|Keywords:||Biologie; Magnaporthe oryzae; xylan degradation; regulation; Xlr1; pentose catabolic pathway; Pyricularia|
|Full text PDF:||http://dspace.library.uu.nl:8080/handle/1874/311177|
Magnaporthe oryzae is a fungal plant pathogen of many grasses including rice. Since arabinoxylan is one of the major components of the plant cell wall of grasses, M. oryzae is likely to degrade this polysaccharide for supporting its growth in infected leaves. D-xylose is released from arabinoxylan by fungal xylanolytic enzymes and catabolised through the pentose pathway. This PhD thesis describes the characterisation of the pathway for pentose utilisation in M. oryzae and the discovery of a novel pentose reductase. In fungi, the expression of genes involved in xylan degradation and D-xylose utilisation is under control of the transcriptional activator XlnR. A detailed characterisation of the homolog of XlnR in M. oryzae, Xlr1, was performed in the course of this thesis. Investigation of an XLR1 disruption strain demonstrated that XLR1 encodes the transcriptional activator of the pentose catabolic pathway in M. oryzae. However, the xylanolytic system of this fungus was induced even in the absence of Xlr1. A detailed transcriptome analysis demonstrated that a number of genes involved in xylan degradation were strongly dependent on Xlr1 while a second set of xylanolytic genes appeared to be under control of another yet unknown regulatory system. XlnR homologs are commonly found in filamentous ascomycetes and often assumed to have the same function in different fungi. A comparison of five filamentous fungi showed significant differences in the proteome secreted by these fungi in response to xylan as well as regarding the set of genes that is controlled by XlnR in the individual species. 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. This PhD thesis deepens our knowledge about regulation of plant polysaccharide degradation and utilisation in filamentous fungi with a special focus on the rice blast fungus M. oryzae. The family, to which M. oryzae belongs to (Magnaporthaceae), also includes other important plant pathogens (e.g. rice stem rot fungus, summer patch). The taxonomic relationships of Magnaporthe and Pyricularia species were investigated which led to the identification of novel species, which are also described in this PhD thesis.