Cannella David (Orcid ID: 0000-0002-0850-1278) The Oxidized Cellooligosaccharides Confer Thermotolerance in Arabidopsis by Priming Ethylene via Heat Shock Factor A2 Marco Zarattini, Ali Choaibi, Silvia Magri, Christian Hermans, and David Cannella* PhotoBiocatalysis Unit - Crop Production and Biostimulation Laboratory, Université libre de Bruxelles, Campus Plaine, Boulevard du Triomphe, Brussels, Belgium * David.Cannella@ulb.be Abstract Global climate change, especially heatwaves and aridity, is a major threat to agricultural production and food security. This requires common efforts from the scientific community to find effective solutions to better understand and protect the plant's vulnerabilities to high temperatures. The current study demonstrates the potential of cellooligosaccharides (COS), which are native and oxidized signaling molecules released during cell wall degradation by microbial pathogens. The extracellular perception of COS leads to the activation of damage-triggered immunity, often protecting the plant against biotic stress. However, how these signaling molecules affect abiotic stress tolerance is poorly understood. Here, we show that native COS and oxidized COS (oxiCOS) perception increase the transcript levels of several HEAT SHOCK FACTORS (HSFs) and HEAT SHOCK PROTEINS (HSPs) genes in Arabidopsis plants. However, only oxiCOS treatment triggers ethylene priming and increases thermotolerance. Furthermore, the function of the transcription factor HSFA2 is required for these processes. Altogether, our results indicate that the perception of Damage-Associated Molecular Patterns (DAMPs) may improve tolerance to adverse abiotic conditions, like exposure to high temperatures. Keywords (in alphabetical order): Cellooligosaccharides, Defense, HSFA2, Priming, Thermotolerance 1-Introduction High temperature (HT) conditions pose a serious threat to global agriculture and often co-occur with other adverse environmental conditions such as water shortage (Cohen et al., 2020; Zandalinas et al., 2021; Siddiqui et al., 2022). Plant exposure to HT affects various metabolic, physiological, and developmental processes. These can lead to cellular disorganization and ultimately to growth inhibition (Wahid et al. , 2007). Transcriptional reprogramming, excessive membrane fluidization, reactive oxygen species accumulation and protein denaturation are associated with detrimental effects. One mechanism of thermotolerance is to anticipate the damaging conditions early enough by accumulating heat-shock proteins (HSPs) and factors (HSFs) involved in cellular protection against heat stress. Hence, This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1111/ppl.13737 This article is protected by copyright. All rights reserved.