Ubiquitin E3-ligases and cell polarity control in the model plant Arabidopsis thaliana
Abstract
Polarity acquisition during organismal differentiation coordinates morphogenesis. In higher plants, polarity determinants have been identified in recent years, including the plant hormone auxin. Specifically, directional transport of the growth regulator throughout the plant body establishes morphogenetic cues, triggering developmental programs, underlying polarity establishment and growth axis formation. Canonical PIN- FORMED (PIN) auxin transport proteins mediate cellular auxin efflux, and control direction of the resulting auxin flow, by means of their polar asymmetric distribution at the plasma membrane. PIN polarity and variations therein are subject to tight control, influencing protein localization, activity and abundance, and regulators involved in such control are subject of intense research. In this application, I propose the characterization of so far unknown determinants of PIN polarity. Mutations in a small family of Arabidopsis RING-finger E3 ubiquitin ligases were found to cause severe aberrations in directional root growth. This relates to alterations in auxin distribution and/or signaling in mutant root meristems, likely causing deficiencies in root tropisms. Importantly, whilst these E3-ligases do not influence PIN protein abundance, defects in these genes cause an apical-to-basal shift in the localization of PIN2 in root meristems, suggesting a role in the regulation of polar protein sorting. Genetic analysis and interaction assays established links between these E3-ligases and the PID/WAG—PP2A/PP6 regulatory module, which has been demonstrated to influence polar PIN distribution via reversible phosphorylation events. Crosstalk between variations in protein phosphorylation and ubiquitylation, thus appears to influence PIN protein sorting decisions. Goal of this proposal is the identification of mechanisms by which the E3-ligases act on polarity of PIN2 and further PINs. This will involve a characterization of enzymatic activities, to elucidate ubiquitylation modes and specificity of these enzymes. Moreover, based on the identification of interacting proteins by means of split-ubiquitin screening and co-immunoprecipitation/LC-MS analysis, we intend to establish a network of regulatory events, by which the E3-ligases impact on polar sorting decisions. Particular emphasis will be given to an in-depth analysis of the crosstalk between E3-ligases and the machinery controlling PIN phosphorylation, to identify mechanisms by which these proteins interact. This, together with genetic and cell biological approaches, suitable for integration of the E3-ligases into established signaling and protein sorting networks, should define so far unknown mechanisms of polarity control in higher plants.
keywords PIN2 E3-Ligase Auxin ***
Publikationen
Project staff
Christian Luschnig
Assoc. Prof. Dr. Christian Luschnig
christian.luschnig@boku.ac.at
Tel: +43 1 47654-94230
Project Leader
01.10.2018 - 30.09.2023