Mediates both low-affinity uptake and efflux of sugar across the plasma membrane. Regulates cell viability under high salinity. Promotes senescence and sensitivity to salt stress (PubMed:20963606). Contributes to seed filling by triggering sucrose efflux involved in the transfer of sugars from seed coat to embryos (PubMed:25988582). Forms heterooligomers with SWEET1, SWEET6, SWEET8, SWEET11 and SWEET17. Accumulates in leaves during senescence, in a SA-independent manner. Expressed in the lateral roots and in flowers. Expressed in developing seeds (PubMed:25794936). In seedlings, expressed at low levels in the petioles (at protein level) (PubMed:25794936). In young plants, mainly expressed in the roots, particularly in the tips and primordia of lateral roots. In flowering plants, first observed at high levels in young buds of the inflorescence (at protein level), later detected in reproductive tissues, such as pollen grains and ovules. In developing seeds, accumulates specifically at different stages. At globular stage, mostly present in outer integument, but also in endosperm and embryo. At the heart stage, only observed in endosperm and embryo. From the linear mature cotyledon stage until mature seed, accumulates in outer integument and in micropylar endosperm. Detected at low levels in senescent leaves (at protein level) despite a high transcription induction during senescence (PubMed:25794936). Induced by the pathogenic bacteria P.syringae pv. tomato and the fungal pathogen B.cinerea, as well as by salicylic acid (SA) and abscisic acid (ABA). Induced by osmotic stresses (e.g. cold, high salinity, drought, mannitol, and sorbitol) via an abscisic acid-dependent pathway. Highly induced during senescence (PubMed:25794936). Triggered by NAC072/RD26 during senescence (PubMed:29659022). Reduced sensitivity to high salinity. In plants lacking SWEET11, SWEET12 and SWEET15, severe seed defects, which include retarded embryo development, reduced seed weight, and reduced starch and lipid content, causing a wrinkled seed phenotype. Altered sucrose efflux involved in the transfer of sugars from seed coat to embryos thus leading to starch accumulation in the seed coat but not in the embryo (PubMed:25794936). Belongs to the SWEET sugar transporter family.