Professor Dmitry Filatov, Oxford
Evolution of separate sexes and sex chromosomes in plants
Males and females differ significantly in their appearance, behaviour, physiology and morphology. This is more surprising than it may seem as the two sexes share almost identical sets of genes. How long does it take to develop sexual dimorphism when a species switches from a hermaphroditic state to separate sexes? What happens at the genome and transcriptome levels when such transition occurs? Such transitions are quite common in plants when a hermaphrodite evolves separate male and female individuals. We are addressing these questions using a plant species, Silene latifolia, that evolved separate sexes (dioecy) and sex chromosomes only a few million years ago. Despite relatively recent transition to dioecy many phenotypic traits are already sexually dimorphic and our RNAseq data revealed widespread sexual dimorphism in gene expression. A large proportion of genes that evolved sexual dimorphism are not sex-linked, while sex-linked genes show signs of genetic degeneration (on the Y) and dosage compensation (on the X). Y-chromosome degeneration we observed in Silene, is apparently slower than what would be expected based on our knowledge from animals. This disparity may arise from fundamental difference of plant and animal life cycles: unlike animals, plants have alteration of haploid and diploid generation and widespread haploid expression may result in stronger purifying selection.