Carotenoids are an important source of bioactive compounds in plants, including phytohormones (abscisic acid, strigolactones). We recently identified new growth regulators and signaling molecules derived from the oxidation of ß-carotene in the chloroplasts of plants under environmental constraints, such as ß-cyclocitral and its oxidized derivative ß-cyclocitric acid. Application of these apocarotenoids to plants triggers defense mechanisms which increase their tolerance against climatic stresses including drought. ApoStress will delineate this newly discovered retrograde signaling pathway connecting photosynthesis to stress acclimation, by identifying the receptor(s) of those apocarotenoids, their signaling pathways and their protective modes of action against drought stress in the model plant Arabidopsis thaliana. We will also investigate the formation and metabolism of these compounds in planta as well as their emission in the atmosphere. An important aspect of this project is to evaluate the potential of those compounds as phytoprotectors in a crop species, grapevine (Vitis vinifera). The diversity of vine varieties will be exploited to further explore the link between carotenoid oxidative cleavage and drought tolerance and to confirm the findings gathered in Arabidopsis plants on ß-cyclocitral metabolism and physiological processes of interest in this crop species. In the long term, this research could provide new bioactive molecules and new gene targets for improving drought tolerance of plants.