The genome of Ectocarpus subulatus highlights unique mechanisms for stress tolerance in brown algae

Authors: Dittami, Simon M. and Corre, Erwan and Brillet-Gueguen, Loraine and Pontoizeau, Noe and Aite, Meziane and Avia, Komlan and Caron, Christophe and Cho, Chung Hyun and Collen, Jonas and Cormier, Alexandre and Delage, Ludovic and Doubleau, Sylvie and Frioux, Clemence and Gobet, Angelique and Gonzalez-Navarrete, Irene and Groisillier, Agnes and Herve, Cecile and Jollivet, Didier and KleinJan, Hetty and Leblanc, Catherine and Lipinska, Agnieszka P. and Liu, Xi and Marie, Dominique and Markov, Gabriel V. and Minoche, Andre E. and Monsoor, Misharl and Pericard, Pierre and Perrineau, Marie-Mathilde and Peters, Akira F. and Siegel, Anne and Simeon, Amandine and Trottier, Camille and Yoon, Hwan So and Himmelbauer, Heinz and Boyen, Catherine and Tonon, Thierry

Brown algae are multicellular photosynthetic organisms belonging to the stramenopile lineage. They are successful colonizers of marine rocky shores world-wide. The genus Ectocarpus, and especially strain Ec32, has been established as a genetic and genomic model for brown algae. A related species, Ectocarpus subulatus Kuetzing, is characterized by its high tolerance of abiotic stress. Here we present the genome and metabolic network of 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 Ectocarpus sp. 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 Ectocarpus species, 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 algae with respect to their stress tolerance mechanisms as well as the significance of establishing E. subulatus as a comparative model for future functional studies.

Journal: BioRxiv
DOI: 10.1101/307165
Year: 2018

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