High rates of spontaneous chromosomal duplications are compensated by translational regulation in a photosynthetic unicellular eukaryote

While duplications have long been recognized as a fundamental process driving major evolutionary innovations, direct estimations of spontaneous chromosome duplication rates are scarce. Here, we provide the first estimations of spontaneous whole chromosome duplication rates in four green algae and in one diatom species from mutation accumulation (MA) experiments. The spontaneous whole duplication events are 7 to 70 times less frequent than spontaneous point mutations per cell division. Comparative transcriptome analyses between the control versus a MA line with a whole chromosome duplication indicate a ~1.94-fold higher relative level of mRNAs in genes located within the duplicated regions. However, comparative analyses of the translation rate of mRNAs demonstrate that the excess of mRNAs is compensated by a proportional decrease to ~0.67 in translation rates of genes located on duplicated chromosomes. This provides evidence that translation regulation mechanisms orchestrate dosage compensation in duplicated chromosomes. We further investigate the role of the poly(A) tail length in tempering mRNA translation and suggest that poly(A) tail length is regulated and shorter for transcripts linked to the chromosome duplication. These results point out the existence of a post-transcriptional mechanism co-ordinating the translation of hundreds of transcripts from genes located on duplicated regions in eukaryotes. ### Competing Interest Statement The authors have declared no competing interest.