Wheat with transgene for low-molecular-weight glutenin showed
anomalies in glutenin production and some plants had reduced levels of
other storage proteins.
Manipulated Organism:
Spring wheat (Triticum aestivum L.), cultivar Bobwhite.
Inserted Transgenes:
Low-molecular-weight glutenin subunit gene for producing glutenin,
derived from the wheat variety "Cheyenne," driven by its own promoter. A
marker gene (UBI:BAR) conferring resistance to the herbicide BASTA
(bialaphos) was part of the gene construct.
Goal:
Increase the amount of glutenin stored in wheat kernels. Glutenin
is a protein important for the elasticity of wheat dough used for
baking. Researchers hope to improve the baking quality of wheat flour.
Target Effect:
In one (of eleven) transgenic line there was a 12- to 16-fold increase
in the expression of transgenic glutenin above normal glutenin expression
levels.
Nontarget Effects:
-
Flour from the transgenic wheat kernels had, in contrast to the authors'
expectations, poorer "visco-elastic properties" (p. 220).
-
Eleven lines were determined to be transgenic because of their ability
to grow in a medium containing the herbicide bialaphos, but 10 of these
lines showed no increase in the amount of the low-molecular-weight
glutenin subunit.
-
The increased expression of the low-molecular-weight glutenin subunit was
associated with a decrease in gliadin synthesis. Wheat gluten consists
of both gliadin and glutenin.
-
In some transgenic plants in the fourth generation "a high level of
transgene over-expression was associated with lower levels of other
storage proteins, including high molecular weight glutenin subunits and
gliadins. . . . This decrease may be the result of the diversion of the
seed protein nitrogen reserves into making huge amounts of the transgenic
[protein] at the expense of all the other seed proteins" (p. 219).
-
After the first generation, the number of plants expressing the transgene
was lower than expected: only about one-third of the plants in each
generation showed elevated expression, while the authors expected that
three-fourths would have raised levels of the transgenic protein. "These
observations could be indicative of transgene silencing or co-suppression
in a subpopulation of the seeds, or of instability of the chromosome(s)
carrying the transgenes" (p. 219).
Source:
Masci, S., R. D'Ovidio, F. Scossa, C. Patacchini et
al. (2003). "Production and Characterization of a Transgenic Bread Wheat
Line Over-Expressing a Low-Molecular-Weight Glutenin Subunit Gene,"
Molecular Breeding vol. 12, pp. 209-22.
Author Affiliations:
University of Tuscia, Italy, and U.S. Department of Agriculture,
Agricultural Research Service.
Funding:
Italian government.
Product Status:
Not on the market as of 2008.
Copyright 2008 The Nature
Institute.
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