A glimpse into the basis of vision in the kingdom Mycota

Abstract

Virtually all organisms exposed to light are capable of sensing this environmental signal. In recent years the photoreceptors that mediate the ability of fungi to "see" have been identified in diverse species, and increasingly characterized. The small sizes of fungal genomes and ease in genetic and molecular biology manipulations make this kingdom ideal amongst the eukaryotes for understanding photosensing. The most widespread and conserved photosensory protein in the fungi is White collar 1 (WC-1), a flavin-binding photoreceptor that functions with WC-2 as a transcription factor complex. Other photosensory proteins in fungi include opsins, phytochromes and cryptochromes whose roles in fungal photobiology are not fully resolved and their distribution in the fungi requires further taxon sampling. Additional unknown photoreceptors await discovery. This review discusses the effects of light on fungi and the evolutionary processes that may have shaped the ability of species to sense and respond to this signal.

Fig. 1

Distribution of photosensory proteins and their copy numbers in species across the fungal kingdom, based on whole-genome sequence information. Wherever possible, a representative example is provided rather than all sequenced members of a clade (eg. Fusarium, the Saccharomycotina yeasts, Schizosaccharomyces, Microsporum and Trichophyton). The terms zygomycete and chytrid do not refer to monophyletic groups. Presence or absence is inferred primarily by BLASTp analysis against GenBank and fungal genome databases at the Broad Institute and Department of Energy. For the cryptochrome category, the CPD-photolyase class is not included (but see Bayram et al., 2008a), and opsins consider type I only.

Fig. 2

From response to receptor: 160 years to demonstrate WC-1 is a photosensor in N. crassa. These events demonstrate the multidimensional process of demonstrating a protein is a photoreceptor. [Additional references from figure (Froehlich et al., 2002; He et al., 2002; Payen, 1843; Perkins et al., 1962; Sargent and Briggs, 1967; Went, 1904; Zalokar, 1955)].

Fig. 3

Phylogentic tree of WC-1 proteins. Homologs were downloaded from GenBank (gi numbers in grey; EST accession for C. coriobolus) or genome sequencing centers (P. chrysosporium, S. roseus, S. punctatus, A. macrogynus, P. graminis), aligned in ClustalW, the alignment edited in MacClade, and this alignment analyzed by maximum likelihood in PHYLIP. Bootstrap values above 50% adjacent to the nodes represent 100 replicates. The names of the genes encoding these proteins are provided after the species when known. Boxes represent lineages without the zinc finger DNA-binding domain or, in the case of the zygomycete group, a divergence from canonical form. Note that the terms zygomycete and chytrid no longer refer to monophyletic groups.