Novel Interactions of Adrenodoxin-Related [2Fe-2S] Plant Ferredoxins MFDX1 and MFDX2 Indicate Their Involvement in a Wide Spectrum of Functions in Plant Mitochondria

Electron transfer chains of plant organelles (both chloroplasts and mitochondria) contain their own special set of ferredoxins. The relatively recently described adrenodoxin-like [2Fe-2S]-ferredoxins MFDX1 and MFDX2 of plant mitochondria are among the least studied of these. Until now, the only established function for them is participation in the final stage of biotin biosynthesis. In this work, using genetic and biochemical approaches, we searched for possible partners of these proteins in the genomes and proteomes of tobacco (Nicotiana tabacum L.) and foxglove (Digitalis purpurea L.) plants. MORF9 protein, one of the auxiliary components of the RNA editing complex of organelles (editosome), was found among the most prominent protein partners of adrenodoxin-like [2Fe-2S] tobacco ferredoxins. According to the results obtained from the yeast two-hybrid system, NtMFDX1 and NtMFDX2 of tobacco also bind and interact productively with the previously uncharacterised long non-coding polyadenylated RNA, which, based on its structural features, is capable of regulating the function of a number of components of complexes I (Nad1, Nad5) and III (protein of the cytochrome c synthesis system CcmF) and contributes to the formation of Fe/S-clusters in the corresponding protein complexes of the respiratory chain of plant mitochondria. We found one of the main components of the thiazol synthase complex (mitochondrial protein DpTHI1) to be the partner of ferredoxin DpMFDX2 of Digitalis purpurea. Finally, additional arguments were obtained in favour of the possible participation of MFDX1 and MFDX2 in the very ancient, but only recently described ‘progesterone’ steroid hormonal regulatory system: in leaves of the previously constructed CYP11A1-transgenic tomato plants, only the mature form of mitochondrial cytochrome P450scc (CYP11A1) of mammals is able to enter the mitochondria, where the above-mentioned components of the electron transport chain are localised. In summary, all of the newly revealed interactions of adrenodoxin-like [2Fe-2S] ferredoxins MFDX1 and MFDX2 indicate their participation in a wide range of functions in plant mitochondria.