Assessment of the pectin degrading enzyme network of Aspergillus niger by functional genomics

The saprobic fungus Aspergillus niger is an efficient producer of a suite of extracellular enzymes involved in carbohydrate modification and degradation. Genome mining has resulted in the prediction of at least 39 genes encoding enzymes involved in the depolymerisation of the backbone of pectin. Additional genes,encoding enzymatic activities required for the degradation of the arabinan and arabinogalactan sidechains were predicted as well. DNA microarray analysis was used to study the condition-dependent expression of these genes, and to generate insights in possible synergistic interactions between the individual members of the pectin degrading enzyme network. For this purpose, A. niger was grown on sugarbeet pectin and on galacturonic acid, rhamnose and xylose, the main monomeric sugar constituents of pectin. An analysis of the corresponding transcriptomes revealed expression of 46 genes encoding pectinolytic enzymes. Their transcriptional profiles are discussed in detail and a cascade model of pectin degradation is proposed.