Conversion of viridicatic acid to crustosic acid by cytochrome P450 enzyme-catalysed hydroxylation and spontaneous cyclisation

Cytochrome P450 monooxygenases (P450s) are considered nature's most versatile catalysts and play a crucial role in regio- and stereoselective oxidation reactions on a broad range of organic molecules. The oxyfunctionalisation of unactivated carbon-hydrogen (C-H) bonds, in particular, represents a key step in the biosynthesis of many natural products as it provides substrates with increased reactivity for tailoring reactions. In this study, we investigated the function of the P450 enzyme TraB in the terrestric acid biosynthetic pathway. We firstly deleted the gene coding for the DNA repair subunit protein Ku70 by using split marker-based deletion plasmids for convenient recycling of the selection marker to improve gene targeting in Penicillium crustosum. Hereby, we reduced ectopic DNA integration and facilitated genetic manipulation in P. crustosum. Afterward, gene deletion in the Δku70 mutant of the native producer P. crustosum and heterologous expression in Aspergillus nidulans with precursor feeding proved the involvement of TraB in the formation of crustosic acid by catalysing the essential hydroxylation reaction of viridicatic acid. KEY POINTS: •Deletion of Ku70 by using split marker approach for selection marker recycling. •Functional identification of the cytochrome P450 enzyme TraB. •Fulfilling the reaction steps in the terrestric acid biosynthesis.

Golden Gate vectors for efficient gene fusion and gene deletion in diverse filamentous fungi

The cloning of plasmids can be time-consuming or expensive. Yet, cloning is a prerequisite for many standard experiments for the functional analysis of genes, including the generation of deletion mutants and the localization of gene products. Here, we provide Golden Gate vectors for fast and easy cloning of gene fusion as well as gene deletion vectors applicable to diverse fungi. In Golden Gate cloning, restriction and ligation occur simultaneously in a one-pot reaction. Our vector set contains recognition sites for the commonly used type IIS restriction endonuclease BsaI. We generated plasmids for C- as well as N-terminal tagging with GFP, mRFP and 3xFLAG. For gene deletion, we provide five different donor vectors for selection marker cassettes. These include standard cassettes for hygromycin B, nourseothricin and phleomycin resistance genes as well as FLP/FRT-based marker recycling cassettes for hygromycin B and nourseothricin resistance genes. To make cloning most feasible, we provide robust protocols, namely (1) an overview of cloning procedures described in this paper, (2) specific Golden Gate reaction protocols and (3) standard primers for cloning and sequencing of plasmids and generation of deletion cassettes by PCR and split-marker PCR. We show that our vector set is applicable for the biotechnologically relevant Penicillium chrysogenum and the developmental model system Sordaria macrospora. We thus expect these vectors to be beneficial for other fungi as well. Finally, the vectors can easily be adapted to organisms beyond the kingdom fungi.