Functional Characterization of the Promoter and Second Intron of CUM1 During Flower Development in Cucumber (Cucumis sativus L.)

The characterization of flower specific promoter is critical during flower development by cucumber transformation technology. AGAMOUS (AG) is an organ identity gene that is required for carpel and stamen development in Arabidopsis. The promoter and second intron of AG contain multiple regulatory elements that confer proper spatial and temporal expression. Cucumber is an important vegetable with unisexual flowers. Cucumber MADS-box 1 (CUM1) is the AG homolog in cucumber, belonging to the euAG lineage along with AG. In situ hybridization showed that CUM1 was specifically expressed in the stamens and carpels of cucumber. GUS staining indicated that the second intron of CUM1 confers stamen-specific expression, while the promoter of CUM1 drives both stamen- and carpel-specific expression during the early stages of flower development, but is restricted to carpel- and connectivum-specific expression during the late stages of flower development. Furthermore, a yeast one-hybrid assay demonstrated that two auxin response factors (CsARF13 and CsARF17) had bound directly to the second intron of CUM1. Our data suggest that different regulatory circuits operate in AG homologs in plant species with distinct sex types.