Two ubiquitous aldo-keto reductases in the genus Papaver support a patchwork model for morphine pathway evolution.

Area of Science:

• Plant biochemistry
• Molecular evolution
• Chemotaxonomy

Background:

• Morphinan alkaloid biosynthesis in Papaver species is complex, involving gene duplication, fusion, neofunctionalization, and deletion.
• A key gene fusion event created the bifunctional enzyme reticuline epimerase (REPI), crucial for morphine biosynthesis in opium poppy (Papaver somniferum).
• Ancestrally related enzymes, aldo-keto reductases 1,2-dehydroreticuline reductase (DRR) and codeinone reductase (COR), play roles in the pathway from (S)-reticuline to morphine.

Purpose of the Study:

• To investigate the evolutionary history of morphinan alkaloid biosynthesis in the Papaver genus.
• To understand the molecular events and gene fusion leading to key enzymes like REPI.
• To elucidate the structure-function relationships of DRR and COR orthologs and their role in pathway evolution.

Main Methods:

• Transcriptome analysis of 12 Papaver species.
• Enzymatic assays of orthologous genes to determine their catalytic activities.
• Comparative structural and substrate preference analysis of DRR and COR orthologs.

Main Results:

• Enzymes from various Papaver species catalyze reactions representing intermediate states of the metabolic pathway, supporting a patchwork evolution model.
• The gene fusion event leading to REPI was identified as a critical evolutionary step.
• Structure-function analysis revealed insights into the functional latency of DRR and COR orthologs, explaining their roles in pathway evolution.

Conclusions:

• The evolution of morphinan alkaloid biosynthesis in Papaver is characterized by a patchwork model, with gene fusion and neofunctionalization playing significant roles.
• Understanding the evolutionary trajectory of enzymes like REPI, DRR, and COR provides crucial insights into the development of plant metabolic pathways.
• This study illuminates the molecular mechanisms underlying the evolution of complex secondary metabolite production in plants.