|Kim, Sang Ic|
Submitted to: Planta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/28/2010
Publication Date: 8/24/2010
Citation: Kim, S., Tai, T. 2010. Genetic analysis of two OsLpa1-like genes in Arabidopsis reveals that only one is required for wild-type seed phytic acid levels. Planta. 232:1241-1250.
Interpretive Summary: Phytic acid is the primary storage form of phosphorus in plant seeds accounting for 65-85% of the total phosphorus. Due to its chemical properties, phytic acid is considered an anti-nutrient and reducing the amount of phosphorus stored in this form improves the nutritional quality of seeds used as food and feed. We recently isolated a rice gene called OsLpa1 which is involved in phytic acid biosynthesis and/or accumulation and may be a target for developing seeds with reduced phytic acid but normal levels of total phosphorus. Using the model plant Arabidopsis, we have isolated and characterized the Arabidopsis version of this gene which has revealed that the gene is likely to be involved in biosynthesis rather than accumulation of seed phytic acid and that it may be acting early in a key biosynthetic pathway. Furthermore, studying Arabidopsis has enabled us to determine that a second very similar gene found in both Arabidopsis and rice is in fact not involved in seed phytic acid metabolism. The resources we were able to apply in this study were not available in rice. The use of Arabidopsis and the available tools for this model plant have facilitated new findings that can be applied directly to our ongoing studies in rice.
Technical Abstract: Phytic acid (inositol-1,2,3,4,5,6-hexakisphosphate or InsP6) is the primary storage form of phosphorus in plant seeds. The rice OsLpa1 encodes a novel protein required for wild-type levels of seed InsP6 and was identified from a low phytic acid (lpa) mutant exhibiting a 45-50% reduction in seed InsP6. OsLpa1 is highly conserved in plants and Arabidopsis contains two OsLpa1-like genes, At3g45090 and At5g60760. Analysis of homozygous T-DNA insertion mutants of At5g60760 revealed significantly reduced levels of seed InsP6 while no changes were observed in seeds of At3g45090 mutants. A double knockout mutant of At5g60760 and At3g45090 was created and its seed InsP6 content was similar to that of the At5g60760 mutant indicating that At3g45090 does not provide functional redundancy. OsLpa1 was confirmed to be the ortholog of At5g60760 by complementation of a knockout mutant with a cDNA clone corresponding to the largest of three alternative transcripts of OsLpa1. Interestingly, the large reduction in InsP6 and increase in inorganic phosphate in the At5g60760 mutant was accompanied by a small but reproducible decrease in inositol bisphosphate (InsP2). This result suggested a possible role of At5g60760/OsLpa1 in the phosphorylation of inositol-3-monophosphate (InsP1), a key step in the inositol lipid-independent InsP6 biosynthetic pathway. The expression of At5g60760 was also consistent with its involvement in seed InsP6 biosynthesis.