gm-wheat/report-4

Wheat expressing transgenic glutenin shows reduction in yield, varying production of glutenin, and altered morphology.

Manipulated Organism: Spring Wheat (Triticum aestivum L.), cultivar Bobwhite.

Inserted Transgenes: High-molecular-weight glutenin subunit (HMW-GS) genes for producing glutenin. For the generation of some transgenic lines, the gene was derived from the wheat variety Cheyenne, and for others the gene was a novel "hybrid" HMW-GS. The transgenes were under the control of their native promoters. Fifty lines of transgenic plants derived from fifteen different bombardment experiments in which the immature embryos were bombarded with one of six different gene constructs containing different configurations of glutenin genes.

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.

Intended Effect: Fifty lines of transgenic wheat plants were grown that had raised levels of glutenin in field trials.

Unintended Effects: The authors emphasize the success of this experiment, since most transgenic lines performed similarly to normal cultivar Bobwhite, from which they were derived. However, there were effects other than increased grain glutenin content:

Fifteen of 50 lines (30%) at one field site and 7 of 50 lines (14%) at the other two sites showed some reduction in yield. (They show that this is not related to somaclonal variation due to tissue culturing and probably related to how the gene construct was integrated into the plants chromosomes ["integration effect"].)
Ten lines (20%) showed some co-suppression of native glutenin, meaning they produced less nontransgenic glutenin than normal while producing more transgenic glutenin.
Lines that had been transformed by the same construct showed "clear differences in [glutenin gene] expression levels" (p. 1556).
In visual appearance the majority of transgenic lines were similar to the untransformed variety (Bobwhite), but "often their appearance was less uniform. The nonuniformity was difficult to quantify" (p. 1556); in three lines there were marked differences in appearance.
Although 49 lines contained the bar marker gene that is supposed to convey herbicide resistance, only 25% were sensitive to herbicide.

Source: Bregitzer, P., A.E. Blechl, D. Fiedler, J. Lin et al. (2006). "Changes in High Molecular Weight Glutenin Subunit Composition Can Be Genetically Engineered without Affecting Wheat Agronomic Performance," Crop Science vol. 46, pp. 1553-63.

Author Affiliations: USDA Agricultural Research Service (ARS), and University of California, Davis.

Funding: USDA Agricultural Research Service (ARS).

Product Status: Not on the market as of 2008.

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Seth JordanAugust 27, 2020