Sucrose transporters (SUCs/SUTs) play crucial roles in apoplast transport and long-distance distribution of sucrose throughout the whole plant. However, whether and how the Arabidopsis AtSUC4 modulates sucrose import from apoplast to cytosol remains unclear. In the present study, we found that AtSUC4 protein was localized to the plasma membrane in the root. Expression of AtSUC4 in roots was gradually induced with the increasing sucrose concentrations (0%, 2%, 4% and 6%). When feeding high concentrations (4%...