Deficiency of Arabidopsis thaliana frataxin alters activity of mitochondrial Fe-S proteins and induces oxidative stress.

Frataxin, a protein crucial for the biogenesis of mitochondria in different organisms, was recently identified in Arabidopsis thaliana. To investigate the role of frataxin in higher plants, we analyze two knock-out and one knock-down T-DNA insertion mutants. The knock-out mutants present an embryo-lethal phenotype, indicating an essential role for frataxin. The knock-down mutant has reduced frataxin mRNA and protein levels. This mutant also presents retarded growth, reduced fresh weight of fruits and reduced number of seeds per fruit. Surprisingly, transcription of aconitase and the Fe-S subunit of succinate dehydrogenase (SDH2-1) are increased in mutant plants; however, the activity of these proteins is reduced, indicating a role for frataxin in Fe-S cluster assembly or insertion of Fe-S clusters into proteins. Mutant plants also have increased CO(2) assimilation rates, exhibit increased formation of reactive oxygen species (ROS) and have increased levels of transcripts for proteins known to be involved in the ROS stress responses. These results indicate that frataxin is an essential protein in plants, required for full activity of mitochondrial Fe-S proteins and playing a protective role against oxidative damage.