Towards understanding the EPigenetic control of SEX determination in cucurbits – EPISEX

How the gender of a flower or plant is determined is an important issue in plant developmental biology. Understanding this process also has practical applications in agriculture and plant breeding, as the gender of a flower or plant often limits how it is bred and cultivated. Sex determination is a process that leads to the physical separation of male and female gamete producing structures in separate flowers on the same plant (monoecious species) or on separate individuals (dioecious species). Several species in the Cucurbitaceae, including melon, have bisexual floral primordia, but often have flowers limited to a single sex. Sex determination occurs by the selective arrest of either the male stamen or female carpel during development. In melon, sex determination is governed by three genes andromonoecious (M), androecious gene (A) and gynoecious (G) and the interplay of alleles of these three genes results in a range of sexual types. In addition, cucurbit sex expression patterns can be modified by hormones, such as ethylene, and by environmental factors.

Partner 1 and 3 have previously collaborated on the cloning and characterization of M, G and A genes and have shown that the gynoecious (G) gene encodes for a zinc finger transcription factor, CmWIP1, the andromonoecious (M) gene encodes for an ethylene biosynthesis enzyme, CmACS-7 and the androecious gene (A) encodes CmACS11. Now that the identity of the androecy, monoecy and gynoecy sex genes are revealed and genetic pathway controlling sex determination in Cucurbitaceae discovered, among the next challenges are to decipher how the sex determination signals are perceived and how the information is translated to cause organ-specific abortion at the flower and the plant level.

Here, following a set of discoveries in Parner 1 and 3 laboratories, we propose to investigate the importance of epigenetic regulations during unisexual flower development in melon. For that we propose a project articulated around five major unbiased axes that will allow us to characterize both transcriptome and epigenome before and after sex determination. The proposed strategy relies on complementary expertise of 3 partners and integrative analyses of datasets that will be obtained from the combination of different “omics” tools. The hypotheses and the concepts will be validated using the genetic approach. The ultimate goal of the EPISEX project is to produce stable melon plant prototypes of different sexual morphs and to test them for agronomic importance. The finding and the concepts that will be gathered on the melon model system will be transferred to other Cucurbitaceae at later stage of the project