RNA editing converts hundreds of cytidine residues in transcripts of higher plant mitochondria to uracil. As a consequence, numerous changes in the amino acid sequences, stop codons, and splice sites are generated. Using an in organello RNA editing system, we characterized higher plant mitochondria RNA and analyzed the ability of maize and cauli-flower mitochondria to edit heterologous transcripts. Indeed, editing was observed for almost all sites, indicating the possibility that the editing information may be stored in the secondary or tertiary RNA structure. Furthermore, an Arabidopsis thaliana in organello editing system was established for the first time, which will be quite useful for further analysis of higher plant RNA editing as well as other RNA processing events. Together with previous research data, these findings suggest a model for higher plant RNA editing that in-cludes transcript- and editing site-specific factors.