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Research review paper
Transgenic plants for enhanced biodegradation and phytoremediation of organic xenobiotics P.C. Abhilash, Sarah Jamil, Nandita Singh ⁎
Eco-Auditing Group, National Botanical Research Institute, Council of Scientiﬁc & Industrial Research, Rana Pratap Marg, Lucknow 226 001, Uttar Pradesh, India
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Phytoremediation — the use of plants to clean up polluted soil and water resources — has received much attention in the last few years. Although plants have the inherent ability to detoxify xenobiotics, they generally lack the catabolic pathway for the complete degradation of these compounds compared to microorganisms. There are also concerns over the potential for the introduction of contaminants into the food chain. The question of how to dispose of plants that accumulate xenobiotics is also a serious concern. Hence the feasibility of phytoremediation as an approach to remediate environmental contamination is still somewhat in question. For these reasons, researchers have endeavored to engineer plants with genes that can bestow superior degradation abilities. A direct method for enhancing the efﬁcacy of phytoremediation is to overexpress in plants the genes involved in metabolism, uptake, or transport of speciﬁc pollutants. Furthermore, the expression of suitable genes in root system enhances the rhizodegradation of highly recalcitrant compounds like PAHs, PCBs etc. Hence, the idea to amplify plant biodegradation of xenobiotics by genetic manipulation was developed, following a strategy similar to that used to develop transgenic crops. Genes from human, microbes, plants, and animals are being used successfully for this venture. The introduction of these genes can be readily achieved for many plant species using Agrobacterium tumefaciens-mediated plant transformation or direct DNA methods of gene transfer. One of the promising developments in transgenic technology is the insertion of multiple genes (for phase 1 metabolism (cytochrome P450s) and phase 2 metabolism (GSH, GT etc.) for the complete degradation of the xenobiotics within the plant system. In addition to the use of transgenic plants overexpressed with P450 and GSTgenes, various transgenic plants expressing bacterial genes can be used for the enhanced degradation and remediation of herbicides, explosives, PCBs etc. Another approach to enhancing phytoremediation ability is the construction of plants that secrete chemical degrading enzymes into the rhizosphere. Recent studies revealed that accelerated ethylene production in response to stress induced by contaminants is known to inhibit root growth and is considered as major limitation in improving phytoremediation efﬁciency. However, this can be overcome by the selective expression of bacterial ACC deaminase (which regulates ethylene levels in plants) in plants together with multiple genes for the different phases of xenobiotic degradation. This review examines the recent developments in use of transgenic-plants for the enhanced metabolism, degradation and phytoremediation of organic xenobiotics and its future directions. © 2009 Elsevier Inc. All rights reserved.
Article history: Received 14 October 2008 Received in revised form 26 March 2009 Accepted 3 April 2009 Available online 14 April 2009 Keywords: Phytoremediation Cytochrome P450s Glutathione S-tranferases Bacterial enzymes Transgenic plants Metabolism Organic xenobiotics
Contents 1. 2. 3. 4. 5. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Transgenic plants for environmental remediation . . . . . . . . . . . . . . . . . . . . . Degradation pathways in plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cytochrome P450s:...