Genome-wide identification of apple auxin receptor family genes and functional characterization of MdAFB1

The auxin receptor (TIR1/AFBs) family encodes the F-box protein subunit, which is involved in the formation of the E3 ubiquitin ligase SCFTIR1/AFBs complex, a key component of the auxin signaling pathway. However, there are few studies on the auxin receptor family in apple (Malus × domestica). In this study, eight MdAFBs were identified, and phylogenetic analysis showed that they were classified into four groups and distributed on eight chromosomes. Herein, a comprehensive analysis of the MdAFB gene family was conducted to identify cis-acting elements, gene structures, protein structures, aligned sequences, conserved motifs, conserved amino acids, and the protein–protein interaction network. The results of yeast two-hybrid assays showed that MdAFB1 interacted with three auxin repressor proteins. The results of qRT-PCR showed that MdAFB1 responded to osmotic and salt stress. The overexpression of MdAFB1 increased osmotic and salt resistance in apple calli, and the ectopic expression of MdAFB1 enhanced osmotic and salt tolerance in Arabidopsis. This study provided a basis for the identification of auxin receptor genes in apple and their functions in mediating osmotic and salt stress.