Abstract:

Previous study demonstrates that CsAP3，the B class floral organ identity gene in cucumber，participate in the process of stamen arrest in female flower by regulating the expression of ethylene receptor CsETR1. To further understand the conserved role of ethylene in stamen arrestment，AP3 homologue genes in Momordica charantia，Luffa cylindrica，Cucumis melo，Citrullus lanatus，Cucurbita maxima and Cucurbita pepo were analyzed in this study. The sequences of AP3 homologous genes in Momordica charantia and Luffa cylindrica were obtained by degenerate PCR，and the homologous sequences in Cucumis melo，Citrullus lanatus，Cucurbita maxima and Cucurbita pepo were obtained from the published genome data. Sequence alignment revealed that there are non-synonymous mutations in the coding region of the short GV repeats in the C-terminus of AP3 protein in these species. Electrophoretic mobility shift assay（EMSA）and dual luciferase transient expression assay in tobacco leaves showed that，like the cucumber CsAP3 protein，the AP3 homologous proteins of melon，watermelon and pumpkin have potential to bind the ETR1 promoter，and positively regulate the ETR1 homologous gene in the corresponding species. This study provides a new angle for the study of the development of unisexual flower，and supplies important information for revealing the origin of the unisexual flower of Cucurbitaceous plant.

Key words: Cucurbitaceae, unisexual flower, AP3 homologous gene, ethylene receptor