Sugar Transporter GmSWEET38 Controls Nodule Development and Seed Yield in Soybean

The transport of sugars produced by photosynthesis between source and sink tissues controls multiple biological processes in growth and development. However, the key factors, both genetic and environmental, that influence sugar transport and crop yield are largely unknown. We identified a plasma membrane-localized sugar transporter, GmSWEET38, that facilitates the translocation of sugars to seeds and nodules in soybean (Glycine max L.). GmSWEET38 exhibited both efflux and influx activities of sucrose and fructose in Xenopus oocytes. GmSWEET38 expression was high in the vascular system of roots and nodules, and overexpression of GmSWEET38 enhanced the sugar contents of roots and seeds, consequently promoting nodule development and seed production. Loss of GmSWEET38 function exerted the opposite effects. Intriguingly, GmSWEET38 specifically transported fructose into the rhizosphere, where it is used by beneficial bacteria. By modulating sugar transport and allocation to enhance symbiotic nitrogen fixation, GmSWEET38 can be used for the breeding of high-yielding soybean cultivars.