Uncovering the Secrets of Secretory Fluids During the Reproductive Process in Ginkgo biloba

Abstract Reproduction is an essential process for all organisms. Although our understanding of the reproductive mechanism in angiosperms has rapidly advanced in recent years, it still lags behind that of gymnosperms. As an ancient gymnosperm, Ginkgo biloba has a remarkable evolutionary history and occupies an important phylogenetic position, representing one of the most ancient and primitive modes of reproduction among seed plants. G. biloba is an archegoniate, where an egg cell develops inside an archegonium; it has a particular pollen chamber and archegonial chamber along with flagellated gametes (spermatozoids). Among these processes, secretions play an important role. In this study, we review the progress on understanding the mechanisms underlying the production and function of pollination drops (PDs), and fertilization fluid in G. biloba. We also highlight recent achievements that have considerably advanced our understanding of the interactions between PDs and pollen, and how PDs are endogenously and intracellularly transported. Finally, we discuss novel insights into the small RNAs of PD transport and the mechanisms of precisely guiding pollen tube growth in G. biloba. By reviewing these results, we demonstrate the structural patterns of G. biloba pollination and fertilization, thus reproducing the uniqueness of the sexual reproduction of ancient plants.