LightResponse

The influence of light on living organisms is critical, not only because of its importance as the main source of energy for the biosphere, but also due to its capacity to induce changes in the behaviour and morphology of nearly all forms of life. The common soil fungus Trichoderma atroviride responds to blue-light in a synchronized manner, in time and space, by forming a ring of green conidia at what had been the colony perimeter at the time of exposure (photoconidiation). The complex putatively formed by the BLR-1 and BLR-2 proteins in T. atroviride appears to play an essential role as a sensor and transcriptional regulator in photoconidiation. Expression analyses using microarrays containing 1438 unigenes were carried out in order to identify early light response genes. We found that 2.8% of the genes were light responsive, 2% induced and 0.8% repressed. Exposure of Trichoderma to continuous light allowed us to establish that the light responsive genes are subjected to photoadaptation. Expression analysis in blr deletion mutants allowed us to demonstrate the occurrence of two types of light responses, a blr-independent response in addition to the expected brl-dependent one, as well as a new role of the BLR proteins in repression of transcription. Finally, we show evidence of red light regulated gene expression. Keywords: Light Response, microarrays Three independent replicates of each mycelial treatment, RNA isolation and labelling, and microarray hybridization were performed. To estimate ‘system noise’ that may be due to differences in Cy-dye labelling between samples, we performed a ‘swap’ hybridization for each biological replicates.