The Rice OsLpa1 Gene Encodes a Novel Protein Involved in Phytic Acid Metabolism

The rice low phytic acid 1 (lpa1) mutant was originally identified using a forward genetics approach. This mutant exhibits a 45% reduction in rice seed phytic acid with a molar-equivalent increase in inorganic phosphorus; however, it does not appear to differ significantly in productivity from its wild-type progenitor. A second lpa1 mutant was identified from additional screening for high seed inorganic phosphorus phenotypes. Using a positional cloning strategy, we identified a single candidate gene at the rice Lpa1 locus. Sequence analysis of the candidate gene from the lpa1 mutants revealed two independent mutations (a single base pair substitution and a single base pair deletion) that confirmed the identification of this candidate as the rice low phytic acid 1 gene, OsLpa1. The OsLpa1 gene has three splice variants. The location and nature of the two mutations suggests that these lesions only affect the translation of the predicted protein derived from the longest transcript. The 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-bisphosphoglycerate from 2-phosphoglycerate. OsLpa1 represents a novel gene involved in phytic acid metabolism.