The (hemi-) cellulolytic transcriptional activator XlnR (Xlr1/Xyr1) is a major regulator in fungal xylan and cellulose degradation as well as in the utilization of D-xylose via the pentose catabolic pathway. XlnR homologs are commonly found in filamentous ascomycetes and often assumed to have the same function in different fungi. However, a comparison of the saprobe Aspergillus niger and the plant pathogen Magnaporthe oryzae showed different phenotypes for deletion strains of XlnR. In this study wild type and xlnR/xlr1/xyr1mutants of six fungi were compared: Fusarium graminearum, M. oryzae, Trichoderma reesei, A. niger, Aspergillus nidulans and Aspergillus oryzae. The comparison included growth profiling on relevant substrates and detailed analysis of protein profiles of extracellular enzymes as well as extracellular enzyme activities. The resulting data demonstrated significant differences in the influence of XlnR and its orthologs on plant polysaccharide degradation by these fungi. For example, in A. niger cellulolytic enzymes, such as cellobiohydrolase and b-glucosidase are strongly down-regulated in the mutant strain, whereas this is not the case for the other two Aspergillus species. Moreover, in A. oryzae the L-arabinose releasing enzyme a-arabinofuranosidase is clearly regulated by AoXlnR, whereas this enzyme is known to be under control of another regulator, AraR, in A. niger and not affected by XlnR. In contrast, M. oryzae Xlr1 does not significantly affect enzyme activities in this study. Based on extracellular protein profiles, disruption of Xyr1 results in the disappearance of only some bands in F. graminearum, while nearly all bands disappear in T. reeseiDxyr1. This comparison emphasizes the functional diversity of a fine-tuned (hemi-) cellulolytic regulatory system in filamentous fungi, which might be related to the adaptation of fungi to their specific biotopes.
Full conference title:
27th Fungal Genetics Conference
- FGC 27th (2013)