Genetically Modified Heat Shock Protein90s and Polyamine Oxidases in <i>Arabidopsis</i> Reveal Their Interaction under Heat Stress Affecting Polyamine Acetylation, Oxidation and Homeostasis of Reactive Oxygen Species

• Main Authors: Imene Toumi, Marianthi G. Pagoulatou, Theoni Margaritopoulou, Dimitra Milioni, Kalliopi A. Roubelakis-Angelakis
• Format: Article
• Language: English
• Published: MDPI AG 2019-09-01
• Series: Plants
• Subjects: heat shock proteins; heat stress; polyamines; polyamine oxidases; PA acetylation; PA oxidation; PA back-conversion; hydrogen peroxide
• Online Access: https://www.mdpi.com/2223-7747/8/9/323

The chaperones, heat shock proteins (HSPs), stabilize proteins to minimize proteotoxic stress, especially during heat stress (HS) and polyamine (PA) oxidases (PAOs) participate in the modulation of the cellular homeostasis of PAs and reactive oxygen species (ROS). An interesting interaction of HSP90s and PAOs was revealed in <i>Arabidopsis thaliana</i> by using the <i>pLFY:HSP90RNAi</i> line against the four <i>AtHSP90</i> genes encoding cytosolic proteins, the T-DNA <i>Athsp90-1</i> and <i>Athsp90-4</i> insertional mutants, the <i>Atpao3</i> mutant and pharmacological inhibitors of HSP90s and PAOs. Silencing of all cytosolic <i>HSP90</i> genes resulted in several-fold higher levels of soluble spermidine (S-Spd), acetylated Spd (N⁸-acetyl-Spd) and acetylated spermine (N¹-acetyl-Spm) in the transgenic <i>Arabidopsis thaliana</i> leaves. Heat shock induced increase of soluble-PAs (S-PAs) and soluble hydrolyzed-PAs (SH-PAs), especially of SH-Spm, and more importantly of acetylated Spd and Spm. The silencing of <i>HSP90</i> genes or pharmacological inhibition of the HSP90 proteins by the specific inhibitor radicicol, under HS stimulatory conditions, resulted in a further increase of PA titers, N⁸-acetyl-Spd and N¹-acetyl-Spm, and also stimulated the expression of PAO genes. The increased PA titers and PAO enzymatic activity resulted in a profound increase of PAO-derived hydrogen peroxide (H₂O₂) levels, which was terminated by the addition of the PAO-specific inhibitor guazatine. Interestingly, the loss-of-function <i>Atpao3</i> mutant exhibited increased mRNA levels of selected <i>AtHSP90</i> genes. Taken together, the results herein reveal a novel function of HSP90 and suggest that HSP90s and PAOs cross-talk to orchestrate PA acetylation, oxidation, and PA/H₂O₂ homeostasis.