초록
<P><B>Background</B></P><P>Agricultural residue is more efficient than purified cellulose at inducing lignocellulolytic enzyme production in <I>Penicillium oxalicum</I> GZ-2, but in <I>Trichoderma reesei</I> RUT-C30, cellulose induces a more efficient response. To understand the reasons, we designed an artificially simulated plant biomass (cellulose plus xylan) to study the roles and relationships of each component in the production of lignocellulolytic enzymes by <I>P. oxalicum</I> GZ-2.</P><P><B>Results</B></P><P>The changes in lignocellulolytic enzyme activity, gene expression involving (hemi)cellulolytic enzymes, and the secretome of cultures grown on Avicel (A), xylan (X), or a mixture of both (AX) were studied. The addition of xylan to the cellulose culture did not affect fungal growth but significantly increased the activity of cellulase and hemicellulase. In the AX treatment, the transcripts of cellulase genes (<I>egl1</I>, <I>egl2</I>, <I>egl3</I>, <I>sow</I>, and <I>cbh2</I>) and hemicellulase genes (<I>xyl3</I> and <I>xyl4</I>) were significantly upregulated (<I>P</I> <0.05). The proportion of biomass-degrading proteins in the secretome was altered; in particular, the percentage of cellulases and hemicellulases was increased. The percentage of cellulases and hemicellulases in the AX secretome increased from 4.5% and 7.6% to 10.3% and 21.8%, respectively, compared to the secretome of the A treatment. Cellobiohydrolase II (encoded by <I>cbh2</I>) and xylanase II (encoded by <I>xyl2</I>) were the main proteins in the secretome, and their corresponding genes (<I>cbh2</I> and <I>xyl2</I>) were transcripted at the highest levels among the cellulolytic and xylanolytic genes. Several important proteins such as swollenin, cellobiohydrolase, and endo-beta-1,4-xylanase were only induced by AX. Bray-Curtis similarity indices, a dendrogram analysis, and a diversity index all demonstrated that the secretome produced by <I>P. oxalicum</I> GZ-2 depended on the substrate and that strain GZ-2 directionally adjusted the compositions of lignocellulolytic enzymes in its secretome to preferably degrade a complex substrate.</P><P><B>Conclusion</B></P><P>The addition of xylan to the cellulose medium not only induces more hemicellulases but also strongly activates cellulase production. The proportion of the biomass-degrading proteins in the secretome was altered significantly, with the proportion of cellulases and hemicellulases especially increased. Xylan and cellulose have positively synergistic effects, and they play a key role in the induction of highly efficient lignocellulolytic enzymes.</P><P><B>Electronic supplementary material</B></P><P>The online version of this article (doi:10.1186/s13068-014-0162-2) contains supplementary material, which is available to authorized users.</P>