The evolution and regulation of major transitions in sexual systems: new insights from the brown algae

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Sexual reproduction is a pervasive phenomenon that produces new genetic combinations in nearly all eukaryotic lineages. Whilst the core processes that define meiotic sex (meiosis and syngamy) are universal, sex determination systems are not evolutionary conserved but are bewilderingly diverse and have had rapid turnover rates during evolution. Transitions among sex determination systems have profound evolutionary and ecological consequences, but our understanding of the mechanisms, ultimate causes, and the consequences of transitions is still surprisingly incomplete. The goal of the Tethys project is to exploit the exceptional richness of sexual features of the brown algae to gain novel insights into the functional bases and ultimate forces associated with transitions between sexual systems, and their impact on the evolution of this important group of eukaryotes. First, we will exploit the amenability of model brown algae to genetic and genomic approaches to uncover the mechanisms and evolutionary forces driving switches between sexual systems across this group. Secondly, we will investigate the regulation and evolution of the genes involved in sexual reproduction in the context of sexual system transitions, by delineating a comprehensive transcriptional and chromatin state roadmap across key brown algal species. Finally, we will examine patterns of correlated evolution between sexual, functional and genomic traits and incorporate ecological information in order to link ecological factors to reproductive transitions and evaluate their consequences on genome structure and species diversification. Collectively, these multilevel analyses will help answer long-standing evolutionary questions about the diversity and turnover of sex determining systems in eukaryotes, but will also provide unprecedented insights into the biology of an important but virtually unexplored eukaryotic supergroup.