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The Plastid Genome in Cladophorales Green Algae Is Encoded by Hairpin Chromosomes

Del Cortona, A; Leliaert, F; Bogaert, KA; Turmel, M; Boedeker, C; Janouskovec, J; Lopez-Bautista, JM; ... De Clerck, O; + view all (2017) The Plastid Genome in Cladophorales Green Algae Is Encoded by Hairpin Chromosomes. Current Biology , 27 (24) pp. 3771-3782. 10.1016/j.cub.2017.11.004. Green open access

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Abstract

Virtually all plastid (chloroplast) genomes are circular double-stranded DNA molecules, typically between 100 and 200 kb in size and encoding circa 80–250 genes. Exceptions to this universal plastid genome architecture are very few and include the dinoflagellates, where genes are located on DNA minicircles. Here we report on the highly deviant chloroplast genome of Cladophorales green algae, which is entirely fragmented into hairpin chromosomes. Short- and long-read high-throughput sequencing of DNA and RNA demonstrated that the chloroplast genes of Boodlea composita are encoded on 1- to 7-kb DNA contigs with an exceptionally high GC content, each containing a long inverted repeat with one or two protein-coding genes and conserved non-coding regions putatively involved in replication and/or expression. We propose that these contigs correspond to linear single-stranded DNA molecules that fold onto themselves to form hairpin chromosomes. The Boodlea chloroplast genes are highly divergent from their corresponding orthologs, and display an alternative genetic code. The origin of this highly deviant chloroplast genome most likely occurred before the emergence of the Cladophorales, and coincided with an elevated transfer of chloroplast genes to the nucleus. A chloroplast genome that is composed only of linear DNA molecules is unprecedented among eukaryotes, and highlights unexpected variation in plastid genome architecture.

Type: Article
Title: The Plastid Genome in Cladophorales Green Algae Is Encoded by Hairpin Chromosomes
Open access status: An open access version is available from UCL Discovery
DOI: 10.1016/j.cub.2017.11.004
Publisher version: http://doi.org/10.1016/j.cub.2017.11.004
Language: English
Additional information: This version is the author accepted manuscript. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords: chloroplast genome,hairpin chromosome,genetic code,algae,Ulvophyceae,Cladophorales
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences > Div of Biosciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences > Div of Biosciences > Genetics, Evolution and Environment
URI: https://discovery.ucl.ac.uk/id/eprint/10042941
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