Functional Characterization of Two Ripening-related Sucrose Transporters from Grape Berries

The ripening of grape (Vitis vinifera L.) berries is associated with a large accumulation of glucose and fructose in the vacuoles of the fruit cells. These hexoses are derived from sucrose, which is released from the phloem and may be taken up by parenchyma cells prior to hydrolysis. We have expressed two putative ripening-related sucrose transporters from grape berries, VvSUC11 (synonymous with VvSUT1) and VvSUC12, in an invertase deficient yeast strain to characterize their transport activities. Sucrose was taken up by yeast transformed with either transporter at an optimum pH of