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Population genomics of picophytoplankton unveils novel chromosome hypervariability

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posted on 2023-06-09, 07:27 authored by Romain Blanc-Mathieu, Marc Krasovec, Maxime Hebrard, Sheree Yau, Elodie Desgranges, Joel Martin, Wendy Schackwitz, Alan Kuo, Gerald Salin, Cecile Donnadieu, Yves Desdevises, Sophie Sanchez-Ferandin, Hervé Moreau, Eric Rivals, Igor V Grigoriev, Nigel Grimsley, Adam Eyre-WalkerAdam Eyre-Walker, Gwenael Piganeau
Tiny photosynthetic microorganisms that form the picoplankton (between 0.3 and 3 mm in diameter) are at the base of the food web in many marine ecosystems, and their adaptability to environmental change hinges on standing genetic variation. Although the genomic and phenotypic diversity of the bacterial component of the oceans has been intensively studied, little is known about the genomic and phenotypic diversity within each of the diverse eukaryotic species present. We report the level of genomic diversity in a natural population of Ostreococcus tauri (Chlorophyta, Mamiellophyceae), the smallest photosynthetic eukaryote. Contrary to the expec- tations of clonal evolution or cryptic species, the spectrum of genomic polymorphism observed suggests a large panmictic population (an effective population size of 1.2 × 107) with pervasive evidence of sexual reproduction. De novo assemblies of low-coverage chromosomes reveal two large candidate mating-type loci with suppressed recom- bination, whose origin may pre-date the speciation events in the class Mamiellophyceae. This high genetic diversity is associated with large phenotypic differences between strains. Strikingly, resistance of isolates to large double- stranded DNA viruses, which abound in their natural environment, is positively correlated with the size of a single hypervariable chromosome, which contains 44 to 156 kb of strain-specific sequences. Our findings highlight the role of viruses in shaping genome diversity in marine picoeukaryotes.

History

Publication status

  • Published

File Version

  • Published version

Journal

Science Advances

ISSN

2375-2548

Publisher

American Association for the Advancement of Science

Issue

7

Volume

3

Article number

e1700239

Department affiliated with

  • Evolution, Behaviour and Environment Publications

Full text available

  • Yes

Peer reviewed?

  • Yes

Legacy Posted Date

2017-07-27

First Open Access (FOA) Date

2017-07-27

First Compliant Deposit (FCD) Date

2017-07-27

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