The role of dorsoventral cell type boundaries in controlling Arabidopsis leaf development

Abstract

An important developmental mechanism utilized by metazoans is the establishment of specialized cells, or organizers that act to pattern tissues in a non-cell autonomous manner. In plants, for which multicellularity evolved independently, the mechanisms that organize tissue level patterning are not well understood. In this thesis, I investigate the role of adaxial-abaxial boundaries as putative organizers of leaf development. Firstly, I show that boundaries between adaxial Class III HD-ZIP and abaxial KANADI gene expression in the shoot apical meristem play an instructive role in positioning new leaves and determining their subsequent patterns of morphogenesis. These data, together with previous results, suggest a model in which ad-ab boundaries influence organogenesis due to the presence of a domain in between Class III HD-ZIP and KAN expression domains where neither set of genes is expressed. Using mosaic analysis I test this model by generating ectopic REV / KAN boundaries in which the Class III HD-ZIP and KAN expression domains are directly juxtaposed. My results indicate that the presence of a region in between REV and KAN expression is important for localized growth at the boundary and lamina morphogenesis, supporting the proposed model. However I also find evidence of non- cell autonomous signaling from REV expressing clones that promotes boundary identity regardless of whether a separated boundary region is present or not. Taken together, these findings reveal striking similarities and differences in the development of plants and animals and start to provide an integrative conceptual framework that helps clarify broad aspects of plant architecture.