Enzymatic twists evolved stereo-divergent alkaloids in the Solanaceae family

Steroidal alkaloids play a crucial role in plant defense and exhibit distinct stereochemistry at C25, forming either the tomato-type (25S) or eggplant-type (25R) isomers. Here, we uncover the molecular mechanisms shaping this stereochemical diversity. Phylogenetic analysis of GLYCOALKALOID METABOLISM 8 (GAME8) cytochrome P450 hydroxylases across the Solanaceae family revealed two distinct clades producing either 25S or 25R isomers. Ancestral GAME8 likely favored 25R, with gene duplications giving rise to 25S-producing enzymes in more recent Solanum species. In S. nigrum and S. dulcamara, multiple GAME8 copies generate mixed isomeric profiles. Notably, in wild S. cheesmaniae from the Gal & aacute;pagos, mutations in GAME8 have driven a shift from 25S back to the ancestral 25R, suggesting reverse evolution. Our findings highlight how GAME8 evolution has shaped alkaloid diversity in the genus Solanum, demonstrating a complex interplay between enzyme function, genetic variation, and evolutionary adaptation.