Microarray analysis of the Aspergillus niger revealed that XlnR plays an important role in the regulation of different pathways

The XlnR proteinwas initially identified as a transcription activator of different genes encoding cellulolytic and xylanolytic enzymes in Aspergillus niger. A number of experiments have been performed to elucidate the regulation mechanism of xlnR and the results suggest that the transcription of the xlnR gene is induced by the presence of d-xylose in the culturing media and repressed by d-glucose. As the mRNA levels of XlnR gene are very low, and they can hardly be detected by Northern blot analysis, further research is necessary to confirm these results. To study the XlnR regulon, XlnR mutants were grown under inducing (d-xylose and xylan), repressing (d-glucose) and neutral (sorbitol) culturing conditions. The whole transcriptome was examined by microarray analysis. The XlnR mutants used in these experiments are an xlnR knock out mutant, a mutant where XlnR is constitutively expressed, and the wild type phenotype. Comparison of the transcriptome of different XlnR strains under inducing and repressing conditions showed that XlnR regulates several genes that are involved in different pathways. Among these are genes encoding proteins involved in signal transduction, in the regulation of transcription, in sugar transport but also genes encoding enzymes. Previous work suggested that the CreA transcription factor might play a role in the transcriptional egulation of the XlnR regulon. This has been shown for the enzyme encoding genes of the regulon, but whether CreA regulates the transcription of the xlnR gene still was uncertain. In order to investigate this the transcriptome of different single and double CreA erepressed and XlnR mutants were compared using both microarray and qPCR analysis. The results of these experiments lead to a new model for the transcription regulation of XlnR