Plasma membrane broad-spectrum sugar-proton symporter. Mediates the uptake of linear polyols such as sorbitol, xylitol, erythritol or glycerol. Can transport the cyclic polyol myo-inositol and different hexoses, pentoses (including ribose), tetroses and sugar alcohols. Determined at -60 mV (membrane potential) and an extracellular pH of 5.5. Optimum extracellular pH is 4.5 for sorbitol as substrate. Highly expressed in roots. Expressed in vascular tissue of leaves, sepals and siliques. By wounding and insect feeding. Belongs to the major facilitator superfamily. Sugar transporter (TC 2.A.1.1) family.