30 Aug 2018

Abstract

Morphinan-based painkillers are derived from opium poppy. We report a draft of the opium poppy genome, with 2.72 Gb assembled into 11 chromosomes with contig N50 and scaffold N50 of 1.77 Mb and 204 Mb, respectively. Synteny analysis suggests a whole genome duplication at approximately 7.8 million years ago (MYA) and ancient segmental or whole genome duplication(s) that occurred before the Papaveraceae-Ranunculaceae divergence 110 MYA. Syntenic blocks representative of phthalideisoquinoline and morphinan components of a benzylisoquinoline alkaloid cluster of 15 genes provides insight into how it evolved. Paralog analysis identified P450 and oxidoreductase genes that combined to form the STORR gene fusion essential for morphinan biosynthesis in opium poppy. Thus gene duplication, rearrangement and fusion events have led to evolution of specialized metabolic products in opium poppy.

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Fig. 1 Opium poppy genome features and whole genome duplication.

(A) Characteristics of the eleven chromosomes of Papaver somniferum. Track a-c are the distribution of gene density, repeat density and GC density respectively, with densities calculated in 2Mb windows. Track dshows syntenic blocks. Band width is proportional to syntenic block size.

(B) Comparison with ancestral eudicot karyotype (AEK) chromosomes reveals synteny. The syntenic AEK blocks are painted onto P. somniferumchromosomes.

(C) Synonymous substitution rate (Ks) distributions of syntenic blocks for P. somniferum paralogs and orthologs with other eudicots are shown in colored lines as indicated.

(D) Inferred phylogenetic tree with 48 single-copy orthologs of eleven species identified by OrthoFinder (13). Posterior probabilities for all branches exceed 0.99. Timing of P. somniferum whole genome duplication (WGD) was estimated in this study and other reported whole genome triplication (WGT)/WGD timings are superimposed on the tree. Divergence timings are estimated using BEAST (14) and indicated by light blue bars at the internodes with 95% highest posterior density (HPD).