Building a plant: cell fate specification in the early Arabidopsis embryo

Abstract

Embryogenesis is the beginning of plant development, yet the cell fate decisions and patterning steps that occur during this time are reiterated during development to build the post-embryonic architecture. In Arabidopsis, embryogenesis follows a simple and predictable pattern, making it an ideal model with which to understand how cellular and tissue developmental processes are controlled. Here, we review the early stages of Arabidopsis embryogenesis, focusing on the globular stage, during which time stem cells are first specified and all major tissues obtain their identities. We discuss four different aspects of development: the formation of outer versus inner layers; the specification of vascular and ground tissues; the determination of shoot and root domains; and the establishment of the first stem cells.

Auxin response cell-autonomously controls ground tissue initiation in the early Arabidopsis embryo

“…The three main tissue identities: epidermis, ground tissue, and vascular tissue, are specified early during Arabidopsis embryo development, and auxin is a prominent regulator of this stage of development (13,43). Auxin mainly acts through the activity of the key auxin effector ARF5/MP at the globular stage of embryo development, and the mp mutant is impaired in multiple cell specification events at this stage.…”

“…In addition, SCR and the heat shock transcription factor SCHIZORIZA (SCZ) regulate asymmetric cell divisions within the ground tissue (11,12). Open questions, however, are what molecular mechanisms drive establishment of the ground tissue and how this is connected to the regulatory network that controls ground tissue maintenance (13).…”

“…The establishment of the ground tissue and the initiation of the root meristem occur at the globular stage of embryogenesis, when the three main tissue identities, and the precursor cell of the organizing center of the root, the hypophysis, are specified from uncommitted precursor cells during a few cell division rounds (13) (Fig. 1A).…”

The pivotal role of small non-coding RNAs in the regulation of seed development

“…Most studies conducted to date on the role of sRNAs in embryo development have been performed in Arabidopsis because the pattern of cell divisions is simple and predictable (Hove et al 2015). At the onset of embryogenesis, upstream regulators that seem to be auxin-and miRNAindependent provide positional information relevant for the separation of the inner cells and outer cell layer (Takada and Jürgens 2007;Nodine and Bartel 2010;Hove et al 2015).…”

NatA is required for suspensor development in Arabidopsis

“…Cell division and differentiation within the embryo proper and suspensor are regulated by both an internal genetic program and environmental signals. 1,2 Polar auxin distribution, established by auxin transporters called PINs, is essential for embryogenesis. 3 Defects in auxin responses, perception, transport, or biogenesis can cause defects in embryogenesis and embryo formation.…”