<b> <i>Arabidopsis AUX1</i> </b> Gene: A Permease-Like Regulator of Root Gravitropism

TLDR

Auxin controls root development and gravitropism, and the AUX1 permease‑like protein, homologous to amino‑acid permeases, is thought to transport an auxin‑like signaling molecule such as indole‑3‑acetic acid. Loss‑of‑function mutations in AUX1 produce auxin‑resistant roots that fail to curve during gravitropism, while transgenic expression of the cloned gene restores auxin responsiveness and is localized to root apical tissues that control curvature.

Abstract

The plant hormone auxin regulates various developmental processes including root formation, vascular development, and gravitropism. Mutations within the AUX1 gene confer an auxin-resistant root growth phenotype and abolish root gravitropic curvature. Polypeptide sequence similarity to amino acid permeases suggests that AUX1 mediates the transport of an amino acid-like signaling molecule. Indole-3-acetic acid, the major form of auxin in higher plants, is structurally similar to tryptophan and is a likely substrate for the AUX1 gene product. The cloned AUX1 gene can restore the auxin-responsiveness of transgenic aux1 roots. Spatially, AUX1 is expressed in root apical tissues that regulate root gravitropic curvature.