Biotransformation of 6-Deoxo Type Brassinosteroids in Yeast (Saccharomyces cerevisiae) WAT21 Cells

We recently demonstrated that non-plant cells, yeast WAT21, produce a steroidal plant hormone, castasterone. To understand how castasterone is generated in WAT21 cells, deuterium-labeled (26, 28-²H∧6) 6-deoxoteasterone, 6-deoxotyphasterol and 6-deoxocastasterone were fed to WAT21 cells, and their metabolites were analyzed by gas chromatography-mass spectrometry. When [²H∧6]-6-deoxoteasterone was fed, [²H∧6]-6-deoxo-3-dehydroteasterone and [²H∧6]-6-deoxotyphasterol were identified as metabolites. When [²H∧6]-6-deoxotyphasterol was used, [²H∧6]-6-deoxoteasterone and [²H∧6]-6-deoxo-3-dehydroteasterone and [²H∧6]-6-deoxocastasterone were detected. When [²H∧6]-6-deoxocastasterone was added, [²H∧6]-castasterone was identified. Taken together, a biosynthetic sequence, 6-deoxoteasterone↔6-deoxo-3-dehydroteasterone↔6-deoxotyphasterol→6-deoxocastasterone→castasterone seems to function to produce brassinosteroids in WAT21 cells. Coupled with the presence of a biosynthetic sequence, teasterone→3-dehydroteasterone↔typhasterol→castasterone, this suggests that brassinosteroids in WAT21 cells were biosynthesized via the same kind of pathways established in plants. This study provides a clue for possible mass-production of brassinosteroids in non-plant cells, yeast WAT21 for commercial use in agriculture.