Fertilized eggs divide asymmetrically, establishing the vertical axis of the plant body in both dicotyledonous plants, such as Arabidopsis, and monocotyledonous plants, such as rice and maize. The asymmetric division of fertilized eggs is not specific to angiosperms, but also observed in other land plants model organisms including bryophytes. In addition, fertilized eggs of algae such as Fucus also exhibit asymmetric vertical divisions. However, the knowledge of the mechanisms of embryogenesis in plant species other than Arabidopsis is very limited. Thus, it is unclear if there are universal mechanisms shared among plant species and the evolution of embryogenesis mechanisms remain to be determined.

Therefore, we utilize our findings and experience in Arabidopsis and examine the dynamics of intracellular structures in fertilized eggs of Marchantia polymorpha and Physcomitrella patens. We believe that we can gain insights into the commonality and diversity of the mechanisms responsible for polarization and body axis formation of fertilized eggs. Moreover, different from the vertical divisions observed in liverworts and mosses, fertilized eggs in hornworts have been reported to divide horizontally. Therefore, investigating the internal dynamics and control mechanisms of fertilized eggs in hornworts will help us to better understand the mechanism that determines the division direction of fertilized eggs. Furthermore, by comparing the pattern formation after the first division of fertilized eggs, we aim to clarify how the division direction of the fertilized egg plays a role in subsequent embryogenesis.