Phytoremediation: Transgenic Approach
Authors: Abhilasha Sharma, Suman Sanadhya and Swati

Phytoremediation consists of a set of innovative technologies for environmental cleanup that takes advantage of the unique extractive and metabolic capabilities of plants. This technology presents clear benefits over traditional methods, including wide applicability, ecological value and cost-effectiveness (Schnoor et al., 1995). With respect to their direct roles in remediation processes, plants use several different strategies for dealing with environmental chemicals such as phytoextraction, phytodegradation, phytovolatilization, and rhizodegradation etc. The concept that plants can degrade xenobiotics emerged in 1940s, when plants were shown to metabolize pesticides. Since then, the development of genomics, proteomics, and metabolomics has contributed much to enhance or manipulate the plant metabolism of many xenobiotic pollutants. Phytoremediation efficiency of plants can be substantially improved using genetic engineering technologies. To target plant regarding phytoremediation, one must understand the biochemical and physiochemical mechanism which are involved in accumulation, tolerance, detoxification and degradation to contaminants/pollutants.

Phytoremediation uses different plant processes and mechanisms normally involved in the accumulation, complexation, volatilization, and degradation of organic and inorganic pollutants. Xenobiotic metabolism in human, animals and higher plants usually happen through three main biochemical processes; conversion or transformation (phase I), conjugation (phase II), and compartmentalization or sequestration (phase III). A promising biotechnological approach for enhancing the potential for phytoremediation is to overexpression of genes whose protein products are involved in metal uptake, transport, and sequestration, or act as enzymes involved in the degradation of hazardous organics. Cytochromes P450 (CYP) enzymes are a super family of ubiquitous heme proteins that are involved in Phase I metabolism and clearance of numerous xenobiotics, such as substances of abuse, herbicides and industrial contaminants (Santosh kumar et al., 2012). In addition to P450 oxidation, glutathione conjugation is an important mechanism for xenobiotic detoxification. Glutathione S transferases (GSTs) are a family of multifunctional enzymes involved in the cellular detoxification and excretion of many physiological and endogenous substances. The strategy underlying this approach is to overexpress the genes of these enzymes either with constitutive promoter or tissue specific promoter to enhance phytoremediation. Several CYP enzymes have been engineered based upon knowledge obtained from primary sequences and structure functional analysis, which could drive of these newly engineered CYP enzymes for phytoremediation using transgenic plants (Kumar, 2010). Certain plants, called hyperaccumulator are good candidates in phytoremediation, particularly for the removal of heavy metals. Transferring the genes responsible for the hyperaccumulating phenotype to higher shoot biomass-producing plants has been suggested as a potential avenue for enhancing phytoremediation as a viable commercial technology. Metal homeostasis genes have therefore been used for these purpose (Antosiewicz et al., 2014). Availability of certain metal transporter proteins, translocators, metal responsive transcription factors and Chelators proteins gene could enhance desired level of accumulation and detoxification of heavy metals.

The phenomenon of constitutive over-expression of a large set of genes seems to be a common process in the adaptation of plants to extreme environments. Gene duplication could be a system to get a higher expression of a specific gene, when the phenomenon of gene silencing was not affected. A gene present in higher number of copies could lead to its enhanced expression. At molecular level, in these areas of research genetic transformation, protein engineering and omics approach are expected to cause the greatest impact in forthcoming year for phytoremediation technologies. A better understanding of transporter, translocators, chelators and metabolic enzymes and their steady state level in different tissues and organism would help to develop phytoremediation systems that are more effective.

References:

1. Antosiewicz D M, Barabasz A and Siemianowski O. (2014). Phenotypic and Molecular consequevences of Overexpression of metal-homeostasis genes. Frontier in plant science. (5):1-7.

2. Kumar S (2010). Engineering cytochrome P450 biocatalysts for biotechnology, medicine and bioremediation. Expert Opin Drug Metab Toxicol (6): 115-131.

3. Santosh Kumar, Jin M, Weemhoff JL (2012). Cytochrome P450-Mediated Phytoremediation using Transgenic Plants: A Need for Engineered Cytochrome P450 Enzymes. J Pet Environ Biotechnol (3):127.

4. Schnoor JL, Licht LA, McCutcheon SC, Wolfe NL, Carriera LH. (1995). Phytoremediation of organic and nutrient contaminants. Environ Sci Technol (29):318 Aâ€"323A.


About Author / Additional Info:
I am pursuing Ph.D in molecular Biology and Biotechnology from Rajasthan college of Agriculture, MPUAT, Udaipur, Rajasthan.