ARABIDOPSIS AUX1 GENE - A PERMEASE-LIKE REGULATOR OF ROOT GRAVITROPISM

The plant hormone auxin regulates various developmental processes incl uding root formation, vascular development, and gravitropism. Mutation s within the AUX1 gene confer an auxin-resistant root growth phenotype and abolish root gravitropic curvature. Polypeptide sequence similari ty to amino acid permeases suggests that AUX1 mediates the transport o f an amino acid-like signaling molecule. Indole-3-acetic acid, the maj or form of auxin in higher plants, is structurally similar to tryptoph an and is a likely substrate for the AUX1 gene product. The cloned AUX 1 gene can restore the auxin-responsiveness of transgenic aux1 roots. Spatially, AUX1 is expressed in root apical tissues that regulate root gravitropic curvature.