Novel light-regulated genes in Trichoderma atroviride: a dissection by cDNA microarrays

Abstract

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). A putative complex 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. It was found that 2?8 % of the genes were light responsive: 2 % induced and 0?8 % repressed. Expression analysis in blr deletion mutants allowed the demonstration of the occurrence of two types of light responses, a blr-independent response in addition to the expected blr-dependent one, as well as a new role of the BLR proteins in repression of transcription. Exposure of T. atroviride to continuous light helped to establish that the light-responsive genes are subject to photoadaptation. Finally, evidence is provided of red-light-regulated gene expression and a possible crosstalk between the blue and red light signalling pathways.

Reproduction without sex: conidiation in the filamentous fungus Trichoderma

“…More than 40 genes have been shown to be regulated by BLR-1/BLR-2, possibly including post-transcriptional autoregulation of BLR-2 (Esquivel-Naranjo & Herrera- Estrella, 2007;Mikus et al, 2009;Rosales-Saavedra et al, 2006). In contrast to WC-1 and WC-2, negative regulation of gene expression by BLR-1/BLR-2 has also been demonstrated (Rosales-Saavedra et al, 2006).…”

“…In contrast to WC-1 and WC-2, negative regulation of gene expression by BLR-1/BLR-2 has also been demonstrated (Rosales-Saavedra et al, 2006). Phr1, a DNA photolyase gene, has been demonstrated to be regulated in response to light in a BLR-dependent manner (Berrocal-Tito et al, 1999Rosales-Saavedra et al, 2006). DNA photolyases are flavoproteins that repair UV damage, and it is postulated that their induction in response to blue light is in preparation for more damaging rays.…”

Regulation of Conidiation by Light in Aspergillus nidulans

“…In T. atroviride, 40 genes regulated by white light have been identified using cDNA microarrays, which represents 2.8% of the genes printed in the array. Thirty T. atroviride genes were upregulated (2%) and 10 were downregulated (0.8%) (Rosales-Saavedra et al 2006). Here we report for the first time in A. nidulans the global effect of light exposure on transcription.…”

“…However, unlike N. crassa, the study of the light-regulated processes has not been approached in detail in the Aspergilli but light sensing, including the regulation by red light of conidiation, was described in A. nidulans and other fungi many years ago (Tan 1974;Mooney and Yager 1990;Bayram et al 2010;Rodriguez-Romero et al 2010). Complete expression analysis has been performed by microarray hybridization experiments with different fungi (Rosales-Saavedra et al 2006;Chen et al 2009;Greenwald et al 2010;Idnurm and Heitman 2010). In N. crassa Figure 6 Light-dependent induction of the brlA gene is mediated by FlbA, FlbB, and FlbC.…”

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

“…All blue-lightregulated genes that are BLR-dependent strictly require both functional proteins, indicating that the BLR proteins act as a complex. By analogy with N. crassa, it is assumed that this complex regulates the expression of early blue-light-responsive genes through putative GATA type cis-elements present in the promoter region of blue-lightresponsive genes, similar to the LREs defined in N. crassa (Berrocal-Tito et al, 1999;Casas-Flores et al, 2004;Rosales-Saavedra et al, 2006). Interestingly, the BLR proteins participate in the light-dependent transcriptional activation and repression of early gene expression, a dual role previously not described in any other fungus (RosalesSaavedra et al, 2006).…”