Detalle de: The beta-importin KAP8 (Pse1/Kap121) is required for nuclear import of the cellulase transcriptional regulator XYR1, asexual sporulation and stress resistance in Trichoderma reesei

Summary The ascomycete T richoderma reesei is an industrial producer of cellulolytic and hemicellulolytic enzymes, and serves as a prime model for their genetic regulation. Most of its (hemi‐)cellulolytic enzymes are obligatorily dependent on the transcriptional activator XYR 1. Here, we investigated the nucleo‐cytoplasmic shuttling mechanism that transports XYR 1 across the nuclear pore complex. We identified 14 karyopherins in T . reesei , of which eight were predicted to be involved in nuclear import, and produced single gene‐deletion mutants of all. We found KAP 8, an ortholog of A spergillus nidulans KapI , and S accharomyces cerevisiae K ap121/ P se1, to be essential for nuclear recruitment of GFP ‐ XYR 1 and cellulase gene expression. Transformation with the native gene rescued this effect. Transcriptomic analyses of Δ kap8 revealed that under cellulase‐inducing conditions 42 CAZ ymes, including all cellulases and hemicellulases known to be under XYR 1 control, were significantly down‐regulated. Δ kap8 strains were capable of forming fertile fruiting bodies but exhibited strongly reduced conidiation both in light and darkness, and showed enhanced sensitivity towards abiotic stress, including high osmotic pressure, low pH and high temperature. Together, these data underscore the significance of nuclear import of XYR 1 in cellulase and hemicellulase gene regulation in T . reesei , and identify KAP 8 as the major karyopherin required for this process.