Photobiology in the Zygomycota: multiple photoreceptor genes for complex responses to light.

Light is an environmental signal that modulates many aspects of the biology of zygomycete fungi. Light regulation has been investigated in the zygomycetes Phycomyces blakesleeanus, Mucor circinelloides and Pilobolus crystallinus. Examples of light regulation include the phototropism of the fruiting bodies, the regulation of the development of reproductive structures, and the activation of the biosynthesis of β-carotene. In fungi blue light is perceived by proteins homologous to WC-1, a Neurospora crassa photoreceptor and Zn finger protein that interacts with WC-2 to form a photoresponsive transcription factor complex. Unlike ascomycete and basidiomycete fungi that usually have one wc-1 and one wc-2 gene, several studies have uncovered an unexpected multitude of genes similar to wc-1 and wc-2 in the genomes of several zygomycete fungi. Some of these genes are required for fungal photoresponses, but the function of many of them remains unknown. The presence of multiple wc-1 genes confirms previous suggestions of multiple blue-light photoreceptors in Phycomyces.