RNA editing sites in plant mitochondria and plastids are addressed by pentatricopeptide repeat (PPR) proteins with E or E and DYW domains, which recognize a specific nucleotide motif upstream of the edited nucleotide. In addition, some sites require MORF proteins for efficient RNA editing. Here, we assign the novel E domain-containing PPR protein, MEF13, as being required for editing at eight sites in Arabidopsis thaliana. A SNP in ecotype C24 altering the editing level at only one of the eight target sites was located by genomic mapping. An EMS mutant allele of the gene for MEF13 was identified in a SNaPshot screen of a mutated plant population. At all eight target sites of MEF13, editing levels are reduced in both morf3 and morf8 mutants, but at only one site in morf1 mutants, suggesting that specific MEF13-MORF interactions are required. Yeast two-hybrid analyses detect solid connections of MEF13 with MORF1 and weak contact with MORF3 proteins. Yeast three-hybrid (Y3H) analysis shows that the presence of MORF8 enhances the connection between MEF13 and MORF3, suggesting that a MORF3-MORF8 heteromer may form stably or transiently to establish interaction with MEF13.