Lipofection-mediated genome editing using DNA-free delivery of the Cas9/gRNA ribonucleoprotein into plant cells

Abstract

A novel and robust lipofection-mediated transfection approach for the use of DNA-free Cas9/gRNA RNP for gene editing has demonstrated efficacy in plant cells. Precise genome editing has been revolutionized by CRISPR/Cas9 systems. DNA-based delivery of CRISPR/Cas9 is widely used in various plant species. However, protein-based delivery of the in vitro translated Cas9/guide RNA (gRNA) ribonucleoprotein (RNP) complex into plant cells is still in its infancy even though protein delivery has several advantages. These advantages include DNA-free delivery, gene-edited host plants that are not transgenic, ease of use, low cost, relative ease to be adapted to high-throughput systems, and low off-target cleavage rates. Here, we show a novel lipofection-mediated transfection approach for protein delivery of the preassembled Cas9/gRNA RNP into plant cells for genome editing. Two lipofection reagents, Lipofectamine 3000 and RNAiMAX, were adapted for successful delivery into plant cells of Cas9/gRNA RNP. A green fluorescent protein (GFP) reporter was fused in-frame with the C-terminus of the Cas9 protein and the fusion protein was successfully delivered into non-transgenic tobacco cv. 'Bright Yellow-2' (BY2) protoplasts. The optimal efficiencies for Lipofectamine 3000- and RNAiMAX-mediated protein delivery were 66% and 48%, respectively. Furthermore, we developed a biolistic method for protein delivery based on the known proteolistics technique. A transgenic tobacco BY2 line expressing an orange fluorescence protein reporter pporRFP was targeted for knockout. We found that the targeted mutagenesis frequency for our Lipofectamine 3000-mediated protein delivery was 6%. Our results showed that the newly developed lipofection-mediated transfection approach is robust for the use of the DNA-free Cas9/gRNA technology for genome editing in plant cells.

Keywords: BY2; Biolistics; Cas9/gRNA ribonucleoprotein; Genome editing; Lipofection; Protein delivery; Protoplast; Tobacco.