The genome of Ectocarpus subulatus highlights unique mechanisms for stress tolerance in brown algae
2018
Brown algaeare multicellular photosynthetic organisms belonging to the stramenopile lineage. They are successful colonizers of marine
rocky shoresworld-wide. The genus
Ectocarpus, and especially strain Ec32, has been established as a genetic and genomic model for
brown algae. A related species,
Ectocarpussubulatus Kuetzing, is characterized by its high tolerance of abiotic stress. Here we present the genome and
metabolic networkof a haploid male strain of E. subulatus, establishing it as a comparative model to study the genomic bases of stress tolerance in
Ectocarpus. Our analyses indicate that E. subulatus has separated from
Ectocarpussp. Ec32 via
allopatric speciation. Since this event, its genome has been shaped by the activity of viruses and large
retrotransposons, which in the case of chlorophyll-binding proteins, may be related to the expansion of this gene family. We have identified a number of further genes that we suspect to contribute to stress tolerance in E. subulatus, including an expanded family of heat shock proteins, the reduction of genes involved in the production of halogenated defense compounds, and the presence of fewer cell wall polysaccharide-modifying enzymes. However, 96% of genes that differed between the two examined
Ectocarpusspecies, as well as 90% of genes under positive selection, were found to be lineage-specific and encode proteins of unknown function. This underlines the uniqueness of
brown algaewith respect to their stress tolerance mechanisms as well as the significance of establishing E. subulatus as a comparative model for future functional studies.
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