Deep proteomics reveals incorporation of unedited proteins into mitochondrial protein complexes in Arabidopsis

The mitochondrial proteome consists of numerous types of proteins that are either encoded and
synthesized in the mitochondria, or encoded in the nucleus, synthesized in the cytoplasm and
imported into the mitochondria. Their mitochondrial synthesis depends on editing of primary
transcripts at specific sites. This process, known as "RNA editing", is mainly caused by
deamination of cytidine to uridine and can lead to changes in the amino acid sequences of the
encoded proteins. Since RNA editing occurs at different frequencies at these sites, partially
edited transcripts could also be used for translation. Indeed, such transcripts have been shown
to be loaded onto mitoribosomes. Translation of partially edited transcripts could lead to protein
polymorphisms that affect protein activity or protein-protein interactions. However, the effects of
differential RNA editing have not been systematically investigated at the proteome level. Overall,
mitochondrial RNA editing suggested to be a repair process that compensates for defective
sequences within mitochondrial genes(1).
Here, we have comprehensively characterized the Arabidopsis mitochondrial proteome to analyze
its editing status. The vast majority of mitochondrially encoded proteins are derived from edited
mRNAs, suggesting that complete maturation of the transcripts is a prerequisite for the
biosynthesis of the corresponding proteins. However, we report exceptions for subunits of the
ATP synthase complex and mitoribosomes. Furthermore, we present strong evidence for the
incorporation of these incompletely edited proteins into their corresponding protein complexes
(2). The results of this project as well as preliminary results from mutant studies will be presented
and discussed.

(1) Small, I. D., Schallenberg-Rüdinger, M., Takenaka, M., Mireau, H. & Ostersetzer-Biran,O. (2020) Plant organellar
RNA editing: what 30 years of research has revealed. Plant Journal.$
(2) Rugen, N., Senkler, M. & Braun, H.-P. (2024) Deep proteomics reveals incorporation of unedited proteins into
mitochondrial protein complexes in Arabidopsis. Plant Physiology., in press.