Unintended changes in gene expression were observed in Arabidopsis
plants engineered for resistance to the herbicide glufosinate.
Arabidopsis thaliana (thale cress; mustard family).
bar gene from Streptomyces hygroscopicus, which produces
the enzyme PAT. The PAT enzyme inactivates the herbicide glufosinate,
which is sold under the tradenames Liberty and Basta.
The bar gene, or a closely related gene called pat, has been
inserted into many crops for two reasons. One is for use in cropping
systems where the herbicide glufosinate is sprayed to control weeds.
The second is for use as a selectable marker during tissue culture to
confirm integration of the transgene.
Goal of This Study:
Investigate the effects of bar gene insertion and treatment with
glufosinate on gene expression levels in Arabidopsis.
Results of This Study:
Three different transgenic lines were created, none of which showed
differences in germination, leaf number, root length, or fresh weight
compared with the parent when grown in the laboratory.
Despite the lack of recognizable morphological differences, the gene
expression patterns of the transgenic plants were different than
the control. In particular, "four genes were found to be significantly
repressed only in the three transgenic lines" (p. 267).
Plants were then grown in media containing the herbicide glufosinate at
a concentration sufficient to kill non-transgenic plants but not the
transgenic ones. Compared with plants grown in herbicide-free media,
changes in gene expression were observed for 80 genes in the transgenic
plants. Of these, 51 also changed in non-transgenic plants exposed
to glufosinate, while 29 were unique to the transgenic plants. The
functions of these genes included such diverse roles as detoxification,
embryogenesis, lipid transfer, and cytokinin biosynthesis, and a number
had no known function.
"Although the wild-type plants undergo extensive transcriptional
reprofiling [that is, changes] in response to herbicide-induced stress and,
finally, plant death, the transgenic plants appear to activate other
detoxification processes to offset the toxic effects of the residual
herbicide or its derivatives" (p. 266).
Abdeen, A., and B. Miki (2009). "The Pleiotropic Effects of the bar
Gene and Glufosinate on the Arabidposis Transcriptome," Plant
Biotechnology Journal, vol. 7, pp. 266-82.
Agriculture and Agri-Food Canada.
Canadian Food Inspection Agency.
The bar or pat gene is present in many GM crops on the market.
Copyright 2009 The Nature