摘要：AbstractHalf-size adenosine triphosphate-binding cassette transporter subgroup G (ABCG) genes play crucial roles in regulating the movements of a variety of substrates and have been well studied in several plants. However, half-sizeABCGs have not been characterized in detail in apple (Malus × domesticaBorkh.). Here, we performed a genome-wide identification and expression analysis of the half-sizeABCGgene family in apple. A total of 46 apple half-sizeABCGs were identified and divided into six clusters according to the phylogenetic analysis. A gene structural analysis showed that most half-sizeABCGs in the same cluster shared a similar exon–intron organization. A gene duplication analysis showed that segmental, tandem and whole-genome duplications could account for the expansion of half-sizeABCGtransporters inM. domestica. Moreover, a promoter scan, digital expression analysis and RNA-seq revealed thatMdABCG21may be involved in root's cytokinin transport and thatABCG17may be involved in the lateral bud development ofM. spectabilis‘Bly114’ by mediating cytokinin transport. The data presented here lay the foundation for further investigations into the biological and physiological processes and functions of half-sizeABCGgenes in apple.
