Mercury detoxification using genetic engineered Nicotiana tabacum

Abstract

Phytoremediation is a low cost alternative solution to soil contamination compared with
 traditional removal and/or disposal techniques. One of the phytoremediation technologies is
 the phytovolatilization, whereby the contaminant is not primarily accumulated in above-ground
 tissues, but is instead transformed by the plant into the atmosphere. The detoxification of
 highly toxic organmercurial compounds and subsequent volatilization of elemental mercury is
 a unique example for the successful phytoremediation based on genetic engineering
 approach. For mercury removal techniques we constructed a dicistronic construct containing
 the bacterial mercury detoxification genes merA and merB under the control of the
 Arabidopsis Actin2 promoter and terminator. The resulted construct was introduced to
 Agrobacterium competent cells using heat shock transformation method. In the mean time,
 we germinated tobacco (Nicotiana tabacum var. Gold leaf) seeds on MS media and infected
 leaf discs of 6-8 weeks tobacco seedlings with Agrobacterium containing Ti plasmid harboring
 merA/merB dicistronic construct. The results showed that about 90% of tobacco seedlings
 were carrying the mer genes. Tobacco seeds were collected from wild type and transgenic
 lines and tested for mercury resistance. The results showed that transgenic plants are
 resistant to both Phenyl Mercuric Acetate (PMA) and HgCl2. The root length and dry weight of
 wild and transgenic seedlings growing on both media amended with mercury compounds and
 media without mercury (control) were scored. The results showed that the root lengths and
 dry weight of the transgenic lines are significantly higher by 60 and 17-folds, respectively,
 compared to wild type. The results showed clear evidence that the transgenic plants are
 resistant to both organic and inorganic mercury compounds and can be used to clean up
 mercury contaminated sites.