To be a male or a female flower, a question of ethylene in cucurbits.

Within the Cucurbitaceae family, most of its species develop unisexual female and male flowers, either on the same plant (monoecy) or on different plants (dioecy). As in other plant families, these two sex morphotypes have evolved from hermaphrodite species; however, many evolutionary events have occurred in cucurbits allowing easy conversion from dioecy to monoecy and vice versa. The variability in sex morphotypes is higher in the domesticated species of the family, which together with recent advances in genomics, make cucurbits an ideal model to study the genetic and molecular mechanisms that control sex determination in plants. Conventional studies demonstrated that ethylene was the master regulator of sex determination in cucurbits, although some cultivated species may respond differently to ethylene action. In this article, we survey the new advances in hormonal and genetic control of sex determination in cucurbit species, control which establishes the ethylene biosynthesis and signaling genes as being those that determine the floral meristem towards a male, female or hermaphrodite flower. The interactions between these genes are integrated into a model that explains the occurrence and distribution of unisexal and hermaphrodite flowers within the different sex morphotypes. We underline the significance of this scientific progress with regard to breeding programs for agronomically-important sex-associated traits.