Genetic transformation via somatic embryogenesis to establish herbicide-resistant opium poppy

Genome and transcriptome of Papaver somniferum Chinese landrace CHM indicates that massive genome expansion contributes to high benzylisoquinoline alkaloid biosynthesis

Opium poppy (Papaver somniferum) is a source of morphine, codeine, and semisynthetic derivatives, including oxycodone and naltrexone. Here, we report the de novo assembly and genomic analysis of P. somniferum traditional landrace 'Chinese Herbal Medicine'. Variations between the 2.62 Gb CHM genome and that of the previously sequenced high noscapine 1 (HN1) variety were also explored. Among 79,668 protein-coding genes, we functionally annotated 88.9%, compared to 68.8% reported in the HN1 genome. Gene family and 4DTv comparative analyses with three other Papaveraceae species revealed that opium poppy underwent two whole-genome duplication (WGD) events. The first of these, in ancestral Ranunculales, expanded gene families related to characteristic secondary metabolite production and disease resistance. The more recent species-specific WGD mediated by transposable elements resulted in massive genome expansion. Genes carrying structural variations and large-effect variants associated with agronomically different phenotypes between CHM and HN1 that were identified through our transcriptomic comparison of multiple organs and developmental stages can enable the development of new varieties. These genomic and transcriptomic analyses will provide a valuable resource that informs future basic and agricultural studies of the opium poppy.

Systematic knockdown of morphine pathway enzymes in opium poppy using virus-induced gene silencing

Opium poppy (Papaver somniferum) remains the sole commercial source for several pharmaceutical alkaloids including the narcotic analgesics codeine and morphine, and the semi-synthetic drugs oxycodone, buprenorphine and naltrexone. Although most of the biosynthetic genes have been identified, the post-transcriptional regulation of the morphinan alkaloid pathway has not been determined. We have used virus-induced gene silencing (VIGS) as a functional genomics tool to investigate the regulation of morphine biosynthesis via a systematic reduction in enzyme levels responsible for the final six steps in the pathway. Specific gene silencing was confirmed at the transcript level by real-time quantitative PCR (polymerase chain reaction), and at the protein level by immunoblot analysis using antibodies raised against salutaridine synthase (SalSyn), salutaridine reductase (SalR), salutaridine 7-O-acetyltransferase (SalAT), thebaine 6-O-demethylase (T6ODM), codeinone reductase (COR), and codeine O-demethylase (CODM). In some cases, silencing a specific biosynthetic gene resulted in a predictable accumulation of the substrate for the corresponding enzyme. Reduced SalSyn, SalR, T6ODM and CODM protein levels correlated with lower morphine levels and a substantial increase in the accumulation of reticuline, salutaridine, thebaine and codeine, respectively. In contrast, the silencing of genes encoding SalAT and COR resulted in the accumulation of salutaridine and reticuline, respectively, which are not the corresponding enzymatic substrates. The silencing of alkaloid biosynthetic genes using VIGS confirms the physiological function of enzymes previously characterized in vitro, provides insight into the biochemical regulation of morphine biosynthesis, and demonstrates the immense potential for metabolic engineering in opium poppy.