Chondrus crispus Stackhouse (Gigartinales) also known as Irish Moss is a red seaweed up to 15 cm long. It commonly occurs on rocky shores and other hard substrata, inter- and subtidally, in the Northern North Atlantic. At some sites it is the dominant algal species but occurs also mixed with other species, for example Mastocarpus stellatus. Chondrus crispus has a typical triphasic red algal life cycle which is unique among eukaryotes; the three life cycle phases are the carposporophyte, the tetrasporophyte and the gametophyte (Figure 1).
The life history of Chondrus crispus
The tetrasporophyte produces haploid tetraspores after meiosis which develop as either male or female gametophytes; the male gametophytes release non-flagellated spermatia that fertilize the carpogonium located on the female sporophytes; the zygote forms a multicellular carposporophyte which later releases carpospores, giving rise to the tetrasporophyte. The gametophytes and tetraphytes can be distinguished in the field since the gametophytes normally show a blue iridescence. When fertilized, the females can be distinguished in the field by the carposporophytes or, sometimes, holes corresponding to old carposporophytes. The fertile tetrasporophyte shows a spottedpattern easily recognized in the field. Fertile males show small narrow, branched, pale sori usually in the terminal 3-4 mm.
Chondrus crispus has attracted, for a macroalga, a relatively important research effort. The interactions with endo- and epiphytes and subsequent defence reactions have been elucidated in some detail. The responses to abiotic stress have also been relatively well studied, for examples effects of UV, temperature and light.
Being an important red alga there have been an interest for its genomes and genes., for example the mitochondrial genome has been sequenced and studied1,2,8,9,10,11. Expressed sequences tags and microarrays have also been used to increase our knowledge of the genes and physiology of this organism .
To learn more about red algae an international consortium has analyzed the genome of Chondrus crispus. The consortium was led by the Station Biologique de Roscoff in Brittany, France, belonging to Le Centre national de la recherche scientifique (CNRS) and Université Pierre et Marie Curie (UPMC). The genome was sequenced and informatically annotated by the French National Sequencing Center, Genoscope. The genome information was published in 20133.
Abstract Chondrus genome
Red seaweeds are key components of coastal ecosystems and are economically important as food and as a source of gelling agents, but their genes and genomes have received little attention. Here we report the sequencing of the 105-Mbp genome of the florideophyte Chondrus crispus (Irish moss) and the annotation of the 9,606 genes. The genome features an unusual structure characterized by gene-dense regions surrounded by repeat-rich regions dominated by transposable elements. Despite its fairly large size, this genome shows features typical of compact genomes, e.g., on average only 0.3 introns per gene, short introns, low median distance between genes, small gene families, and no indication of large-scale genome duplication. The genome also gives insights into the metabolism of marine red algae and adaptations to the marine environment, including genes related to halogen metabolism, oxylipins, and multicellularity (microRNA processing and transcription factors). Particularly interesting are features related to carbohydrate metabolism, which include a minimalistic gene set for starch biosynthesis, the presence of cellulose synthases acquired before the primary endosymbiosis showing the polyphyly of cellulose synthesis in Archaeplastida, and cellulases absent in terrestrial plants as well as the occurrence of a mannosylglycerate synthase potentially originating from a marine bacterium. To explain the observations on genome structure and gene content, we propose an evolutionary scenario involving an ancestral red alga that was driven by early ecological forces to lose genes, introns, and intergenetic DNA; this loss was followed by an expansion of genome.
Jonas Collén ou Catherine Boyen, Research group Abiotic stress and functional genomics of seaweeds, UMR 7139 CNRS-UPMC, Station Biologique, Place Georges Teissier, CS 90074, 29688 Roscoff, France
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- Collén J, Porcel B, Carre W, Ball S, Chaparro C, Barbeyron T, Michel G, Noel B, Valentin K, Artiguenave F, Arun A, Aury J-M, Barbosa-Neto JF, Bothwell J, Bouget F-Y, Brillet L, Cabello-Hurtado F, Capella-Gutíerrez S, Charrier B, Cladiere L, Cock JM, Coelho SM, Colleoni C, Mirjam C, Da Silva C, Delage L, Denoeud F, Deschamps P, Dittami SM, Elias M, Gabaldón T, Gachon CMM, Groisillier A, Hervé C, Jabbari K, Katinka M, Kloareg B, Kowalczyk N, Labadie K, Leblanc C, Lopez PJ, McLachlan D, Meslet-Cladiere L, Moustafa A, Nehr Z, Nyvall Collén P, Panaud O, Partensky F, Poulain J, Rensing SA, Rousvoal S, Samson G, Symeonidi A, Tonon T, Zambounis A, Wincker P & Boyen C (2013) Genome structure and metabolic features in the red seaweed Chondrus crispus shed light on evolution of the Archaeplastida. PNAS 110: 5247-5252
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