Sex determination in plants leads to the development of unisexual flowers from an originally bisexual floral meristem. This mechanism results in the enhancement of outcrossing and promotes genetic variability, the consequences of which are advantageous to the evolution of a species. In melon, sexual forms are controlled by identity of the alleles at the andromonoecious (a) and gynoecious (g) loci. We previously showed that the a gene encodes an ethylene biosynthesis enzyme, CmACS-7, that represses stamen development in female flowers. Here we show that the transition from male to female flowers in gynoecious lines results from epigenetic changes in the promoter of a transcription factor, CmWIP1. This natural and heritable epigenetic change resulted from the insertion of a transposon, which is required for initiation and maintenance of the spreading of DNA methylation to the CmWIP1 promoter. Expression of CmWIP1 leads to carpel abortion, resulting in the development of unisexual male flowers. Moreover, we show that CmWIP1 indirectly represses the expression of the andromonoecious gene, CmACS-7, to allow stamen development. Together our data indicate a model in which CmACS-7 and CmWIP1 interact to control the development of male, female and hermaphrodite flowers in melon.

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Abstract. The study was conducted for four years (2016 to 2019) in Olive germoplasm collection at Bouka, Latakia, Syria, to evaluate flower characteristics and sexual compatibility of olive cultivar Coratina under Syrian coast conditions. “Coratina” was characterized by low level of pistil abortion, average number of flowers per inflorescence and good pollen germinablity. ISI of “Coratina” showed that this cultivar was highly self- incompatible. A new threshold depends on flowering load and final fruit set were adapted to evaluate pollinizers. The two autochthonous olive cultivars “Khodeiri” and “Dermlali” were good pollinizers for “Coratina” but with some annual differences in pollination efficiency. Reverse pollination results confirmed that “Khoderi” is inter-compatible with „Coratina“ in both directions. It is suggested to plant “Coratina” in mixed orchards with “Khoderi” because they’re inter-compatible, having regular bearing habit and overlapping in flowering period.