Multiplex CRIPR-Cas9 has been used in some crops, but promoter optimization
is hardly reported. Researcher Ryosuke Hashimoto and colleagues from
Tokushima University in Japan used various Cas9 expression promoters with
different gRNA expression combinations to edit genes in tomato.

The researchers design "all-in-one" plasmids with different promoters for
multiplex gene editing and selected transformed calli through GFP
fluorescence. They find varying promoter-dependent mutation patterns among
the tomato calli employed with the designed plasmids via PCR. Among the
designed promoters, the tomato ELONGATION FACTOR-1á (SlEF1á) promoter drove
the highest efficiency for CRISPR-Cas9 genome editing, with specific
mutation patterns produced. These results highlight promoter optimization
for CRISPR-Cas9 editing will enable precise disruptions of functional
domains in tomato.

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