Identification and characterization of the verticillin biosynthetic gene cluster in Clonostachys rogersoniana

Verticillin is one of the dimeric epipolythiodioxopiperazines (ETPs) which are toxic secondary metabolites produced only by fungi. ETPs have received substantial attention since its complex molecular architecture and a wide range of biological activities. Although biosynthesis of the monomeric gliotoxin has been studied extensively, the biosynthetic pathway of dimeric ETPs is far from being studied. To investigate the biosynthesis of dimeric ETPs and expand our understanding of their dimerization, the verticillin biosynthetic gene cluster (ver) was identified and cloned from a genomic DNA fosmid library of the Cordyceps-colonizing fungus Clonostachys rogersoniana with the designed primers based on the sequence of a nonribosomal peptide synthetase (NRPS) ChaP which was predicted to be responsible for chaetocin biosynthesis in Chaetomium virescens. To validate it, the chaP homologous gene verP in the ver cluster was disrupted. HPLC-MS analysis demonstrated that the verP disruption mutant (AverP) completely abolished verticillin production, and it could be restored by introducing a copy of the wild-type verP gene. Further gene disruptions and chemical analysis demonstrated that most genes of this ver cluster were essential for verticillin biosynthesis. Intriguingly, disruption of verP almost abolished the conidiation of Clonostachys rogersoniana and it was partially restored by addition of the fermentation extract which contains verticillin, implying that verticillin or its intermediate plays a role in the Cordyceps-colonizing fungal morphological differentiation.