Abstract

Plants are unique in the way Fe-S protein assembly is compartmentalized : the ISC pathway is located in mitochondria, the SUF pathway in chloroplasts and the CIA machinery in the cytosol. To investigate whether these systems are linked, and by which compound(s), we have functionally characterized the ABC transporters of the mitochondria (ATMs) in the model plant Arabidopsis thaliana. Arabidopsis has three ATM genes, namely ATM1 , ATM2 and ATM3 . Using a collection of mutants, we show that only ATM3 has an important function for plant growth. Analyses of selected metal enzymes showed that the activity of cytosolic aconitase (Fe-S) was strongly decreased across the range of atm3 alleles, whereas mitochondrial and plastid Fe-S enzymes were unaffected. In contrast to mutants in the yeast and mammalian orthologues, Arabidopsis atm3 mutants did not display a significant iron homeostasis defect and did not accumulate iron in mitochondria. The putative nature of the substrate of ATM3 and the origin of the chlorosis observed in all atm3 mutants will also be discussed.