The involvement of a PPR protein of the P subfamily in partial RNA editing of an Arabidopsis mitochondrial transcript.

C-to-U RNA editing (i.e., alteration of a C in the genomic sequence to U in the transcript) has been confirmed widely in angiosperm organellar genomes. During the C-to-U RNA editing event, incomplete edited transcripts have been observed at many sites in the steady-state mRNA population (partial editing). Here, by using coexpression analysis and the surveillance of whole editing status on the mitochondrial genome, we have revealed that a pentatricopeptide repeat (PPR) protein classified into the P subfamily (PPR596) has site-specific influence on the efficiency of C-to-U RNA editing events at partial editing sites on the Arabidopsis thaliana mitochondrial genome. Previous works have revealed that PPR proteins classified into the PLS subfamily containing the E or E and DYW motif are involved in RNA editing as trans-factors; they are believed to recruit deaminase at editing sites. In contrast with the mutant analyses of PLS-subfamily PPR proteins, the editing efficiency at rps3eU1344SS was revealed to be significantly increased in ppr596 mutants. Our study implies P-subfamily PPR protein is involved in the control of the degree of partial editing.

Arabidopsis ELONGATED MITOCHONDRIA1 is required for localization of DYNAMIN-RELATED PROTEIN3A to mitochondrial fission sites.

Mitochondrial fission is achieved partially by the activity of self-assembling dynamin-related proteins (DRPs) in diverse organisms. Mitochondrial fission in Arabidopsis thaliana is mediated by DRP3A and DRP3B, but the other genes and molecular mechanisms involved have yet to be elucidated. To identify these genes, we screened and analyzed Arabidopsis mutants with longer and fewer mitochondria than those of the wild type. ELM1 was found to be responsible for the phenotype of elongated mitochondria. This phenotype was also observed in drp3a plants. EST and genomic sequences similar to ELM1 were found in seed plants but not in other eukaryotes. ELM1:green fluorescent protein (GFP) was found to surround mitochondria, and ELM1 interacts with both DPR3A and DRP3B. In the elm1 mutant, DRP3A:GFP was observed in the cytosol, whereas in wild-type Arabidopsis, DRP3A:GFP localized to the ends and constricted sites of mitochondria. These results collectively suggest that mitochondrial fission in Arabidopsis is mediated by the plant-specific factor ELM1, which is required for the relocalization of DRP3A (and possibly also DRP3B) from the cytosol to mitochondrial fission sites.