Targeted genome editing is becoming an increasingly important tool for
precise plant breeding. A team led by Tal Dahan$B!>(BMeir from Weizmann
Institute of Science in Israel used a combination of the CRISPR-Cas9 system
and the bean yellow dwarf virus rolling circle replicon to facilitate
targeted mutagenesis and gene replacement in tomato.

The team chose to target the carotenoid isomerase (CRTISO) and phytoene
synthase 1 (PSY1) genes from the carotenoid biosynthesis pathway due to
their easily detectable phenotype. The team used the geminiviral replicon
amplification to provide a large amount of donor template for gene
replacement experiment.

The team achieved precise modification of the CRTISO and PSY1 loci at an
efficiency of up to 90%. In the gene replacement experiment, the target was
a crtiso allele that contained a 281bp deletion. The deletion was repaired
using the donor template through homologous recombination. The gene
replacement experiment was successful in 25% of the plants transformed.

This shows that efficient targeted mutagenesis and gene replacement can be
achieved using a single construct and can be adapted to other tomato genes
as well as other crops.

[onlinelibrary.wiley.com]