London (1.1.09)
– It is only comparatively recently, after two decades or so of experience
in the lab. and a decade in the field, that a detailed understanding of genetic
changes in transgenic plants is beginning to emerge. What recent data show
is that, aside from the specific genes transferred – and the fears of
opponents of transgene technology notwithstanding – there is remarkably
little change in the rest of the recipient plant's genome.
In the UK, workers at Rothamsted Research, and at Bristol and Nottingham universities,
have obtained detailed global gene expression profiles for a series of transgenic
and conventionally bred wheat lines expressing additional genes encoding high
molecular weight subunits of glutenin; these constitute a group of endosperm-specific
seed storage proteins which determine dough strength and therefore bread-making
quality (1).
The original plants were compared with transgenics containing just the transgenes
or also carrying marker genes. Analysis showed the differences between the
“transcriptomes” – the whole gamut of messenger RNAs transcribed
from the plants’ DNA (and so an indication of all the proteins being
synthesized from the genetic information in the DNAs) – to be “extremely
small”. Comparisons of conventionally bred strains gave much larger
effects than those between transgenic and untransformed lines showing the
same complements of gluten subunits. The authors concluded that the presence
of the transgenes did not significantly alter gene expression; at this genetic
level of analysis, the transgenic plants could be regarded as substantially
equivalent to the untransformed parental lines.
Similar conclusions have emerged from a soybean study (2). Exploring the possibility
that transgene expression could lead to unintended effects, the study used
transcriptome profiling as a non-targeted approach to evaluate overall molecular
changes in transgenic soybean cultivars. The results showed that gene expression
differs more between two conventional cultivars than between the transgenics
and their closest conventional cultivar investigated; the magnitudes of the
differences measured in gene expression and genotype (determined by simple-sequence
repeat analysis) do not necessarily correlate.
A third study, carried out at two UK sites, involved a series of transgenic
wheat lines expressing additional high molecular weight (HMW) subunit genes
and the corresponding control lines cultivated through successive generations
over a three-year period (3). Statistical analyses showed that the transgenic
and non-transgenic lines did not differ in terms of stability of the HMW subunit
gene expression or grain nitrogen, dry weight or dough strength, either between
the three years or between sites and plots. Thus, the transgenic and control
lines were substantially equivalent in terms of stability of gene expression
between generations and environments.
These data confirm conclusions already widely accepted that, except for the
specific property transferred, such gene transfers at any rate have no more
than minor or negligible effects on the recipient plants.
Sources:
1. María Marcela Baudo, Rebecca Lyons, Stephen Powers, Gabriela M.
Pastori, Keith J. Edwards, Michael J. Holdsworth and Peter R. Shewry (2006).
Transgenesis has less impact on the transcriptome of wheat grain than
conventional breeding. Plant Biotechnology Journal, 4,
369–380 (http://www3.interscience.wiley.com/journal/118585495/abstract?CRETRY=1&SRETRY=0)
2. K. C. Cheng, J. Beaulieu, E. Iquira, F. J. Belzile, M. G. Fortin, and M.
V. Strömvik (April 23, 2008). Effect of transgenes on global gene
expression in soybean is within the natural range of variation of conventional
cultivar. Journal of Agricultural and Food Chemistry, 56(9),
3057–3067 (http://pubs.acs.org/cgi-bin/abstract.cgi/jafcau/2008/56/i09/abs/jf073505i.html)
3. Peter R. Shewry, Stephen Powers, J. Michael Field, Roger J. Fido, Huw D.
Jones, Gillian M. Arnold, Jevon West, Paul A. Lazzeri, Pilar Barcelo, Francisco
Barro, Arthur S. Tatham, Frank Bekes. Barbara Butow and Helen Darlington (2006).
Comparative field performance over 3 years and two sites of transgenic
wheat lines expressing HMW subunit transgenes. Theoretical and Applied
Genetics, 113, 128–136 (http://www.springerlink.com/content/023656503126rtr6)
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