Functional analysis of an indole-diterpene gene cluster for lolitrem B biosynthesis in the grass endosymbiont Epichloë festucae

► We examined lolitrem B biosynthesis in the endosymbiotic fungus Epichloë festucae. ► Gene deletion analysis and cell feeding experiment identified key biosynthetic steps. ► Indole-diterpene metabolic diversity by Epichloë festucae in planta was observed. ► Scheme to account for metabolic diversity observed in Epichloe festucae is proposed.