Substitutional Editing of Transcripts from Genes of Cyanobacterial Origin in the Dinoflagellate Ceratium Horridum

Peridinin-containing dinoflagellates, a group of alveolate organisms, harbour small plasmids called minicircles. As most of these minicircles encode genes of cyanobacterial origin, which are also found in plastid genomes of stramenopiles, they were thought to represent the plastid genome of peridinin-containing dinoflagellates. The analyses of minicircle derived mRNAs and the 16S rRNA showed that extensive editing of minicircle gene transcripts is common for Ceratium horridum. Posttranscriptional changes occur predominantly by editing A into G, but other types of editing including a previously unreported A to C transversion were also detected. This leads to amino acid changes in most cases or, in one case, to the elimination of a stop-codon. Interestingly, the edited mRNAs show higher identities to homologous sequences of other peridinin-containing dinoflagellates than their genomic copy. Thus, our results imply that transcript editing of genes of cyanobacterial origin is species specific in peridinin-containing dinoflagellates and demonstrate that editing of genes of cyanobacterial origin is not restricted to land plants.