This paper describes the analysis of the effect of the restorer gene Rfo on the expression of the ORF138 protein associated with Ogura cytoplasmic male sterility (CMS) which has been engineered in rapeseed by protoplast fusion. We show that the presence of the Rfo gene in the genome of the plants decreases the amount of ORF138 protein in floral buds, this effect being the most dramatic in anthers at the stage of development when the sterile phenotype is normally expressed. However, the amount of orf138 transcripts is not affected by the Rfo gene in the same organs at the same stages. Total polysome analyses of buds and anthers show that the orf138 transcripts are translated with the same efficiency in sterile and restored plants. From these results we infer that the Rfo gene product acts on the post-translational stability of the ORF138 protein, leading to a decrease in the accumulation of the protein and a restoration of fertility.