The iron-responsive element (IRE)/iron-regulatory protein 1 (IRP1)–cytosolic aconitase iron-regulatory switch does not operate in plants

Abstract

Animal cytosolic ACO (aconitase) and bacteria ACO are able to switch to RNA-binding proteins [IRPs (iron-regulatory proteins)], thereby playing a key role in the regulation of iron homoeostasis. In the model plant Arabidopsis thaliana, we have identified three IRP1 homologues, named ACO1-3. To determine whether or not they may encode functional IRP proteins and regulate iron homoeostasis in plants, we have isolated loss-of-function mutants in the three genes. The aco1-1 and aco3-1 mutants show a clear decrease in cytosolic ACO activity. However, none of the mutants is affected in respect of the accumulation of the ferritin transcript or protein in response to iron excess. cis-acting elements potentially able to bind to the IRP have been searched for in silico in the Arabidopsis genome. They appear to be very rare sequences, found in the 5 -UTR (5 -untranslated region) or 3 -UTR of a few genes unrelated to iron metabolism. They are therefore unlikely to play a functional role in the regulation of iron homoeostasis. Taken together, our results demonstrate that, in plants, the cytosolic ACO is not converted into an IRP and does not regulate iron homoeostasis. In contrast with animals, the RNA binding activity of plant ACO, if any, would be more likely to be attributable to a structural element, rather than to a canonical sequence.

Monoubiquitin-dependent endocytosis of the IRON-REGULATED TRANSPORTER 1 (IRT1) transporter controls iron uptake in plants

“…The IRT1 polyclonal antibody was raised in rabbits against two synthetic peptides, H2N-CMASNSALLMKTIFLV-CONH2 and H2N-CPANDVTLPIKEDDSS-CONH2 (18). Immunodetection of ferritins was performed using an antiferritin antibody recognizing all four isoforms (48). The PIP2 aquaporin was monitored using a primary antibody raised against a 17-amino acid C-terminal peptide of AtPIP2;1 (49).…”

An Allelic Mutant Series of ATM3 Reveals Its Key Role in the Biogenesis of Cytosolic Iron-Sulfur Proteins in Arabidopsis

“…Since ACO2 and ACO3 are both localized in mitochondria, and have normal enzyme activities in atm3 mutants, in contrast to the cytosolic ACO1, the interchanged nomenclature does not affect the conclusions of the article. We apologize for any confusion and we fully support the nomenclature of Arnaud et al (2007). Vol.…”

“…The aco1, aco2, aco3, and nfu2.1 mutant lines (GK-138A08, SALK_014661, SALK_054196, and SALK_039254, respectively) were obtained from the Nottingham Arabidopsis Stock Centre and have been described previously (Touraine et al, 2004;Yabe et al, 2004;Arnaud et al, 2007;Moeder et al, 2007).…”

“…The ACO3 protein and the aco3 mutant in this article correspond to, respectively, the ACO2 (AT4G26970) protein and the aco2-1 mutant in Arnaud et al (2007). ACO2 and aco2 in this article correspond to ACO3 (AT2G05710) in Arnaud et al (2007) and KO-661 in Moeder et al (2007).…”

“…ACO2 and aco2 in this article correspond to ACO3 (AT2G05710) in Arnaud et al (2007) and KO-661 in Moeder et al (2007). The link between the mutant symbols and the stock center codes in this article can be found in the ''Materials and Methods'' and is correct.…”