Ectopic expression of a soybean phytase in developing seeds of <Emphasis Type="Italic">Glycine max</Emphasis> to improve phosphorus availability

A transgenic approach was used to alter soybean seed phytate content by expressing a soybean phytase gene (GmPhy) during seed development to degrade accumulating phytic acid (IP₆). An expression vector containing the soybean phytase cDNA controlled by the seed-specific -conglycinin promoter (-subunit) was used to transform embryogenic soybean cultures. Plants from four independent transgenic lines were analyzed for transgene integration and seed IP₆ levels. The reduction in IP₆ levels in transgenic seeds compared to control Jack soybeans ranged from 12.6 to 24.8 as determined by HPLC. A low copy transformant was propagated to the T₄ generation and examined in more detail for phytase expression and enzyme activity during seed development. Expression of phytase mRNA and phytase activity increased during seed development, consistent with the use of an embryo-specific promoter. Ectopic phytase expression during seed development offers potential as an effective strategy for reducing phytate content in soybean seed.