Crucial factors of the light perception machinery and their impact on growth and cellulase gene transcription in Trichoderma reesei Francisco Castellanos a,1 , Monika Schmoll b,1 , Pedro Martínez a , Doris Tisch b , Christian P. Kubicek b , Alfredo Herrera-Estrella a, * , Edgardo Ulises Esquivel-Naranjo a a Laboratorio Nacional de Genómica para la Biodiversidad, and Departamento de Ingeniería Genética de Plantas, CINVESTAV Irapuato, Apartado Postal 629, Irapuato 36821, Mexico b Research Area Gene Technology and Applied Biochemistry, Institute of Chemical Engineering, Vienna University of Technology, Getreidemarkt 9/166-5, 1060 Vienna, Austria article info Article history: Received 22 December 2009 Accepted 1 February 2010 Available online 6 February 2010 Keywords: Photoconidiation Cellulases Vivid White collar Photoreceptor Blue light Hypocrea abstract In Trichoderma reesei light stimulates transcription of cellulase genes and this regulation has been found to occur, at least in part, through the protein ENVOY. Here we analyzed the role of the BLR photoreceptor complex (BLR1/BLR2) in photoconidiation and the regulation of gene expression. Both responses were dependent on both BLR proteins. Analyses of Dblr1, Dblr2 and Denv1 mutants showed that the BLR pro- teins regulate growth under illumination. Analysis of env1 mutant strains indicated that ENVOY allows the fungus to tolerate continuous exposure to light, damped the capacity of Trichoderma to perceive changes in light intensity, and suggested that it participates in a negative regulatory feedback. Its activity as repressor establishes a period of insensitivity to a second light treatment. Interestingly, the stimulation of cellulase gene expression by light was also modulated by both blr1 and blr2, indicating a key role of the BLR proteins in this pathway. Ó 2010 Elsevier Inc. All rights reserved. 1. Introduction Light provides critical information to filamentous fungi about orientation, or impending stress (Herrera-Estrella and Horwitz, 2007). Their best-studied responses to light are carotenogenesis, development, morphogenesis, tropism and resetting of the circa- dian clock (Idnurm et al., 2006; Linden et al., 1997; Liu et al., 2003; Lu et al., 2005; Silva et al., 2006). In spite of the presence of multiple genes encoding potential light receptors in their genome, cells of filamentous fungi appear to sense blue/UVA light through two unique transcription factors constituting the white-collar com- plex (WCC). The white-collar complex is formed by the proteins White Collar 1 and 2 (WC-1 and WC-2), which are essential for all light responses observed in Neurospora crassa (Ballario et al., 1996; Linden and Macino, 1997). Both proteins are PAS (Per-Arnt- Sim) domain-containing transcription factors with GATA-type zinc finger DNA binding domains. These proteins are highly conserved in all fungi, a finding which has led to the proposal that the WCC arose early in fungal evolution (Corrochano, 2007; Herrera-Estrella and Horwitz, 2007). WC-1 and WC-2 form complexes through the inter- action of their PAS domains (Cheng et al., 2002, 2003). After a light treatment, these complexes bind transiently to the Light Response Element (LRE), a DNA motif found in the promoters of light-regu- lated genes (Froehlich et al., 2002; He and Liu, 2005; Káldi et al., 2006). Homologs of wc-1 (blr1) and wc-2 (blr2) have been character- ized in Trichoderma atroviride (Casas-Flores et al., 2004). LREs are apparently conserved in blue light-regulated genes from two Trich- oderma spp., and suggest a similar action mode of the BLR proteins in these fungi (Berrocal-Tito et al., 1999; Rosales-Saavedra et al., 2006; Schmoll et al., 2009). Transcript levels of light responsive genes have been used to cluster them in early and late expression genes in N. crassa, and a transcriptional factor with early induction by light (SUB-1) regulates the expression of some of the late genes (Chen-Hui et al., 2009). However, the activity of SUB-1 is light dependent and its mechanism of action is not clear, as its over- expression in the dark had no effect on the regulation of late expres- sion genes. A specialized PAS domain called LOV (Light, Oxygen and Volt- age), which is essential for blue/UVA light perception and binds fla- vin adenine dinucleotide (FAD), has been identified in the WC-1 protein (Froehlich et al., 2002; He et al., 2002). WC-1 acts as pho- toreceptor that, in combination with WC-2, tunes light input directly by activating the expression of genes required for the different responses described in N. crassa (Froehlich et al., 2002; He et al., 2002). VIVID, a small protein containing a single LOV domain, is another blue-light photoreceptor described in N. crassa 1087-1845/$ - see front matter Ó 2010 Elsevier Inc. All rights reserved. doi:10.1016/j.fgb.2010.02.001 * Corresponding author. Address: National Laboratory of Genomics for Biodiver- sity, Centro de Investigación y de Estudios Avanzados del IPN, Campus Guanajuato, Apartado Postal 629, Irapuato 36821, Guanajuato, Mexico. Fax: +52 462 6245849. E-mail address: aherrera@ira.cinvestav.mx (A. Herrera-Estrella). 1 These authors contributed equally to this work. Fungal Genetics and Biology 47 (2010) 468–476 Contents lists available at ScienceDirect Fungal Genetics and Biology journal homepage: www.elsevier.com/locate/yfgbi