Flashes of UV-C light are perceived by UVR8, the photoreceptor of UV-B light

The confocal microscope was funded by the European Regional Development Fund, the French government, the Sud Provence-Alpes-Côte d’Azur Region, the Departmental Council of Vaucluse and the Urban Community of Avignon.; International audience; Light is an important regulator of plant morphogenesis and plant-pathogen interactions via specific photoreceptors and signaling pathways. Besides visible light, other electromagnetic radiations may play roles, notably ultraviolet (UV) light. The UV part of the electromagnetic spectrum includes UV-A (315 nm - 400 nm), UV-B (280 nm - 315 nm) and UV-C radiations (200 nm - 280 nm). UV-B and UV-C have been reported to increase plant resistance to plant pathogens after the UV perception and signaling stages. The perception of UV-B radiation is achieved by the dimer protein UVR8 (UV RESISTANCE LOCUS 8). Even though the action spectrum of this photoreceptor overlaps in the UV-C domain, it has never been formally demonstrated that UVR8 could also act as a photoreceptor of UV-C light. We provide here original observations showing that UVR8 can indeed perceive UV-C light provided that the latter is in the form of flashes (1s) and not continuous illuminations (the 60s). Our observations also show that the response of UVR8 to flashes of UV-C light is dose-dependent. They could explain why flashes of UV-C light are more effective for stimulating plant defenses than continuous illuminations for the same amount of energy delivered to plants (J/m2). Eventually, our observations support ongoing trials that aim at using UV-C light as an environmental-friendly plant resistance inducer in field conditions.