The Origin and Evolution of Sex Chromosomes, Revealed by Sequencing of the Silene latifolia Female Genome
Published:13 Jul.2023 Source:Current Biology
White campion (Silene latifolia, Caryophyllaceae) was the first vascular plant where sex chromosomes were discovered. This species is a classic model for studies on plant sex chromosomes due to presence of large, clearly distinguishable X and Y chromosomes that originated de novo about 11 million years ago (mya), but lack of genomic resources for this relatively large genome (~2.8 Gb) remains a significant hurdle.
Here we report S. latifolia female genome assembly integrated with sex-specific genetic maps of this species, focusing on sex chromosomes and their evolution. The analysis reveals a highly heterogeneous recombination landscape with strong reduction in recombination rate in the central parts of all chromosomes. Recombination on the X chromosome in female meiosis primarily occurs at the very ends, and over 85% of the X chromosome length is located in a massive (~330 Mb) gene-poor, rarely recombining pericentromeric region (Xpr). The results indicate that the non-recombining region on the Y chromosome (NRY) initially evolved in a relatively small (~15 Mb), actively recombining region at the end of the q-arm, possibly as a result of inversion on the nascent X chromosome.
The NRY expanded about 6 mya via linkage between the Xpr and the sex-determining region, which may have been caused by expanding pericentromeric recombination suppression on the X chromosome. These findings shed light on the origin of sex chromosomes in S. latifolia and yield genomic resources to assist ongoing and future investigations into sex chromosome evolution.