The Cellular Basis of Multicellular Pattern Formation

The formation of plant organs (leaves, roots, flowers) depends on the activity of stem cells (SC), located in stem cell niches (meristems) together with adjoining organizer cells (OC) that prevent SC differentiation. Despite their importance, SC and OC have been poorly described at molecular and cellular level and mechanisms for their coordinated specification are only partially understood. We study the specification of the very first SC and OC for the root in the early Arabidopsis embryo where cell divisions are almost invariant and, in the absence of cell motility, highly predictable. Previously we have established a central role for the transcription factor MONOPTEROS (MP) in OC specification and we have recently found that MP also controls SC specification. Hence, MP offers a unique entry point into studying the genomic and cellular reprogramming that underlies coordinated SC and OC specification. Our recent identification of MP target genes has shown that its function in SC specification is cell-autonomous, while MP-dependent OC specification involves a mobile transcription factor.
In recent years we have developed a set of resources to systematically study embryonic root meristem initiation, and are now in a unique position to answer the following questions in this ERC project:

1. What transcriptional reprogramming underlies the first specification of SC and OC in the plant embryo?
2. What cellular changes follow from transcriptional reprogramming and mediate elongation and asymmetric division of SC and OC?
3. What is the mechanism of directional protein transport that ensures spatiotemporal coordination between SC and OC?

The project will provide genome-wide insight in the cellular reprogramming underlying the coordinated formation of a multicellular structure. Finally, this work will shed light on mechanisms of stem cell and stem cell niche formation.