Résumé
Water deficit caused by osmotic stresses to roots, including salinity and drought, presents a significantenvironmental challenge to plant growth and crop yield. In seconds to hours, it results in diverse responses inplants, including impairment of cell wall integrity, decline in turgor potential, generation and signaling ofabscisic acid, as well as reprogramming of gene expression. These processes have been studied extensively but,so far, there is no clear picture of when and where the physical nature of a water deficit is perceived by plantsand turned into a biological signal. In a work published in 2023, a combination of physiology and transcriptomicapproaches allowed us to unravel that both turgor pressure changes in root cortical cells and external osmoticpotential are able to trigger specific transcriptional regulations. We identified genes whose mRNA abundancein roots was quantitatively correlated to one or the other of the components of water potential. We recentlyfocused our efforts on two of those candidates, and unravel that plasmolysis is a turning point in their dynamicof response to osmotic stress. Both promoter activity and mRNA decay pathways are required for their properregulation. Finally, we created a luciferase-based, genetically encoded, construct that is able to report earlyhydraulic changes. This “hydro-reporter” is ABA-responsive but its regulation by water deficit is ABA-independent and, although initially designed in roots, can also be observed in shoots.