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Abstract

Red algae (Rhodophyta) belong to the oldest evolutionary lineages of photosynthetic eukaryotes and comprise one of the largest phyla of algae on the planet. Most of the red algal species are multicellular and macroscopic, live in marine environment and have a complex life history with alternation of three, rather than two, generations. Particularly interesting are the aspects of the evolution of sex determination during the haploid life stage (UV sex chromosomes), however, the sex chromosomes in Rhodophyta have never been described to date. In this study, we used high-quality genomic, transcriptomic and genetic marker data to provide the first report of the red algal UV sex chromosomes using three species from the order Gracilariales. We report the genomic architecture and gene content of the male (V) and female (U) sex chromosomes and their nonrecombining regions. The UV system in Gracilariales shows distinct evolutionary history not only from the well-studied XY and ZW systems but also from the other algal UV systems described so far. Nevertheless, some striking similarities exist, indicating remarkable universality of the underlying processes shaping sex chromosome evolution across major eukaryotic supergroups.