Quantitative 4D tracking analysis and chemical induction of heat shock granules during cytosolic misfolded protein stress

Abstract

Heat Shock Granules (HSGs) are subcellular structures composed of small Heat Shock Proteins (sHSPs) and misfolded proteins that form in response to heat stress in plants. While sHSPs are found in other organisms, HSGs have only been reported in plant cells and only in response to heat stress. This thesis examines the signaling pathways that regulate the transcription of sHSPs and the formation of HSGs and investigates whether heat is the only stress that could activate these pathways. By visualizing HSGs in an Arabidopsis thaliana BOBBERl:GFP reporter line using still and 4-D confocal microscopy, we characterize HSG formation and HSG structural qualities such as volume and shape. 4D tracking is used to describe dynamic behavior. We also show that inducing protein misfolding by treating live seedlings with amino acid analog L-Azetidine2-Carboxylic Acid (AZC) or proteasome inhibitor MG132 induces granule formation. We propose that the term Heat Shock Granule is a misnomer, since HSG formation can be catalyzed by misfolded protein stress in the absence of heat treatment