Alkoxy-auxins Are Selective Inhibitors of Auxin Transport Mediated by PIN, ABCB, and AUX1 Transporters

Angus S. Murphy,Yukiko Uehara,Masakazu Hirose,Takeshi Nishimura,Ken-ichiro Hayashi,Masahiko Furutani,Tatsuya Sakai,Tomokazu Koshiba,Haibing Yang,Etsuko Tsuda,Hiroshi Nozaki

doi:10.1074/jbc.m110.171165

Abstract

Polar auxin movement is a primary regulator of programmed and plastic plant development. Auxin transport is highly regulated at the cellular level and is mediated by coordinated transport activity of plasma membrane-localized PIN, ABCB, and AUX1/LAX transporters. The activity of these transporters has been extensively analyzed using a combination of pharmacological inhibitors, synthetic auxins, and knock-out mutants in Arabidopsis. However, efforts to analyze auxin-dependent growth in other species that are less tractable to genetic manipulation require more selective inhibitors than are currently available. In this report, we characterize the inhibitory activity of 5-alkoxy derivatives of indole 3-acetic acid and 7-alkoxy derivatives of naphthalene 1-acetic acid, finding that the hexyloxy and benzyloxy derivatives act as potent inhibitors of auxin action in plants. These alkoxy-auxin analogs inhibit polar auxin transport and tropic responses associated with asymmetric auxin distribution in Arabidopsis and maize. The alkoxy-auxin analogs inhibit auxin transport mediated by AUX1, PIN, and ABCB proteins expressed in yeast. However, these analogs did not inhibit or activate SCF(TIR1) auxin signaling and had no effect on the subcellular trafficking of PIN proteins. Together these results indicate that alkoxy-auxins are inactive auxin analogs for auxin signaling, but are recognized by PIN, ABCB, and AUX1 auxin transport proteins. Alkoxy-auxins are powerful new tools for analyses of auxin-dependent development.

Highlights

Polar auxin movement is a primary regulator of programmed and plastic plant development
Both PIN and ATP-binding cassette group B (ABCB) auxin efflux activities are noncompetitively inhibited by treatment with 1-naphthylphthalamic acid (NPA), 3 The abbreviations used are: NAA, naphthalene 1-acetic acid; indole-3-acetic acid (IAA), indole 3-acetic acid; 2,4-D, 2,4-dichlorophenoxy acetic acid; Bz, benzyloxy; Hex, hexyloxy; NPA, 1-naphthylphthalamic acid; PBA, pyrenoyl benzoic acid; Triiodobenzoic acid (TIBA), 2,3,5-triiodobenzoic acid; BFA, brefeldin A; OS, Okada and Shimura medium
Inhibition of root gravitropism is a common and characteristic activity of auxin transport inhibitors. 5-Alkoxy-IAA (5a– 7a) and 7-alkoxy NAA (3b–7b) derivatives inhibited of root gravitropism (Fig. 1, A and B), with a group of 7-alkoxy-NAA compounds (5b–7b) showing the greatest effect (Fig. 1B and supplemental Fig. S1)

Summary

Introduction

Polar auxin movement is a primary regulator of programmed and plastic plant development. We show that 5-alkoxy-IAA and 7-alkoxy-NAA auxin analogs inhibit polar auxin transport streams and auxin-dependent tropic responses in maize and Arabidopsis. The alkoxy-auxin analogs inhibited the auxin transport activities of PIN, ABCB, and AUX1 transporters expressed in yeast cells.

Results

Conclusion