Optimization of the Genome Editing CRISPR-Cas9 Technology in Scedosporium apiospermum.

Abstract

Scedosporium species are opportunistic pathogens causing a large variety of human infections. To date, there is limited information on the pathogenic mechanisms of these fungi, partly because of the limited number of genetic tools available. Here, the CRISPR-Cas9 technology, which provided promising results for functional genomic studies in filamentous fungi, was optimized for Scedosporium species using in vitro assembled Cas9 ribonucleoprotein (RNP) complexes. In these fungi, functional genomic studies are particularly complex in a wild-type strain, because of the high frequency of non-homologous recombination. Prior disruption of the KU70 gene encoding one of the components of the non-homologous end joining system is required, which necessitates the use of a first selection marker. The cleavage of the target gene at each end using a dual RNA-guided Cas9 complex, followed by recombination with a repair template containing the hygromycin resistance gene, allowed disruption of the target gene in the ΔKU70 mutant. Four genes encoding dioxygenases, catalyzing the critical ring-opening step in aromatic hydrocarbons, were successfully disrupted, and the optimum efficiency was observed using 5 μg of the HygR repair cassette. Alternatively, in the wild-type strain, the exclusive use of two Cas9 RNP complexes was enough to achieve an efficient deletion method; one dioxygenase gene was successfully deleted in up to 20% of the obtained colonies. These last experimental conditions path the way to multiple gene deletions and complementation experiments, which cannot be reached using our first procedure since only two selection markers are available for Scedosporium species.