Science in Society Archive

The article below has been submitted on behalf of the Independent Science Panel to the Niigata Prefecture in Japan, in support of legal action taken by 12 Japanese citizens seeking to halt the trial of transgenic rice producing antimicrobial peptides.  Please circulate widely and send to your elected representatives.

Submit it also to the US Environmental Protection Agency and demand comprehensive risk assessment for transgenic plants producing another antimicrobial peptide that have been widely field-tested and may be poised for deregulation.

No to Releases of Transgenic Plants with Antimicrobial Peptides

Professor Joe Cummins and Dr. Mae-Wan Ho

Anti-microbial peptides provide the first line of defence against invading microbes in both plants and animals. The peptides are involved in innate immunity, and are 15 to 40 amino acids in length, most of them hydrophobic (water-hating) and cationic (positively charged). They provide protection from bacteria, fungi and viruses, acting mainly at the cell membrane of pathogens [1,2]. The peptides are beginning to be employed in medicine and in crop protection.

A synthetic peptide D4E1 based on the cecropin B peptide toxin (obtained from the moth, Cecropia), consists of a linear sequence of 17 amino acids: FKLRAKIKVRLRAKIKL (F for phenylalanine, K for lysine, L for leucine, R for arginine, A for alanine, I for isoleucine, V for valine). The peptide protected against Aspergillus and Fusarium fungi.  It acted by binding to ergosterol, a sterol present in fungal cell walls [3]. On further tests, D4E1 was found to have broad-spectrum antimicrobial action, and was active against fungi belonging to the orders Ascomycete, Basidiomycete, Deuteromycete and Oomycetes, as well as bacterial pathogens Psuedomonas and Xanthomonas [4]. The D4E1 toxin also proved effective in the treatment of human Chlamydia infection [5].

Transgenic tobacco plants transformed with a gene for the peptide D4E1 (driven by a double CaMV promoter and terminated by the nos transcription terminator, accompanied by a kanamycin resistance marker) was resistant to fungal pathogens [6]. Poplar trees transformed as in the transgenic tobacco was resistant to bacterial pathogens A. tumefacians and X. populi but not to the fungal pathogen Hypoxylon mammatum [7]. Cotton plants transformed similarly with the gene coding for D4E1 showed resistance to fungi including Fusarium, Verticillium and Aspergillus, hence the synthetic peptide was proposed to be effective against mycotoxin-causing fungal pathogens [8].

Field tests have been conducted on D4E1 transgenic plants in the United States, transgenic cotton in Arizona and California, and transgenic potatoes in Idaho [9]. It seems inevitable that petitions to remove the transgenic crops containing D4E1 from regulation are not far off. As the D4E1 gene and its peptide product are both fully synthetic, it will be a stretch to assume that the product is “substantially equivalent” to the natural product.  

Meanwhile, researchers at the National Agricultural Research Center, Niigata, in Japan have created transgenic rice with genes of the antimicrobial peptide, defensin, from Brassica. The transgenic rice plants were resistant to rice blast disease caused by the fungus Magnaporthe grisea. The researchers went a step further and systematically altered the genetic code for defensin to produce synthetic peptides that were far more toxic to the fungus than the natural peptides [10]. Rice with the synthetic genes and peptides are being proposed for field-testing prior to commercial release in Japan, and little effort appears to have been devoted to evaluate the safety for human health and the environment.

We agree with microbiologist Dr. Takahiro Kanagawa, a senior scientist at one of Japan’s leading research institutes that releases of transgenic plants containing anti-microbial peptides are dangerous [11]. Defensins and other peptides are, for plants and animals, their first defence against pathogens. Just as D4E1 was effective against Clamydia infections [5], alpha-defensins, identified in long-term nonprogressors with HIV-1 infection [12], may well have applications in preventing AIDS disease.

The danger highlighted by Dr. Kanagawa is that environmental releases of these antimicrobial peptides will lead to the evolution of resistance among microbial pathogens. As Dr. Kanagawa points out, there is already a report of yeast evolving resistance to defensin from Dahlia after two days of co-cultivation [13].

The evolution of resistance to antimicrobial peptides will severely compromise both the natural defence of the human immune system against disease and the possibilities of effective therapies emerging in the wake of the disaster of widespread antibiotic resistance. As versions of the peptides also provide defence against pathogens in other animals and plants, the ecological impact of resistant pathogens could be devastating.

Another factor adding to the hazards to health and the environment is that the synthetic transgenes code for peptides that are significantly different from the natural versions. This may itself be responsible for toxic or other harmful effects that cannot be known unless thoroughly tested.

Article first published 19/09/05



References

  1. Bulet P, Stocklin R. and  Menin L. Anti-microbial peptides: from invertebrates to vertebrates Immunol Rev. 2004 ,198,169-84,
  2. Boman, H. Antibacterial peptides: basic facts and emerging concepts. J Intern Med. 2003, 254(3), 197-215.
  3. De Lucca AJ, Bland JM, Grimm C, Jacks TJ, Cary JW, Jaynes JM, Cleveland TE and Walsh TJ. Fungicidal properties, sterol binding, and proteolytic resistance of the synthetic peptide D4E1. Can J Microbiol. 1998, 44, 514-20.
  4. Rajasekaran K, Stromberg KD, Cary JW and Cleveland TE. Broad-spectrum antimicrobial activity in vitro of the synthetic peptide D4E1. J Agric Food Chem. 2001, 49, 2799-803.
  5. Ballweber LM, Jaynes JE, Stamm WE and  Lampe MF. In vitro microbicidal activities of cecropin peptides D2A21 and D4E1 and gel formulations containing 0.1 to 2% D2A21 against Chlamydia trachomatis. Antimicrob Agents Chemother. 2002, 46, 34-41.
  6. Cary JW, Rajasekaran1 K, Jaynes JM and Cleveland TE. Transgenic expression of a gene encoding a synthetic antimicrobial peptide results in inhibition of fungal growth in vitro and in planta. Plant Sci. 2000, 29,154,171-181.
  7. Mentag R, Luckevich M, Morency MJ and  Seguin A. Bacterial disease resistance of transgenic hybrid poplar expressing the synthetic antimicrobial peptide D4E1. Tree Physiol. 2003, 23,405-11.
  8. Rajaskaran K, Cary J, Jaynes J. and Clevland T. Disease resistance conferred by the expression of a gene encoding a synthetic peptide in transgenic cotton (Gossypium hirsutumL.) plants. Plant Biotechnology Journal 2005, 3 in press  doi: 10.1111/j.1467-7652.2005.00145
  9. Environmental Releases Database for the U.S. 2005 http://www.nbiap.vt.edu/cfdocs/fieldtests3.cfm
  10. Kawata,M, Nakajima,T, Yamamoto,T, Mori,K, Oikawa, T, Fukomoto, F. and  Kuroda, S. Genetic Engineering for Disease Resistance in Rice (Oryza sativa L.) Using Antimicrobial Peptides JARQ 2003 , 37 (2), 71 – 76 http://www.jircas.affrc.go.jp
  11. Open letter from Dr. Takahiro Kanagawa 6 September 2005, forwarded by Akiko Frid, http://www.gmwatch.org/archive2.asp?arcid=5689
  12. Zhang L, Yu W, He T et al. Contribution of human a-defensin 1, 2, and 3 to the anti-HIV-! activity of CD8 antiviral factor. Science 2002, 298, 995-1000.
  13. Thevissen K, Osborn RW, Acland DP and Broekaert WF. Specific binding sites for an antifungal plant defensin from Dahlia (Kahlia Merckii) on fungal cells are required for antifungal activity. Molecular plant-Microbe Interactions 2000, 13, 55-61.

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