The LOV-domain blue-light receptor LreA of the fungus Alternaria alternata binds predominantly FAD as chromophore and acts as a light and temperature sensor

Light and temperature sensing are important features of many organisms. Light may provide energy but may also be
used by non-photosynthetic organisms for orientation in the environment. Recent evidence suggests that plant and fungal
phytochrome and plant phototropin serve dual functions as light and temperature sensors. Here we characterized the fungal LOV-domain blue-light receptor LreA of Alternaria
alternata and show that it predominantly contains FAD as chromophore. Blue-light illumination induced ROS production
followed by protein agglomeration in vitro. In vivo ROS may control LreA activity. LreA acts as a blue-light photoreceptor
but also triggers temperature-shift-induced gene expression. Both responses required the conserved amino acid cysteine
421. We therefore propose that temperature mimics the photoresponse, which could be the ancient function of the chro-
moprotein. Temperature-dependent gene expression control with LreA was distinct from the response with phytochrome
suggesting fine-tuned, photoreceptor-specific gene regulation.