Letter to Electronic Journal of Biotechnology
Wednesday 14, August, 2002
The recent Letter to Nature "Transgenic DNA introgressed
into traditional maize landraces in Oaxaca, Mexico" by D Quist
and IH Chapela, (29 November 2001 issue (Vol 414, pp 541-543)) attempts
to make the point that engineered genes have been incorporated into
native Mexican maize varieties. We performed a detailed examination
of the data provided by the authors, and cannot verify their key results.
Without proper data, the authors can neither prove nor disprove the
presence of engineered genes in Mexico's corn landraces.
To their credit, Quist and Chapela used a logical two-step approach in
their efforts to prove transgenes were present in Mexican maize. First
they used the Polymerase Chain Reaction (PCR) to detect the presence of
transgenes. However PCR only detects a possible presence- it is no proof-
so the authors used inverse PCR to prove the genes were integrated into
the maize genome.
The use of PCR and iPCR leaves tell-tale marks on the amplified DNA sequences
when the PCR works as intended- there should have been predictable CaMV
35S promoter DNA sequences present, as well as a diagnostic enzyme restriction
site in the sequences they amplified, but these are incomplete or missing
altogether. The inescapable conclusion is that the authors did not amplify
the transgene sequences they thought they were amplifying.
A major problem is that a primer used for iPCR was designed incorrectly.
The authors chose vector pMON273 as a template, but this vector has a
different DNA sequence than other commonly used vectors. As a result,
only the one end of primer iCMV4 recognizes the promoter sequences. The
other end appears to recognize retroelement sequences naturally occurring
in maize, which helps explain why the authors did not recover the intended
sequences and arrived at the wrong conclusions.
The information provided falls short of proving the presence of transgenes,
and clearly cannot support any claims of introgression of transgenes into
Mexican land races. Nevertheless, it is probably inevitable that eventually
engineered genes will be found in Mexican corn, as gene flow is a normal
and natural phenomenon with maize. Such gene flow - by chance or intent
- has given rise to a large amount of biodiversity, which is balanced
as farmers select for specific characteristics that make each local maize
variety unique. As is there is no reason to believe transgenic corn will
pose a greater or lesser risk to native varieties than any of foreign
maize varieties already brought to Mexico.
Included is a detailed analysis of the data reported by Quist and Chapela:
Analyses of the data presented in "Transgenic
DNA introgressed into traditional maize landraces in Oaxaca, Mexico"
by D Quist and IH Chapela, (Nature 29 November 2001 issue (Vol 414, pp
541-543)).
Robert Wager
Department of Biology
Malaspina University-College
900 Fifth Street
Nanaimo, B.C., Canada V9R 5S5
E-mail: wagerr@mala.bc.ca
Peter LaFayette
Department of Crop and Soil Sciences
The University of Georgia
Athens, GA 30605-7272
USA
Tel: 706-542-0928
Fax: 706-542-0914
Wayne Parrott
Department of Crop and Soil Sciences
The University of Georgia
Athens, GA 30605-7272
USA
Tel: 706-542-0928
Fax: 706-542-0914
E-mail: wparrott@uga.edu
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