RIN is a member of the SEPALLATA subfamily
of MADS-box genes, whereas MC is a member
of the APETALA 1 subfamily (Litt and Irish 2003;
Malcomber and Kellogg 2005). As MADS-box proteins
have been shown to act together in multimeric
complexes, it is possible that other MADS-box genes
act together with RIN to regulate fruit ripening in
tomato. Indeed, expression analysis and data mining
of EST collections have revealed several possible
candidates to fulfill this role (Fei and others 2004;
Giovannoni 2004). The Cnr mutation is the result of
an epigenetic mutation that causes hypermethylation
and reduced expression of a SQUAMOSA PROMOTER
BINDING PROTEIN (SBP) gene (Manning
and others 2006).