Abstract
The mechanism of sex differentiation in cucurbitaceous plants has been studied for more than 80 years. Sex expression in cucumber (Cucumis sativus L.) plants is genetically controlled by the F and M genes. Similarly, it is controlled by the A and G genes in melon (Cucumis melo L.) plants. These genes interact to produce four different sex phenotypes; gynoecious (M-F-) (A-gg), monoecious (M-ff) (A-G-), hermaphroditic (mmF-) (aagg), and andromonoecious (mmff) (aaG-). The gynoecious type produces only female flowers, whereas the monoecious type produces both male and female flowers on the same plant. The hermaphroditic type produces bisexual flowers with both staminate and pistillate organs, while the andromonoecious type produces bisexual and male flowers on the same plant. Sex expression in both cucumber and melon plants is mainly controlled by a plant hormone, ethylene. Thus, the mechanism of sex expression may be similar or even identical in cucumber and melon plants. The F gene was identified more than 10 years ago, whereas the M, A, and G genes were identified recently. The F, M, and A genes encode ACC synthase, which catalyzes the production of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) from S-adenosyl methionine (SAM). This article reviews the similarities and differences in the mechanism of sex expression in cucumber and melon plants and proposes a genetic model of sex expression.
