Abstract
BackgroundTrichoderma species are among the most effective cell factories to produce recombinant proteins, whose productivity relies on the molecular toolkit and promoters available for the expression of the target protein. Although inducible promoter systems have been developed for producing recombinant proteins in Trichoderma, constitutive promoters are often a desirable alternative. Constitutive promoters are simple to use, do not require external stimuli or chemical inducers to be activated, and lead to purer enzyme preparations. Moreover, most of the promoters for homologous and heterologous expression reported in Trichoderma have been commonly evaluated by directly assessing production of industrial enzymes, requiring optimization of laborious protocols.ResultsHere we report the identification of Pccg6, a novel Trichoderma atroviride constitutive promoter, that has similar transcriptional strength as that of the commonly used pki1 promoter. Pccg6 displayed conserved arrangements of transcription factor binding sites between promoter sequences of Trichoderma ccg6 orthologues genes, potentially involved in their regulatory properties. The predicted ccg6-encoded protein potentially belongs to the SPE1/SPI1 protein family and shares high identity with CCG6 orthologue sequences from other fungal species including Trichoderma reesei, Trichoderma virens, Trichoderma asperellum, and to a lesser extent to that of Neurospora crassa. We also report the use of the Pccg6 promoter to drive the expression of PTXD, a phosphite oxidoreductase of bacterial origin, which allowed T. atroviride to utilize phosphite as a sole source of phosphorus. We propose ptxD as a growth reporter gene that allows real-time comparison of the functionality of different promoters by monitoring growth of Trichoderma transgenic lines and enzymatic activity of PTXD. Finally, we show that constitutive expression of ptxD provided T. atroviride a competitive advantage to outgrow bacterial contaminants when supplied with phosphite as a sole source of phosphorus.ConclusionsA new constitutive promoter, ccg6, for expression of homologous and heterologous proteins has been identified and tested in T. atroviride to express PTXD, which resulted in an effective and visible phenotype to evaluate transcriptional activity of sequence promoters. Use of PTXD as a growth marker holds great potential for assessing activity of other promoters and for biotechnological applications as a contamination control system.
Highlights
Trichoderma species are among the most effective cell factories to produce recombinant proteins, whose productivity relies on the molecular toolkit and promoters available for the expression of the target protein
Identification of the ccg6 promoter in T. atroviride Environmental stimuli greatly influence the development of filamentous fungi
We found that the transcript of the Clock-controlled gene-6 from Trichoderma atroviride IMI 206040 (Taccg6) gene
Summary
Trichoderma species are among the most effective cell factories to produce recombinant proteins, whose productivity relies on the molecular toolkit and promoters available for the expression of the target protein. Carreras‐Villaseñor et al Microb Cell Fact (2020) 19:69 conditions These characteristics, together with factors such as their high capacity to produce and secrete proteins and bioactive compounds, as well as the availability of protocols and molecular tools for their genetic manipulation, have posed Trichoderma as a model organism to study fungal biology and to develop biotechnological applications for different industries [1]. Special interest has been focused on the use of Trichoderma and other filamentous fungi for the expression of homologous and heterologous proteins and for the production of fungal metabolites of industrial interest. The application of mixed cultures of filamentous fungi (i.e. Trichoderma reesei and Aspergillus niger) resulted in a positive synergistic effect to obtain higher enzyme production (i.e. xylanase, endoglucanase, amylase, inulinase, β-glucosidases) [5,6,7,8]. The availability of molecular elements (i.e. promoters, terminators, enhancers) to manipulate gene expression in Trichoderma is essential for the successful production of recombinant proteins
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