Development of transgenic yellow poplar for mercury phytoremediation

Abstract

We examined the ability of yellow poplar (Liriodendron tulipifera) tissue cultures and plantlets to express modified mercuric reductase (merA) gene constructs. Mercury-resistant bacteria express merA to convert highly toxic, ionic mercury, Hg(II), to much less toxic, elemental mercury, Hg(O). Expression of merA in transgenic plants might provide an ecologically compatible approach for the remediation of mercury pollution. Because the alteration of the bacterial merA gene sequence is necessary for high-level expression in Arabidopsis thaliana, yellow poplar proembryogenic masses (PEMs) were transformed with three modified merA constructs via microprojectile bombardment. Each construct was synthesized to have altered flanking regions with increasing amounts of modified coding sequence. All merA constructs conferred resistance to toxic, ionic mercury in independently transformed PEM colonies. Stability of merA transgene expression increased in parallel with the extent of gene coding sequence modification. Regenerated plantlets containing the most modified merA gene (merA18) germinated and grew vigorously in media containing normally toxic levels of ionic mercury. The merA18 plantlets released elemental mercury at approximately 10 times the rate of untransformed plantlets. These results indicate that plants expressing modified merA constructs may provide a means for the phytoremediation of mercury pollution.

A critical review on the bio-removal of hazardous heavy metals from contaminated soils: Issues, progress, eco-environmental concerns and opportunities

“…As we see from Fig. 2, methylmercury is converted to Hg(2), which is 100-fold less toxic than the former one [27][28][29].…”

“…This is good for us because generally crops bear grains aboveground and the fear that heavy metals may enrich in edible part is eliminated. Another big advantage is that some microbes produce antibiotics to enhance plants immunity and some produce necessary nutrients and even plant growth hormones [25][26][27][28][29][30][31][32]. Therefore the future of this method would be bright.…”

Genetic engineering in the improvement of plants for phytoremediation of metal polluted soils

“…No full-length merA RNA or merA-encoded protein were detected. The original bacterial merA sequence is rich in CpG dinucleotide having a highly skewed codon usage, both of which are particularly unfavorable to e cient expression in plants, because they are exposed to methylation and subsequent gene silencing (Rugh et al, 1998). Rugh et al (1996), therefore, constructed a mutagenized merA sequence (merApe9), modifying 9% of the coding region and transformed it to Arabidopsis thaliana.…”

“…by the fact that the resistance is normally encoded by a large plasmid containing an operon with many genes involved in the resistance mechanism. So far, only a single gene from such an operon has been transferred (Rugh et al, 1998). In the following, some candidate genes are discussed along with strategies for generating more metal-tolerant/accumulator plants using genetic engineering (Fig.…”

Stable Expression of the Chlorocatechol Dioxygenase Gene fromRalstonia eutrophaNH9 in Hybrid Poplar Cells

“…Therefore, poplar can be an appropriate host for heterologous enzyme production. There have been several reports on transgenic poplar plants expressing microbial genes and successfully removing pollutants, 4,5) but degradation of halogenated chemical compounds by transgenic poplar has not been reported. We have found that the cbnA gene is expressed in an active form in rice, 6) one of the most important monocotyledonous crops in Asian countries.…”