Gene delivery into the plant mitochondria via organelle-specific peptides

We report a method for genetically engineering the mitochondria of plant cells. Several peptides selected from sorting signal sequences of plant mitochondrial proteins were tested for cell-penetrating, specific organelle-targeting and nucleic acid-binding properties. Selected sequences were named mitochondrial targeting peptides (mTPs). Five of them were used to deliver a linear dsDNA gene construct into AC Ultima spring triticale (X. Triticosecale Wittmack) protoplasts and microspores. The mitochondrial transient expression of the aadA:gfp reporter gene was qualitatively determined with confocal microscopy and quantitatively measured using qRT-PCR. Significant aadA:gfp transcript abundance was reported in protoplasts from deliveries of all five mTPs, while this transcript abundance remained low in microspores. mTP1 transfected microspores were cultured to produce green plantlets and screened for aadA:gfp by endpoint PCR. Targeted gene integration into the mitochondrial genome of eight regenerated haploid triticale lines was confirmed by sequencing. This represents the first report of a successful in vivo transfection of crop plant somatic and germ cells via mitochondrial peptides and a method that can be used to study transient gene expression and to stably deliver genes into the mitochondria of a plant.