Catalyzes the majority of myo-inositol synthesis required for plant growth and development. Acts as a repressor of programmed cell death and protects plant cells against cell death under high light intensity or long days. Controls its own transcription by inhibiting ATXR6 activity. Reduces the deposition of inhibitory histone marks on its own promoter. D-glucose 6-phosphate = 1D-myo-inositol 3-phosphate kcat is 6.4 min(-1) for D-glucose 6-phosphate. kcat is 5.0 min(-1) for NAD(+). Polyol metabolism; myo-inositol biosynthesis; myo-inositol from D-glucose 6-phosphate: step 1/2. Homotrimer or homotetramer. Interacts with ATXR5 and ATXR6. Expressed in siliques, leaves, roots, seed endosperm, but not in embryos. Highest expression in leaves, but restricted to vascular tissue in older leaves. Up-regulated by the IPS1 protein itself. Down-regulate upon flagellin treatment. Shorter seedlings with deformed cotyledons and altered root cap organization. Spontaneous lesion formation on mature leaves when plants are transferred under long days. Enhanced basal resistance to pathogens and increased sensitivity to abscisic acid during seed germination and root growth. Belongs to the myo-inositol 1-phosphate synthase family. Was called MIPS2.