How vacuolar sugar transporters evolve and control cellular sugar homeostasis, organ development and crop yield.

Sugar exchange among different subcellular compartments is central for achieving cellular sugar homeostasis and directly affects the yield and quality of many horticultural and field crops. While a portion of photosynthesis-originated sugars is metabolized through glycolysis upon entering the cytosol, the remainder is reversibly channelled to the vacuole, mediated by different families of vacuolar sugar transporter (VST) located on the vacuolar membrane, the tonoplast. Historically, sugar transporters operating on plasma membranes have been studied more than those on tonoplasts. Recently, however, several breakthroughs have shed light on (1) the distinct roles of VSTs in plant development and stress responses and (2) how seemingly unrelated classes of VSTs act together to modulate sugar influx into and efflux from the vacuoles. Here we evaluate these advances, analyse the evolution of VSTs and identify knowledge gaps and future directions for better understanding and manipulation of cytosolic-vacuolar sugar exchange to optimize plant performance.