Genome-wide Identification of the Auxin Transporter Gene Families in Sweet Potato (Ipomoea batatas) and their Expression During Tuberization

Auxin is a plant phytohormone that is essential for the initiation of tuberization in sweet potato (Ipomoea batatas (L.) Lam.). Auxin exerts these effects via polar auxin transport facilitated by various auxin influx and efflux carriers. It is unclear which members of the auxin transporter families: PIN, PILS, Aux/LAX, and ABCB, are involved in sweet potato tuber initiation and development. Therefore, a genome-wide analysis of the I. batatas auxin transporter genes was conducted, and their expression patterns during storage root initiation and development were analyzed. Five IbLAX, 16 IbPIN, 12 IbPILS, and 34 IbABCB family members were identified. These genes showed high conservation among families based on their intron-exon structure, motif composition, and phylogenetic analysis. Additionally, the promoter regions of these genes had various cis-acting regulatory elements involved in hormone, light, and developmental responses. The auxin transporter genes were expressed in various sweet potato tissues, and many were differentially expressed during storage root development. IbLAX1, IbPIN13, IbPILS7, IbABCB1, and IbABCB14 showed up-regulated expression during tuber initiation. This study characterizes these auxin transporter gene families for the first time. These results are an important reference for validation studies to determine the specific functions of these genes and their auxin transporting capability.