MERCURIC ION REDUCTION AND RESISTANCE IN TRANSGENIC ARABIDOPSIS-THALIANA PLANTS EXPRESSING A MODIFIED BACTERIAL MERA GENE

With global heavy metal contamination increasing, plants that can proc ess heavy metals might provide efficient and ecologically sound approa ches to sequestration and removal, Mercuric ion reductase, MerA, conve rts toxic Hg2+ to the less toxic, relatively inert metallic mercury (H g-0), The bacterial merA sequence is rich in CpG dinucleotides and has a highly skewed codon usage, both of which are particularly unfavorab le to efficient expression in plants, We constructed a mutagenized mer A sequence, merApe9, modifying the flanking region and 9% of the codin g region and placing this sequence under control of plant regulatory e lements, Transgenic Arabidopsis thaliana seeds expressing merApe9 germ inated, and these seedlings grew, flowered, and set seed on medium con taining HgCl2 concentrations of 25-100 mu M (5-20 ppm), levels toxic t o several controls, Transgenic merApe9 seedlings evolved considerable amounts of Hg-0 relative to control plants, The rate of mercury evolut ion and the level of resistance were proportional to the steady-state mRNA level, confirming that resistance was due to expression of the Me rApe9 enzyme, Plants and bacteria expressing merApe9 were also resista nt to toxic levels of Au3+. These and other data suggest that there ar e potentially viable molecular genetic approaches to the phytoremediat ion of metal ion pollution.