Dosage compensation by upregulation of maternal X alleles in both males and females in young plant sex chromosomes

Abstract

During the evolution of sex chromosomes, the Y degenerates and its expression gets reduced relative to the X and autosomes. Various dosage compensation mechanisms that recover ancestral expression levels in males have been described in animals. However, the early steps in the evolution of dosage compensation remain unknown, and dosage compensation outside of the animal kingdom is poorly understood. Here, we studied the evolutionary recent XY system of the plant Silene latifolia. We show that dosage compensation is achieved in this plant by a genomic imprinting mechanism where the maternal X chromosome is upregulated wherever in males or females. This first time observed situation is probably non-optimal for females and may reflect that dosage compensation evolution is in its early stage in this species. These observations strikingly resemble the first stage of the path proposed by Ohno for the evolution of X inactivation in mammals.