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BIOCHEMICAL PROCESSES AND MACROMOLECULAR STRUCTURES

Quantitative Conversion of Phytate to Inorganic Phosphorus in Soybean Seeds Expressing a Bacterial Phytase^1,[OA]

United States Department of Agriculture Agricultural Research Service, Plant Genetics Research Unit, Columbia, Missouri 65211 (K.D.B., H.B.K., A.B., P.R.B.); and Biochemistry Department (P.Z., P.C., J.C.P.), and Plant Transformation Core Facility, Division of Plant Sciences (Z.J.Z.), University of Missouri, Columbia, Missouri 65211

Phytic acid (PA) contains the major portion of the phosphorus in the soybean (Glycine max) seed and chelates divalent cations. During germination, both minerals and phosphate are released upon phytase-catalyzed degradation of PA. We generated a soybean line (CAPPA) in which an Escherichia coli periplasmic phytase, the product of the appA gene, was expressed in the cytoplasm of developing cotyledons. CAPPA exhibited high levels of phytase expression, 90% reduction in seed PA, and concomitant increases in total free phosphate. These traits were stable, and, although resulted in a trend for reduced emergence and a statistically significant reduction in germination rates, had no effect on the number of seeds per plant or seed weight. Because phytate is not digested by monogastric animals, untreated soymeal does not provide monogastrics with sufficient phosphorus and minerals, and PA in the waste stream leads to phosphorus runoff. The expression of a cytoplasmic phytase in the CAPPA line therefore improves phosphorus availability and surpasses gains achieved by other reported transgenic and mutational strategies by combining in seeds both high phytase expression 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 PA of admixed meals, such as cornmeal, directly to utilizable inorganic phosphorus.

² Present address: Department of Nature Sciences, College of Agriculture and Technology, SUNY, Cobleskill, NY 12043.

³ Present address: Departamento de Bioquímica, Facultad de Química, Universidad Nacional Autónoma de México, 04510 México DF, México.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Joe C. Polacco (polaccoj{at}missouri.edu).

^[OA] Open Access articles can be viewed online without a subscription.

www.plantphysiol.org/cgi/doi/10.1104/pp.107.113480

^* Corresponding author; e-mail polaccoj{at}missouri.edu.

Received November 19, 2007; accepted December 13, 2007; published December 27, 2007.

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On the Inside

Peter V. Minorsky
Plant Physiol. 2008 146: 323-324. [Full Text]