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An improved genome of the model marine alga [i]Ostreococcus tauri[/i] unfolds by assessing Illumina [i]de novo[/i] assemblies

By Romain Blanc Mathieu, Bram Verhelst, Evelyne Derelle, Stephane Rombauts, Francois-Yves Bouget, Isabelle Carré, Annie Chateau, Adam Eyre Walker, Nigel Grimsley, Hervé Moreau, Benoît Piégu, Eric Rivals, Wendy Schackwitz, Yves Van De Peer and Gwenaël Piganeau

Abstract

International audienceBackground: Cost effective next generation sequencing technologies now enable the production of genomic datasets for many novel planktonic eukaryotes, representing an understudied reservoir of genetic diversity. O. tauri is the smallest free-living photosynthetic eukaryote known to date, a coccoid green alga that was first isolated in 1995 in a lagoon by the Mediterranean sea. Its simple features, ease of culture and the sequencing of its 13 Mb haploid nuclear genome have promoted this microalga as a new model organism for cell biology. Here, we investigated the quality of genome assemblies of Illumina GAIIx 75 bp paired end reads from Ustreococcus touri, thereby also improving the existing assembly and showing the genome to be stably maintained in culture. Results: The 3 assemblers used, ABySS, CLCBio and Velvet, produced 95% complete genomes in 1402 to 2080 scaffolds with a very low rate of misassembly. Reciprocally, these assemblies improved the original genome assembly by filling in 930 gaps. Combined with additional analysis of raw reads and PCR sequencing effort, 1194 gaps have been solved in total adding up to 460 kb of sequence. Mapping of RNAseq II lumina data on this updated genome led to a twofold reduction in the proportion of multi-exon protein coding genes, representing 19% of the total 7699 protein coding genes. The comparison of the DNA extracted in 2001 and 2009 revealed the fixation of 8 single nucleotide substitutions and 2 deletions during the approximately 6000 generations in the lab. The deletions either knocked out or truncated two predicted transmembrane proteins, including a glutamate receptor like gene. Conclusion: High coverage (>80 fold) paired end Illumina sequencing enables a high quality 95% complete genome assembly of a compact 13 Mb haploid eukaryote. This genome sequence has remained stable for 6000 generations of lab culture

Topics: plant glutamate receptor, domestication of microalgae, genome evolution, illumina re sequencing, ostreococcus tauri, correctness of short reads assembly, picoeukaryote, [SDV.OT]Life Sciences [q-bio]/Other [q-bio.OT], [SDV.BIO]Life Sciences [q-bio]/Biotechnology
Publisher: 'Springer Science and Business Media LLC'
Year: 2014
DOI identifier: 10.1186/1471-2164-15-1103
OAI identifier: oai:HAL:hal-01130514v1
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