Mercury-tolerant Transgenic Poplars Expressing Two Bacterial Mercury-metabolizing Genes

Mercury is one of the most toxic metals to various organisms, including humans. Genes involved in mercury metabolism have been cloned fromStaphylococcus aureus, and were modified here to be expressed in plants. Transgenic poplars containing both chimeric genes (p35S-merA andp35S-merB) were developed via two rounds of transformation usingnos-nptll andnos-hpt genes as selectable markers. Although expression levels varied among transgenic lines, tolerance to either ionic mercury or organic mercury matched well with the degree of expression revealed by northern hybridization. In culture, these trees were tolerant to 50 μM HgCl₂ and 2 μM CH₃HgCI. Variations in mercury tolerance among the transgenic lines indicates that vigorous selection is required to select the best clones for use in phytoremediation.