Single crossover-mediated targeted nucleotide substitution and knock-in strategies with CRISPR/Cas9 system in the rice blast fungus

Clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9)-mediated genome editing has become a promising approach for efficient and versatile genetic engineering in various organisms; however, simple and precise nucleotide modification methods in filamentous fungi have been restricted to double crossover type homologous recombination (HR). In this study, we developed a novel genome editing strategy via single crossover-mediated HR in the model filamentous fungus Pyricularia (Magnaporthe) oryzae. This method includes the CRISPR/Cas9 system and a donor vector harboring a single homology arm with point mutations at the CRISPR/Cas9 cleavage site. Using this strategy, we demonstrated highly efficient and freely programmable base substitutions within the desired genomic locus, and target gene disrupted mutants were also obtained via a shortened (100-1000 bp) single homology arm. We further demonstrated that this method allowed a one-step GFP gene knock-in at the C-terminus of the targeted gene. Since the genomic recombination does not require an intact protospacer-adjacent motif within the donor construct and any additional modifications of host components, this method can be used in various filamentous fungi for CRISPR/Cas9-based basic and applied biological analyses.