Sugar transporters PpSWEET9a and PpSWEET14 synergistically mediate peach sucrose allocation from source leaves to fruit

Sugar content is a critical indicator of fruit quality. Sugars will eventually be exported transporters (SWEET) proteins play an indispensable role in sugar allocation between and within plant organs. Sucrose is the major sugar and the predominant form of sugar translocated in peach. However, the role of the multiple peach SWEET genes in sucrose allocation to fruit remains elusive. In this study, a total of 19 SWEET genes were identified in the peach genome, and two Clade III SWEET genes, PpSWEET9a and PpSWEET14 , were found to be highly expressed in mature source leaves and branches. Complementation assays, transgene manipulations, and protein interaction studies revealed that PpSWEET9a and PpSWEET14 served as sucrose efflux proteins and formed a heterooligomer that synergistically directed sucrose allocation from source leaves to fruits. Our findings provide insights into the effect of SWEETs on sugar accumulation in peach fruit and identify genetic candidates for improving fruit quality.