Plasmid-Free CRISPR/Cpf1 Genome Editing With In Vivo T7 RNA Polymerase-Transcribed CRISPR RNA From Short Double-Stranded DNA.

Plasmids are commonly employed in the delivery of clustered regularly interspaced shortpalindromic repeats (CRISPR)/CRISPR-associated (Cas) components for genome editing. However, the absence of heritable plasmids in numerous organisms limits the development of CRISPR/Cas genome editing tools. Moreover, cumbersome procedures for plasmid construction and curing render genome editing time-consuming. In this study, we developed a plasmid-free CRISPR/Cpf1 genome editing system for Saccharomyces cerevisiae and Starmerella bombicola. This system leveraged integrative expression of the Cpf1 nuclease and T7 RNA polymerase (T7RNAP), as well as the delivery of linear fragments including (i) a marker cassette for integration and selection, (ii) short double-stranded DNA (crDNA) for in vivo transcription of crRNA by T7RNAP, and (iii) donor DNA for homology-directed repair. We demonstrated that this editing system enabled efficient multiplexed and iterative genome editing without the need for marker recycling and plasmid curing. The use of short crDNA (87 bp) and donor DNA (≤ 120 bp), both readily prepared from ordered oligonucleotides via annealing or overlap extension, dramatically simplified the editing process. Successful implementation in S. bombicola, which lacks heritable plasmids for genetic engineering, highlighted the potential of this approach especially for genome engineering of genetically intractable organisms in a plasmid-free way.