Several expression systems for multiple gRNAs have been developed in the
CRISPR-Cas9 system to induce multiple-gene modifications in plants. The team
of Ryosuke Hashimoto from Tokushima University in Japan evaluated the
mutation efficiencies in the tomato genome using multiplex CRISPR-Cas9
vectors consisting of various Cas9 expression promoters with multiple gRNA
In tomato calli induced with these vectors, mutation patterns varied
depending on the promoters used to express Cas9. Notably, a high efficiency
of mutations was achieved in the tomato genome when the Cas9 was driven by
the tomato ELONGATION FACTOR-1á (SlEF1á) promoter.
These results suggest that optimizing the Cas9 expression promoter used in
CRISPR-Cas9 can improve multiplex genome editing.