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March 5, 2000


re: re: re: re: Does plant genome contains foreign DNA?


AgBioView - http://www.agbioworld.org

>AgBioView - http://www.agbioworld.org
>Here is a question for AbBioView readers. Is there DNA evidence that the
>plant genome contains foreign DNA? I can think of retrotransposons which
>may by their movement activate endogenous genes and certainly this is
>happening as an integral part of evolution. There is of course the DNA of
>ancient endosymbionts, some of which is now in the nucleus. Are there
>other examples for the incorporation of DNA other than in pathogenicity
>(eg Agrobacterium)?
>I probably should know the answer to this, but I cannot think of examples.
>Maarten Chrispeels
>(University of California, San Diego)


I suspect you're trying to find evidence for 'natural' inter-species
DNA/gene transfer. However, 'foreign' DNA is difficult to define. The
simplest example, of course, is wheat - a Frankenstein 'natural' hybrid of
three separate species. What is foreign DNA in this context? There is
plenty of evidence for mammalian retroviruses transferring fragments of DNA
between genomes of host species - is this known in plants? For example,
banana streak virus was unknown until breeders created Musa hybrids,
resulting in activation of the integrated viral DNA, giving rise to
infectious particles that now constitute a significant threat to banana
production. Does the viral genome pick up and transfer bits of Musa DNA?

This leads to an interesting point that I had intended bringing to
AgBioView. In both mammals and plants we find that, in inter-species
hybrids, dormant low-copy retrotransposons are activated and grossly
amplified. The consequence of this massive number of random integration
events is undoubtedly(?) massive and random disruption of genome function.
Yet we observe the phenomenon, obviously, in viable hybrid progeny.

One of the more sophisticated objections to GM plants is that, since we
don't control the site of transgene integration, it could integrate into a
site that subtly affects gene action, causing unpredictable and unknowable
pleiotropic effects. Forgetting for a moment the empirical testing and
analysis that is used to eliminate such events, the point I'm getting at is
that traditional plant breeding across species (within species?) causes
genome disruption on a far, far greater scale than does integration of a
single transgene. In other words, potential risks from unknown genomic
disruption are far, far greater with traditional breeding than with


Dr Ken C Reed
Director, Qld Agricultural Biotech Centre Phone: +61 7 3365 4961
Dept of Primary Industries _--_| A/H Ph: +61 7 3371 8668
Gehrmann Labs L4 / |_ Fax: +61 7 3365 4980
The University of Queensland _.--._/ A/H Fax: +61 7 3871 3301
Brisbane QLD 4072 v Mobile: 0407 379 175
AUSTRALIA email: k.reed@mailbox.uq.edu.au
internet: http://www.dpi.qld.gov.au/qabc/Welcome.html