A cysteine-dependent redox modification of the iron-sulfur cluster glutaredoxin GRXS17 activates its holdase activity and protects plants from heat stress AUTHOR CONTRIBUTION

Arabidopsis histone deacetylase HDA19 is required for gene expression programs of a large spectrum of plant developmental and stress-responsive pathways. How this enzyme senses cellular environment to control its activity remains unclear. In this work, we show that HDA19 is post-translationally modified by Snitrosylation at 4 Cysteine (Cys) residues. HDA19 S-nitrosylation depends on the cellular nitric oxide level, which is enhanced under oxidative stress. We find that HDA19 is required for cellular redox homeostasis and plant tolerance to oxidative stress, which in turn stimulates its nuclear enrichment, S-nitrosylation and epigenetic functions including binding to genomic targets, histone deacetylation and gene repression. The Cys137 of the protein is involved in basal and stress-induced S-nitrosylation, and is required for HDA19 functions in developmental, stress-responsive and epigenetic controls. Together, these results indicate that Snitrosylation regulates HDA19 activity and is a mechanism of redox-sensing for chromatin regulation of plant tolerance to stress.

As sessile organisms, plants are particularly affected by climate change and will face more frequent and extreme temperature variations in the future. Plants have developed a large panel of mechanisms allowing them to perceive and respond to these environmental constraints, which requires sophisticated signalling mechanisms. Reactive oxygen species (ROS) are generated in plants exposed to various stress conditions including high temperatures and are presumed to be involved in stress response reactions. The diversity of ROS-generating pathways and the ability of ROS to propagate from cell to cell, to diffuse through cellular compartments and even across membranes between subcellular compartments put them at the centre of signalling pathways. In addition, their capacities to modify the cellular redox status and to modulate functions of target proteins, notably through cysteine oxidation, involve them in major stress response transduction pathways. ROS scavenging and thiol reductase systems also participate in the transmission of oxidation-dependent stress signals. In this review, we summarize current knowledge on the functions of ROS and oxidoreductase systems in integrating high temperature signals, towards the activation of stress responses and developmental acclimation mechanisms.