Transgenic Soybean Seeds Accumulating the Nutraceutical Carotenoid ƒ"-Carotene Also Exhibit Collateral Phenotypes.

Transgenic soybean (Glycine max) plants overexpressing a seed-specific chloroplast targeted phytoene synthase gene from Pantoea ananatis accumulated 845 μg carotene g^-1 dry seed weight with a 12:1 ratio of b to a. The b carotene accumulating seeds exhibited a shift in oil composition increasing oleic acid with a concomitant decrease in linoleic acid.  Specifically, the crtB transgenic seeds contained 45% oleic acid compared to 24% in the wildtype, a 1.8 fold increase. Elevated oleic acid has been a target trait in soybean industry due to both its performance and health benefits.  This mid level oleic acid trait was achieved independently of the suppression of the fatty acid desaturase 2 enzyme (FAD2), the metabolic step typically associated with oleic acid production.  In addition to oil composition change, an increase in seed protein content by up 8% (w/w) was also observed in the crtB transgenics. The b-carotene accumulating seeds develop and germinate with the same timing and efficiency as nontransgenics. This is the first report of two desired collateral traits, high oleate and high protein, achieved by the expedient of increasing b-carotene content. Proteomic, transcriptomic and metabolomic analysis of the midmaturation b-carotene cotyledons compared to the nontransgenic did not reveal any significant differences that would account for the altered phenotypes of high oleate and high protein content.  The elevated b-carotene, oleic acid, and protein traits in these transgenic soybeans confer a substantial additive nutritional quality to soybeans with a single gene insertion.