In plants, sugar plays an important role in plant transport signaling, resistance to stress,and nutrient storage. Sugars will eventually be exported transporters(SWEET) proteins play an indispensable role in sugar allocation between and within plant organs. Sucrose is the major sugar in many fruits and the predominant form of sugar translocated in mulberry(Morus spp., Moraceae). However, the role of the multiple mulberry SWEET genes in sucrose allocation to fruit remains elusive. Here, we provide evidence that mulberry SWEET protein, MaSWEET15, which are members of a sugar transport family, is located on the plasma membrane and is able to mediate cellular sucrose uptake when expressed in yeast.Then, we found ectopic overexpression of MaSWEET15 in tomato can change the sugar content, made the tomato fruit smaller and reduce the number of seeds in plant. In addition, we find that MaSWEET15 in response to the regulation of the hormone JA and is an important positive regulator of resistance to C.shiraiana infection in mulberry. Our findings provide insights into the effect of SWEETs on sugar accumulation in mulberry and its crucial roles in seed development and biotic resistance.