Molecular approaches for producing low-phytic-acid grains in rice

Abstract

Phytic acid (myo-inositol hexakisphosphate) is the storage form of phosphorus in plant seeds. Reduction of phytic acid levels in seeds leads to both an increase in the availability of phosphorus and a reduction in the environmental load. Myo-inositol-1-phosphate (Ins(3)P₁) synthase (EC 5.5.1.4) catalyzes the first step in phytic acid biosynthesis. We attempted to reduce the phytic acid content of seeds through manipulation of the expression of the Ins(3)P₁ synthase gene. A rice Ins(3)P₁ synthase gene, RINO1, was transformed into rice plants in the antisense or sense orientation under the control of the CaMV 35S promoter or the RINO1 promoter. Some T₁ seeds that transformed both with RINO1 promoter::antisense RINO1 gene and with 35S promoter::sense RINO1 gene increased the amount of inorganic phosphates, as compared to those of non-transgenic plants. This result suggested a molar-equivalent decrease in phytic acid. We also examined RINO1 promoter activity using a β-glucuronidase (GUS) reporter gene. Finally, we discuss the strategy of molecular breeding to reduce phytic acid levels in seeds.