Blakeslea trispora Photoreceptors: Identification and Functional Analysis.

is an industrial fungal species used for large-scale production of carotenoids. However, light-regulated physiological processes, such as carotenoid biosynthesis and phototropism, are not fully understood. In this study, we isolated and characterized three photoreceptor genes, , , and , in Bioinformatics analyses of these genes and their protein sequences revealed that the functional domains (PAS/LOV [Per-ARNT-Sim/light-oxygen-voltage] domain and zinc finger structure) of the proteins have significant homology to those of other fungal blue-light regulator proteins expressed by and The photoreceptor proteins were synthesized by heterologous expression in The chromogenic groups consisting of flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN) were detected to accompany BTWC-1 proteins by using high-performance liquid chromatography (HPLC) and fluorescence spectrometry, demonstrating that the proteins may be photosensitive. The absorbance changes of the purified BTWC-1 proteins seen under dark and light conditions indicated that they were light responsive and underwent a characteristic photocycle by light induction. Site-directed mutagenesis of the cysteine residual (Cys) in BTWC-1 did not affect the normal expression of the protein in but did lead to the loss of photocycle response, indicating that Cys represents a flavin-binding domain for photon detection. We then analyzed the functions of BTWC-1 proteins by complementing , , and into the counterpart knockout strains of for each gene. Transformation of the complement into knockout strains restored the positive phototropism, while the addition of complement remedied the deficiency of carotene biosynthesis in the knockout strains under conditions of illumination. These results indicate that and are involved in phototropism and light-inducible carotenogenesis. Thus, genes share a conserved flavin-binding domain and act as photoreceptors for control of different light transduction pathways in Studies have confirmed that light-regulated carotenogenesis is prevalent in filamentous fungi, especially in mucorales. However, few investigations have been done to understand photoinduced synthesis of carotenoids and related mechanisms in , a well-known industrial microbial strains. In the present study, three photoreceptor genes in were cloned, expressed, and characterized by bioinformatics and photoreception analyses, and then functional analyses of these genes were constructed in The results of this study will lead to a better understanding of photoreception and light-regulated carotenoid synthesis and other physiological responses in .