Investigations On Cell Fate Determination During Early Embryogenesis And Embryogenesis Potential Of Suspensor Cells

The early embryogenesis process of the angiosperms has two important events. The first is maternal transition into the zygote; it’s defined by the elimination of maternal transcription and by the de novo transcription of the zygote genome. During the maternal-to-zygotic transition, the plant transited from gametophyte development to sporophytic development. The second is the zygote become polarized, and gives rise to two daughter cells, apical and basal cell. They are distinct in volume, morphology and developmental fates. The basal cell produces a suspensor and the apical cell produces a embryo proper. During the early embryo development, there are two questions drawn our attention:The first one is the timing of the transition from maternal to zygote; it means the timing of the transition from gametophyte to sporophyte. Is there a marker of this transition? The second one is whether the distinct character and cell fates of apical-basal cell, as well as their derived cells, are due to the polarity of the zygote or the interaction between them. These two questions involve the mechanism of embryo origin, thus, the investigations to seek the answers have important and unique impact in understanding the regulation mechanism of the early plant embryogenesis. Aiming at these questions, we have carried out following works based on different embryogenesis systems.Firstly, we found a gene, NtDRP, can mark the transition from gametophyte to sporophyte, it can not only mark the transition of the egg and zygote but also the gametophyte to sporophyte transition during microspore embryogenesis, Our study offers the first tool to following the gametophyte to sporophyte transition and a unique opportunity to seek into the molecular mechanism regulating this transition process.Secondly, we found the dehisced exine could lead to the polarization of the exine-dehiscing microspores (EDM), and the two daughter cells after first division of EDM have distinct cell fates, one developed into suspensor and the other into embryo proper, they have some difference detected in both cellular and molecular level:the distribution of vacuole and other cell organelle; the BnWOX8expression, the distribution of PIN protein. Our result reveals a close link between EDM polarity and different fates of its daughter cells in early embryogenesis, suggesting the polarity is necessary for the cell fate determination during early embryogenesis.Thirdly, The interaction between suspensor and proper may play important role in plant embryogenesis, so we established an in vivo laser capture microdisection system and cut the conection of embryo proper and suspensor in living golubular embryo in vivo. After more than3-day’s culture, we observed the suspensor cells could divid into embryo-like structure and the original embryo proper could continue to develop although the process was slow down. This obsveration supports the proposal that the ability of the suspensor developping into an embryo is indeed suppressed by the embryo proper. The suspensor could support the development of the embryo proper, but the golpbular embryo proper could continue to develop without suspensor.