Structures and mechanism of the AUX/LAX transporters involved in auxin import

Kien Lam Ung; Lukas Schulz; Lorena Zuzic; Bjørn Lildal Amsinck; Sarah Koutnik-Abele; Ines Benhammouche; Camilla Gottlieb Andersen; Lynette Nel; Birgit Schiøtt; David L. Stokes; Ulrich Zeno Hammes; Bjørn Panyella Pedersen

doi:10.1038/s41477-025-02056-z

Structures and mechanism of the AUX/LAX transporters involved in auxin import

Kien Lam Ung
, Lukas Schulz
, Lorena Zuzic
, Bjørn Lildal Amsinck
, Sarah Koutnik-Abele
, Ines Benhammouche
, Camilla Gottlieb Andersen
, Lynette Nel
, Birgit Schiøtt
, David L. Stokes
, Ulrich Zeno Hammes
, Bjørn Panyella Pedersen^*

^*Corresponding author af dette arbejde

Publikation: Bidrag til tidsskrift/Konferencebidrag i tidsskrift /Bidrag til avis › Tidsskriftartikel › Forskning › peer review

2 Citationer (Scopus)

Abstract

Auxins are plant hormones that direct the growth and development of organisms on the basis of environmental cues. Indole-3-acetic acid (IAA) is the most abundant auxin in most plants. A variety of membrane transport proteins work together to distribute auxins. These include the AUX/LAX protein family that mediate auxin import from the apoplast to the cytosol. Here we use structural and biophysical approaches combined with molecular dynamics to study transport by Arabidopsis thaliana LAX3, which is essential for plant root formation. Transport assays document high-affinity transport of IAA, as well as competitive behaviour of the synthetic phenoxyacetic acid auxin herbicide 2,4-dichlorophenoxyacetic acid and the auxin transport inhibitors 1-naphthoxyacetic acid and 2-naphthoxyacetic acid. Four cryo-EM structures were solved with resolutions of 2.9–3.4 Å: an inward open apo structure, two inward semi-occluded structures in complex with IAA and 2,4-dichlorophenoxyacetic acid, and a fully occluded structure in complex with 2-naphthoxyacetic acid. Structurally, LAX3 consists of a bundle and a scaffold domain. The ligand-binding site is sandwiched between these domains with two histidines occupying positions analogous to the sodium-binding sites in distantly related sodium:neurotransmitter transporters. This architecture suggests that these histidines couple transport to the proton motive force. Molecular dynamics simulations are used to explore substrate binding and release, including their dependence on specific protonation states. This study advances our understanding of auxin recognition and transport by AUX/LAX, providing insights into a fundamental aspect of plant physiology and development.

Originalsprog	Engelsk
Tidsskrift	Nature Plants
Vol/bind	11
Nummer	8
Sider (fra-til)	1670-1680
Antal sider	11
ISSN	2055-0278
DOI	https://doi.org/10.1038/s41477-025-02056-z
Status	Udgivet - aug. 2025

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title = "Structures and mechanism of the AUX/LAX transporters involved in auxin import",

abstract = "Auxins are plant hormones that direct the growth and development of organisms on the basis of environmental cues. Indole-3-acetic acid (IAA) is the most abundant auxin in most plants. A variety of membrane transport proteins work together to distribute auxins. These include the AUX/LAX protein family that mediate auxin import from the apoplast to the cytosol. Here we use structural and biophysical approaches combined with molecular dynamics to study transport by Arabidopsis thaliana LAX3, which is essential for plant root formation. Transport assays document high-affinity transport of IAA, as well as competitive behaviour of the synthetic phenoxyacetic acid auxin herbicide 2,4-dichlorophenoxyacetic acid and the auxin transport inhibitors 1-naphthoxyacetic acid and 2-naphthoxyacetic acid. Four cryo-EM structures were solved with resolutions of 2.9–3.4 {\AA}: an inward open apo structure, two inward semi-occluded structures in complex with IAA and 2,4-dichlorophenoxyacetic acid, and a fully occluded structure in complex with 2-naphthoxyacetic acid. Structurally, LAX3 consists of a bundle and a scaffold domain. The ligand-binding site is sandwiched between these domains with two histidines occupying positions analogous to the sodium-binding sites in distantly related sodium:neurotransmitter transporters. This architecture suggests that these histidines couple transport to the proton motive force. Molecular dynamics simulations are used to explore substrate binding and release, including their dependence on specific protonation states. This study advances our understanding of auxin recognition and transport by AUX/LAX, providing insights into a fundamental aspect of plant physiology and development.",

author = "Ung, \{Kien Lam\} and Lukas Schulz and Lorena Zuzic and Amsinck, \{Bj{\o}rn Lildal\} and Sarah Koutnik-Abele and Ines Benhammouche and Andersen, \{Camilla Gottlieb\} and Lynette Nel and Birgit Schi{\o}tt and Stokes, \{David L.\} and Hammes, \{Ulrich Zeno\} and Pedersen, \{Bj{\o}rn Panyella\}",

note = "Publisher Copyright: {\textcopyright} The Author(s) 2025.",

year = "2025",

month = aug,

doi = "10.1038/s41477-025-02056-z",

language = "English",

volume = "11",

pages = "1670--1680",

journal = "Nature Plants",

issn = "2055-0278",

publisher = "Springer Nature",

number = "8",

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TY - JOUR

T1 - Structures and mechanism of the AUX/LAX transporters involved in auxin import

AU - Ung, Kien Lam

AU - Schulz, Lukas

AU - Zuzic, Lorena

AU - Amsinck, Bjørn Lildal

AU - Koutnik-Abele, Sarah

AU - Benhammouche, Ines

AU - Andersen, Camilla Gottlieb

AU - Nel, Lynette

AU - Schiøtt, Birgit

AU - Stokes, David L.

AU - Hammes, Ulrich Zeno

AU - Pedersen, Bjørn Panyella

PY - 2025/8

Y1 - 2025/8

N2 - Auxins are plant hormones that direct the growth and development of organisms on the basis of environmental cues. Indole-3-acetic acid (IAA) is the most abundant auxin in most plants. A variety of membrane transport proteins work together to distribute auxins. These include the AUX/LAX protein family that mediate auxin import from the apoplast to the cytosol. Here we use structural and biophysical approaches combined with molecular dynamics to study transport by Arabidopsis thaliana LAX3, which is essential for plant root formation. Transport assays document high-affinity transport of IAA, as well as competitive behaviour of the synthetic phenoxyacetic acid auxin herbicide 2,4-dichlorophenoxyacetic acid and the auxin transport inhibitors 1-naphthoxyacetic acid and 2-naphthoxyacetic acid. Four cryo-EM structures were solved with resolutions of 2.9–3.4 Å: an inward open apo structure, two inward semi-occluded structures in complex with IAA and 2,4-dichlorophenoxyacetic acid, and a fully occluded structure in complex with 2-naphthoxyacetic acid. Structurally, LAX3 consists of a bundle and a scaffold domain. The ligand-binding site is sandwiched between these domains with two histidines occupying positions analogous to the sodium-binding sites in distantly related sodium:neurotransmitter transporters. This architecture suggests that these histidines couple transport to the proton motive force. Molecular dynamics simulations are used to explore substrate binding and release, including their dependence on specific protonation states. This study advances our understanding of auxin recognition and transport by AUX/LAX, providing insights into a fundamental aspect of plant physiology and development.

AB - Auxins are plant hormones that direct the growth and development of organisms on the basis of environmental cues. Indole-3-acetic acid (IAA) is the most abundant auxin in most plants. A variety of membrane transport proteins work together to distribute auxins. These include the AUX/LAX protein family that mediate auxin import from the apoplast to the cytosol. Here we use structural and biophysical approaches combined with molecular dynamics to study transport by Arabidopsis thaliana LAX3, which is essential for plant root formation. Transport assays document high-affinity transport of IAA, as well as competitive behaviour of the synthetic phenoxyacetic acid auxin herbicide 2,4-dichlorophenoxyacetic acid and the auxin transport inhibitors 1-naphthoxyacetic acid and 2-naphthoxyacetic acid. Four cryo-EM structures were solved with resolutions of 2.9–3.4 Å: an inward open apo structure, two inward semi-occluded structures in complex with IAA and 2,4-dichlorophenoxyacetic acid, and a fully occluded structure in complex with 2-naphthoxyacetic acid. Structurally, LAX3 consists of a bundle and a scaffold domain. The ligand-binding site is sandwiched between these domains with two histidines occupying positions analogous to the sodium-binding sites in distantly related sodium:neurotransmitter transporters. This architecture suggests that these histidines couple transport to the proton motive force. Molecular dynamics simulations are used to explore substrate binding and release, including their dependence on specific protonation states. This study advances our understanding of auxin recognition and transport by AUX/LAX, providing insights into a fundamental aspect of plant physiology and development.

UR - https://www.scopus.com/pages/publications/105012394568

U2 - 10.1038/s41477-025-02056-z

DO - 10.1038/s41477-025-02056-z

M3 - Journal article

C2 - 40759769

AN - SCOPUS:105012394568

SN - 2055-0278

VL - 11

SP - 1670

EP - 1680

JO - Nature Plants

JF - Nature Plants

IS - 8

ER -

Structures and mechanism of the AUX/LAX transporters involved in auxin import

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