Protein Palmitoylation Is Critical For The Polar Growth Of Root Hairs In Arabidopsis

A majority of eukaryotic proteins are subject to post-translational modifications, which regulate their activity, stability, subcellular localization, protein-protein interactions and so on. Palmitoylation, also known as S-acylation, is the reversible addition of a 16-carbon saturated palmitate group to the sulfhydryl group of a cysteine to form a thioester, playing critical roles in dynamic cellular activities such as signalling transduction, membrane trafficking, protein sorting and protein-protein interactions. Only a few plant proteins have been experimentally verified to be subject to palmitoylation, such as ROP GTPases, calcineurin B like proteins(CBLs), and subunits of heterotrimeric G proteins. However, emerging evidence from palmitoyl proteomics hinted that protein palmitoylation might be widespread. Nonetheless, due to the large number of genes encoding PATs and the lack of consensus motifs for palmitoylation, progress on the roles of protein palmitoylation in plants has been slow.By using root hairs as a model and combining pharmacological and genetic approaches, we examined the role of protein palmitoylation in root hair polar growth. The main results and conclusions presented in this thesis are as follows:(1) Multiple PATs from different endomembrane compartments may participate in root hair growth, among which the Golgi-localized PAT24/TIP GROWTH DEFECTIVE1(TIP1) plays a major role while the tonoplast-localized PAT10 plays a secondary role in root hair polar growth.(2) A specific inhibitor for protein palmitoylation, 2-bromopalmitate(2-BP), compromised root hair elongation and polarity.(3) 2-BP disrupts actin MF polymerization and the asymmetric PM localization of PIP2.(4) RabA4b-positive post-Golgi secretion was impaired by 2-BP in root hairs.(5) 2-BP inhibits endocytic and vacuolar trafficking.Inhibition of protein palmitoylation by 2-BP disturbed key intracellular activities in root hairs. Although some of these effects are likely indirect, the cytological data reported here will contribute to a deep understanding of protein palmitoylation during tip growth in plants.