Genomic imprinting mediates dosage compensation in a young plant XY system

Degeneration of the Y during sex chromosome evolution results in reduced expression relative to the X and autosomes. Diverse dosage compensation mechanisms that recover ancestral expression levels in males have been described in animals, but the early steps in the evolution of dosage compensation remain unknown. Our study of the evolutionarily young XY sex determination system in the plant Silene latifolia revealed a novel dosage compensation mechanism. Genomic imprinting results in higher expression from the maternal X chromosome in both males and females. X overexpression in females may be detrimental and represent a transient early stage in the evolution of dosage compensation. Our finding has striking resemblance to the first stage proposed by Ohno for the evolution of X inactivation in mammals.