Hetero/Homo-Complexes of Sucrose Transporters May Be a Subtle Mode to Regulate Sucrose Transportation in Grape Berries.

The sugar distribution mechanism in fruits has been the focus of research worldwide; however, it remains unclear. In order to elucidate the relevant mechanisms in grape berries, the expression, localization, function, and regulation of three sucrose transporters were studied in three representative varieties. Both and expression levels were positively correlated with sugar accumulation in grape berries, whereas showed a negative relationship. The alignment analysis and sucrose transport ability of isolated SUCs were determined to reflect coding region variations among , Ruper, and , indicating that functional variation existed in one SUT from different varieties. Furthermore, potentially oligomerized abilities of VvSUCs colocalized in the sieve elements of the phloem as plasma membrane proteins were verified. The effects of oligomerization on transport properties were characterized in yeast. VvSUC11 and VvSUC12 are high-affinity/low-capacity types of SUTs that stimulate each other by upregulating and , inhibiting sucrose transport, and downregulating the of VvSUC27. Thus, changes in the distribution of different SUTs in the same cell govern functional regulation. The activation and inhibition of sucrose transport could be achieved in different stages and tissues of grape development to achieve an effective distribution of sugar.