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Warren Lushia walush0 at ukcc.uky.edu
Mon Oct 13 13:24:22 EST 1997

David Shivak wrote:

> I find it hard to believe that plants could have merely not been exposed
> to DNA viruses mutable enough to replicate within them sometime in the
> last few million years.  It may be that the "founder effect" is
> reinforced by an initial defense that forms a large stumbling block to a
> virus trying to jump into a new system.  

Initial defense, or a lack of compatibility?

>Thus, a virus not only has to
> "happen" to be able to replicate in plants, but also has to be lucky
> enough to evade hypothetical defense X, making the odds against a successful
> interphyla jump an order of magnitude worse.

Replication seems to me to be the likliest to be compatible between 
plants and animals, since the mechanisms for gene expression are 
essentially the same (eukaryotes) [For example, see Paul Ahlquist's 
group work on plant virus (BMV) replication in yeast].  Hypothetical 
defense X is not likely to exist, because a plant would have no need to 
form an active defense against a pathogen the will not be able to invade 
the host beyond the initially infected cell, should it replicate and 
accumulate in such cell.
> >Seeing as we are so terrestrially oriented in our search for /
> >knowledge of viruses, this collection represents most of what we know
> >about viruses: however, as has been amply demonstrated in recent
> >years, there are a vast number of viruses in every litre of sea
> >water, most of which have never been described - and most virus
> >diversity may in fact still be out there, waiyting for
> >characterisation.  Why do algae have such big dsDNA viruses, while
> >land plants do not?  A case of the one that stayed behind developing
> >a new kind of virus?  Viral "founder effects"?
> >
> >                     Ed Rybicki, PhD
> My own guess is that someone will find an exception that proves the rule
> in land plants, and any DNA virus that replicates in plants will
> demonstrate a neat ability to jump through a previously unrecognized hoop
> in the defense system of plants.

I'm not sure if I am misunderstanding your response, but there ARE DNA 
higher plant viruses (both ss and ds)....I believe Dr. Rybicki was 
simply pondering the lack of, to date, LARGE dsDNA higher plant viruses.

Interesting discussion.....

Warren Lushia
University of Kentucky

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