Cytoplasmic male sterility-associated ORF79 is toxic to plant regeneration when expressed with mitochondrial targeting sequence of ATPase gamma subunit

Cytoplasmic male sterility (CMS) is a maternally inherited trait that results in the inability of plants to produce functional pollen. CMS is considered as a phenomenon caused by aberrant mitochondrial genomes. In BT-type CMS of rice (Oryza sativa L.), a CMS-associated mitochondrial gene has been reported to be an orf79 gene. To confirm the effect of ORF79 on cell fate, we introduced the orf79 gene with or without a mitochondrial targeting sequence into Taichung 65 carrying normal cytoplasm. It was revealed that ORF79 was toxic to plant regeneration when expressed as a fusion with mitochondrial targeting sequence of the ATPase gamma subunit. This result implicates ORF79 as cytotoxic, and its toxicity depends on its combination with a mitochondrial targeting sequence.