The information highways of a biotechnological workhorse--signal transduction in Hypocrea jecorina

Abstract

Background: The ascomycete Hypocrea jecorina (anamorph Trichoderma reesei) is one of the most prolific producers of biomass-degrading enzymes and frequently termed an industrial workhorse. To compete for nutrients in its habitat despite its shortcoming in certain degradative enzymes, efficient perception and interpretation of environmental signals is indispensable. A better understanding of these signals as well as their transmission machinery can provide sources for improvement of biotechnological processes.

Results: The genome of H. jecorina was analysed for the presence and composition of common signal transduction pathways including heterotrimeric G-protein cascades, cAMP signaling, mitogen activated protein kinases, two component phosphorelay systems, proteins involved in circadian rhythmicity and light response, calcium signaling and the superfamily of Ras small GTPases. The results of this survey are discussed in the context of current knowledge in order to assess putative functions as well as potential impact of alterations of the respective pathways.

Conclusion: Important findings include an additional, bacterial type phospholipase C protein and an additional 6-4 photolyase. Moreover the presence of 4 RGS-(Regulator of G-protein Signaling) proteins and 3 GprK-type G-protein coupled receptors comprising an RGS-domain suggest a more complex posttranslational regulation of G-protein signaling than in other ascomycetes. Also the finding, that H. jecorina, unlike yeast possesses class I phosducins which are involved in phototransduction in mammals warrants further investigation. An alteration in the regulation of circadian rhythmicity may be deduced from the extension of both the class I and II of casein kinases, homologues of which are implicated in phosphorylation of FRQ in Neurospora crassa. On the other hand, a shortage in the number of the pathogenicity related PTH11-type G-protein coupled receptors (GPCRs) as well as a lack of microbial opsins was detected. Considering its efficient enzyme system for breakdown of cellulosic materials, it came as a surprise that H. jecorina does not possess a carbon sensing GPCR.

Figure 1

Alignment and phylogenetic analysis of G-protein alpha subunits. The H. jecorina genome comprises 3 G-alpha subunits belonging to the three subgroups common in other fungi. Accession numbers (corresponding database: GenBank) of the protein sequences used are those of the nearest neighbours of Trichoderma reesei (Hypocrea jecorina) (TR) in Saccharomyces cerevisiae (SC), Schizosaccharomyces pombe (SP), Neurospora crassa (NC), Aspergillus fumigatus (AF), Gibberella zeae (GZ), Fusarium oxysporum (FO), Magnaporthe grisea (MG), Cryphonectria parasitica (CP), Rattus norvegicus (RN), Canis familiaris (CF), Drosophila melaongaster (DM), Oryza sativa (OS), Pisum sativum (PS) and Glycine max (GM), are as listed in Table 1. Accession numbers (corresponding database: GenBank) of the G-protein alpha subunits of Ustilago maydis (UM) are: GPA1 P87032, GPA2 P87033, GPA3 P87034 and GPA4 P87035. (A) Alignment of GTP-binding domains and GTPase domains of G-protein alpha subunits including the two additional putative G-protein alpha subunits of H. jecorina (tre43177 and tre38187). While the GTPase domain of these two proteins matches the consensus (DXXGQ), the GTP binding domain is altered at the same position as in U. maydis Gpr4p (GXGXXGKS/T) [32]. (B) Phylogenetic analysis of G-alpha subunits using the Minimum evolution method and 500 Bootstrap replications as test of phylogeny.

Figure 2

Phylogenetic analysis of phoducin-like proteins. In contrast to S. cerevisiae, H. jecorina and other filamentous ascomycetes possess class I phosducin-like proteins, but no class III phosducin-like proteins. GenBank accession numbers of the protein sequences used are those of the nearest neighbours of Trichoderma reesei (Hypocrea jecorina) (treXXXXX) in Saccharomyces cerevisiae (SC), Schizosaccharomyces pombe (SP), Neurospora crassa (NC), Aspergillus nidulans (AN), Gibberella zeae (GZ), Magnaporthe grisea (MG), Cryphonectria parasitica (CP), Dictyostelium discoideum (Dd), Drosophila melaongaster (DM), Oryza sativa (OS), Homo sapiens (HS) and Arabidopsis thaliana (At). The analysis was performed using the Minimum Evolution method and 500 Bootstrap replications as test of phylogeny.

Figure 3

Alignment of regions similar to the G-beta-gamma binding conserved helix 1 of Homo sapiens PhlP1 and Pdc in filamentous ascomycetes. The conserved sequence is given in bold for Trichoderma reesei (Hypocrea jecorina) (treXXXXX), Neurospora crassa (NC), Aspergillus nidulans (AN), Gibberella zeae (GZ), Magnaporthe grisea (MG), Cryphonectria parasitica (CP), Dictyostelium discoideum (Dd), and Homo sapiens (HS).

Figure 4

Model for proposed MAP kinase cascades. Pathways are given as deduced from reported functions and interactions of the respective nearest neighbours in S. cerevisiae and other filamentous ascomycetes. Therefore this model should be considered only a suggestion for further research needed to confirm these pathways.

Figure 5

Schematic representation of two component phosphorelay systems (adapted from [180]). In response to an environmental signal the two component phosphorelay signaling cascade is initiated by ATP-dependent autophosphorylation of the histidine kinase (HK) at a conserved histidine residue. Then this phosphate is transferred to a conserved aspartic acid within a response regulator (RR) domain, which ultimately causes a change in transcription of the respective target gene or regulation of a mitogen-activated protein kinase pathway [101].

Figure 6

Domain structure of two component phosphorelay histidine kinases and their putative interactors in H. jecorina. Models of the predicted proteins as annotated in the Trichoderma reesei Genome database v2.0 are drawn to scale. Position and significance of the respective domains was determined by InterPro search and NCBI CDD search.