Auxin transport: ABC proteins join the club.

The isolation of potential auxin carriers from Arabidopsis thaliana marks a breakthrough in the characterization of elements involved in auxin delivery. Current models suggest that asymmetrical localization of auxin uptake and efflux carriers within the plasma membrane control the establishment of auxin gradients via facilitated transport. Now, the analysis of mutants defective in Arabidopsis ABC proteins indicates that primary active transport might participate in the control of auxin homeostasis as well.