Quantitative conversion of phytate to inorganic phosphorus in soybean seeds expressing a bacterial phytase.
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, >or=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.
Bilyeu
Kristin D
KD
United States Department of Agriculture, Agricultural Research Service, Plant Genetics Research Unit, Columbia, Missouri 65211, USA.
Zeng
Peiyu
P
Coello
Patricia
P
Zhang
Zhanyuan J
ZJ
Krishnan
Hari B
HB
Bailey
April
A
Beuselinck
Paul R
PR
Polacco
Joe C
JC
D010832:6-Phytase / Q000235:genetics* / Q000378:metabolism*; D000135:Acid Phosphatase / Q000235:genetics* / Q000378:metabolism*; D000821:Animal Feed / Q000032:analysis; D029968:Escherichia coli Proteins / Q000235:genetics* / Q000378:metabolism*; D015870:Gene Expression; D018525:Germination; D010758:Phosphorus / Q000378:metabolism*; D010833:Phytic Acid / Q000737:chemistry / Q000378:metabolism*; D030821:Plants, Genetically Modified; D012639:Seeds / Q000235:genetics / Q000378:metabolism*; D013025:Glycine max / Q000166:cytology / Q000235:genetics / Q000378:metabolism*
D029968:Escherichia coli Proteins; D010758:Phosphorus; D010833:Phytic Acid; D000135:Acid Phosphatase; D010832:6-Phytase; C406788:appA protein, E coli