|Kim, Sang Ic|
Submitted to: Journal of Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/30/2008
Publication Date: 6/20/2008
Citation: Kim, S., Andaya, C.B., Goyal, S.S., Tai, T. 2008. The rice OsLpa1 gene encodse a novel protein involved in phytic acid metabolism. Journal of Theoretical and Applied Genetics. 117:769-779.
Interpretive Summary: Cereal seeds contain large amounts of a compound called phytic acid which is the major storage form of phosphorus. There is an inverse relationship between the amount of phytic acid and the amount of free or inorganic phosphorus in seeds. Normal seeds have relatively high amounts of phytic acid and low amounts of inorganic phosphorus which limits their nutritional value. The rice low phytic acid 1 mutant line was originally identified by screening for seeds with high levels of inorganic phosphorus (HIP), which usually corresponds to low phytic acid. Genetic and chemical analyses indicated that this HIP trait results from a mutation in a single gene. In this study, we isolated the low phytic acid 1 gene using genetic mapping and comparing the DNA sequence of two mutant plants to plants with normal phytic acid levels. The new gene, which we call OsLpa1 (Oryza sativa low phytic acid 1) has not been previously identified as being involved in the metabolism of phytic acid. This novel gene may be a target for manipulation to develop cereal grain crops that have lower seed phytic acid, thus enhancing their nutritional value.
Technical Abstract: The rice low phytic acid 1 (OsLpa1) gene was originally identified using a forward genetics approach. Mutation of this gene resulted in a 45% reduction in rice seed phytic acid with a molar-equivalent increase in inorganic phosphorus; however, the rice lpa1 mutant does not appear to differ significantly in productivity from its wild-type progenitor. Using a positional cloning strategy, we have identified a single candidate gene at the OsLpa1 locus on chromosome 2. Sequence analysis of the original lpa1 mutant and a second allelic mutant revealed two different mutations in this candidate (a single base pair substitution and a single base pair deletion), indicating that this gene is OsLpa1. The OsLpa1 gene encodes three splice variants, all of which are expressed. Both mutations appear to affect the protein encoded by the longest splice variant. The predicted proteins encoded by OsLpa1 do not have homology to any of the inositol phosphate metabolism genes recently characterized in plants, although there is homology to 2-phosphoglycerate kinase, an enzyme found in hyperthermophilic methanogens that catalyzes the formation of 2,3-diphosphoglycerate from 2-phosphoglycerate. OsLpa1 represents a novel gene involved in phytic acid metabolism.