Significance Plants depend on strict regulation of carbon transport to keep the activities of different parts in balance under various environmental conditions. In most crops and the model plant Arabidopsis thaliana , sucrose transporters (SUCs) that are strategically positioned in the leaf veins are responsible for carbon export from photosynthetically active leaves. Despite their central role, relatively little is known about the regulation of SUCs. This study identified two regulatory proteins of Arabidopsis SUC2 and investigated how they modulate sucrose transport activity. Both proteins proved important for the environmental acclimation of leaf carbon export. Furthermore, the increased biomass and yield of plants lacking a regulator observed here demonstrate that manipulation of SUC regulation can be a viable path to enhance plant productivity.