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Sucrose synthase (SUS) comprises a family of enzymes which play pivotal roles in plant development,carbon partitioning and sink strength.A total of 11 SUS genes were identified in apple genome.Phylogenetic analysis revealed that the SUS genes were divided into three groups,designated SUS1,SUS2 and SUS3.The SUS1 and SUS4 group include four homologs respectively,whereas SUS2 group consists of three homologs.The SUS genes belonged to same group showed similar structural characteristics in exon number,size and length distribution.Divergence in expression level was occurred among all SUS family members.Four SUS genes containing MdSUS4.2/4.4,MdSUS4.1,and MdSUS4.3 shared similar expression patterns,and exhibited lower expression level in mature leaves,while MdSUS2.1,MdSUS2.2,MdSUS5.1 and MdSUS5.3 displayed a lower expression level in mature fruits.MdSUS5.3 expressed only in young root tips and young fruits and MdSUS3 with highest expression level in all the apple tissues was detected.The expression level of all of the SUS genes excepted MdSUS4.2/4.4,MdSUS4.1,and MdSUS4.3 showed a decrement at various stages of fruit development.Furthermore,the expression level of all SUS genes in apple shoot tips were up-regulated in lower sorbitol content transgenic lines comparative with wild type,suggested that SUS genes may play distinct roles in the sink-source sugar cycle in apple.