MDR-like ABC transporter AtPGP4 is involved in auxin-mediated lateral root and root hair development.

Previous data have suggested an involvement of MDR/PGP-like ABC transporters in transport of the plant hor- mone auxin and, recently, AtPGP1 has been demonstrated to catalyze the primary active export of auxin. Here we show that related isoform AtPGP4 is expressed pre- dominantly during early root development. AtPGP4 loss-of-func- tion plants reveal enhanced lateral root initiation and root hair lengths both known to be under the control of auxin. Further, atpgp4 plants show altered sensitivities toward auxin and the auxin transport inhibitor, NPA. Finally, mutant roots reveal ele- vated free auxin levels and reduced auxin transport capacities. These results together with yeast growth assays suggest a direct involvement of AtPGP4 in auxin transport processes controlling lateral root and root hair development.