Immunophilin-like TWISTED DWARF1 Modulates Auxin Efflux Activities of Arabidopsis P-glycoproteins

Angus S. Murphy,Rodolphe Bouchard,Stefano Mancuso,Markus Geisler,Burkhard Schulz,Vincent Vincenzetti,Klaus Palme,Ivan Paponov,Aurélien Bailly,Sophie C. Oehring,Ok Ran Lee,Joshua J. Blakeslee

doi:10.1074/jbc.m604604200

Abstract

The immunophilin-like protein TWISTED DWARF1 (TWD1/FKBP42) has been shown to physically interact with the multidrug resistance/P-glycoprotein (PGP) ATP-binding cassette transporters PGP1 and PGP19 (MDR1). Overlapping phenotypes of pgp1/pgp19 and twd1 mutant plants suggested a positive regulatory role of TWD1 in PGP-mediated export of the plant hormone auxin, which controls plant development. Here, we provide evidence at the cellular and plant levels that TWD1 controls PGP-mediated auxin transport. twd1 and pgp1/pgp19 cells showed greatly reduced export of the native auxin indole-3-acetic acid (IAA). Constitutive overexpression of PGP1 and PGP19, but not TWD1, enhanced auxin export. Coexpression of TWD1 and PGP1 in yeast and mammalian cells verified the specificity of the regulatory effect. Employing an IAA-specific microelectrode demonstrated that IAA influx in the root elongation zone was perturbed and apically shifted in pgp1/pgp19 and twd1 roots. Mature roots of pgp1/pgp19 and twd1 plants revealed elevated levels of free IAA, which seemed to account for agravitropic root behavior. Our data suggest a novel mode of PGP regulation via FK506-binding protein-like immunophilins, implicating possible alternative strategies to overcome multidrug resistance.

Highlights

Mammalian neurotransmitter signaling [3, 49], auxin is generally classified as a phytohormone because of its transport from sites of synthesis to loci of activity
The C terminus of PGP1 has been identified in a yeast twohybrid screen using the soluble portion of the putative glycosylphosphatidylinositol-anchored immunophilin-like protein TWISTED DWARF1 (TWD1/FKBP42) as bait [16]
Cellular and Polar Transport of indole3-acetic acid (IAA) Is Reduced in twd1 and pgp1/pgp19 Mutants, Indicating a Regulatory Role for TWD1— Recently, interactions between TWD1 and the multidrug resistance (MDR)/PGP-type transporter PGP1 and its closest homolog, PGP19, were demonstrated [16]

Summary

Introduction

Mammalian neurotransmitter signaling [3, 49], auxin is generally classified as a phytohormone because of its transport from sites of synthesis to loci of activity. PGP19 Mediates Auxin Export When Expressed in HeLa Cells— Cellular IAA efflux experiments using plant protoplasts suggested that PGP19 might function in auxin export in a manner similar to PGP1 [17].

Results

Conclusion