High ambient temperatures due to climate change impact plant growth and survival. Recent data indicate that chromatin modification is an essential process of gene expression reprogramming during plant response to elevated growth temperature. Histone deacetylases (HDAC) that regulate histone acetylation levels were shown to play important roles in plant adaptation to environment. In addition, HDACs are also involved in deacetylation of non-histone proteins such as metabolic enzymes and transcription factors to control their activity. Our preliminary data indicate that Arabidopsis HDAC members play distinct roles in plant response to high ambient temperature. In addition, we found that high ambient temperature alters plant cell redox environment and that cellular redox environment regulates HDAC subcellular localization and deacetylase activity. The objective of this proposal is to elucidate the molecular mechanisms of interplay between cellular redox and chromatin modification that regulate plant response to high ambient temperature. In particular, the project aims to elucidate how cellular redox environment regulates HDAC activity to control lysine acetylation of histone and non-histone proteins involved in either epigenetic regulation of gene expression or metabolism and/or signaling during plant response to high ambient temperature, and to identify and study implicated redox regulators. We propose to first identify redox post-translational modifications of Arabidopsis HDACs under normal and high ambient temperature conditions by using biochemical and mass spectrometry approaches. Then, we will examine effects of redox modifications on HDAC enzymatic activity, subcellular localization, and function in plant response to high ambient temperature thanks to plants expressing tagged HDAC proteins in wild-type and mutated versions of redox-sensitive residues. Then, we plan to identify and validate redox regulators involved in modifications of the HDACs by both biochemical and genetic approaches and to study the role of redox regulators in plant response to high temperature. Next, we will study the effects of redox modifications on HDAC epigenetic function in terms of chromatin structure, genome-wide histone modifications, DNA methylation and gene expression by high throughput sequencing and cell biology approaches. Finally, we will investigate the effect of redox modifications on HDAC functions in regulating lysine acetylation of non-histone proteins in order to identify HDAC-regulated key metabolic enzymes and signaling proteins involved in plant response to high ambient temperature. This project aiming to elucidate redox-epigenetics-metabolism networks in plants will deepen current understanding of how plants adapt or resist to a changing environment. More specifically, the project will decipher the molecular basis of HDAC regulation in response to stress and how thiol modifications modulate their functions. Noteworthy, this study will reveal the function of HDAC-dependent lysine acetylation in regulating activity of non-histone proteins which is largely unknown at present time. We believe that the results obtained from this project will lead to establish a general link and reveal the molecular mechanisms of interplay between redox signaling, epigenetic regulation and plant adaptation to environment. The REPHARE project assembles complementary expertise in the fields of epigenetic regulation and redox signaling from the two partners who have already built a solid basis which will lead the project to success.