Envoy, a PAS/LOV Domain Protein of Hypocrea jecorina (Anamorph Trichoderma reesei ), Modulates Cellulase Gene Transcription in Response to Light

Abstract

Envoy, a PAS/LOV domain protein with similarity to the Neurospora light regulator Vivid, which has been cloned due to its lack of expression in a cellulase-negative mutant, links cellulase induction by cellulose to light signaling in Hypocrea jecorina. Despite their similarity, env1 could not compensate for the lack of vvd function. Besides the effect of light on sporulation, we observed a reduced growth rate in constant light. An env1 PAS؊ mutant of H. jecorina grows significantly slower in the presence of light but remains unaffected in darkness compared to the wild-type strain QM9414. env1 rapidly responds to a light pulse, with this response being different upon growth on glucose or glycerol, and it encodes a regulator essential for H. jecorina light tolerance. The induction of cellulase transcription in H. jecorina by cellulose is enhanced by light in the wild-type strain QM9414 compared to that in constant darkness, whereas a delayed induction in light and only a transient up-regulation in constant darkness of cbh1 was observed in the env1 PAS؊ mutant. However, light does not lead to cellulase expression in the absence of an inducer. We conclude that Envoy connects the light response to carbon source signaling and thus that light must be considered an additional external factor influencing gene expression analysis in this fungus.

Enhanced responsiveness and sensitivity to blue light by blr-2 overexpression in Trichoderma atroviride

“…This effect was intensified when only the blue or red regions of the spectrum were applied (Casas-Flores et al, 2004). Additionally, growth of a T. reesei strain with a mutation in envoy, encoding a putative secondary light receptor (ENVOY), was strongly affected by white light (Schmoll et al, 2005). In Tuber borchii and N. crassa, light also affects radial growth during light-dark periods which is partially modulated through WC-1 (Ambra et al, 2004).…”

“…However, we did not find significant changes in the expression pattern of light-regulated genes under continuous light exposure, indicating that various mechanisms may be operating in photoadaptation of T. atroviride. Although the envoy mutant is defective in growth under constant illumination, and the corresponding gene is clearly light-regulated (Schmoll et al, 2005) through the action of BLR proteins (unpublished data), we did not observe such strong inhibition in the Dblr mutants, indicating that, at least in part, the BLR proteins are negative modulators of mycelial growth and that ENVOY may participate in a negative feedback loop that desensitizes the light input through the BLR complex, as indicated in Fig. 9(a).…”

“…In N. crassa, a negative feedback loop involving the flavoprotein VIVID and phosphorylation by different kinases that destabilize WC-1, and block the transcriptional activity of the WC complex, are the main mechanisms that control adaptation under continuous exposure to light (Schwerdtfeger & Linden, 2003;He & Liu, 2005). T. reesei, a close relative of T. atroviride, has a homologue (ENVOY) of VIVID that might play a similar role in photoadaptation (Schmoll et al, 2005). In our view, the mechanisms controlling the expression of blr-2 at the post-transcriptional level and, possibly, mycelial growth under continuous exposure to light differ from those reported for N. crassa.…”

Reproduction without sex: conidiation in the filamentous fungus Trichoderma

“…The presence/absence of light within an experiment and the influence that this may have on the results is seldom considered (Schmoll et al, 2005); however, it is becoming clear from the literature that there is an interactive effect between light and nutritional influences on conidiation. The source of carbon has been suggested to be the primary determinant for both conidiation in the dark and light-induced conidiation in T. viride and T. atroviride (Chovanec et al, 2001;Friedl et al, 2008).…”

“…Refractory periods between which light doses are effective have also been demonstrated in T. atroviride (Deitzer et al, 1988;Gressel & Galun, 1967). An orthologue of VIVID, designated ENVOY, has been found in Hypocrea jecorina (anamorph Trichoderma reesei) and shown to regulate photoadaptation of BLR-1/BLR-2-regulated, blue-light-inducible genes (Castellanos et al, 2010;Schmoll et al, 2005Schmoll et al, , 2010Schuster et al, 2007).…”