Mediates both low-affinity uptake and efflux of sugar across the plasma membrane. Involved in nurturing the male gametophyte (PubMed:25988582). Forms heterooligomers with SWEET1, SWEET3, SWEET6, SWEET7, SWEET8, SWEET9, SWEET11 and SWEET17. Expressed at low levels in leaves. Slightly induced by the fungal pathogen B.cinerea. Belongs to the SWEET sugar transporter family.