Identification of novel rice low phytic acid mutations via TILLING by sequencing

Phytic acid (myo-inositol-1,2,3,4,5,6-hexakisphosphate or InsP(6)) accounts for 75-85 % of the total phosphorus in seeds. Low phytic acid (lpa) mutants exhibit decreases in seed InsP(6) with corresponding increases in inorganic P which, unlike phytic acid P, is readily utilized by humans and monogastric animals. Since InsP(6) may also reduce the bioavailability of essential mineral cations, development of lpa seed crops for animal feeds and whole-grain consumers is of significant interest and requires better understanding of the metabolism of InsP(6) and the role it plays in other plant processes. To date, well over 20 lpa mutants have been reported in a number of species, most of which have been identified through forward genetic screens. In this study, we used a publicly available rice Targeting of Induced Local Lesions IN Genomes (TILLING) resource to identify four novel lpa mutations, two in one member of the inositol(1,3,4)P-3 5/6-kinase (ITPK) gene family (LOC_Os09g34300) and two in a multi-drug resistance-associated protein (MRP) gene (LOC_Os03g04920). The mutations in the ITPK gene resulted in significant reductions in InsP(6) (46 and 68 %), while those found in MRP gene were more modest (20 and 30 %). Evaluation of these lines indicates that one of the ITPK mutants (46 % InsP(6) reduction) and both MRP mutants are similar to wild-type plants in seed weight, germination, and seedling growth. The four mutants identified here represent new resources for the genetic dissection of phytic acid metabolism in rice and the development of germplasm and strategies for breeding lpa rice varieties.