Signaling of light-induced oxidative stress in the acclimation mechanisms of plants to climatic changes – SLOSAM

Climatic changes are expected to cause more heat, drought or pathogen stress and also to be associated with more extreme variations of environmental factors. Most of those environmental changes can affect the photosynthetic activity of plants. In general, stress-induced inhibition of photosynthesis leads to excess light energy in chloroplasts resulting in excitation/electron transfer to molecular oxygen and hence in the formation of reactive oxygen species (ROS), especially singlet oxygen (1O2). The latter ROS has dual effect: it is toxic, engaging readily with biomolecules, and it functions as a signal molecule that can lead to acclimation to 1O2 stress. The SLOSAM project is aimed at understanding the genetic bases that determine the adaptability of plants to environmental changes that generate 1O2 in chloroplasts. It brings together two partners with complementary expertise: the LEMP at CEA/Cadarache and the LGBP at the Luminy campus of Aix Marseille University. By federating and coordinating the research done in those groups, we think that a strong research spot on photooxidative stress signaling could be established in France through this project. Using two 1O2-overproducing mutants of the model plant Arabidopsis thaliana, the flu and ch1 mutants, the 1O2 signaling pathway leading to acclimation will be investigated from the initial site of 1O2 production in the chloroplasts to the cytosol and the nucleus. The gene responses to 1O2 in the flu and ch1 mutants showed many similarities, but key differences were also observed, suggesting that the site of 1O2 production (photosystems vs. thylakoid membranes) modulates gene responses and emphasizing the necessity to analyze both mutants in a comparative study. Although a few components of the 1O2 signaling pathway have been identified, the mechanisms by which the 1O2 signal is perceived in the chloroplast and conveyed to the nucleus for changes in gene expression remain largely unknown. The main goal of this project is to shed light on many unknown aspects of this pathway. The main source of 1O2 in plants is the reaction center of Photosystem II (PSII), and recent works in the LEMP have identified compounds (such as b-cyclocitral) generated from PSII by 1O2 oxidation of the carotenoid b-carotene as initial messengers of 1O2 stress. The mode of action of these upstream signals will be investigated using a genetic approach based on the screening of Arabidopsis mutants that do not respond to these carotenoid-derived signals. In parallel, we will use a more targeted approach based on previous data on gene expression regulation during acclimation of Arabidopsis to 1O2. Part of our efforts will also be concentrated on downstream steps of the 1O2 signaling pathway at the nuclear DNA level. Based on the recent discovery by the LGBP that Topoisomerase VI is required for the expression of 1O2-responsive genes in the flu mutant, the role of chromatin dynamics in gene responsiveness will be studied during the 1O2-triggered acclimatory response. Another important level of gene regulation which was overlooked in previous works on photooxidative stress is post-transcriptional gene regulation. This aspect will be investigated in the context of acclimation to 1O2, using various approaches including ribosome profiling, analysis of small RNAs and their mRNA targets and bioinformatics. Thus, the main deliveries of the proposed work are a detailed picture of the gene regulation and the identification of essential genes involved in the acclimatory response of plants to 1O2. Considering the central role played by this ROS in the response of plants to abiotic and biotic stresses, the expected results will be important to understand the adaptation of plants to climatic changes and could provide the bases for the development of photosynthetic organisms tolerant to photooxidative stress in order to secure food production in changing environments and improve biofuel production