The transport of sugar across membranes is essential for maintaining cellular sugar homeostasis and metabolic balance in plant cells, but there is limited information about the sugar transporter family in economically important fleshy fruits. Here, 130 sugar transporter genes were identified in the updated apple genome (GDDH13 v1.1). The sugar transporter (ST) genes clustered into ten subfamilies. The apple ST genes mapped to all 17 apple chromosomes and had experienced whole-genome duplication (WGD)/segmental duplication and tandem duplication during the process of apple domestication. Expression profiles of the STs were analyzed in different tissues and during the stages of fruit development. In Malus × domestica, 57 ST genes were expressed in the cultivar ‘Greensleeves’, and 59 in ‘Fuji’. Different ST genes were highly expressed in mature leaves, shoot tips, young fruits, and mature fruits, indicating their divergent functions in different tissues. Heterologous expression experiments in yeast strains lacking STs indicated that MdHT14.1 is the sugar transporter with the highest affinity for glucose and fructose, while MdSUT2.1/2.2 and MdSWEET15.2 had the highest affinity for sucrose. Transient overexpression in apple fruits of MdVGT1 and MdpGlcT2.1 significantly increased glucose concentration, while overexpression of MdSUT2.1 increased sucrose level or of MdSOT1 increased sorbitol concentration. This study demonstrated the expansion and functional divergence of the sugar transporter gene family in domesticated apple and will enable further investigation of the molecular mechanisms of sugar transport and metabolism in apple and other important fleshy fruit crops.

跨膜糖转运对于维持植物细胞中的细胞糖稳态和代谢平衡至关重要，但关于具有经济意义的肉质水果中的糖转运蛋白家族的信息有限。在这里，在更新的苹果基因组 (GDDH13 v1.1) 中鉴定了 130 个糖转运蛋白基因。糖转运蛋白 (ST) 基因聚集成十个亚家族。苹果ST基因定位于所有17条苹果染色体，在苹果驯化过程中经历了全基因组重复（WGD）/节段重复和串联重复。在不同组织和果实发育阶段分析了 STs 的表达谱。在Malus × domestica，57个ST基因在品种'Greensleeves'中表达，59个在'Fuji'中表达。不同的ST基因在成熟叶、梢梢、幼果和成熟果中高表达，表明它们在不同组织中的功能不同。在缺乏STs的酵母菌株中的异源表达实验表明，MdHT14.1是对葡萄糖和果糖亲和力最高的糖转运蛋白，而MdSUT2.1/2.2和MdSWEET15.2对蔗糖的亲和力最高。MdVGT1和MdpGlcT2.1在苹果果实中的瞬时过表达显着增加了葡萄糖浓度，而MdSUT2.1的过表达增加了蔗糖水平或MdSOT1山梨醇浓度增加。该研究证明了驯化苹果中糖转运蛋白基因家族的扩展和功能分化，并将有助于进一步研究苹果和其他重要肉质水果作物中糖转运和代谢的分子机制。