Plant Sugar Transporters (SWEET): An Emerging Role in Carbon–Lipid Homeostasis

Abstract In plants, the directed distribution of photosynthetic products from source organs to heterotrophic sink organs forms the material basis for biomass accumulation and crop yield. SWEETs (sugars will eventually be exported transporters) facilitate passive sucrose efflux to link source and sink transport during phloem loading for plant carbon allocation. However, it remains unclear how SWEET-mediated sugar transport coordinates carbon allocation and lipid metabolism. Therefore, this Review integrates the structural evolution, transport mechanisms, and physiological functions of SWEETs. It investigates how SWEET-mediated sucrose transport establishes carbon availability and potentially links sugar-signaling networks to fatty acid biosynthesis. Furthermore, it discusses how the SWEET-mediated carbon flux influences seed oil accumulation by modulating intracellular carbon flux and acetyl-CoA production. Finally, the potential applications of biotechnology to regulate SWEET gene expression are outlined to enhance the carbon-to-lipid conversion efficiency and develop crops with superior traits.