Transgenic plant release--seminar summary

Thu Mar 24 13:42:53 EST 1994

     On Monday, March 21, 1994, Prof. Gus de Zoeten of Michigan State 
University presented a seminar to scientists at Oklahoma State University.  I 
post an unauthorized summary of the presentation because I feel the issues that 
he raises and has raised (Phytopathology (1991) 81:585) are worthy of 
attention.  The take-home message of the talk was that plant virologists' 
attitudes towards the release of transgenic plants containing parts of viral 
genomes are too much based on "gut reactions" and too little on scientific 
     He considered two main potential risks of the release of plants transgenic 
for viral coat protein genes:  transcapsidation and recombination.  In 
transcapsidation, the genome of an infecting virus becomes encapsidated, wholly 
or in part, by the coat protein made from the transgene.  The possibly harmful 
consequence of transencapsidation is wider spread of the virus.  Coat proteins 
often contain determinants that lead to acquisition of virions by insect 
vectors.  An insect vector specific for the transgenic coat protein would thus 
be able to pick up the transcapsidated viral genome and deliver it to a plant 
species not visited by the vectors that normally transmit the infecting virus.  
Other insects could transmit that virus to still other species.
     After a brief summary of recombination in plant viruses, Prof. de Zoeten 
touted the recent paper by Greene and Allison (Science (1994) 263:1423) in 
which recombination between a defective cowpea chlorotic mottle virus (CCMV) 
coat protein transgene and a defective CCMV genome in an inoculum was 
demonstrated.  This paper debunks an assertion made by prominent virologists 
that even though RNA recombination can be demonstrated between coinfecting 
RNA's, recombination between transgene RNA and inoculum RNA is unlikely because 
the transgene RNA is unlikely to be produced in an amount and at the place 
needed for recombination.  He criticized the conclusions of the accompanying 
"perspectives" piece of Falk and Bruening (Science (1994) 263:1395) as being 
speculations not based in fact.
     Prof. de Zoeten read a list of about ten assertions by virologists 
minimizing the risks of release of transgenic plants containing parts of viral 
genomes.  At each assertion, he discussed how either the assertion was since 
proven wrong or that there is not enough information to judge the veracity of 
the assertion.
     Prof. de Zoeten concluded his talk with an appeal for serious research 
into the assessment of the risks associated with release of transgenic plants.  
He defined risk as the product of the frequency of the event, the duration of 
time in which the event may happen, and a value measuring the harm of the 
event.  He considered measurement of frequency to be the most important, since 
if the frequency is zero, the product risk is also zero.
     In seminars of this type, of necessity, only one point of view is 
presented adequately.  Are there folks out there willing to defend the Falk-
Bruening point of view?

Ulrich Melcher
Dept. Biochem. & Mol. Biol.
Oklahoma State University
Stillwater OK

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