The ABC of ABC Transporters

Abstract ATP-binding cassette (ABC) proteins are mainly active primary transporters and, in plants, form a large family of more than 120 members, which are organized into eight subfamilies. In this chapter, we first briefly describe the general structural and enzymatic properties of ABC transporters. We review the major functions of plant ABC transporters such as hormone transport, response to biotic stress, building surface structures, or cell detoxification. In each case, we discuss how the substrates were identified. We then raise several issues that should be addressed in future research: the requirement of an active transporter for hydrophobic substrates, the problem of identifying the substrates in the absence of transport assays, and the existence of pleiotropic plant ABC transporters with multiple structurally unrelated substrates.