Mediates both low-affinity uptake and efflux of sugar across the vacuolar membrane. Regulates sugars homeostasis in leaves and roots by exporting/importing them through the tonoplast regarding metabolic demand (PubMed:24028846). Acts as a vacuolar hexose transporter, such as glucose (Glc), fructose (Fru), and sucrose (Suc) (PubMed:25988582, PubMed:24381066, PubMed:24028846). Vmax with glucose as substrate is 0.68 nmol/hour/Xenopus laevis oocyte. Vmax with fructose as substrate is 0.27 nmol/hour/Xenopus laevis oocyte. Vmax with sucrose as substrate is 0.14 nmol/hour/Xenopus laevis oocyte. Forms homooligomers and heterooligomers with SWEET1, SWEET7, SWEET8, SWEET9 and SWEET17. Mostly expressed in the cortex of mature roots, and, to a lower extent, in aerial organs such as leaves, stems, and flowers (PubMed:24381066). Mainly present in vascular parenchyma cells, especially in the petiole vasculature, flower stalks and at the base of individual, not fully developed flowers (PubMed:24028846). Induced by nitrogen. Repressed by glucose (Glc), fructose (Fru), sucrose (Suc), cold, osmotic stress, and nitrogen starvation. Increased root sensitivity to high levels of fructose. Belongs to the SWEET sugar transporter family.