Abstract
Three reading frames called ccmF(N1), ccmF(N2), and ccmF(c) are found in the mitochondrial genome of Arabidopsis. These sequences are similar to regions of the bacterial gene ccmF involved in cytochrome c maturation. ccmF genes are always absent from animal and fungi genomes but are found in mitochondrial genomes of land plant and several evolutionary distant eukaryotes. In Arabidopsis, ccmF(N2) despite the absence of a classical initiation codon is not a pseudo gene. The 3 ccmF genes of Arabidopsis are expressed at the protein level. Their products are integral proteins of the mitochondrial inner membrane with in total 11 to 13 predicted transmembrane helices. The conserved WWD domain of CcmF(N2) is localized in the inter membrane space. The 3 CcmF proteins are all detected in a high molecular mass complex of 500 kDa by Blue Native PAGE. Direct interaction between CcmF(N2) and both CcmF(N1) and CcmF(C) is shown with the yeast two-hybrid split ubiquitin system, but no interaction is observed between CcmF(N1) and CcmF(C). Similarly, interaction is detected between CcmF(N2) and apocytochrome c but also with apocytochrome c(1). Finally, CcmF(N1) and CcmF(N2) both interact with CCMH previously shown to interact as well with cytochrome c. This strengthens the hypothesis that CcmF and CCMH make a complex that performs the assembly of heme with c-type apocytochromes in plant mitochondria.
Highlights
In Arabidopsis, CCMA, CCME, and CCMH genes are encoded in the nucleus [8, 9], whereas ccmB, ccmC, ccmFN1, ccmFN2, and ccmFc are encoded in the mitochondrial genome, at 5 different loci [2]
CcmF in Mitochondrial Genomes—In plants, ccm genes were inherited from the ␣ proteobacterial ancestor of mitochondria
We have searched mitochondrial genomes deposited in GOBASE to try to understand the evolutionary history of ccmF genes among eukaryotes. ccmF, similar to all ccm genes has been lost from all holozoa and from fungi
Summary
These results confirm at the protein level the differential organization of ccmF genes between wheat and Arabidopsis (supplementary Fig. S1B). The 3 CcmF proteins are all detected in complexes of 500 kDa. This does not prove a direct interaction between the 3 Arabidopsis
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