A cucurbit androecy gene reveals how unisexual flowers develop and dioecy emerges

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Science  06 Nov 2015:
Vol. 350, Issue 6261, pp. 688-691
DOI: 10.1126/science.aac8370

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How flowers separate males and females

Most flowering plant families have bisexual flowers with both male and female function. However, most members of the Cucurbiticeae family, which includes melons, cucumbers, and gourds, have unisexual flowers. To understand this difference in sex expression, Boualem et al. identified a cucumber gene expressed in the female flowers. Mutations in this gene were associated with solely male flowers. By integrating this finding into a sex determination model, the authors explain how unisexual flowers can coexist in the same plant.

Science, this issue p. 688


Understanding the evolution of sex determination in plants requires identifying the mechanisms underlying the transition from monoecious plants, where male and female flowers coexist, to unisexual individuals found in dioecious species. We show that in melon and cucumber, the androecy gene controls female flower development and encodes a limiting enzyme of ethylene biosynthesis, ACS11. ACS11 is expressed in phloem cells connected to flowers programmed to become female, and ACS11 loss-of-function mutants lead to male plants (androecy). CmACS11 represses the expression of the male promoting gene CmWIP1 to control the development and the coexistence of male and female flowers in monoecious species. Because monoecy can lead to dioecy, we show how a combination of alleles of CmACS11 and CmWIP1 can create artificial dioecy.

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