Quantitative conversion of phytate to inorganic phosphorus in soybean seeds expressing a bacterial phytase

Kristin D. Bilyeu , Peiyu Zeng , Patricia Coello , Zhanyuan J. Zhang , Hari B. Krishnan , April Bailey , Paul R. Beuselinck , and Joe C. Polacco ^*

USDA-ARS, Plant Genetics Research Unit, 110 Waters Hall, Columbia, MO 65211, USA; Biochemistry Department, 117 Schweitzer Hall, University of Missouri, Columbia, MO 65211; Plant Transformation Core Facility, Division of Plant Sciences, University of Missouri, Columbia, MO 65211

^* Corresponding author; email: polaccoj{at}missouri.edu.

Phytic acid contains the major portion of the phosphorus inthe soybean seed and chelates divalent cations. During germinationboth minerals and phosphate are released upon phytase-catalyzeddegradation of phytic acid. We generated a soybean line (CAPPA)in which an E. coli periplasmic phytase, the product of theappA gene, was expressed in the cytoplasm of developing cotyledons.CAPPA exhibited high levels of phytase expression, $≥$ 90% reductionin seed phytic acid and concomitant increases in total freephosphate. These traits were stable, and although resulted ina trend for reduced emergence and a statistically significantreduction in germination rates, had no effect on the numberof seeds per plant or seed weight. Since phytate is not digestedby monogastric animals, untreated soymeal does not provide monogastricssufficient phosphorus and minerals, and phytic acid in the wastestream leads to phosphorus run-off. The expression of a cytoplasmicphytase in the CAPPA line therefore improves phosphorus availability,and surpasses gains achieved by other reported transgenic andmutational strategies by combining in seeds both high phytaseexpression and significant increases in available phosphorus.Thus, in addition to its value as a high-phosphate meal source,soymeal from CAPPA could be used to convert phytic acid of admixedmeals, such as cornmeal, directly to utilizable inorganic phosphorus.