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ERC

SEXYPARTH Report Summary

Project ID: 341076
Funded under: FP7-IDEAS-ERC
Country: France

Mid-Term Report Summary - SEXYPARTH (Unraveling sex determination and parthenocarpy mechanisms to improve crops)

The majority of flowering plants are hermaphrodite, producing exclusively bisexual flowers. Sex determination is a developmental process, where selection has led to the evolution of unisexual flowers in ~10% of the species. Monoecious species exhibit male and female flowers on the same plant. Dioecious species have separate male and female individuals. The evolutionary pathways from hermaphroditism to dioecy in flowering plants are a matter of ongoing debate. Dioecy appears to have evolved most frequently via monoecy through a series of mutations which alter the ratio of male and female flowers. Dioecy may have also evolved through emergence of unisexual individuals that coexist with hermaphrodites, such as gynodioecy or androdioecy.

Cucurbitaceae is a large plant family of species that display mostly unisexual flowers. Throughout evolution of Cucurbitaceae, there have been numerous shifts between monoecy and dioecy, which makes this plant family a practical model to investigate the molecular mechanisms controlling sex determination. Several Cucurbitaceae species, including cucumber and melon, show different sexual morphs. Through the cloning and characterization of natural mutations showing a transition from monoecy to different sexual morphs we have brought new insight to the sex determination pathway. The gynoecious (g) gene controls male flower development and encodes for a zinc finger transcription factor, CmWIP1. Loss of CmWIP1 function in a monoecious genetic background leads to purely female plants. How female flowers develop and how male plants emerge in a monoecious population was until recently unclear. The carpel repressor, CmWIP1, is not expressed in the flowers programmed to become female, which suggested the existence of an antagonistic genetic determinant function relative to CmWIP1 that promotes carpel development. We identified ACS11 as such antagonistic genetic determinant. The gene ACS11 is expressed in sap-carrying phloem cells. Through the phloem a signal is triggered to inhibit the male promoting gene, CmWIP1 and the bloom develops female organs. The inhibition of CmWIP1lead to the expression of a second key gene of sex determination: CmACS-7 that inhibit the development of the male part. If the function of CmACS-7 is altered by mutations, the plant grows male and female parts in the same bloom. Because monoecy can lead to dioecy, we have also demonstrated how a combination of alleles of CmACS11 and CmWIP1 can create artificial dioecy.

This work has practical applications, as the gender of a flower or plant often limits how the plant is bred and cultivated. The Cucurbitaceae family comprises many neglected cultivated species that are major food crops in many developing countries. Because of their complex sexual reproduction systems, yield is usually low. The discovery of the sex determination genes will permit to produce sexual morphs that ease breeding and optimize the synchronization of male and female flower development on the same plant to improve fruit setting.

Reported by

INSTITUT NATIONAL DE LA RECHERCHE AGRONOMIQUE
France
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