The genome of flax (Linum usitatissimum) assembled de novo from short shotgun sequence reads
Flax (Linum usitatissimum) is an ancient crop that is widely cultivated as a source of fiber, oil and medicinally relevant compounds. To accelerate crop improvement, we performed whole‐genome shotgun sequencing of the nuclear genome of flax. Seven paired‐end libraries ranging in size from 300 bp to 10 kb were sequenced using an Illumina genome analyzer. A de novo assembly, comprised exclusively of deep‐coverage (approximately 94× raw, approximately 69× filtered) short‐sequence reads (44–100 bp), produced a set of scaffolds with N 50 = 694 kb, including contigs with N 50 = 20.1 kb. The contig assembly contained 302 Mb of non‐redundant sequence representing an estimated 81% genome coverage. Up to 96% of published flax ESTs aligned to the whole‐genome shotgun scaffolds. However, comparisons with independently sequenced BACs and fosmids showed some mis‐assembly of regions at the genome scale. A total of 43 384 protein‐coding genes were predicted in the whole‐genome shotgun assembly, and up to 93% of published flax ESTs, and 86% of A. thaliana genes aligned to these predicted genes, indicating excellent coverage and accuracy at the gene level. Analysis of the synonymous substitution rates (K s) observed within duplicate gene pairs was consistent with a recent (5–9 MYA) whole‐genome duplication in flax. Within the predicted proteome, we observed enrichment of many conserved domains (Pfam‐A) that may contribute to the unique properties of this crop, including agglutinin proteins. Together these results show that de novo assembly, based solely on whole‐genome shotgun short‐sequence reads, is an efficient means of obtaining nearly complete genome sequence information for some plant species.
Document Type: Research Article
Affiliations: 1: BGI-Shenzen, Bei Shan Industrial Zone, Yantian District, Shenzhen 518083, China 2: Department of Biological Sciences, University of Alberta, Edmonton, Alberta, T6G 2E9, Canada 3: Université Lille-Nord de France, Lille 1 Unité Mixte de Recherche Institut National de la Recherche Agronomique 1281, Stress Abiotiques et Différenciation des Végétaux, F-59650 Villeneuve d’Ascq Cedex, France 4: Université Lille-Nord de France, Lille 1 Unité Mixte de Recherche Institut National de la Recherche Agronomique 1281, Stress Abiotiques et Différenciation des Végétaux, F-59650 Villeneuve d’Ascq Cedex, France 5: National Research Council of Canada, Plant Biotechnology Institute, Saskatoon, Saskatchewan, S7N 0W9, Canada 6: University of Arizona, School of Plant Sciences and BIO5 Institute, Tucson, AZ 85721, USA 7: Department of Botany, University of British Columbia, Vancouver, British Columbia, V6T 1Z4, Canada 8: Case Western Reserve University, Cleveland, OH 44106, USA 9: National Research Centre on Plant Biotechnology, Indian Agricultural Research Institute, Pusa Campus, New Delhi 110012, India
Publication date: November 1, 2012