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This paper is the result of a long-standing collaboration between the Institute of Plant Sciences Paris-Saclay (IPS2) and GAFL and highlights the use of melon genetic resources to understand the mechanisms of flower and fruit development. It was on the cover of Current Biology on 6 June 2022: https://www.cell.com/issue/S0960-9822(21)X0012-7#closeFullCover.

Shapes of vegetables and fruits are the result of adaptive evolution and human selection. We describe here the characterization of a melon mutation rf1 (round fruit 1), leading to round fruit. Histological analysis of rf1 flower and fruits revealed fruit shape is determined at flower stage 8, after sex determination and before flower fertilization. Using positional cloning, we identified the causal gene as the monoecy sex determination gene CmACS7. Moreover, a survey of melon germplasms maintained at GAFL CRBLeg showed strong association between fruit shape and sexual types. We showed that CmACS7-mediated ethylene production in carpel primordia enhances cell expansion and represses cell division, leading to elongated fruit. To pinpoint the gene networks controlling elongated versus round fruit phenotype, we analyzed the transcriptomes of laser capture microdissected carpels of wild-type and rf1 mutant. These high-resolution spatiotemporal gene expression dynamics revealed the implication of two regulatory modules. The first module implicates E2F-DP transcription factors, controlling cell elongation versus cell division. The second module implicates OVATE- and TRM5-related proteins, controlling cell division patterns. Our finding highlights the dual role of ethylene in the inhibition of the stamina development and the elongation of ovary and fruit in cucurbits.