The yeast platform engineered for synthetic gRNA-landing pads enables multiple gene integrations by a single gRNA/Cas9 system

Saccharomyces cerevisiae is a versatile microbial platform to build synthetic metabolic pathways for production of diverse chemicals. To expedite the construction of complex metabolic pathways by multiplex CRISPR-Cas9 genome-edit, eight desirable intergenic loci, located adjacent to highly expressed genes selected from top 100 expressers, were identified and fully characterized for three criteria after integrating green fluorescent protein (GFP) gene - CRISPR-mediated GFP integration efficiency, expression competency assessed by levels of GFP fluorescence, and assessing growth rates of GFP integrated strains. Five best performing intergenic loci were selected to build a multiplex CRISPR platform, and a synthetic 23-bp DNA comprised of 20-bp synthetic DNA with a protospacer adjacent motif (PAM) was integrated into the five loci using CRISPR-Cas9 in a sequential manner. This process resulted in five different yeast strains harbouring 1-5 synthetic gRNA-binding sites in their genomes. Using these pre-engineered yeast strains, simultaneous integrations of 2-, 3-, 4-, or 5-genes to the targeted loci were demonstrated with efficiencies from 85% to 98% using beet pigment betalain (3-gene pathway), hygromycin and geneticin resistance markers. Integrations of the multiple, foreign genes in the targeted loci with 100% precision were validated by genotyping. Finally, we further developed the strain to have 6th gRNA synthetic gRNA-binding site, and the resulting yeast strain was used to generate a yeast strain producing a sesquiterpene lactone, kauniolide by simultaneous 6-gene integrations. This study demonstrates the effectiveness of a single gRNA-mediated CRISPR platform to build complex metabolic pathways in yeast.

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