Fig. 9.

Model of the role of the transcriptional regulator Blu7 in the molecular response of T. atroviride to light. a Molecular responses to a pulse of blue light. Exposure of T. atroviride to low fluence blue light perceived by the BLRC results in the transcriptional activation of blu7, sub1, azf1, xlnr and 20 other TF encoding genes, as well as the induction of Envoy. Blu7 tunes photoconidiation by repressing the expression of the 5’-3’ cAMP phosphodiesterase encoding gene (PD). Likewise, the induction of env1 enhances PD repression, while transitory accumulation of cAMP activates PKA that in turn regulates photoconidiation genes [34]. Nitrogen mobilization (amino acid transporters) is indirectly regulated by Blu7 and modulates the balance between conidiation and mycelial growth. b Molecular responses to continuous light exposure. Under constant white light, blu7 induction by the BLRC is regulated by the carbon source available in the medium. ENV1 negatively regulates BLRC target genes for adaptation to constant light. When T. atroviride is grown on glucose containing medium, blu7 limits the induction of env1. Blu7 is required for nitrogen mobilization through the inhibition of the orthologue of AreA by the negative regulator NmrA up-regulation. In addition, hyphal growth and conidiation are tightly regulated by the amount of FlbC to induce the sequential expression of the transcription factors C2H2 ➜AbaA ➜ WetA. Black lines indicate control points supported by our RNA-seq data and gray lines are based on previously reported experimental evidence