THE TRANSCRIPTIONAL ACTIVATOR XLNR REGULATES BOTH XYLANOLYTIC AND ENDOGLUCANASE GENE-EXPRESSION IN ASPERGILLUS-NIGER

The expression of genes encoding enzymes involved in xylan degradation and two endoglucanases involved in cellulose degradation was studied at the mRNA Level in the filamentous fungus Aspergillus niger. A strai n with a loss-of-function mutation in the xlnR gene encoding the trans criptional activator XlnR and a strain with multiple copies of this ge ne were investigated in order to define which genes are controlled by XlnR. The data presented in this paper show that the transcriptional a ctivator XlnR regulates the transcription of the xlnB, xlnC, and xlnD genes encoding the main xylanolytic enzymes (endoxylanases B and C and beta-xylosidase, respectively). Also, the transcription of the genes encoding the accessory enzymes involved in xylan degradation, includin g alpha-glucuronidase A, acetylxylan esterase A, arabinoxylan arabinof uranohydrolase A, and feruloyl esterase A, was found to be controlled by XlnR. In addition, XlnR also activates transcription of two endoglu canase-encoding genes, eglA and eglB, indicating that transcriptional regulation by XlnR goes beyond the genes encoding xylanolytic enzymes and includes regulation of two endoglucanase-encoding genes.