Proteomic analysis of plant cell polarity mechanisms.

Summary Living organisms require directional information for proper organ formation. In plants, cell polarity is yet not well studied, with only several known polar proteins. Our aim is to understand the chain of events leading to cell polarization and find new polar proteins including the ones determining polar axes. We will use iterative proximity labelling approach to identify interactors of known polar proteins and analyze their functions among the plant kingdom. The aim of our study is to find out new unknown polar proteins and identify key polar determinants among them. We will focus on Arabidopsis root meristem as it contains three dimensional polar axes. We are going to conduct proximity labelling screening of polar proteome using SOKs and a few of their already known interactors as baits fused to TurboID biotin ligase enzyme, and then identify labelled peptides by mass spectrometry. We will also expand our candidate list by iterating this approach using newly identified polar proteins as baits as well as exploring the interactome of several known polar domain markers. We hypothesize this extensive screening will lead to discovering proteins with either robust persistent polar localization or with temporal functions in transmitting polar signals. Upon identification of polar candidates, we will perform their functional analysis and evolutionary studies (including exploring their functions in basal land plant Marchantia polymorpha). We will also investigate the interactions among new polar proteins to define the order of their actions in polarity establishment. Integrated with other polarity projects in the lab, it will unravel the chain of events resulting in polarization and asymmetrical cell divisions.