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Abstract

Brown algae (Phaeophyceae) represent a unique group to study aspects of sexual reproduction due to the rich variation of life cycles, fertilization modes and sex determination systems found in this class. Particularly interesting are the aspects of the evolution of sex determination during the haploid life stage (UV sex chromosomes) and the various degrees of sexual dimorphism between gametes of closely related species, ranging from isogamy to oogamy. With the advent of -omics techniques we now have access to the whole genome sequences and transcriptomic data for males and females of several brown algal species, which allows us to investigate the genomic architecture and evolutionary history of the sex chromosomes across Phaeophyceae and correlate it with the different life history traits. In this study, we applied specific bioinformatic pipelines to identify and analyze the structural and evolutionary features of the male (V) sex chromosomes across two major brown algal orders, the Ectocarpales and the Laminariales. We used high-quality genomic, transcriptomic and genetic marker data to construct genetic maps, annotate genic regions and determine the sex-chromosomes containing the sex-determining regions (SDRs) in S. japonica and D. herbacea. Comparative genomic analysis with the model brown alga Ectocarpus suggests that a core set of sex-linked genes is conserved across all the investigated species, however, the sex-chromosome regions are highly dynamic with modifications occurring in a lineage-specific fashion.