Characterization of myo-inositol-1-phosphate synthase (MIPS) gene expression and phytic acid accumulation in oat (Avena sativa) during seed development

Phytic acid (myo-inositol 1,2,3,4,5,6-hexakisphosphate; InsP6) is the main storage form of phosphorus in plant seeds, and it decreases the bioavailability of minerals in the feed of monogastric animals. The enzyme myo-inositol-1-phosphate synthase (MIPS, EC 5.1.1.4) catalyzes the conversion of D-glucose-6-phosphate to myo-inositol-1-phosphate, which is the initial step of phytic acid biosynthesis. To date, there is no information about the relationship between the expression of MIPS and the accumulation of phytic acid in developing oat seeds. In the present study, MIPS was isolated by rapid amplification of cDNA ends (RACE)-PCR method from the early developing oat seeds by using three consensus primers which were designed from highly conserved regions in the MIPS sequence from other plants. We examined the changes in the expression of MIPS and accumulation of phytic acid in different seed development stages, as well as the changes in total P (TP), Ca, and Mg concentrations during seed maturation. The results of RACE-PCR and northern blot showed that the maximal MIPS transcription level was observed at 5 days after flowering (DAF), and it was not detected in stems and leaves. Phytic acid was first detected at 25 DAF, when the inorganic P (Pi) level was 8.4-fold lower and the phytic acid P (Phy-P) level was 7.3-fold higher than those after 30 DAF. The TP, Ca, and Mg concentrations increased with the progress of seed maturation. These results indicate that MIPS was only expressed in seeds at the early stage of seed development, after which the seeds started to accumulate phytic acid. In addition, TP, Ca, and Mg are accumulated during seeds maturation.