A Critical View on ABC Transporters and Their Interacting Partners in Auxin Transport

Different subclasses of ATP-binding cassette (ABC) transporters have been implicated in the transport of native variants of the phytohormone auxin. Here, the putative, individual roles of key members belonging to the ABCB, ABCD and ABCG families, respectively, are highlighted and the knowledge of their assumed expression and transport routes is reviewed and compared with their mutant phenotypes. Protein-protein interactions between ABC transporters and regulatory components during auxin transport are summarized and their importance is critically discussed. There is a focus on the functional interaction between members of the ABCB family and the FKBP42, TWISTED DWARF1, acting as a chaperone during plasma membrane trafficking of ABCBs. Further, the mode and relevance of functional ABCB-PIN interactions is diagnostically re-evaluated. A new nomenclature describing precisely the most likely ABCB-PIN interaction scenarios is suggested. Finally, available tools for the detection and prediction of ABC transporter interactomes are summarized and the potential of future ABC transporter interactome maps is highlighted.