Phytoremediation of persistent organic pollutants (POPs) utilizing transgenic hairy root cultures: Past and future perspectives

Abstract

Persistent organic pollutants (POPs) are halogenated compounds that were once widely used. Common properties of POPs are persistence in the environment, high toxicity to s and wildlife, bioaccumulation in biological tissues, biomagnification through food chains, and long-range transport. Although they are now banned or restricted in many countries owing to their persistence in the environment, POPs are of particular concern for continuing potentially adverse effects on human health and the environment. Therefore, urgent action is required to address the global elimination, remediation, cleanup, and safe disposal of POPs. Phytoremediation has received attention for mitigating POPs pollution and is appropriate for in situ degradation of pollutants over a large area, which contributes to its cost-effectiveness. However, ordinary plant species are unable to take up POPs from soil. Furthermore, there is no specific enzyme that degrades or detoxifies POPs in plants. Some plant species, for example, Cucurbita species, possess the unique ability for uptake of significant amounts of POPs and are considered hyperaccumulators of POPs. Genes encoding POPs-degrading enzymes have been isolated from POPs-degrading microorganisms. Generating transgenic hyperaccumulator plants expressing POPs-degrading enzymes might have promise as a practical means of phytoremediation of POPs. However, production of transgenic plants is laborious and time-consuming. The hairy root culture system has several advantages compared to other tissue culture systems. In addition, we discuss the utility of “composite plants,” chimeras containing wild-type shoots with transgenic hairy roots, from the perspective of biosafety and rapid evaluation of phytoremediation ability in a POPs-contaminated field.