The term ‘genetic pollution was popularized by environmentalist Jeremy Rifkin in his book “The Biotech Century”(1998). Genetic pollution accounts to the uncontrolled spread of genetic information (frequently referring to transgenes) into the genomes of organisms in which such genes are not present in nature. Genetically engineered (GE) plants contains genes which have been transferred from unrelated species. These may come from bacteria, viruses, other plants or even animals. If these “foreign” genes are then transferred into other organisms, this causes genetic contamination or pollution of the natural gene pool.

Genetic pollution is usually associated with the gene flow from a genetically engineered (GE) organism (or genetically modified organism- GMO) to a non-GM organism. "Genetic pollution" and collateral damage from GE field crops already have begun to wreak environmental havoc. Wind, rain, birds, bees, and insect pollinators have begun carrying genetically-altered pollen into adjoining fields, polluting the DNA of crops of organic and non-GE crop fields.

Transgene escape, a major environmental and regulatory concern in transgenic crop cultivation, could be alleviated by removing transgenes from pollen, the most frequent vector for transgene flow. A transgene excision vector containing a codon-optimized serine resolvase CinH recombinase (CinH), and its recognition sites RS2 were constructed and transformed into tobacco (Nicotiana tabacum cv. Xanthi). CinH recombinase recognized 119 bp of nucleic acid sequences, RS2 in pollen and excised the transgene flanked by the RS2 sites. In this system, the pollen specific LAT52 promoter from tomato was employed to control the expression of CinH recombinase (Moon et al. 2011).

Transgene containment strategies have been proposed to suppress or eliminate unintentional transgene escape from transgenic plant populations. Two categories of transgene containment strategies exist : physical and biological. Physical transgene containment strategies include trap crops, spatial isolation, fences, the removal of flowers. Molecular strategies for gene containment in transgenic crops with potential for controlling gene flow among crops and weeds have thus far focused on maternal inheritance, male sterility and seed sterility and terminator technology (Daniell, 2002).

Recent advancements in biotechnology resulted in rapid adoption of genetically modified (GM) crops in the agriculture systems. At the same time, transgene escape has also been reported and examples reveal global dimension of the problem. Pollen mediated gene flow (PMGF) is the major pathway for transgene escape. Almost all transgenes have been escaped into their Non GM counterpart part and wild relatives. Although gene flow varies between species, crops and ecological zones but intra specific gene flow (> 10%) is not uncommon in adjacent populations. It is well documented that transgene flow is deteriorating different production systems in agriculture and farmers choice to cultivate GM, conventional and organic crops (Rizwan et al. 2019).

Potential of specific intercrops to mitigate PGF from GM crops, while simultaneously reducing pest abundance in the crop, they have resulted the greater attractiveness of sunflower and buckwheat to pollinators and beneficial predators and parasitoids, in comparison to cotton mono culture. This strengthens regulations of GM crops due to the growing public concerns about their potential ecological hazards , a carefully selected intercrop could be a useful tool to constrain PGF in cotton and other insect pollinated GM crops, while simultaneously reducing densities of pest (Yan et al. 2020).

Gene flow from glufosinate ammonium resistant soybean to its wild relative and they have resulted that pollen mediated gene flow from GR soybean to wild soybean ranged from 0.292% (mixed planting) to 0.027% at 8m distance and also the result suggest that transgenes of the GR soybean might disperse into wild populations and persist in the agro ecosystem of the genetic origin regions due to the pollen mediated gene flow and the relatively high fitness of the hybrid progeny (Yook et al. 2021).

Molecular strategies for gene containment in transgenic crops with potential for controlling gene flow among crops and weeds have thus far focused on maternal inheritance, male sterility and seed sterility (Daniell, 2002). Several other containment strategies may also prove useful in restricting gene flow, including apomixis (vegetative propagation and asexual seed formation), cleistogamy (self-fertilization without opening of the flower), genome incompatibility, chemical induction and deletion of transgenes, fruit specific excision of transgenes and transgenic mitigation (transgenes that compromise fitness in the hybrid).

Escape of transgene from GM crop plants to non GM and wild relatives may pose potential environment risks. Understanding of transgene escape will facilitate the sustainable and safe cultivation of GM varieties of different crops. Therefore, to favor the GM technology, we should take into consideration the biosafety measures as well as potential techniques to contain or mitigate the transgene effect. As yet, however, no molecular strategies have proved broadly applicable to all crop species and a combination of approaches may prove most effective for engineering the next generation of GM crops.

REFERENCES:

DANIELL, H. R., 2002, Molecular strategies for gene containment in transgenic crops, Nature Biot., 20(6): 581-586.

MOON, S. H., ABERCROMBIE, L. L., EDA, S., BLANVILLAIN, R., THOMSON, G. J., OW W D AND STEWART, C. N., 2011, Transgene excision in pollen using a codon optimized serine resolvase CinH-RS2 site-specific recombination system, Plant Mol. Biol., 75: 621-31.

RIZWAN, M., HUSSAIN, M., SHIMELIS, H., HAMEED, M. U., ATIF, R. M., AZHAR, M.T., QAMAR, Z., AND ASIF, M., 2019, Gene flow from major genetically modified crops and strategies for containment and mitigation of transgene escape. App. Eco. Env. Res., 17(5): 11191-11208.

YAN, S., YU, J., HAN, M., MICHAUD, J. P., GUO, L., ZENG, B., ZHANG, Q. W., AND LIU, X, 2020., Intercrops can mitigate pollen-mediated gene flow from transgenic cotton while simultaneously reducing pest densities. Sci. Total Environ., 711: 134-55.

YOOK, M. J., PARK, H. R., ZHANG, C. J., LIM, S. H., JEONG, S. C., CHUNG, Y. S., AND KIM, D. S., 2021., Environmental risk assessment of glufosinate-resistant soybean by pollen-mediated gene flow underfield conditions in the region of the genetic origin. Sci. Total Environ., 762: 143-73.