Mitochondrial gene expression was studied using an electrotransformation protocol to introduce foreign DNA into purified wheat mitochondria. Optimal conditions for DNA uptake and transient gene expression were determined. We show here that a DNA plasmid containing either a cognate or a non-cognate gene under the control of a plant mitochondrial promoter is incorporated into the organelle and faithfully recognized by the transcription machinery. Transcripts generated by a plasmid bearing the intron-containing cox II gene were correctly spliced. Moreover, the transcripts were edited at the expected target C residues. The expression and maturation process of the transgene is dependent on the integrity of functional elements such as the promotor or the presence of structural domains necessary for splicing. The mitochondrial transformation described in this report is an important tool to study the multiple steps involved in plant mitochondrial gene expression at conditions closer to those found in vivo.