Tomato (Solanum lycopersicum) rin mutants completely fail to ripen. These
mutants do not produce red pigmentation, soften, or induce an ethylene
burst. Therefore, RIN has long been believed to function as a major
regulator for the induction of ripening. The team of Yasuhiro Ito from the
National Agriculture and Food Research Organization in Japan aimed to
contradict this concept of RIN function and show fruit ripening induction in
the absence of RIN.
The team first developed RIN-knockout tomato mutants using CRISPR-Cas9. The
resulting mutants did not exhibit repressed initiation of ripening and the
mutant fruits actually showed moderate red coloring. Moreover, inactivation
of the mutant allele in rin mutants partially restored the induction of
RIN is not required for the initiation of ripening in tomato. Further
analysis also found that the rin mutant does not actually have a null
mutation, but has a gain-of-function mutation. This then produces a protein
that represses ripening.