A new reducing polyketide synthase gene from the lichen-forming fungus Cladonia metacorallifera

Lichens produce unique polyketide secondary metabolites including depsides, depsidones, dibenzofurans and depsones. The biosynthesis of these compounds is governed by polyketide synthase (PKS), but the mechanism via which they are produced has remained unclear until now. We reported the 6-methylsalicylic acid synthase (6-MSAS) type of PKS gene, which is a member of the fungal-reducing PKSs. A cultured mycobiont of Cladonia metacorallifera was employed in the isolation and characterization of a polyketide synthase gene (CmPKS1). The complete sequence information for CmPKS1 was acquired via the screening of a Fosmid genomic library with a 456 bp fragment corresponding to part of the acyl transferase (AT) domain as a probe. CmPKS1 contains β-ketoacyl synthase (KS), AT, dehydratase (DH), ketoreductase (KR) and phosphopantetheine attachment site (PP) domains.: The domain organization of CmPKS1 (KS-AT-DH-KR-PP) is a typical 6-MSAS-type PKS, and the results of phylogenetic analysis showed that CmPKS1 grouped with other fungal-reducing PKSs. Quantitative real time PCR analyses showed that CmPKS1 was expressed preferentially in the early growth stage of the axenically cultured mycobiont. Furthermore CmPKS1 expression was found to be dependent on the carbon sources and concentrations in the medium.