In female gametophytes, eight nuclei are separated into four cell types after three rounds of nuclear divisions without cell division. After the cellularization and nuclear fusion, they develop into a mature seven-cell embryo sac, including an egg cell(ec), a central cell(cc), two synergid cells(sc) and three antipodal cells. It’s important to ensure that all the cells in the embryo sac have normal functions, so that they are well prepared for the double fertilization. In this part, we focus on the critical molecules participating in this process and the intercellular signaling among these cells. Besides, we also concentrate on the evolution of embryo sac development. The knowledge and tools arising from our research informs basic understanding of female gamete development and the reproductive process of plants.