Fig. 9

A simplified model of the role of RIN-like genes during fruit maturation and ripening in different scpecies. RIN expression (blue line) correlates with ethylene production (E). Once the fruit is competent to ripen (C) RIN can induce ethylene dependent ripening (Phase 2 ripening PR2), but in the absence of ethylene (and RIN), ethylene independent ripening progresses (Phase 1 ripening PR1). In tomato RIN activates both ethylene and itself (Alba et al. 2005, Fujisawa et al. 2013) [29, 56] progressing PR1 and PR2 ripening simultaneously, while in kiwifruit and grape there is a down regulation of RIN expression following competence to ripen (and in grape veraison) (Pilati et al. 2007) [57] allowing PR1 ripening to occur independently. In kiwifruit this repression can be reversed later in maturity, or with the application of ethylene. Kiwifruit thus shows a hybrid ethylene independent-dependent mechanism with phase 2 ripening being likely to be controlled by SEP4/RIN