The gynoecious CmWIP1 transcription factor interacts with CmbZIP48 to inhibit carpel development

In angiosperms, sex determination leads to development of unisexual flowers. In Cucumis melo , development of unisexual male flowers results from the expression of the sex determination gene, CmWIP1 , in carpel primordia. To bring new insight on the molecular mechanisms through which CmWIP1 leads to carpel abortion in male flowers, we used the yeast two-hybrid approach to look for CmWIP1-interacting proteins. We found that CmWIP1 physically interacts with an S2 bZIP transcription factor, CmbZIP48. We further determined the region mediating the interaction and showed that it involves the N-terminal part of CmWIP1. Using laser capture microdissection coupled with quantitative real-time gene expression analysis, we demonstrated that CmWIP1 and CmbZIP48 share a similar spatiotemporal expression pattern, providing the plant organ context for the CmWIP1-CmbZIP48 protein interaction. Using sex transition mutants, we demonstrated that the expression of the male promoting gene CmWIP1 correlates with the expression of CmbZIP48 . Altogether, our data support a model in which the coexpression and the physical interaction of CmWIP1 and CmbZIP48 trigger carpel primordia abortion, leading to the development of unisexual male flowers.