%0 Generic
%A Schmidt, Vanessa Aphaia Fiona
%C Heidelberg
%D 2022
%F heidok:29311
%R 10.11588/heidok.00029311
%T Polarization of a small GTPase at the plasma membrane of the root hair initiation domain
%U https://archiv.ub.uni-heidelberg.de/volltextserver/29311/
%X Functional specialization of singles cells but also of whole tissues requires the division of labor and leads to the establishment of unequal distribution and polar organization. As a consequence, a diverse spectrum of cells with polar shapes has arisen in all kingdoms of life and conceptual similarities between these cells indicate the presence of a general unifying machinery. Even though we have a good understanding of the process of polar growth itself, we still know very little about the initial steps that lead to cellular asymmetry and polarity establishment.  The root hair system of Arabidopsis thaliana is an excellent model to study all aspects of polarity and especially its initiation. One of the first proteins to localize at the root hair initiation domain (RHID) in Arabidopsis is the small GTPase RHO-OF PLANTS 2 (ROP2), which is a central regulator of the root hair growth machinery. ROP2 is a molecular switch that shuffles between an active (GTP-bound) and an inactive (GDP-bound) state. It is obvious that the spatio-temporal control of ROP2 positioning and its activation is of critical importance for proper root hair development, however to date it remains unclear how ROP2 is recruited to the RHID, how ROP2 polarization is timed and how its polar accumulation is maintained.  In this thesis I could show that the poly-basic region close to the C-terminus of ROP2 is necessary, but not sufficient for its accumulation at the RHID. I could further demonstrate that polar accumulation of ROP2 depends on its N-terminus, which we have reported to be involved in the interaction with its putative activator and landmark protein GEF3. I found that the ability to shuffle between its active and inactive state is critical for ROP2 polarization and have presented evidence for an activation-dependent immobilization of ROP2 that involves the interaction with GEF3, activation of GDP-ROP2 and differential protein mobility.  Using single-molecule localization microscopy I was able to show that ROP2, GEF3 and other proteins of the root hair growth machinery localize into nanoclusters at the PM. To fully characterize the proteome of these nanoclusters, I established biotin-ligase based proximity labelling in Arabidopsis root hairs. This will allow us to elucidate whether the structuring of the PM (at the RHID) into nanoclusters plays a role in the establishment, maintenance and plasticity of cellular polarity.