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EJB ELECTRONIC JOURNAL OF BIOTECHNOLOGY ....MOVING FROM SCIENCE TO DEVELOPMENT... |
| Letter received on Wednesday 14, August, 2002
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 Peter LaFayette Wayne Parrott |