Crucial factors of the light perception machinery and their impact on growth and cellulase gene transcription in Trichoderma reesei

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 Δblr1, Δblr2 and Δenv1 mutants showed that the BLR proteins 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.