Title: Approaches and Challenges to Engineering Seed Phytate and Total Phosphorus Author
Submitted to: Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 19, 2009
Publication Date: July 3, 2009
Repository URL: http://riley.nal.usda.gov/nal_web/digi/submission.html
Citation: Raboy, V. 2009. Approaches and Challenges to Engineering Seed Phytate and Total Phosphorus. Plant Science 177:281-296. Interpretive Summary: Both the total amount of phosphorus in seeds, and the chemistry of seed phosphorus, are important to end-use quality of seed crops and to the sustainability and environmental impact of agricultural production. The current status of the genetics and breeding of seed phytic acid, the major form of phosphorus in seeds, and of seed total phosphorus, is critically evaluated. The various challenges to developing low phytic acid crops and alternative approaches are evaluated. Future directions in the development of seed crops optimized for the management of phosphorus use in agriculture is discussed.
Technical Abstract: About 75% of seed total phosphorus (P) is found in a single compound, phytic acid (myo-inositol-1,2,3,4,5,6-hexakisphosphate or InsP6). Phytic acid is not efficiently utilized by monogastric animals (poultry, swine, fish), which creates phosphorus management and environmental impact problems in animal production. Phytic acid also functions as an antinutrient when consumed in human and animal diets. These problems can be addressed via feed or food supplementation with P and other minerals or phytase, or more efficiently and sustainably at their source by crop breeding or bioengineering of low-phytic acid/high available P crops. However, since phytic acid and its synthetic pathways are central to a number of metabolic, developmental and signaling pathways important to plant function and productivity, low-phytate can translate into low-yield or stress susceptibility. The biological functions of phytic acid and identification of genetic resources and strategies useful in engineering high-yielding, stress-tolerant low-phytate germplasm will be reviewed here. One promising approach that can avoid undesirable outcomes due to impacts on phytic acid metabolism is to engineer “high-phytase” seeds. In contrast to the issue of seed phytic acid, there has been relatively little interest in seed total P as a trait of agricultural importance. However, seed total P is very important to the long-term goal of sustainable and environmentally friendly agricultural production. Certain low-phytate genotypes are also "low total P", which might represent the ideal seed P trait for nearly all end-uses, including uses in ruminant and non-ruminant feeds and in biofuels production. Future research directions will include screening for additional genetic resources such as seed total P mutants.