DEVELOPMENT OF TRANSGENIC YELLOW-POPLAR FOR MERCURY PHYTOREMEDIATION

We examined the ability of yellow poplar (Liriodendron tulipifera) tis sue cultures and plantlets to express modified mercuric reductase (mer A) gene constructs. Mercury-resistant bacteria express merA to convert highly toxic, ionic mercury, Hg(II), to much less toxic, elemental me rcury, Hg(0). Expression of merA in transgenic plants might provide an ecologically compatible approach for the remediation of mercury pollu tion. Because the alteration of the bacterial merA gene sequence is ne cessary for high-level expression in Arabidopsis thaliana, yellow popl ar proembryogenic masses (PEMs) were transformed with three modified m erA constructs via microprojectile bombardment. Each construct was syn thesized to have altered flanking regions with increasing amounts of m odified coding sequence. All merA constructs conferred resistance to t oxic, ionic mercury in independently transformed PEM colonies. Stabili ty 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 i n media containing normally toxic levels of ionic mercury. The merA18 plantlets released elemental mercury at approximately 10 times the rat e of untransformed plantlets. These results indicate that plants expre ssing modified merA constructs may provide a means for the phytoremedi ation of mercury pollution.