CRISPR-Cas9 can be used to produce two types of gene edits, namely NHEJ and
HDR repairs. The NHEJ repair is done by allowing the natural repairing
system of the cells inside the plant to create new combinations or mutations
in the DNA sequence, whereas HDR is done by providing a template DNA
sequence to the cell so that this template would replace the original one.
Comparing the two, HDR is relatively more difficult to produce.
Nevertheless, researchers from Israel present a method for gene targeting
and HDR in tomato.
Tal Dahan-Meir of Weizmann Institute of Science in Israel and colleagues use
the replicon to serve as the template-provider for the gene-editing system.
Genes CRTISO and PSY1 were precisely modified in tomato using CRISPR-Cas9
system, together with the "bean yellow dwarf virus rolling circle" replicon
at 90 percent targeting efficiency. The researchers mentioned the utility of
this method in other tomato genes and other crops.