| Budget Amount *help |
¥3,200,000 (Direct Cost: ¥3,200,000)
Fiscal Year 2000: ¥1,700,000 (Direct Cost: ¥1,700,000)
Fiscal Year 1999: ¥1,500,000 (Direct Cost: ¥1,500,000)
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| Research Abstract |
1L-myo-inositol-1-phosphate [Ins(3)P_1] synthase catalyzes the first step of myo-inositol biosynthesis, represented by the formation of Ins(3)P_1 from glucose 6-phosphate. Of the various metabolic routes diverging from Ins(3)P_1, one is the biosynthesis of phytin (inositol hexakisphosphate), a storage form of phosphate in seeds. We have isolated a rice cDNA clone, pRINO1, which is highly homologous to Ins(3)P_1 from yeast and plants. In situ hybridization and histological analyses of developing seeds revealed that the accumulation pattern of the RINO1 transcripts coincided well With the localization of phytin-containing particles. Both the RINO1 transcripts and the particles accumulated to high levels within the scutellum and the aleurone layer. In addition, the accumulation of the RINO1 transcripts was found to precede the appearance of the phytin particles. These findings suggested that Ins(3)P_1 synthase plays a key role in phytin biosynthesis in developing seeds in rice.
It is well
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known that ABA regulates many genes in developing seeds. Glucose 6-phosphate, the substrate of Ins(3)P_1 synthase, is one of the metabolites of sucrose that is translocated from the source tissues. Therefore, we investigated the effects of ABA and sucrose on the expression of the Ins(3)P_1 synthase gene in cultured cells induced from the scutellum of mature rice seeds. Higher levels of the Ins(3)P_1 transcript accumulation were evident after the treatment of either sugar or ABA.The expression level depended on sucrose concentration (10 to 100mM) and ABA concentration (10^<-8>M to 10^<-4>M). Both sucrose and glucose were effective in the gene induction but mannitol was not. Treatment with both ABA and sucrose resulted in much higher levels of transcript accumulation. A combined treatment of ABA and sucrose revealed that they work synergistically in the induction of the Ins(3)P_1 synthase gene. The level of transcript increased 2 to 4 hours after treatment, when it began to decrease gradually. The promoter analysis of the RINO1 gene revealed that many cis-acting elements responsible for ABA response, seed-specific expression, and heavy metal response existed in the RINO1 promoter. Less
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