Light Controls Growth and Development via a Conserved Pathway in the Fungal Kingdom

Abstract

Light inhibits mating and haploid fruiting of the human fungal pathogen Cryptococcus neoformans, but the mechanisms involved were unknown. Two genes controlling light responses were discovered through candidate gene and insertional mutagenesis approaches. Deletion of candidate genes encoding a predicted opsin or phytochrome had no effect on mating, while strains mutated in the white collar 1 homolog gene BWC1 mated equally well in the light or the dark. The predicted Bwc1 protein shares identity with Neurospora crassa WC-1, but lacks the zinc finger DNA binding domain. BWC1 regulates cell fusion and repression of hyphal development after fusion in response to blue light. In addition, bwc1 mutant strains are hypersensitive to ultraviolet light. To identify other components required for responses to light, a novel self-fertile haploid strain was created and subjected to Agrobacterium-mediated insertional mutagenesis. One UV-sensitive mutant that filaments equally well in the light and the dark was identified and found to have an insertion in the BWC2 gene, whose product is structurally similar to N. crassa WC-2. The C. neoformans Bwc1 and Bwc2 proteins interact in the yeast two-hybrid assay. Deletion of BWC1 or BWC2 reduces the virulence of C. neoformans in a murine model of infection; the Bwc1-Bwc2 system thus represents a novel protein complex that influences both development and virulence in a pathogenic fungus. These results demonstrate that a role for blue/UV light in controlling development is an ancient process that predates the divergence of the fungi into the ascomycete and basidiomycete phyla.

Fungal Morphogenesis

“…(Image provided by S. Esher and K. Selvig, Duke University.) X. Lin et al Idnurm and Heitman 2005;Brand et al 2007). In contrast, yeasts or yeast-like cells (including conidia, endospores, etc.)…”

Trichoderma: sensing the environment for survival and dispersal

“…Some of them have symbiotic associations with plants and algae, while others are used as biocontrol agents against phytopathogenic organisms (Druzhinina & Kubicek, 2005). Further, some groups of fungi are infectious agents and can cause a wide variety of diseases in animals, plants and humans (Idnurm & Heitman, 2005). Consequently, it is of major importance to understand the mechanisms of fungal development and reproduction in order to increase the benefits and decrease the costs that they represent.…”

More Than a Repair Enzyme:Aspergillus nidulansPhotolyase-like CryA Is a Regulator of Sexual Development

“…WC proteins have been well characterized in the filamentous ascomycete Neurospora crassa (Ballario et al, 1996;Linden and Macino, 1997;Froehlich et al, 2002;He et al, 2002), and homologues have been identified in ascomycetes, basidiomycetes, and zygomycetes (for review, see Corrochano, 2007 (Idnurm and Heitman, 2005;Lu et al, 2005). WHITE COLLAR orthologues are also encoded in the genome of A. nidulans (Greene et al, 2003), and the corresponding gene products have recently been shown to influence light sensing, sexual development, and mycotoxin production (Purschwitz et al, 2008).…”

“…For example, Phycomyces blakesleeanus mutants defective in blue-light-dependent phototrophism may contain mutations in the madA gene, which encodes a protein similar to WC-1 of N. crassa (Idnurm et al, 2006). Inactivation of a wc-1 homologue in the human pathogen Cryptococcus neoformans results in a blind phenotype (Idnurm and Heitman, 2005;Lu et al, 2005). WHITE COLLAR orthologues are also encoded in the genome of A. nidulans (Greene et al, 2003), and the corresponding gene products have recently been shown to influence light sensing, sexual development, and mycotoxin production (Purschwitz et al, 2008).…”