The Diversity of Plant Sex Chromosomes Highlighted through Advances in Genome Sequencing

Abstract

For centuries, scientists have been intrigued by the origin of dioecy in plants, characterizing sex-specific development, uncovering cytological differences between the sexes, and developing theoretical models. Through the invention and continued improvements in genomic technologies, we have truly begun to unlock the genetic basis of dioecy in many species. Here we broadly review the advances in research on dioecy and sex chromosomes. We start by first discussing the early works that built the foundation for current studies and the advances in genome sequencing that have facilitated more-recent findings. We next discuss the analyses of sex chromosomes and sex-determination genes uncovered by genome sequencing. We synthesize these results to find some patterns are emerging, such as the role of duplications, the involvement of hormones in sex-determination, and support for the two-locus model for the origin of dioecy. Though across systems, there are also many novel insights into how sex chromosomes evolve, including different sex-determining genes and routes to suppressed recombination. We propose the future of research in plant sex chromosomes should involve interdisciplinary approaches, combining cutting-edge technologies with the classics to unravel the patterns that can be found across the hundreds of independent origins.

Chromosome-scale assembly with a phased sex-determining region resolves features of early Z and W chromosome differentiation in a wild octoploid strawberry

“…The most similar is Populus alba with ZW sex determination and a 69 kb SDR with 12 W-specific genes ( Yang et al 2021 ), compared to 31 kb and 5 W-specific genes in F. chiloensis . The ability to obtain high-quality chromosome-scale genome assemblies is poised to greatly accelerate the characterization of sex chromosomes ( Carey et al 2021 ), and will clarify whether the features of SDR translocation observed here are general phenomena for plants. Acquisition of haplotype-resolved assemblies, even partially phased such as in this study, will allow a better understanding of autosomal haplotype divergence (exacerbated by repeat sequences), and how this shapes the origin of sex chromosomes.…”

A convergent mechanism of sex determination in dioecious plants: Distinct sex-determining genes display converged regulation on floral B-class genes

“…The rapid development of high-throughput sequencing techniques has enabled a full flourish of plant genomics. Sexdetermining genes have been identified based on combined genomic and experimental approaches in certain dioecious plants with both Type I and II flowers (Carey et al, 2021;Renner and Müller, 2022). Taken together, these findings make it possible for us to elucidate the mechanism of sex determination in dioecious plants.…”

The contributions of Nettie Stevens to the field of sex chromosome biology

“…Contrastingly, a few systems have strong evidence of a single gene initiating female versus male development, as shown in persimmons and poplars [ 103 , 104 ]. Complementary to the many independent evolutions of dioecy, in each of these species examined, different genes have been identified as sex-determining and they function at varying parts of floral development (see reviews in [ 43 , 105 ]). Studies of additional independent origins of sex chromosomes in plants may indeed identify more novel genes involved in carpel and stamen pathways.…”