Photomorphogenesis in the hypogeous fungus Tuber borchii: isolation and characterization of Tbwc-1, the homologue of the blue-light photoreceptor of Neurospora crassa

Abstract

Truffles form a group of plant-symbiotic Ascomycetes whose hypogeous life cycle is poorly understood. Here we present initial evidence for the influence of light on Tuber borchii mycelial growth and the identification and cloning of a gene, Tbwc-1, homologous to a blue-light photoreceptor of Neurospora crassa. Blue-light irradiation of T. borchii colonies inhibits their apical growth. It also alters apical growth in N. crassa. In Neurospora, the response is controlled by a nuclear photoreceptor, NcWC-1 (White Collar-1), which consists of a sensor domain (LOV) and a transcriptional factor moiety. We isolated a gene (Tbwc-1) whose deduced amino acid sequence shows a high similarity and colinearity of domains with NcWC-1, except for the polyglutamine regions. As previously found in Neurospora, Tbwc-1 mRNA is under light control and its steady state level increases upon irradiation. In silico analysis of the TbWC-1 sensor domain (LOV) supports the hypothesis that TbWC-1 is a photoreceptor, while the absence of the two polyglutamine regions involved in transcriptional activation in Neurospora suggests that this function in Tuber could be lost.