Genome-based discovery of two previously unreported fungal bifunctional terpene synthases (BFTSs) from phytopathogenic fungi are reported: FoFS catalyzing the formation of fusoxypenes A-C (1-3) and (-)-astellatene (4) and AtAS capable of synthesizing preaspterpenacid I (6). Interestingly, FoFS and AtAS catalyzed the formation of enantiomeric sesterterpenes with a 5-6-7-3-5 ring system. C22-oxidative modification of preaspterpenacid I by AtP450 was characterized as well. Plausible cyclization pathways of the fusoxypenes were illustrated by DFT calculations.