Cell-cell communication during double fertilization.

Double fertilization in flowering seed plants requires intercellular signaling events between many interacting partners. The four cell types of the seven-celled female gametophyte communicate with each other to establish and maintain their identity. They secrete signaling molecules to guide the male gametophyte and to mediate sperm cell discharge and transport towards the two female gametes (the egg and central cell). After fusion of the gametes, guidance signals have to be removed to prevent polyspermy, embryo and endosperm development is induced generating daughter cells or nuclear regions of a different fate, and cell death is induced in the surrounding ovular cells. Until recently, little was known about the molecular nature of the signaling molecules that are involved in these processes. Now, small secreted proteins and peptides have been identified as prime candidates mediating several of these communication events.