Genome mining and characterization of bifunctional Clerodane Diterpene synthase from a fungus Myrothecium sp

Clerodane diterpenoids are a promising group of pharmacological molecules and are rarely discovered in fungi. The clerodane diterpene synthase has not yet been characterized in fungi. Herein, we discovered a gene, mterA, encoding chimeric protein with the bifunction of class II and class I synthases from a fungus Myrothecium sp. by genome mining. Heterologous co-expression of mterA and mterB in engineered yeast led to the production of a clerodane diterpene product (5S, 8R, 9R, 10S)-terpentetriene (1), confirming the existence of a fungi-derived special clerodane diterpene synthase. Site-directed mutagenesis on conserved motifs revealed a strong influence on terpentetriene accumulation. Gene inactivation of mterA indicated that the mter gene cluster was likely cryptic or weakly expressed in the host under the laboratory conditions. Compound 1 exhibited significant inhibitory activity against the plant pathogen Bacillus subtilis with a MIC value of 8 μg/mL and activated the plant immune response. MterA representes the first chimeric bifunctional clerodane diterpene synthase.