phytoremediation of metal contaminants.

New Approaches for Bioaugmentation as a Remediation Technology

“…Since the appropriate microorganisms may not be present at a given site and may also be difficult to establish via bioaugmentation, researchers have investigated the insertion of microbial genes for remediation processes directly into plants. 18,51,72,78,79,98,207,231 Phytoaugmentation is a term used to describe the addition of remediation genes to a site via an engineered plant that contains the microbial genes. By incorporation of these genes into plants, it is also easier to control the persistence and spread of genes introduced into the environment than via an analogous GEM.…”

“…Similar results have observed by other researchers for methylmercury detoxification and for copper and lead accumulation. 18,19,78,231 Plants have also been engineered with microbial genes for the metabolism of organic pollutants. Shimizu et al 207 introduced the chlorocatechol dioxygenase gene (cbnA) from Ralstonia eutropha NH9 into rice plants.…”

Remediation of heavy metal contaminated ecosystem: an overview on technology advancement

“…It has great potential in metal remediation studies (Papoyan and Kochian 2004). Thomas et al (2003) have show that transgenic plants expressing metallothioneins exhibited enhanced tolerance to high metal concentrations. To increase metal uptake, the yeast metallothionein CUP1 was introduced into tobacco plants, and this gene is expressed in plants.…”

Metal hyperaccumulation and bioremediation

“…On one hand, they complex the metal ions to inactivate and store them in the vacuole and on the other, they transfer the essential metal to the newly synthesized apoenzymes that require Cu 2+ or Zn 2+ for catalytic activity or to nucleic acid structures such as Zn-fingers (Thumann et al 1991).…”