Rapid and dynamic evolution of a giant Y chromosome inSilene latifolia

Abstract To test hypotheses about the evolution of massive sex-linked regions in plants, we sequenced the genome of Silene latifolia , whose giant heteromorphic sex chromosomes were first discovered in 1923. It has long been known that the Y consists mainly of a male-specific region which does not recombine with the X in male meiosis, and that this region carries the primary sex-determining genes, and other genes contributing to male functioning. However, only with a whole Y chromosome assembly can the candidates be validated experimentally, as we describe. Our new results also illuminate the genomic changes as the ancestral chromosome evolved into the current XY pair, testing ideas about why large regions of sex-linkage evolve, and the mechanisms creating the present recombination pattern. One sentence summary Based on the whole genome sequences of Silene latifolia , a model species for plant sex chromosome evolution, we describe discovery of genes underlying male-female flower differences, and relate the results to ideas about the evolution of the vast non-recombining regions of the Y chromosome.