Temporal and spatial patterns of accumulation of the transcript of Myo-inositol-1-phosphate synthase and phytin-containing particles during seed development in rice

Myo-inositol-1-phosphate (I[1]P) synthase (EC 5.5.1.4) catalyzes the reacti on from glucose 6-phosphate to I(1)P, the first step of myo-inositol biosyn thesis. Among the metabolites of I(1)P is inositol hexakisphosphate, which forms a mixed salt called phytin or phytate, a storage form of phosphate an d cations in seeds. We have isolated a rice (Oryza sativa L.) cDNA clone, p RINO1, that is highly homologous to the I(1)P synthase from yeast and plant s. Northern analysis of total RNA showed that the transcript accumulated to high levels in embryos but was undetectable in shoots, roots, and flowers. In situ hybridization of developing seeds showed that the transcript first appeared in the apical region of globular-stage embryos 2 d after anthesis (DAA). Strong signals were detected in the scutellum and aleurone layer af ter 4 DAA. The level of the transcript in these cells increased until 7 DAA , after which time it gradually decreased. Phytin-containing particles call ed globoids appeared 4 DAA in the scutellum and aleurone layer, coinciding with the localization of the RINO1 transcript. The temporal and spatial pat terns of accumulation of the RINO1 transcript and globoids suggest that I(1 )P synthase directs phytin biosynthesis in rice seeds.