Mediates both low-affinity uptake and efflux of sugar across the plasma membrane (By similarity). May play roles in nurturing the male gametophyte (PubMed:25988582). Forms homooligomers and heterooligomers with SWEET6, SWEET8, SWEET9, SWEET11 and SWEET12. Expressed in the vegetative cell during the later stages of pollen development, mostly in tricellular pollen grains, and, to a lower extent, in bicellular pollen grains. Slightly induced by the powdery mildew fungus G.cichoracearum and the pathogenic bacteria P.syringae pv. tomato. Belongs to the SWEET sugar transporter family.