1. Proc Nat Acad Sci (early Dec 98) published an article by Jeffrey
Palmer and colleagues of Indiana Univ., on an apparent
accelerated "jumping" of a genetic parasite belonging to yeast into
higher plants recently. The parasite, she says, is a "piece of DNA
called a group I intron that can splice itself in and out of a
particular gene in the genome of mitochondria". Apparently, until
1995, it was thought that the parasite affected only yeast, and only
one genus of higher plants (of 25 surveyed) also had the parasite.
By 1998, 48 of 335 recently surveyed genera are known to have the
parasite, and the DNA base sequence is more than 92% identical. This
and other evidence suggests that a) the horizontal gene transfer
events were independent and b) must have occurred very recently.
The scary bit is that "this massive wave of lateral transfers is of
entirely recent occurence, perhaps triggered by some key shift in the
intron's invasiveness within angiosperms (i.e. higher plants)".
Dr. Ho goes on to explain that movement of the parasite into plants
could have occurred through viruses, insects or bacteria. However,
as you noted earlier, in order to do this, it would have to have
overcome species barriers (a 20 base pair site in the host genome
that must be "recognized" by the parasite) AND in order for the
parasite splicing gene to be expressed (to insert the parasite into
the host genome), it must have a signal that is recognized by the
host genome. Thus - there must have been recognition in two
directions, from both the parasite and the host, in order for the
insertion to occur. And recall, they concluded that this insertion
has occurred frequently (35 species) just recently.
Dr. Ho states that the researchers at Indiana U "raise concerns about
releasing transgenic crops into the environment if horizontal gene
transfer is so widespread." Would be worthwhile to get ahold of that
article.
She goes on to report another article, in Nature (late in 98),
showing that genes transferred into transgenic plants can be up to 30
times more likely to escape from the host genome than the plant's own
genes. This is, if I recall, because of the method used to insert
the transgenes in the first place using specially modified agents
that lose their host specificity. In effect, it would mean that the
likelihood of horizontal gene transfer conveying transgenes out of
the host plant (Bt-corn; RR-soybean) and into something else (plant,
bug, microbe) is much higher than normal.
So, getting back to the original thread on scale, this evidence lends
further weight to the risk of a catastrophic response to large scale
production of a single GE hybrid or cultivar over millions of
hectares each year. Not only are we providing the "raw material" -
every single cell of every one of the 60,000 corn plants/hectare x
millions of hectares contains the same novel genetic construct - but
we are also "daring" the transgenes to jump by equipping them with
"stealth" capability. Great. Just great. Ann
ACLARK@plant.uoguelph.ca
Dr. E. Ann Clark
Associate Professor
Crop Science
University of Guelph
Guelph, ON N1G 2W1
Phone: 519-824-4120 Ext. 2508
FAX: 519 763-8933
http://www.oac.uoguelph.ca/www/CRSC/faculty/eac.htm
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