Additional filters were used for blue-light exposure (Corning broadband blue filter with maximum transmission at 440 nm) or for red-light exposure (two Plexiglas red filters). work in other fungi. ASEXUAL sporulation in the fungusNeurospora crassaleads to the development of asexual spores called macroconidia. Other types of conidia, microconidia and arthroconidia, are produced by Neurospora (Springer1993), but macroconidia are most abundant, and we will focus on the regulation of macroconidiation, or conidiation, from here on. Conidiation is usually induced by several environmental signals, including desiccation, carbon and nitrogen starvation, and exposure to blue light (Springer1993;Davis2000). In addition, conidiation is controlled by an endogenous circadian clock (Dunlapand Loros2004;Tanet al.2004;Heintzenand Liu2007;Brunnerand Kldi2008). During conidial development, vegetative hyphae grow away from the substrate to form a mass of aerial hyphae. About 4 hr after conidial induction, hyphal growth changes from apical elongation to apical budding, leading to the formation of chains of proconidia divided by minor constrictions. Budding continues in proconidial chains, and major constrictions appear 8 hr after the induction of conidiation. Interconidial junctions are cleaved several hours later, but conidia are held together by fragile connective threads until they are dispersed by wind currents (Springer1993). Several genes are required for conidiation. Strains with mutations inaconidiate-2(acon-2) orfluffyoid(fld) are blocked in the transition from filamentous to budding growth. Mutations inaconidiate-3(acon-3) orfluffy(fl) allow the production of minor, BNC375 BNC375 but not major, constriction chains. Mutations in twoconidial separationgenes (csp-1andcsp-2) prevent the separation of cross walls to release free conidia (Springer1993). Two developmental genes,fl(NCU08726) andcsp-1(NCU02713), have been identified, and the corresponding proteins are putative zinc-finger transcription factors (Baileyand Ebbole1998;Lambreghtset al.2009). Theflgene has been investigated in some detail. The FL protein is usually a 792-amino-acid polypeptide made up of a Zn2Cys6binuclear zinc cluster domain name belonging to the Gal4p family (Baileyand Ebbole1998). A mutation inflblocks conidiation at the minor constriction stage, 4 hr after induction (Springerand Yanofsky1989), andflmRNA is usually observed 6 hr after the initiation of conidiation when major constrictions appear in proconidial chains (Baileyand Ebbole1998). The presence offlmRNA in aerial hyphae where conidiation-specific genes are expressed suggests a major role for FL in conidiation and in conidial-specific gene expression (Bailey-Shrodeand Ebbole2004). However,flis transiently induced 30 min after the induction of conidiation, suggesting an additional role for FL in the formation of aerial hyphae (Correaand Bell-Pedersen2002). The relevance of FL as a major regulator of conidiation in Neurospora is usually supported by the observation of conidial development whenflexpression is forced in vegetative hyphae (Bailey-Shrodeand Ebbole2004), a condition that leads to the expression ofeas(Bailey-Shrodeand Ebbole2004), the gene for the hydrophobin rodlet protein that is located on the surface of matured conidia (Bell-Pedersenet al.1992;Lauteret al.1992). This is consistent with the observed binding of FL to theeaspromoter (Rerngsamranet al.2005). Other genes are upregulated in thefl-overexpressing strain, including the conidiation-specific genescon-6andcon-10(Rerngsamranet al.2005), supporting the proposal of FL as a conidiation-specific transcription factor. The aconidial phenotype of anflstrain is usually partially suppressed by a mutation invib-1, BNC375 a gene involved in heterokaryon incompatibility, suggesting that FL may regulate conidiation through the repression of VIB-1 (Xiangand Glass2004). Light regulation of conidiation has been described via the activity of the proteins WC-1 and WC-2 (Lauteret al.1997). WC-1 contains a zinc finger, a chromophore-binding domain name, and ZC3H13 PAS domains for proteinprotein interactions (Ballarioet al.1996;Crosthwaiteet al.1997). The chromophore-binding domain name binds the flavin FAD, allowing WC-1 to act as a blue-light photoreceptor (Froehlichet al.2002;Heet al.2002). The protein WC-2 contains a zinc finger and a PAS domain name and interacts with WC-1 (Lindenand Macino1997) to form awhitecollarcomplex (WCC). This complex, upon light exposure, binds transiently to the promoters of light-inducible genes, presumably to activate their transcription (Froehlichet al.2002;Heand Liu2005;Beldenet al.2007b). The increase in conidiation observed in Neurospora cultures exposed to light suggests that light may activate the transcription of key regulatory genes, such asfl. Indeed, mRNAs for bothflandcsp-1accumulate after light exposure, suggesting that this corresponding genes are activated by light (Beldenet al.2007a;Chenet al.2009). We describe here a detailed characterization of the regulation by light offlin vegetative hyphae. We show that this WCC directly regulatesfltranscription in response to blue light after transiently binding the promoter and that developmental regulators are not required for light regulation offl. BNC375 We propose that light regulates conidiation in Neurospora through the activation offl, a key developmental regulatory gene..