Regulation of Iron Homeostasis in Arabidopsis thaliana by the Clock Regulator Time for Coffee

Céline Duc,Françoise Cellier,Stéphane Lobréaux,Jean-François Briat,Frédéric Gaymard

doi:10.1074/jbc.m109.059873

Abstract

In plants, iron homeostasis is tightly regulated to supply sufficient amounts of this metal for an optimal growth while preventing excess accumulation to avoid oxidative stress. To identify new regulators of iron homeostasis, a luciferase-based genetic screen using the Arabidopsis AtFer1 ferritin promoter as a target was developed. This screen identified TIME FOR COFFEE (TIC) as a regulator of AtFer1 gene expression. TIC was previously described as a nuclear regulator of the circadian clock. Mutants in the TIC gene exhibited a chlorotic phenotype rescued by exogenous iron addition and are hypersensitive to iron during the early stages of development. We showed that iron overload-responsive genes are regulated by TIC and by the central oscillator of the circadian clock. TIC represses their expression under low iron conditions, and its activity requires light and light/dark cycles. Regarding AtFer1, this repression is independent of the previously characterized cis-acting element iron-dependent regulatory sequence, known to be involved in AtFer1 repression. These results showed that the regulation of iron homeostasis in plants is a major output of the TIC- and central oscillator-dependent signaling pathways.

Highlights

This last decade, a wealth of information has been obtained on the molecular characterization of genes involved in iron acquisition by roots, in iron allocation to various organs, and in subcellular compartmentalization of iron in plants
Regarding AtFer1, this repression is independent of the previously characterized cis-acting element iron-dependent regulatory sequence, known to be involved in AtFer1 repression. These results showed that the regulation of iron homeostasis in plants is a major output of the TIME FOR COFFEE (TIC)- and central oscillator-dependent signaling pathways
Identification of A. thaliana Mutants Affected in the Regulation of the AtFer1 Ferritin Gene—To identify genes involved in the transcriptional regulation of AtFer1 in response to iron, transgenic lines in the Col-0 background carrying the AtFer1 promoter fused to the LUC reporter gene were produced for the screen

Summary

Introduction

This last decade, a wealth of information has been obtained on the molecular characterization of genes involved in iron acquisition by roots, in iron allocation to various organs, and in subcellular compartmentalization of iron in plants (reviewed in Refs. 4 and 5). Our results showed that TIC and a functional central oscillator of the circadian clock are required for the expression of iron-regulated genes. We investigated the involvement of TIC, described as an upstream regulator of the central oscillator [12, 31], on AtFer1 expression for 48 h in plants grown in LD conditions (Fig. 3D).

Results

Conclusion