ABSTRACTSordaria fimicola, a coprophilous ascomycete, is a homothallic fungus that can undergo sexual differentiation with cellular and morphological changes followed by multicellular tissue development to complete its sexual cycle. In this study, we identified and characterized the blue-light photoreceptor gene inS. fimicola. TheS. fimicolawhite collar-1 photoreceptor (SfWC-1) contains light-oxygen-voltage-sensing (LOV), Per-Arnt-Sim (PAS), and other conserved domains and is homologous to the WC-1 blue-light photoreceptor ofNeurospora crassa. The LOV domain ofSfwc-1was deleted by homologous recombination usingAgrobacterium-mediated protoplast transformation. TheSfwc-1(Δlov)mutant showed normal vegetative growth but produced less carotenoid pigment under illumination. The mutant showed delayed and less-pronounced fruiting-body formation, was defective in phototropism of the perithecial beaks, and lacked the fruiting-body zonation pattern compared with the wild type under the illumination condition. Gene expression analyses supported the light-induced functions of theSfwc-1gene in the physiology and developmental process of perithecial formation inS. fimicola. Moreover, green fluorescent protein (GFP)-tagged SfWC-1 fluorescence signals were transiently strong upon light induction and prominently located inside the nuclei of living hyphae. Our studies focused on the putative blue-light photoreceptor in a model ascomycete and contribute to a better understanding of the photoregulatory functions and networks mediated by the evolutionarily conserved blue-light photoreceptors across diverse fungal phyla.IMPORTANCESordariasp. has been a model for study of fruiting-body differentiation in fungi. Several environmental factors, including light, affect cellular and morphological changes during multicellular tissue development. Here, we created a light-oxygen-voltage-sensing (LOV) domain-deletedSfwc-1mutant to study blue-light photoresponses inSordaria fimicola. Phototropism and rhythmic zonation of perithecia were defective in theSfwc-1(Δlov)mutant. Moreover, fruiting-body development in the mutant was reduced and also significantly delayed. Gene expression analysis and subcellular localization study further revealed the light-induced differential gene expression and cellular responses upon light stimulation inS. fimicola.