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:
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
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
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.
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
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
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.
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