The expanded Bostrychia moritziana genome unveils evolution in the most diverse and complex order of red algae

Consistent with increased genome size, we identify a substantial increase in gene content in Bostrychia that was shaped both by de novo gene emergence and by the amplification of gene families in common with other Ceramiales seaweeds, providing key insight into the genetic adaptations underpinning the evolutionary success of this species-rich order. Finally, our sex-specific assemblies enabled us to resolve the UV sex chromosomes in Bostrychia, which feature expanded gene-rich sex-linked regions.

Notably, these sex-linked regions each harbour a distinct TALE-HD transcription factor orthologous to ancient regulators of haploid-diploid transitions in other multicellular lineages. Together, our findings offer unique perspectives into the genomic adaptations driving red algal diversity and demonstrate how this highly successful group of red seaweeds can provide insight into the evolutionary origins and common principles of complex multicellular plant life.