Egg Cell–Secreted EC1 Triggers Sperm Cell Activation During Double Fertilization

Double Delivery During Plant Fertilization Double fertilization is a defining feature of flowering plants and involves two nonmotile male gametes (sperm cells) and two female gametes (egg cell and central cell). Both fertilization events are necessary for reproductive success. It is not clear how flowering plants ensure the reliable and on-time fusion of the two pairs of gametes, while preventing polyspermy. Sprunck et al. (p. 1093 ; see the Perspective by Snell ) now show that gamete interactions in Arabidopsis depend on small cysteine-rich EGG CELL 1 (EC1) proteins that accumulate in storage vesicles of the egg cell and that are released during sperm-egg interaction. EC1 peptides trigger the delivery of a fusogen to the sperm cell surface. An intercellular link connects the two sperm cells throughout the gamete fusion process and could play a role in preventing the spontaneous fusion of activated sperm cells.