Zusammenfassung
The recent completion of the Ectocarpus genome is affording fundamental insights into brown algal reproductive biology. Currently, research in our group is focused on understanding two key phenomena during the Ectocarpus life cycle: the genetic control of sexuality and the regulation of the alternation between sporophyte and gametophyte generations. The genetic determination of sex requires either non-recombining chromosome regions or complete sex chromosomes, both of which have evolved independently and repeatedly across different species. Comparative analyses of sexual systems found in land plants and animals and other eukaryotes have played a key role in understanding how sexual systems evolve. In this context, the brown algae represent a highly interesting group not only because of their evolutionary distance from other eukaryotic lineages but also because they exhibit a broad range of levels of gamete dimorphism, ranging from isogamy to oogamy; furthermore, sex is expressed in the haploid phase, which should affect the evolution of sex chromosomes. We report on the mapping and genomic analysis of the male and female sex determining regions in Ectocarpus, elucidating its evolution and regulation. By exploiting resources generated as part of the Ectocarpus genome project we have identified a sex determining region of ∼1 Mbp on the male genome, where recombination is totally suppressed. We are exploring the differences between male and female sequences in this region to retrace their evolutionary history. In parallel, deep transcriptome analysis is unraveling the transcriptional network involved in Ectocarpus sex determination and differentiation. We will discuss how the elucidation of sex determination in this third major eukaryotic lineage will help to test existing theories of the evolutionary dynamics of sex determining regions. Additionally, we will describe how genetic approaches, in particular the identification of life cycle mutants, is helping to shed light on the genetic mechanisms controlling complex life cycles.
