Sordaria 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 in S. fimicola. The S. fimicola white 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 of Neurospora crassa. The LOV domain of Sfwc-1 was deleted by homologous recombination using Agrobacterium-mediated protoplast transformation. The Sfwc-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 the Sfwc-1 gene in the physiology and developmental process of perithecial formation in S. 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. IMPORTANCE Sordaria sp. 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-deleted Sfwc-1 mutant to study blue-light photoresponses in Sordaria fimicola. Phototropism and rhythmic zonation of perithecia were defective in the Sfwc-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 in S. fimicola.

BackgroundThe coprophilous ascomycete Sordaria fimicola usually reproduces sexually. Sexual differentiation in S. fimicola is accompanied by cellular and morphological changes, followed by multicellular tissue development to complete the sexual cycle. Although the morphological features of the sexual reproductive structure in S. fimicola have been well characterized, little is known about the nuclear dynamics and organization during these processes. Therefore, in this study, we successfully developed an Agrobacterium-mediated protoplast transformation protocol and generated histone H2B-mCherry-labeled S. fimicola strains. The life cycle of S. fimicola begins with germination of the ascospore and ends with the formation and discharge of new ascospores from the mature black sexual fruiting bodies, the so-called perithecia. The nuclear dynamics of the fluorescently labeled strains were examined during ascospore germination, hyphal elongation, and hyphal fusion using fluorescent microscopy.ResultsLive imaging revealed that the nuclei in the germlings and fusion hyphae during the pre-contact interaction are located adjacent to the tip.ConclusionsThis is the first report of the application of a fluorescence labeling technique in S. fimicola. This application will help researchers gain a better understanding of nuclear distribution and investigate the protein–protein interaction networks during fruiting body formation for advanced molecular genetic studies in S. fimicola.Electronic supplementary materialThe online version of this article (10.1186/s40529-018-0233-y) contains supplementary material, which is available to authorized users.