Repeated evolution of cytochrome P450-mediated spiroketal steroid biosynthesis in plants

Diosgeninis a spiroketal steroidal natural productextracted from plants and used as the single most important precursor for the world steroid hormoneindustry. The sporadic occurrences of diosgeninin distantly related plants imply possible independent biosynthetic origins. The characteristic 5,6-spiroketal moiety in diosgeninis reminiscent of the spiroketal moiety present in anthelmintic avermectinsisolated from actinomycete bacteria. How plants gained the ability to biosynthesize spiroketal natural productsis unknown. Here, we report the diosgenin-biosynthetic pathways in himalayan paris ( Paris polyphylla), a monocot medicinal plant with hemostaticand antibacterial properties, and fenugreek ( Trigonellafoenum–graecum), an eudicotculinary herb plant commonly used as a galactagogue. Both plants have independently recruited pairs of cytochromes P450 that catalyze oxidative 5,6-spiroketalization of cholesterol to produce diosgenin, with evolutionary progenitors traced to conserved phytohormone metabolism. This study paves the way for engineering the production of diosgeninand derived analogs in heterologous hosts.