Genome-Wide Identification and Characterization of ABC Transporters in Nine Rosaceae Species Identifying MdABCG28 as a Possible Cytokinin Transporter linked to Dwarfing

ATP-binding cassette (ABC) transporters constitute a large, diverse, and ubiquitous superfamily that is involved in a broad range of processes. The completion of genome sequencing provides an opportunity to understand the phylogenetic history of the ABC transporter superfamily among Rosaceae species. This study identified a total of 1323 ABC transporter genes from nine Rosaceae genomes: 191 from Malus domestica, 174 from Pyrus communis, 138 from Prunus persica, 118 from Prunus avium, 141 from Prunus dulcis, 122 from Fragaria vesca, 98 from Rubus occidentalis, 162 from Prunus mume, and 179 from Rosa chinensis. Their chemical characterization, phylogenetic analysis, chromosomal localization, gene structure, gene duplication, and tissue-specific expression were studied. Their subcellular localization, transmembrane structures, and protein motifs were predicted. All the ABC transporter genes were grouped into eight subfamilies on the basis of their phylogenetic relationships and structural features. Furthermore, cis-element and expression analysis of 10 potential phytohormone transporters in MdABCG subfamily genes were also performed. Loss of the W-box in the promoter region of MdABCG28 was found to reduce the gene expression level and was linked to the dwarfing phenotype in apple rootstocks. MdABCG28 overexpression promoted shoot growth of atabcg14 mutants in Arabidopsis.