Secreted small cysteine-rich proteins (CRPs) are emerging as key signaling factors regulating multiple aspects of plant vegetative and reproductive development. Striking features of plant CRPs are their evolutionary diversification in flowering plants (angiosperms) and prominence in reproductive tissues. One of the largest group of CRPs with remarkably restricted expression in the female gametophyte (embryo sac) of angiosperms is the family of ECA1 (early culture abundant 1) gametogenesis-related CRPs. In Arabidopsis thaliana, this family comprises at least 124 members but a function has only assigned for a small subfamily of five closely related proteins termed EC1 (EGG CELL 1). These egg cell-specific CRPs are only secreted cell when the two sperm cells are released from the pollen tube into the embryo sac and render the sperm cells competent to fuse with the female gametes (egg cell and central cell). This project aims to contribute to the understanding of the evolutionary history, functional diversification and differential expression of ECA1 gametogenesis-related CRPs in land plants, with a special focus on the first appearance of EC1 and EC1-related subfamilies. The project will furthermore address the functional conservation of EC1 proteins among different plant species, the EC1 posttranslational modification, and the impact of redox-dependent mechanisms on EC1 secretion and gamete fusion. Functional studies will be also performed on A. thaliana EC1-related proteins to elucidate their role(s) in reproductive development.