Ectocarpus is a genus of filamentous brown alga that includes a model organism for the genomics of multicellularity.[1][2] Among possible model organisms in the brown algae, Ectocarpus was selected for the relatively small size of its mature thallus and the speed with which it completes its life cycle.[3][4] Tools available for Ectocarpus as a model species include a high quality genome sequence[5] and both forward[6] and reverse genetic[7] methodologies, the latter based on CRISPR-Cas9.
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Brown algae are heterokonts, a group that also includes diatoms and oomycetes. Despite their simple filamentous thalli, the Ectocarpales are part of the crown group of brown algal orders and are a sister group to the order Laminariales (kelps).[8] The type species for the genus is Ectocarpus siliculosus (Dillwyn) Lyngbye.[9] In 1809, Dillwyn described Ectocarpus as Conferva siliculosa based on specimens collected by W.J. Hooker from Norfolk and East Sussex. In 1819, Lyngbye subsequently described Ectocarpus using a specimen from Denmark, citing C. siliculosa Dilwyn as its basionym.[10]
Studies on morphology have been limited for Ectocarpus as only two species in the genera (E. siliculosus and E. fasciculatus) are well-described based on morphology and genetic sequence.
Ectocarpus is a filamentous alga that can grow up to 30 cm. Cultured specimens in the laboratory tend to be fertile when they are 1–3 cm in length. Ectocarpus has a normal, branched appearance in unialgal cultures, but in axenic cultures it has a ball-shaped appearance suggesting that bacterial symbionts are required for the alga to attain normal morphology.[11]
Ectocarpus can be found across the globe, in temperate shorelines growing as epiphytes on other flora (e.g. seagrass, other alga) or on rocky substrates (epilithic). While commonly attached to a substrate, thalli of Ectocarpus may also survive while floating. Ectocarpus are more commonly found as epiphytes on marine macroflora rather than epilithic.[12] E. fasciculatus is known as an endophyte of Laminaria digitata, but no study has documented how it bypasses the kelp's defense.[13][14] E. crouaniorum are found in the intertidal zone while E. siliculosus and E. fasciculatus can be found in mid-intertidal and subtidal zones, respectively.[15]
Ectocarpus thalli tend to shelter several marine invertebrates (e.g. crustaceans and nematodes) and some protists.[16] Temperature affects the life cycle of some strains.[17] A study of the life cycles of natural populations in NW France and SW Italy found marked isomorphy between generations in some populations and evidence of populations with modified, asexual life cycles.[18]
In the laboratory, the life history is an isomorphic to slightly heteromorphic alternation of generations, but asexual strains also exist. Ectocarpus has a haploid-diploid life cycle with both sporophyte and gametophyte generations. It can complete its whole life cycle within 3 months in the laboratory. Diploid sporophytes give rise to haploid meiospores which will then produce a haploid gametophyte generation. These gametophytes are dioecious, producing either male or female gametes, which fuse to produce diploid zygotes, restarting the sporophyte stage. Parthenogenesis may also occur when a gamete does not find a gamete of the opposite sex, producing a parthenosporophyte.[19] Deployment of the sporophyte developmental program requires two TALE homeodomain transcription factors, OUROBOROS and SAMSARA.[20] If either of the genes encoding these two proteins is dysfunctional, the alga develops as a gametophyte.
A protocol has been established to culture Ectocarpus in the laboratory. Ectocarpus is able to grow in artificial seawater although the standard medium is Provasoli-enriched seawater (PES). Standard laboratory conditions are growth at 13 degrees Celsius under a 12h:12h light:dark cycle with irradiance at 20 μmol photons m−2 s−1.[21]
Iodide originating from seawater can accumulate to high concentrations in several brown algae but high levels are not observed in Ectocarpus. Genes predicted to encode enzymes involved in iodine metabolism have been identified in Ectocarpus, including haloperoxidases, dehalogenases and haloalkane dehalogenases.[22] These enzymes may be part of the defence mechanism of Ectocarpus against halogenated defenses of brown algal hosts when growing as an epiphyte.[23]
Ectocarpus is vulnerable to an array of pathogens and parasites and is also sensitive to abiotic stresses such as shifts in temperature, light and salinity. Major modifications to the Ectocarpus transcriptome have been observed following stress treatments.[24]
Cock, J. Mark (2023). "The model system Ectocarpus: integrating functional genomics into brown algal research". Journal of Phycology. 59: 4–8. doi:10.1111/jpy.13310. Peters, A.F.; Marie, D.; Scornet, D.; Kloareg, B.; Cock, J.M. (2004). "Proposal of Ectocarpus siliculosus (Ectocarpales, Phaeophyceae) as a model organism for brown algal genetics and genomics". Journal of Phycology. 40 (6): 1079–1088. doi:10.1111/j.1529-8817.2004.04058.x. S2CID 86664046. Dieter G. Müller, Markus Kapp, Rolf Knippers, Viruses in Marine Brown Algae, In: Karl Maramorosch, Frederick A. Murphy and Aaron J. Shatkin, Editor(s), Advances in Virus Research, Academic Press, 1998, Volume 50, Pages 49-67, ISSN 0065-3527, ISBN 9780120398508, doi:10.1016/S0065-3527(08)60805-2 Cormier, Alexandre; Avia, Komlan; Sterck, Lieven; Derrien, Thomas; Wucher, Valentin; Andres, Gwendoline; Monsoor, Misharl; Godfroy, Olivier; Lipinska, Agnieszka; Perrineau, Marie‐Mathilde; Van De Peer, Yves; Hitte, Christophe; Corre, Erwan; Coelho, Susana M.; Cock, J. Mark (2016-11-21). "Re‐annotation, improved large‐scale assembly and establishment of a catalogue of noncoding loci for the genome of the model brown alga Ectocarpus". New Phytologist. 214 (1). Wiley: 219–232. doi:10.1111/nph.14321. ISSN 0028-646X. Macaisne, Nicolas; Liu, Fuli; Scornet, Delphine; Peters, Akira F.; Lipinska, Agnieszka; Perrineau, Marie-Mathilde; Henry, Antoine; Strittmatter, Martina; Coelho, Susana M.; Cock, J. Mark (2017-01-01). "TheEctocarpus IMMEDIATE UPRIGHTgene encodes a member of a novel family of cysteine-rich proteins that have an unusual distribution across the eukaryotes". Development. The Company of Biologists. doi:10.1242/dev.141523. ISSN 1477-9129. Badis, Yacine; Scornet, Delphine; Harada, Minori; Caillard, Céline; Godfroy, Olivier; Raphalen, Morgane; Gachon, Claire M. M.; Coelho, Susana M.; Motomura, Taizo; Nagasato, Chikako; Cock, J. Mark (2021-07-10). "Targeted CRISPR‐Cas9‐based gene knockouts in the model brown alga Ectocarpus". New Phytologist. 231 (5). Wiley: 2077–2091. doi:10.1111/nph.17525. ISSN 0028-646X. Akita, Shingo; Vieira, Christophe; Hanyuda, Takeaki; Rousseau, Florence; Cruaud, Corinne; Couloux, Arnaud; Heesch, Svenja; Cock, J. Mark; Kawai, Hiroshi (2022). "Providing a phylogenetic framework for trait-based analyses in brown algae: Phylogenomic tree inferred from 32 nuclear protein-coding sequences". Molecular Phylogenetics and Evolution. 168: 107408. doi:10.1016/j.ympev.2022.107408. Charrier, Bénédicte; Coelho, Susana M.; Bail, Aude Le; Tonon, Thierry; Michel, Gurvan; Potin, Philippe; Kloareg, Bernard; Boyen, Catherine; Peters, Akira F.; Cock, J. Mark (2008). "Development and physiology of the brown alga Ectocarpus siliculosus: two centuries of research". New Phytologist. 177 (2): 319–332. doi:10.1111/j.1469-8137.2007.02304.x. ISSN 1469-8137. PMID 18181960. Charrier, Bénédicte; Coelho, Susana M.; Bail, Aude Le; Tonon, Thierry; Michel, Gurvan; Potin, Philippe; Kloareg, Bernard; Boyen, Catherine; Peters, Akira F.; Cock, J. Mark (2008). "Development and physiology of the brown alga Ectocarpus siliculosus: two centuries of research". New Phytologist. 177 (2): 319–332. doi:10.1111/j.1469-8137.2007.02304.x. ISSN 1469-8137. PMID 18181960. Peters, Akira F.; Wijk, Serinde J. Van; Cho, Ga Youn; Scornet, Delphine; Hanyuda, Takeaki; Kawai, Hiroshi; Schroeder, Declan C.; Cock, J. Mark; Boo, Sung Min (2010). "Reinstatement of Ectocarpus crouaniorum Thuret in Le Jolis as a third common species of Ectocarpus (Ectocarpales, Phaeophyceae) in Western Europe, and its phenology at Roscoff, Brittany". Phycological Research. 58 (3): 157–170. doi:10.1111/j.1440-1835.2010.00574.x. ISSN 1440-1835. S2CID 82731900. Charrier, Bénédicte; Coelho, Susana M.; Bail, Aude Le; Tonon, Thierry; Michel, Gurvan; Potin, Philippe; Kloareg, Bernard; Boyen, Catherine; Peters, Akira F.; Cock, J. Mark (2008). "Development and physiology of the brown alga Ectocarpus siliculosus: two centuries of research". New Phytologist. 177 (2): 319–332. doi:10.1111/j.1469-8137.2007.02304.x. ISSN 1469-8137. PMID 18181960. Couceiro, Lucía; Le Gac, Mickael; Hunsperger, Heather M.; Mauger, Stéphane; Destombe, Christophe; Cock, J. Mark; Ahmed, Sophia; Coelho, Susana M.; Valero, Myriam; Peters, Akira F. (2015). "Evolution and maintenance of haploid-diploid life cycles in natural populations: The case of the marine brown algaEctocarpus". Evolution. 69 (7). Wiley: 1808–1822. doi:10.1111/evo.12702. ISSN 0014-3820. Charrier, Bénédicte; Coelho, Susana M.; Le Bail, Aude; Tonon, Thierry; Michel, Gurvan; Potin, Philippe; Kloareg, Bernard; Boyen, Catherine; Peters, Akira F.; Cock, J. Mark (January 2008). "Development and physiology of the brown alga Ectocarpus siliculosus : two centuries of research". New Phytologist. 177 (2): 319–332. doi:10.1111/j.1469-8137.2007.02304.x. ISSN 0028-646X. PMID 18181960. Arun, Alok; Coelho, Susana M.; Peters, Akira F.; Bourdareau, Simon; Pérès, Laurent; Scornet, Delphine; Strittmatter, Martina; Lipinska, Agnieszka; Yao, Haiqin; Godfroy, Olivier; Montecinos, Gabriel J.; Avia, Komlan; Macaisne, Nicolas; Troadec, Christelle; Bendahmane, Abdelhafid; Cock, J. Mark (2019). "Convergent recruitment of TALE homeodomain life cycle regulators to direct sporophyte development in land plants and brown algae". eLife. 8: e43101. doi:10.7554/eLife.43101. Cock, J. Mark; Sterck, Lieven; Rouzé, Pierre; Scornet, Delphine; Allen, Andrew E.; Amoutzias, Grigoris; Anthouard, Veronique; Artiguenave, François; Aury, Jean-Marc; Badger, Jonathan H.; Beszteri, Bank (June 2010). "The Ectocarpus genome and the independent evolution of multicellularity in brown algae". Nature. 465 (7298): 617–621. Bibcode:2010Natur.465..617C. doi:10.1038/nature09016. ISSN 1476-4687. PMID 20520714. S2CID 4329490. For information concerning Ectocarpus landsburgii and link to download of the original description (with image) in Harvey, W.H. (1849)—Phycologia britannica see: "Ectocarpus landsburgii Harvey 1849". AlgaeBase. Archived from the original on 2022-11-21. Retrieved 2022-11-21.
Bourdareau, Simon; Tirichine, Leila; Lombard, Bérangère; Loew, Damarys; Scornet, Delphine; Wu, Yue; Coelho, Susana M.; Cock, J. Mark (2021). "Histone modifications during the life cycle of the brown alga Ectocarpus". Genome Biology. 22 (1). Springer Science and Business Media LLC. doi:10.1186/s13059-020-02216-8. ISSN 1474-760X.
Ahmed, Sophia; Cock, J. Mark; Pessia, Eugenie (2014). "A Haploid System of Sex Determination in the Brown Alga Ectocarpus sp". Current Biology. 24 (17): 1945–1957. doi:10.1016/j.cub.2014.07.042. PMID 25176635.
Tarver, James E.; Cormier, Alexandre; Pinzón, Natalia; Taylor, Richard S.; Carré, Wilfrid; Strittmatter, Martina; Seitz, Hervé; Coelho, Susana M.; Cock, J. Mark (2015). "microRNAs and the evolution of complex multicellularity: identification of a large, diverse complement of microRNAs in the brown algaEctocarpus". Nucleic Acids Research. 43 (13). Oxford University Press (OUP): 6384–6398. doi:10.1093/nar/gkv578. ISSN 0305-1048.
Prigent, Sylvian (2014). "The genome-scale metabolic network of Ectocarpus siliculosus (EctoGEM): a resource to study brown algal physiology and beyond". Plant Journal. 80 (2): 367–381. doi:10.1111/tpj.12627. PMID 25065645.
