The CRE1 carbon catabolite repressor of the fungus Trichoderma reesei: a master regulator of carbon assimilation

Abstract

BackgroundThe identification and characterization of the transcriptional regulatory networks governing the physiology and adaptation of microbial cells is a key step in understanding their behaviour. One such wide-domain regulatory circuit, essential to all cells, is carbon catabolite repression (CCR): it allows the cell to prefer some carbon sources, whose assimilation is of high nutritional value, over less profitable ones. In lower multicellular fungi, the C2H2 zinc finger CreA/CRE1 protein has been shown to act as the transcriptional repressor in this process. However, the complete list of its gene targets is not known.ResultsHere, we deciphered the CRE1 regulatory range in the model cellulose and hemicellulose-degrading fungus Trichoderma reesei (anamorph of Hypocrea jecorina) by profiling transcription in a wild-type and a delta-cre1 mutant strain on glucose at constant growth rates known to repress and de-repress CCR-affected genes. Analysis of genome-wide microarrays reveals 2.8% of transcripts whose expression was regulated in at least one of the four experimental conditions: 47.3% of which were repressed by CRE1, whereas 29.0% were actually induced by CRE1, and 17.2% only affected by the growth rate but CRE1 independent. Among CRE1 repressed transcripts, genes encoding unknown proteins and transport proteins were overrepresented. In addition, we found CRE1-repression of nitrogenous substances uptake, components of chromatin remodeling and the transcriptional mediator complex, as well as developmental processes.ConclusionsOur study provides the first global insight into the molecular physiological response of a multicellular fungus to carbon catabolite regulation and identifies several not yet known targets in a growth-controlled environment.

Xylanase Gene Transcription in Trichoderma reesei Is Triggered by Different Inducers Representing Different Hemicellulosic Pentose Polymers

“…T. reesei strain QM9414 (ATCC 26921) (23), which served as the reference strain, and strains with the knockouts ⌬xyl1 (24), ⌬lad1, ⌬xdh1, ⌬lad1/⌬xdh1 (25), ⌬lxr3 (Metz et al, submitted), ⌬xyr1 (26), and ⌬cre1 (27) were precultured for 24 h in 250 ml Mandels-Andreotti (MA) medium (28) containing 1% (wt/vol) glycerol as the sole carbon source on a rotary shaker (250 rpm) at 28°C. Subsequently, mycelia were collected, washed, and transferred to 250 ml MA medium without a carbon source.…”

The Genomes of Three Uneven Siblings: Footprints of the Lifestyles of Three Trichoderma Species

“…More recently, LAE1 (a protein methyltransferase) and VEL1 (a member of the VELVET protein family) were found to be important for the regulation of cellulase gene expression in T. reesei (129,346); in T. reesei, CAZyme-encoding genes are often coregulated upon induction, especially in the presence of cellulosic plant material (328,340,347,348). The largest number of genes and CAZy families induced was detected in the cultures with the hemicellulosic material, bagasse, xylans, and wheat straw (68 to 124 genes in 39 to 47 CAZy families), whereas cultivation in the presence of cellulosic or cellulose-derived materials, Avicel cellulose, pretreated spruce, or sophorose, resulted in a clearly smaller number of genes induced (43 to 58 genes in 28 to 36 families).…”

Transcriptional Regulation and Responses in Filamentous Fungi Exposed to Lignocellulose

“…All of this requires a considerable investment of energy and resources and, unsurprisingly, it is a carefully regulated process. When more easilymetabolised sugars are available in sufficient amounts, carbon catabolite repression (CCR) [28,29] represses a large number of genes [30], including genes encoding lignocellulose-degrading CAZymes under conditions where lignocellulose and other inducers are present [31,32]. How the detection and signalling of the presence or absence of such easily metabolised carbon sources can prepare the fungus for the degradation of lignocellulose is discussed below.…”

“…Section I introduced a key repressor in fungi relevant to transcriptional regulation related to lignocellulose CreA/CRE1 [28,30]. CreA/CRE1 functions in CCR where, in the presence of sufficient glucose and in some cases other sugars, it suppresses the transcription of genes encoding enzymes involved in the metabolism of more complex polysaccharides [28].…”