Abstract
A potential role for ABC transporters in the extrusion of xenobiotics has been suggested. Arabidopsis contains 15 genes encoding the pleiotropic drug resistance-type (PDR) ABC transporter, but the functions of most of them remain unknown. In this study, we isolated a semi-dominant mutant designated as atpdr9-1 conferring increased 2,4-D tolerance. The application of 2,4-D, IAA, or NAA to atpdr9-1 revealed that auxin-resistant phenotype is 2,4-D-specific. The root growth assay using T-DNA insertion line, atpdr9-2, showed clear 2,4-D specific hypersensitivity, confirming that isolated atpdr9-1 mutation is a spontaneous gain-of-function mutation. The site of atpdr9-1 is located in second nucleotide binding domain and the region is completely conserved in reported plant PDR-type transporters. Further combinational analysis using both atpdr9-1 and -2 revealed that AtPDR9 protein is implicated in the extrusion of not only 2,4-D but also related chlorophenoxy family of herbicides and the auxin transport inhibitor, NPA.
