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Unintended Effects of Genetic Manipulation
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Posted: July 2014

Transgene in Corn, Intended to Raise Iron Availability, Also Changed Levels of Other Minerals and Proteins.

Grains such as corn (maize) are poor sources of iron. Genetic engineers have found that they can raise the level of bio-available iron in plants by introducing a gene construct that contains the gene for the ferritin protein (which stores and makes available iron to the organism). They target the transgene for expression in the kernels of the corn ear. In this way they hope to produce genetically modified (GM), iron-fortified plants for human and animal consumption.

Kanobe et al. (2013) were interested in whether the over-expression of a foreign ferritin gene in corn kernels would in any way influence the expression of native corn genes. To investigate this they worked with transgenic corn that, in corn kernels, over-expressed a ferritin gene derived from soybeans.

The researchers found significant unexpected changes associated with over-expression of the soybean gene in corn kernels. Compared with controls (corn that did not contain the transgene) they found the following significant differences:
  • Eight-fold reduction in the mRNA associated with the production of some types of zein storage proteins. In the seven iron homeostasis genes they tested (all related to iron homeostasis proteins) they discovered these differences:
    • In five cases the mRNA abundance associated with the iron homeostasis proteins was raised — at least four times higher in four of the cases.
    • In two cases, the mRNA accumulation was reduced.
  • Calcium, magnesium and iron concentrations were higher.
  • Total protein content was lower.
The genetic manipulation was aimed at higher ferritin expression in corn kernels. The researchers also tested for unintended substance changes in the roots and leaves of the transgenic plants. There they found that the manipulation was associated with only a few changes in the substances they investigated:
  • In roots, one iron homeostasis gene was expressed at high levels; interestingly, it was expressed while the plants were growing and seeds were not yet formed (that is, the ferritin transgene was not yet being expressed in the seeds), and also after seed formation.
  • In leaves, and after ferritin transgene expression had begun in the kernels, there was an over six-fold increase in the amount of one binding protein.
As the authors state, “acceptance of [transgenic agricultural crops] is poor in many countries due to the perception that genetic modification may cause unintended effects on expression of native genes in the host plant.” Their results confirm that such effects existed when levels of bio-available iron in corn were raised. “These results underscore the importance of taking a holistic approach to the evaluation of transgenic events in target plants, comparing the transgenic plant to the untransformed controls.”

Source: Kanobe, M. N., Rodermel, S. R., Bailey, T. et al. (2013). “Changes in Endogenous Gene Transcript and Protein Levels in Maize Plants Expressing the Soybean Ferritin Transgene,” Frontiers in Plant Science vol. 4. doi:10.3389/fpls.2013.00196

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