A C-12-hydroxylating dioxygenase contributes to steroidal glycoalkaloid diversity in wild potato

Steroidal glycoalkaloids (SGAs), a class of specialized metabolites, are predominantly found in Solanum species. These compounds are recognized for their structural diversity and wide range of biological activities, including toxicity toward various plant pathogens and herbivores. The cultivated potato (Solanum tuberosum) primarily accumulates α-solanine and α-chaconine-bitter-tasting, toxic SGAs that together constitute over 90% of total SGAs. In contrast, the wild potato Solanum chacoense produces an array of rare SGAs, some reported to confer resistance to specific pests. However, the biosynthetic pathways of these uncommon SGAs remain poorly defined. In this study, we isolated and structurally characterized six SGAs from S. chacoense absent in cultivated potato, including two novel compounds: 12α-hydroxysolanine and 12α-hydroxychaconine. Recent evidence indicates that 2-oxoglutarate-dependent dioxygenases (DOXs) contribute to SGA structural diversification. Guided by this, we identified five candidate genes encoding DOX enzymes in S. chacoense. Biochemical assays revealed that one enzyme, designated Sc12DOX, catalyzes the C-12α hydroxylation of α-solanine and α-chaconine to yield 12α-hydroxysolanine and 12α-hydroxychaconine, respectively. These findings enhance our understanding of SGA structural and metabolic diversity within Solanum species.