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Life-cycle modification in open oceans accounts for genome variability in a cosmopolitan phytoplankton

06/01/2015
The ISME Journal
9 pp. 1365-1377

Type

Article dans des revues

Authors

Von Dassow Peter
John Uwe
Ogata Hiroyuki
Probert Ian
Bendif El Mahdi
Kegel Jessica
Audic Stéphane
Wincker Patrick
Da Silva Corinne
Claverie Jean-Michel
Doney Scott
Glover David
Mella Flores Daniella
Herrera Yeritza
Lescot Magali
Garet-Delmas Marie-José
De Vargas Colomban

Emiliania huxleyi is the most abundant calcifying plankton in modern oceans with substantial intraspecific genome variability and a biphasic life cycle involving sexual alternation between calcified 2N and flagellated 1N cells. We show that high genome content variability in Emiliania relates to erosion of 1N-specific genes and loss of the ability to form flagellated cells. Analysis of 185 E. huxleyi strains isolated from world oceans suggests that loss of flagella occurred independently in lineages inhabiting oligotrophic open oceans over short evolutionary timescales. This environmentally linked physiogenomic change suggests life cycling is not advantageous in very large/diluted populations experiencing low biotic pressure and low ecological variability. Gene loss did not appear to reflect pressure for genome streamlining in oligotrophic oceans as previously observed in picoplankton. Life-cycle modifications might be common in plankton and cause major functional variability to be hidden from traditional taxonomic or molecular markers.