ARS | Publication request: Conversion of seed phytate to utilizable phosphorus in soybean seeds expressing a bacterial phytase

Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 13, 2007
Publication Date: February 15, 2008
Citation: Bilyeu, K.D., Zeng, P., Coello, P., Zhang, Z.J., Krishnan, H.B., Beuselinck, P.R., Polacco, J.C. 2008. Conversion of seed phytate to utilizable phosphorus in soybean seeds expressing a bacterial phytase. Plant Physiology. 146:468-477.

Interpretive Summary: We report the development of a soybean line modified to convert seed phytic acid to a more nutritionally available form of phosphorus (P). The achievement bears on environmental quality (less P discharge into waste streams), conservation of dwindling P reserves, soybean embryo development, and plant nutrition. Thus, this project impacts animal, plant, and environmental research. In addition, our line is a distinct improvement over genetic and other transgenic approaches to convert seed phytic acid to forms digestible by monogastric animals. It also provides a field-grown, and very economical source of phytase for treatment of corn and soymeals. In this work, we demonstrate that large stores of phytic acid P are not necessary for proper soybean embryo development, so our strategy could conceivably be employed in other plant systems. The value of this research is as a solution for animal agricultural production systems that combine more nutritious feed with a positive impact on the environment.

Technical Abstract: Phytic acid contains the major part of the phosphorus in the soybean, chelates divalent cations, and is not digested by monogastric animals. Untreated soymeal does not provide monogastrics sufficient phosphorus and minerals, and phytic acid in the waste stream leads to phosphorus run-off. We generated a soybean line in which an E. coli periplasmic phytase, the product of the appA gene, was expressed in the cytoplasm of developing cotyledons. This line exhibited high levels of phytase expression, more than or equal to 90% reduction in seed phytic acid and concomitant increases in total free phosphate. These traits were stable at least through the T6 generation, and did not noticeably decrease germination rates or yield. This line improves upon the P availability achieved by other reported transgenic and mutational strategies. In addition, soymeal from this line can directly convert phytic acid of admixed meals, such as corn, to utilizable phosphorus.