Embryogenesis establishes the body organization of multicellular organisms from the fertilized egg cell (zygote) by generating specific cell types in a position-dependent manner. In the flowering plant Arabidopsis thaliana, this process is initiated by the asymmetric division of the elongated zygote, which produces an embryonic apical cell and an extra-embryonic basal cell, thus establishing an axis of polarity. The apical lineage gives rise to the proembryo whereas the basal lineage produces a short cell file (suspensor) that anchors the developing embryo to the wall of the ovule. However, the basal end of the embryo originates from the uppermost cell of the basal lineage, which adopts an embryonic cell fate (hypophysis), initiating the formation of the root stem-cell system, in response to signaling from the adjacent proembryo. Our research addresses molecular mechanisms of plant development, focusing on apical-basal patterning in early embryogenesis of Arabidopsis. Mutant screens have identified key regulators of apical-basal patterning, such as proteins involved in the transport of the signaling molecule auxin or in the gene regulatory response to auxin.