A functionally conserved STORR gene fusion in Papaver species that diverged 16.8 million years ago

The STORR gene fusion event is considered essential for the evolution of the promorphinan/morphinan subclass of benzylisoquinoline alkaloids (BIAs) in opium poppy as the resulting bi-modular protein performs the isomerization of (S)- to (R)-reticuline essential for their biosynthesis. Here, we show that of the 12 Papaver species analysed those containing the STORR gene fusion also contain promorphinans/morphinans with one important exception. P. californicum encodes a functionally conserved STORR but does not produce promorphinans/morphinans. We also show that the gene fusion event occurred only once, between 16.8-24.1 million years ago before the separation of P. californicum from other Clade 2 Papaver species. The most abundant BIA in P. californicum is (R)-glaucine, a member of the aporphine subclass of BIAs, raising the possibility that STORR, once evolved, contributes to the biosynthesis of more than just the promorphinan/morphinan subclass of BIAs in the Papaveraceae. The STORR gene fusion event is a key step in the evolution of benzylisoquinoline alkaloid metabolism in opium poppy. Here, the authors combine phylogenetic, transcriptomic, metabolomic, biochemical and genomic analyses to show the STORR gene fusion occurred only once between 16.8-24.1 million years ago in Papaver species.

Automated summary

The STORR gene fusion event is essential for the evolution of benzylisoquinoline alkaloids in opium poppy, and it occurred only in specific species within the Papaver genus.