Fine-tuning gene expression: pantothenic acid inducible promoters in Trichoderma reesei

T. reesei is the most widely employed producer of cellulases and hemicellulases. Inducible recombinant protein expression in this organism is currently hampered by the relatively small repertoire of suitable promoters, which are derived from (hemi)cellulase encoding genes. Therefore there is an urgent demand for novel tunable promoters acting in a (hemi)cellulase independent fashion. Addition of pantothenic acid to T. reesei did not alter growth or the expression profile of (hemi)cellulase. Using whole transcriptome analysis, five T. reesei genes were found that were strongly induced by the addition of pantothenic acid. One of these genes showed strong sequence similarity to a characterized pantothenic acid permease. The promoter regions of two of those pantothenic acid induced genes were fused to the green fluorescent protein gene (gfp) as reporter. Transcription analysis showed that expression of gfp was pantothenic acid inducible and surpassed the expression of the reference strain with the strong tef1 promoter in one case. This system is inexpensive and can therefore be used as valuable tool for strain engineering of industrial T. reesei strains.