FIGURE 3.

Unified model of sex determination in monoecious and dioecious plants. All experimentally proven systems of sex determination can be combined into a single genetic network comprising female and male suppressors, female and male promoters and high-level sex switches. In the “sex switch systems,” i.e., monoecy and sex determination via one gene, indicated in yellow, an epistatic genetic interaction connects the development of female and male flowers making them in principle mutually exclusive. In sex determination via two genes (“gynodioecy model”) indicated in gray, instead of a genetic interaction, the linkage between the female suppressor (SOFF in asparagus and SyGI in kiwifruit) and a male promoter (TDF1 in asparagus and FyBy in kiwifruit) are essential for connecting female and male flower development. Female and male floral organs are controlled independently, therefore requiring genetic linkage to avoid hermaphrodites or asexual neuters. Female promoters, represented by “F,” have not been identified for any of the studied species to date.