Comparative transcriptomic sequencing of galegine producing plant species

The advent of the genomic biology age has provided powerful tools for elucidation of molecular pathways in non-model organisms. One such non-model organism, French Lilac (Galega officinalis), is a medicinal plant that was used in medieval Europe to treat diabetic-like symptoms. Galega officinalis produces large amounts (0.1-0.3% dry weight) of the specialized guanidine metabolite galegine. Administration of galegine produces acute reductions in blood glucose levels, enabling control of insulin-resistant type II diabetes. Galegine was used briefly in the 1920s as a clinical treatment for diabetes, but side effects from its toxicity, the development of insulin, and the development of less toxic guanidine containing compounds led to its eventual disuse. However, the structural and mechanistic similarity of galegine to the front-line type II diabetes drug Metformin (Glucophage) has ensured its continued study. Despite galegine's relevant medicinal properties and simple yet unusual chemical structure, its biosynthetic pathway remains unknown. Interestingly, galegine biosynthesis seems to have independently arisen at least 2 times in diverse species of poisonous plants. The appearances of independent galegine biosynthesis might represent convergent biosynthetic evolution from similar ancestral enzymes, or parallel evolution from diverse enzyme families. With the goal of deciphering the biosynthetic pathway for galegine, here we report transcriptome sequencing results from two species of galegine producing plants (Galega officinalis and Verbesina encelioides), and one closely related galegine non-producer (Galega orientalis).