Quantitative Conversion of Phytate to Inorganic Phosphorus in Soybean Seeds Expressing a Bacterial Phytase

Abstract

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.

InsP6-Sensitive Variants of the Gle1 mRNA Export Factor Rescue Growth and Fertility Defects of the ipk1 Low-Phytic-Acid Mutation in Arabidopsis

“…Ali et al (2013) also developed low-phytate rice with no apparent developmental defects by seed-specific silencing of IPK1. However, defects in seed weight, germination frequency, and seedling emergence were observed in several other trials, reflecting a role for InsP 6 in seed development (Bilyeu et al, 2008;Kuwano et al, 2009;Li et al, 2014). In this study, we have shown that expression of InsP 6 -sensitive Gle1 variants enhanced plant growth, seed yield, and seed performance of the phytate-deficient ipk1 mutant, suggesting a novel strategy for improving lpa plants.…”

Phytase: An Enzyme to Improve Soybean Nutrition

“…Denbow et al (1998) have observed an improved bioavailability of phytate-P from soybeans transformed with a fungal phytase gene to broilers. Bilyeu et al (2008) have reported that the cytoplasmic expression of an active appA phytase enzyme in developing soybean seeds resulted in the conversion of nearly all seed phytic acid to inorganic P and produced abundant active enzyme in mature seeds capable of releasing significant amounts of phytate-P from soybean meal.…”

Soya, Human Nutrition and Health

“…This does not only result in non-optimal levels of phosphorus and minerals, but also contributes to wastewater pollution. As supplementation is costly and seems to contribute to the pollution problem, one might prefer to make use of a soybean strain expressing a bacterial phytase, resulting in the production of utilizable inorganic phosphorus (Bilyeu et al, 2008). Soybeans are also a known source of vitamin E and folate.…”