Plasma membrane inositol-proton symporter. Specific for several inositol epimers, such as myoinositol and scylloinositol. D-chiroinositol, mucoinositol, alloinositol and pinitol are also transported with a lower activity. Not active with galactinol and phytate. Inhibited by nickel and to a lesser extent by cobalt. Optimum pH is 5.5-7.0. Expressed in the tapetum, but not in pollen grains. Detected in leaf vascular tissue and in roots. The PSI domain (383-450) is not involved in the plasma membrane targeting and is dispensable for the transport function, but is required for the inhibition by nickel. No visible phenotype. Belongs to the major facilitator superfamily. Sugar transporter (TC 2.A.1.1) family.