Role of TIR1/AFB family genes during grafting in Carya cathayensis

Auxins play significant roles in plant growth and development. The transporter inhibitor response1/auxin signaling F-box (TIR1/AFB) gene family encodes the auxin receptor proteins and plays an essential role in the auxin signaling pathway. Here we identified and characterized the TIR1/AFB family in Carya cathayensis (Cc) plants (named as CcTIR1/AFB). Seven CcTIR1/AFBs were identified and further confirmed by cloning. All proteins encoded by these genes conservatively contained two domains, the F-box and leucine-rich repeat (LRR) domains. The CcTIR1/AFBs were located in the nucleus. Phylogenetic analysis suggested that CcTIR1/AFBs were evenly scattered in four different subgroups. The cis-acting element analysis indicates that CcTIR1/AFBs might be activated by auxin. The spatial and temporal expression of CcTIR1/AFBs during grafting suggested that both CcAFB1 and CcAFB2 in scions and CcAFB4 in the rootstocks were significantly upregulated at 3 days after grafting, which indicated the specialization of three CcAFBs during grafting. The Y2H assay indicated that three CcAFBs were capable of interacting with CcIAA16, CcIAA27b, and CcIAA29a, among which CcAFB4 interacted strongly with CcIAA1 and CcIAA16. Our study provides the opportunity to understand the potential role of not only CcTIR1/AFBs but also special CcAFBs (CcAFB1, CcAFB2, and CcAFB4), which is a great aspect to further explore the molecular mechanism during the grafting process.