Photoreceptors in the dark: a functional white collar-like complex and other putative light-sensing components encoded by the genome of the subterranean fungus Tuber melanosporumR Gerace, B Montanini, M Proietto, E Levati, C De Luca, A Brenna, … Fungal Biology

Abstract

Light is perceived and transduced by fungi, where it modulates processes as diverse as growth and morphogenesis, sexual development and secondary metabolism. A special case in point is that of fungi with a subterranean, light-shielded habitat such as Tuber spp. Using as reference the genome sequence of the black truffle Tuber melanosporum, we employed sequence prediction tools and expression data to gain insight on the photoreceptor systems expressed by this hypogeous ectomycorryzal fungus. These include a chromophore-less opsin preferentially expressed in fruiting bodies, a putative red light-sensing phytochrome that is not expressed at detectable levels in any of the examined developmental conditions, and a nearly canonical two-component (WC-1/WC-2) photoreceptor system similar to the Neurospora white collar complex. The latter is expressed at relatively high levels throughout the different developmental stages of T. melanosporum, except for sexual stage fruiting bodies where it is down-regulated. Various evidences, including the growth arrest phenotype elicited by blue light and the ability of a chimeric Tuber/Neurospora WC-1 protein to complement a N. crassa wc-1^koblind strain suggest that the Tuber white collar complex is likely functional and capable of responding to blue-light. The other putative photoreceptor components we have identified in the T. melanosporum genome, especially the chromophore-less opsin and the likely non-functional phytochrome, may represent the signatures of adaptation to a hypogeous (light-shielded) lifestyle.