The ß-importin KAP8 (Pse1/Kap121) is required for nuclear import of the cellulase transcriptional regulator XYR1, asexual sporulation and stress resistance in Trichoderma reesei.
Bottom Line: We found KAP8, an ortholog of Aspergillus nidulans KapI, and Saccharomyces cerevisiae Kap121/Pse1, to be essential for nuclear recruitment of GFP-XYR1 and cellulase gene expression.Δkap8 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 XYR1 in cellulase and hemicellulase gene regulation in T. reesei, and identify KAP8 as the major karyopherin required for this process.
Affiliation: Research Division Biotechnology and Microbiology, Institute of Chemical Engineering, TU Wien, Vienna, 1060, Austria.Show MeSH
Related in: MedlinePlus
Mentions: Our findings that KAP8 regulates XYR1 nuclear import and consequently cellulase and hemicellulase formation in T. reesei prompted us to investigate whether this mechanism is also conserved in other fungi. We chose to test this in A. nidulans because its karyopherins have been studied in detail and mutants are available (Markina-Iñarrairaegui et al., 2011). In order to test whether the KAP8 ortholog KapI is involved in the function of the A. nidulans XYR1 ortholog XlnR, we cultivated ΔkapI and other kap mutant strains on D-glucose, D-xylose, birchwood xylan and carboxymethyl-cellulose, and monitored their growth. Induction of the enzymes required for catabolism of D-xylose, extracellular depolymerization of xylan and (in part) of cellulose has been shown to be dependent on XlnR function in Aspergillus spp. (Tsukagoshi et al., 2001; Tamayo et al., 2008). We thus expected that growth on these carbon sources would be reduced in the A. nidulans ΔkapI strain if KapI imported XlnR into the nucleus. As shown in Fig. 4, the A. nidulans ΔkapI strain grew equally well as the wild-type strain on D-glucose, xylan and cellulose, although a slightly reduced growth was observed on D-xylose. None of the other importin mutants showed any effect on the tested carbon sources. These data illustrate that KapI does not seem to have a major effect on XlnR nuclear import or that its function can be compensated by another karyopherin.
Affiliation: Research Division Biotechnology and Microbiology, Institute of Chemical Engineering, TU Wien, Vienna, 1060, Austria.