Heterotrimeric G-protein signaling and light response

Abstract

Almost all creatures have invented sophisticated mechanisms to adjust their developmental and metabolic processes to the changing light intensities in day and night. Recent findings suggest that one such mechanism is signaling via heterotrimeric G-proteins.¹ The Trichoderma reesei (anamorph of Hypocrea jecorina) G-alpha subunit gene gna3 was found to be responsive to light and influenced by the light regulatory protein ENVOY.² GNA3 significantly impacts regulation of cellulase gene expression only in light.¹ While the exact mechanism of this regulation remains to be determined, first hints point to a regulation at the transcriptional level, since we observed light induced complex formation within the gna3 promotor. At least some of the components of this putatively regulatory protein complex also bind to the env1- promotor. These data indicate that the signal related by GNA3 is of light-dependent significance for H. jecorina and that the pathway of heterotrimeric G-protein signaling may be a target of the light perception machinery in fungi.

Acknowledgements

This work was supported by FWF (Austrian Science Fund)-grant P20004 to Monika Schmoll. Monika Schmoll is recipient of an APART fellowship of the Austrian Academy of Sciences at the Institute of Chemical Engineering, Vienna University of Technology.

Figures and Tables

Figure 1 Characterization of protein complex-binding to EUM1 within the env1 or gna3-promotor. (A) EMSA analysis with annealed and labeled oligonucleotide derived from the env1 or gna3 promotor (env1EUM1F 5′ GAT CTC TTG TCC CTT TAC TCT GTG CTC TCT CTA CCT GCC T 3′; env1EUM1R 5′ GAT CAG GCA GGT AGA GAG AGC ACA GAG TAA AGG GAC AAG A 3′; gna3mEUM1F 5′ GAT CGA CTC GTT GCT GTG CTG TGC TGT GCT GTG CTG TGC TGT 3′ gna3mEUM1R 5′ GAT CAC AGC ACA GCA CAG CAC AGC ACA GCA CAG CAA CGA GTC 3′; lower case letters indicate bases added for labeling) and 30 µg of H. jecorina cell free extracts.24,25 The wild-type strain QM9414 was pregrown in darkness and harvested after illumination for the time indicated. (B) Competition experiments with cell free extracts prepared as described above after 60 minutes of illumination with 10-fold, 50-fold or 100-fold excess of cold competitor. Arrows point at the light-dependent protein complex found binding to both the env1 and the gna3-promotor. Experiments were carried out with both probes on the same gel and in case of self-competitions with 120-fold excess, uncompeted protein extracts were loaded on the same gel as control and exposed to similar signal strength. All experimental procedures after harvesting the mycelia were performed in complete darkness.

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