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ISIS Report - June 12, 2001
GM Crops May Face Genetic Meltdown
All GM crops may be unstable, and worse, they may face total genetic meltdown due to escalating error catastrophes. Prof. Joe Cummins reviews recent research findings suggesting how this might occur.
‘Error catastrophe’ ‘or extinction mutagenesis’ is a theory about mutations and survival of populations. The idea is that mutation contributes to variability and variability drives the success of a population in the face
of a changing environment. However, most mutations are deleterious. Error catastrophe occurs when high mutation rates give rise to so many deleterious mutations that they make the population go extinct. For example, foot and mouth disease virus
treated with mutagens (base analogues fluorouracil and azacytidine) eventually become extinct [1]. Polio virus treated with the mutagenic drug ribavirin similarly went extinct [2]. Error catastrophe theory has led to a strategy of mutagenesis
to control disease viruses.
Somaclonal variation a form of gene and chromosome instability that results from the tissue and embryo culture technique used in making GM plants [3]. Somaclonal variation occurs in tissue and embryo culture even without genetic modification,
but genetic modification often makes it worse. Somaclonal variation is associated with replication of genetic elements called retrotransposons that replicate in the plant cell nucleus and are inserted into structural genes, causing mutation and
chromosome rearrangement [4]. The genetic changes activated in GM may be numerous and subtle, and may produce gradual loss in productivity of GM varieties or unexpected toxic plant products. Transposons have been shown to have powerful impacts
on genetic stability. For example, the P transposon of the fruit fly, Drosophila, when activated under appropriate conditions, causes ‘hybrid dysgenesis’, a slow destruction of the genome receiving the transposon due to
chromosome and gene mutation [5]. Gressel [6] has suggested that hyperactive transposons could be introduced into weed populations in order to eradicate them.
There has not been adequate study of ongoing transposition in GM crops, all of which have been produced by embryo culture. Somaclonal variation has been patented in some crops as a means of producing genetic variability for selection, and it
was assumed that the crops were genetically stable once established. But that assumption was not tested in most instances. Certainly, there has been inadequate study of the factors reactivating dormant transposons following plant embryo
culture. The threat of extinction mutagenesis has never been discussed in governmental reviews that led to the deregulation of experimental GM crops, nor has there been effort to examine the factors leading to subtle yield-depression in GM
crops. It may be only a question of time until GM crops dramatically decrease yield and become extinct. Finally, little or no thought seems to have been given to the havoc that could be wreaked upon the human genome by GM crop retrotransposon
running amok within humans and farm animals.
References
- Sierra S, Davila M, Lowenstein P and Domingo E. Response of foot and mouth disease virus to increased mutagenesis: Influence of viral load and fitness in loss of infectivity. J Virology, 2000, 74,8316-23
- Crotty S, Cameron C and Andino R. RNA virus error catastrophe: Direct molecular test by using ribavirin. Proc. Natnl.Acad.Sci USA, 2001, 98,6895-6900.
- Gressel ,J "Molecular biology of weed control" 2000 Transgenic Res 9,355-82
- Labra M, Savini C, Bracale M, Pelucchi N, Columbo L, Bardini M and Sala F. Genomic changes in transgenic rice plants produced by infecting calli with Agrobacterium tumefacians. 2001 Plant Cell Reports 2001, On line reports
DOI 10.1007/s002990100329
- Agrawal G, Yamazaki M, Kobayashi M, Hirochika R, Miyao A and Hirochika H. Screening of rice viviparous mutants generated by endogenous retrotransposon Tos17 insertion tagging of a zeanthin epoxidase4 gene and a novel OsTATC gene. Plant
Physiology, 2001, 125, 1248-57.
- Kidwell MG, Kidwell JF, and Sved JA. Hybrid dysgenesis in Drosophila melanogaster: a syndrome of aberrant traits including mutation, sterility, and male recombination. Genetics, 1977, 86:813-33.
Key words: Genetic instability, transgenic instability, somaclonal variations, transposons, error catastrophe.
For further information contact Prof. Joe Cummins e-mail: jcummins@uwo.ca
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