Format: ORAL

Silvia Moschin1,2, Elisabetta Offer1,2, Sebastiano Nigris1,2, Barbara Baldan1,2

1 University of Padua, Padua, Italy 2 Botanical Garden of Padua, Padua, Italy

Ginkgo biloba is a dioecious gymnosperm belonging to one of the oldest seed plant lineages. A detailed morphological characterization of both ovules and male cones across all their development allowed us to identify the key stages of the reproductive process and the time and space of occurrence of pollination and fertilization. In gymnosperms, pollination and fertilization events are temporally separated (about four months in Ginkgo biloba), and during this time pollinated ovules undergo a process of development really intriguing and poorly investigated. Ginkgo ovules are windy pollinated: when pollen is ready to be dispersed from the pollen cones, ovules emit a pollination drop from the micropyle in which pollen is captured. The pollen can then enter into the ovule, at the level of the pollen chamber, and can germinate. The pollen tube elongates and penetrates into the available gaps among the nucellar cells, and shortly after, it develops a highly branched haustorial system that anchors the male gametophyte to the nucellar tissue to absorb nutrients and survive during the long time between pollination and fertilization. In the meantime, the ovule goes through a process of growth and development, and the single integument differentiates into the three layers of the seed coat: sarcotesta, sclerotesta and endotesta. Differently from angiosperms, indeed, the seed coat differentiation precedes the fertilization and thanks to our analyses, we pointed out that this process is triggered by pollination, highlighting the critical role of pollen perception and recognition for the further Ginkgo ovule development. We therefore believe it is really interesting to understand how the regulation of reproductive development occurs in Ginkgo, which are the main gene networks involved and how they interact with hormonal regulation.At this aim, we combine omics-analyses with in situ hybridization and immunohistochemical analyses.