Regulation by Blue Light of the fluffy Gene Encoding a Major Regulator of Conidiation in Neurospora crassa

Abstract

The development of asexual spores, that is, the process of conidiation, in the fungus Neurospora crassa is increased by light. The fluffy (fl) gene, encoding a major regulator of conidiation, is activated by light. We describe here a detailed characterization of the regulation by blue light of fl in vegetative hyphae. This induction requires the white collar complex (WCC) while the FLD protein acts as a dark repressor of fl transcription. We show that the WCC directly regulates fl transcription in response to blue light after transiently binding the promoter. We propose that fl is repressed by FLD in vegetative mycelia and that the repression is lost after light exposure and WCC activation. The increase in fl mRNA in vegetative mycelia after light exposure, and the corresponding increase in the amount of the regulatory FL protein, should promote the activation of the conidiation pathway. The activation by light of fl provides a simple mechanism for the activation of conidiation by blue light in Neurospora that may be at work in other fungi.

Transcription Factors in Light and Circadian Clock Signaling Networks Revealed by Genomewide Mapping of Direct Targets for Neurospora White Collar Complex

“…In previous studies, only the frq, vvd, al-3, fl, and sub-1 promoters had been identified as direct targets for the WCC (6,18,24,36). By ChIP-seq, we identified Ͼ400 significant regions of WCC enrichment, with Ͼ200 falling in known or predicted promoters of at least one gene.…”

Regulation of Conidiation by Light in Aspergillus nidulans

“…One possibility is that the photoreceptor complex is signaling some other regulators, including FlbB and FlbC, to bind to the promoter of brlA or that the photoreceptor complex binds itself to the promoter to activate brlA transcription in a mechanism that requires FlbB and FlbC. LreA and LreB are homologs of the white-collar proteins, which are known DNA-binding proteins (Froehlich et al 2002;He et al 2002;Belden et al 2007b;Olmedo et al 2010a) and may directly regulate gene expression in A. nidulans in a similar way. It is interesting that the induction levels of all the genes that we have characterized are similar, possibly reflecting that an increase in the expression of the fluffy genes triggers an equivalent increase in brlA expression.…”

“…In N. crassa, light activates the accumulation of mRNAs for the developmental genes fluffy (fl) (Belden et al 2007a;Olmedo et al 2010a) and csp-1 (Chen et al 2009). The FL protein is a transcription factor that is necessary and sufficient to induce conidiation (Bailey and Ebbole 1998;Bailey-Shrode and Ebbole 2004).…”

“…fl is induced during conidiation along with many other genes in N. crassa (Greenwald et al 2010). The lightdependent activation of fl by the WCC suggested a simple model for the activation of conidiation by light in N. crassa with light-activated WCC increasing fl transcription and the subsequent accumulation of regulatory FL protein activating the conidiation pathway (Olmedo et al 2010a). This model does not appear to be so simple in A. nidulans.…”

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

“…The protein WC-2 contains a zinc-finger and a PAS domain (Linden and Macino, 1997), and interacts with WC-1 to form a White Collar complex (WCC). This complex, upon light exposure, binds transiently to the promoters of light-regulated genes, presumably to activate their transcription (Belden et al, 2007;Froehlich et al, 2002;He and Liu, 2005;Olmedo et al, 2010). The presence of genes similar to wc-1 and wc-2 in representatives of ascomycete, basidiomycete, and zygomycete fungi suggested that the WCC originated very early in fungal evolution as a photoreceptive transcription factor complex (Corrochano, 2007;Herrera-Estrella and Horwitz, 2007).…”