No to Releases of Transgenic Plants with Antimicrobial

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Subjec. t: No to Releases of Transgenic Plants with

Antimicrobial Peptides

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ISIS Press Release 19/09/05

 

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

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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.

 

References

 

Bulet P, Stocklin R. and Menin L. Anti-microbial peptides:

from invertebrates to vertebrates Immunol Rev. 2004

,198,169-84,

 

Boman, H. Antibacterial peptides: basic facts and emerging

concepts. J Intern Med. 2003, 254(3), 197-215.

 

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.

 

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.

 

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.

 

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.

 

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.

 

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

 

Environmental Releases Database for the U.S. 2005

http://www.nbiap.vt.edu/cfdocs/fieldtests3.cfm

 

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

 

Open letter from Dr. Takahiro Kanagawa 6 September 2005,

forwarded by Akiko Frid,

http://www.gmwatch.org/archive2.asp?arcid=5689

 

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.

 

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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