Knockout of frataxin causes embryo lethality in Arabidopsis

Frataxin is a nuclear encoded protein targeted to mitochondrial matrix. In humans, frataxin deficiency is associated with Friedrich’s ataxia, a neurodegenerative and cardiac disorder characterized by accumulation of iron in mitochondria and a diminished activity of various mitochondrial proteins. It has been proposed that frataxin acts as chaperone to assist assembly of [Fe-S] clusters and heme synthesis. Recently, an Arabidopsis gene (AtFH) highly similar to the human frataxin gene and possessing a mitochondrial target domain has been described. Our preliminary RT-PCR analysis of AtFH transcript aboundance shows that AtFH transcript accumulate in cell cultures as well as in various plants organs, and in particular in flowers. However cells treated with excess iron do not accumulate higher AtFH transcript levels than wt. To understand physiological role of frataxin in plants, we identified two independent Arabidopsis heterozygous AtFH knockout mutants (from the Salk collection of insertional mutants); both of them have T-DNA inserted in the AtFH coding region. No homozygous KO lines could be recovered in any of the progeny obtained by selfing the two different mutants. Also, progeny obtained from selfing heterozygous plants segregated with 1 homozygous wt: 2 heterozygous KO ratio.These results are consistent with the hypothesis of lethality of the homozygous null genotypes during embryogenesis. Accordingly, pattern of embryo development in siliques segregating the putative homozygous null embryos show ¼ of all embryos arresting early at 8-16 cell stage. Finally, preliminary in situ hybridization shows accumulation of AtFH transcript in developing wt embryos. Taken together, these results suggest a role of frataxin during embryo development.