Dosage Compensation and Sex-Biased Gene Expression in a Dioecious Plant

Silene latifolia is a dioecious plant species with young (10 MY), heteromorphic sex chromosomes and male and female flowers displaying strong sexual dimorphism. We used a next-generation transcriptome sequencing approach based on multiple male (XY) and female (XX) individuals of S. latifolia to detect sex-linked SNPs and to assess the extent of sex-biased gene expression. We estimated expression levels of X- and Y-linked alleles in males and females and found evidence for ongoing degeneration of the S. latifolia Y chromosome and for X chromosome dosage compensation. This process has so far only been observed in evolutionary old animal sex chromosome systems. Furthermore, we found that a substantial part of the S. latifolia transcriptome is sex-biased and that the proportion of sex-biased genes is significantly higher on sex chromosomes than across the entire genome. Our results thus reveal that genes with sex-biased expression are overrepresented on plant sex chromosomes and that dosage compensation can quickly evolve de novo after the origin of sex chromosomes.