Variation in the enzyme activity and gene expression of myo-inositol-3-phosphate synthase and phytate accumulation during seed development in common bean (Phaseolus vulgaris L.)

The most abundant form in which phosphorus occurs in seeds is phytate (myo-inositol hexakisphosphate), mostly known as an antinutrient for animals, given its ability to complex proteins and minerals, despite its antioxidant and anticarcinogenic properties. However, phytate synthesis is still poorly understood, both in terms of its regulation and metabolic route, and relatively few works have addressed the control mechanism of phytate accumulation during seed development. Aiming at understanding the control mechanism of phytate synthesis, we examined myo-inositol-3-phosphate synthase (MIPS) (EC 5.5.1.4) activity and gene expression during seed development of common bean. Phytate concentration was low at the initial stage of seed development, coinciding with a period of the most intense seed metabolism, but followed by a period of high enzymatic activity and gene expression of MIPS when a decrease in its specific activity and transcription was detected throughout seed development until 20 days after flowering; however, the specific activity of MIPS dropped more expressively than the gene expression, matching with higher phytate concentration. Hence, we show that there is evidence of one control point regulating phytate synthesis with MIPS enzyme.