Submitted to: Journal of Theoretical and Applied Genetics
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/1/2005
Publication Date: 6/1/2005
Citation: Andaya, C.B., Tai, T. 2005. Fine mapping of the rice low phytic acid (lpal) locus. Journal of Theoretical and Applied Genetics. 111:489-495. Interpretive Summary: The low phytic acid (lpa1) mutation of rice results in a substantial reduction in phytic acid in seeds with a concurrent increase in inorganic phosphate. Phytic acid (and its salt form, phytate) serves as the key storage compound for phosphorus, myo-inositol, and mineral cations needed for seedling growth and development. In addition, phytic acid influences animal and human nutrition. Monogastric animals (e.g. pigs, poultry, and fish) are unable to digest phytic acid and their feeds must be supplemented with phosphorus or an enzyme (phytase) which can breakdown phytic acid. Phytic acids ability to bind mineral cations such as iron and zinc and form complexes that prevent their absorption can lead to micronutrient deficiencies in humans who have seed-based diets. Thus, reduced phytic acid in seeds may be a desirable trait. Despite the impact of phytic acid, relatively little is known concerning it metabolism. Identification and characterization of genes such as the rice Lpa1 will contribute in this area. We have used a molecular genetic approach to characterize the chromosomal region containing the rice Lpa1 gene (as defined by the lpa1 mutation). We have identified several candidates. This work has provided a foundation for determining the Lpa1 gene and tools in the form of DNA markers that may be used to transfer the low phytic acid trait into other rice varieties.
Technical Abstract: Phytic acid (myo-inositol hexakisphosphate) is the primary storage form of phosphorus (P) in cereal grains. In addition to being essential for normal seedling growth and development, phytic acid plays an important role in human and animal nutrition. The rice low phytic acid mutant (lpa1) shows a 45% reduction in seed phytic acid with a molar equivalent increase in inorganic P. The lpa1 locus was previously mapped to the long arm of chromosome 2. Using microsatellite markers and a recombinant inbred line population, the locus has been fine mapped between the markers RM3542 and RM482, which encompass a region of 135 kb. Additional markers were developed from the DNA sequence of this region. Two of these markers further delimited the locus to a 47 kb region containing eight putative open reading frames. Cloning and molecular characterization of the lpa1 gene will provide insight into phytic acid biosynthesis in plants. The markers reported here should also be useful in introgressing the low phytic acid phenotype into other rice cultivars.