A CRISPR/Cas9-based genome-editing platform enabling efficient and precise gene replacement in Lipomyces starkeyi.

Lipomyces starkeyi is a promising oleaginous yeast with industrial potential. However, its genome engineering remains constrained by low gene-targeting efficiency and the requirement for long homologous regions. Herein, we established a CRISPR/Cas9 genome-editing platform for L. starkeyi by expressing codon-optimized Streptococcus pyogenes Cas9 fused to an SV40 nuclear localization signal. Furthermore, in vitro-transcribed single-guide RNAs (sgRNAs) were directly delivered into the host, eliminating the need for endogenous RNA polymerase III-dependent sgRNA expression. CRISPR/Cas9 activity was validated using a codon-optimized Aequorea coerulescens GFP reporter. Cas9-induced frameshift mutations caused GFP disruption, leading to fluorescence loss. Gene replacement at the LsURA3 locus was evaluated using donor constructs with homologous regions ranging from 50-3000 bp. In a Cas9-expressing wild-type background, precise gene replacement was dependent on homology arm length, increasing from 36% with 50-bp arms to 80% with 3000-bp arms. Notably, in a Cas9-expressing Δlslig4 strain with suppressed non-homologous end joining (NHEJ), precise gene replacement was achieved with 100% accuracy using 50-bp homology arms under CRISPR/Cas9-dependent conditions. Together, these results demonstrate that a Pol III-independent CRISPR/Cas9 system combined with NHEJ suppression enables precise genome editing in L. starkeyi, providing a foundation for functional genomics and metabolic engineering.