IDENTIFICATION OF AN ARABIDOPSIS MITOFERRINLIKE CARRIER PROTEIN INVOLVED IN CHLOROPLAST IRON METABOLISM

Knowledge of Fe transport into chloroplasts and plant mitochondria is scarce for chloroplasts and very uncertain for plant mitochondria. Our goal is the identification of mitochondrial iron transporters in the model plant Arabidopsis. Since plant cell requirement for iron might be more similar to animal non-erythroid cells than to erythroid ones, we started analysing the Arabidopsis proteins similar to the Danio rerio (zebrafish) Mitoferrin2 MFRN2. Among the various identified putative Arabidopsis mitoferrinlike proteins, we focused on that one encoded by At5g42130, which we named AtMfl1 (MitoFerrinLike1). In fact, AtMfl1 expression strongly correlates with genes coding for proteins involved in chloroplast metabolism; such an unexpected result is supported by the identification, by different research groups, of the protein encoded by At5g42130 and of its homologs from various plant species in the inner chloroplastic envelope membrane proteome whereas neither the protein encoded by At5g42130 nor its homologs from other plant species have been ever identified in the mitochondrial proteome. AtMfl1 gene expression is dependent on Fe supply: AtMfl1 transcript strongly accumulates under Fe excess, moderately under Fe sufficiency and weakly under Fe deficiency. In order to understand the physiological role of AtMfl1, we isolated and characterized two independent AtMfl1 KO mutants, atmfl1-1 and atmfl1-2: AtMfl1 is not an essential gene, since both atmfl1-1 and atmfl1-2 mutants are viable and fertile, though smaller in rosette size. However, when grown under conditions of Fe excess, atmfl1-1 and atmfl1-2 mutants (seedlings, rosette leaves) contain less total Fe than wt and also reduced expression of the iron storage ferritin AtFer1. Arabidopsis mitoferrinlike gene AtMfl1 seems therefore possibly involved in Fe transport into chloroplasts, under different conditions of Fe supply: suppression of its expression alters plant Fe accumulation in various developmental stages. Analysis of a second Arabidopsis mitoferrinlike gene AtMfl2 (MitoFerrinLike2) as well as of the double KO mutant atmfl1-atmfl2 is in progress. Although the identification of a plant mitochondrial iron transporter is still elusive, analysis of AtMfl genes opens the way to a better comprehension of plant subcellular iron trafficking.