Among the fast-growing and high-biomass-yielding plants, poplar is the most commonly studied
because of its rapid growth rate and potential to produce high biomass within a short period of time
(5–8 years). Many of the poplar hybrid varieties have been genetically modified with microbial catabolic
genes and specific transporters for increased remediation [141,142]. For example, mercuric reductase
and γ-glutamylsysteine synthetase genes showed increased resistance to Hg and Cd and Cu, respectively,
through accumulation of higher concentrations of these metals [119,142]. As mentioned earlier,
manipulation of desired plant species with multiple genes will facilitate complete degradation of
pollutants to ensure that the harvested biomass can be utilized completely for additional benefits [143].