White Collar-1, a DNA Binding Transcription Factor and a Light Sensor

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Abstract
Blue light regulates many physiological processes in fungi, but their photoreceptors are not known. In Neurospora crassa, all light responses depend on the Per-Arnt-Sim (PAS) domain–containing transcription factor white collar–1 (wc-1). By removing the WC-1 light, oxygen, or voltage domain, a specialized PAS domain that binds flavin mononucleotide in plant phototropins, we show that light responses are abolished, including light entrainment of the circadian clock. However, the WC-1–mediated dark activation of frq remains normal in this mutant, and the circadian clock can be entrained by temperature. Furthermore, we demonstrate that the purified NeurosporaWC-1–WC-2 protein complex is associated with stoichiometric amounts of the chromophore flavin-adenine dinucleotide. Together, these observations suggest that WC-1 is the blue-light photoreceptor for the circadian clock and other light responses in Neurospora.