AtIAR1 is a Zn transporter that regulates auxin metabolism in Arabidopsis thaliana

• Published in: Journal of experimental botany Vol. 75; no. 5; pp. 1437 - 1450
• Main Authors: Gate, Thomas, Hill, Lionel, Miller, Anthony J, Sanders, Dale
• Format: Journal Article
• Language: English
• Published: UK Oxford University Press 28.02.2024
• Subjects: Research Papers; membrane transport; hormone conjugation; Auxin; IARI; zinc; endoplasmic reticulum
• ISSN: 0022-0957; 1460-2431
• DOI: 10.1093/jxb/erad468

Abstract Root growth in Arabidopsis is inhibited by exogenous auxin–amino acid conjugates, and mutants resistant to one such conjugate [indole-3-acetic acid (IAA)–Ala] map to a gene (AtIAR1) that is a member of a metal transporter family. Here, we test the hypothesis that AtIAR1 controls the hydrolysis of stored conjugated auxin to free auxin through zinc transport. AtIAR1 complements a yeast mutant sensitive to zinc, but not manganese- or iron-sensitive mutants, and the transporter is predicted to be localized to the endoplasmic reticulum/Golgi in plants. A previously identified Atiar1 mutant and a non-expressed T-DNA mutant both exhibit altered auxin metabolism, including decreased IAA–glucose conjugate levels in zinc-deficient conditions and insensitivity to the growth effect of exogenous IAA–Ala conjugates. At a high concentration of zinc, wild-type plants show a novel enhanced response to root growth inhibition by exogenous IAA–Ala which is disrupted in both Atiar1 mutants. Furthermore, both Atiar1 mutants show changes in auxin-related phenotypes, including lateral root density and hypocotyl length. The findings therefore suggest a role for AtIAR1 in controlling zinc release from the secretory system, where zinc homeostasis plays a key role in regulation of auxin metabolism and plant growth regulation. Regulation of intracellular zinc compartmentation by IAR1 plays a key role in the control of auxin activity through zinc-sensitive release of IAA from IAA conjugate stores.