Fig. 7.

Schematic representation of the putative retrograde signalling pathway from the chromoplast to the nucleus for crocetin accumulation and chromoplast development. Different kinds of apocarotenoids are produced by CCDs in the chromoplast of saffron stigma in a developmental-dependent way. Many of these apocarotenoids could diffuse through the chromoplast membranes into the cytosol and act directly as signals for gene expression modulation or could be further modified by CCD1. The resulting apocarotenoids may act as the inducers of gene expression modulation of carotenogenic genes, CsCCD2 and other gene targets related to chromoplast biogenesis and homeostasis during flower development in saffron