Abstract
In Aspergillus nidulans, the xylanolytic regulator XlnR and the arabinanolytic regulator AraR co-regulate pentose catabolism. In nature, the pentose sugars D-xylose and L-arabinose are both main building blocks of the polysaccharide arabinoxylan. In pectin and arabinogalactan, these two monosaccharides are found in combination with D-galactose. GalR, the regulator that responds to the presence of D-galactose, regulates the D-galactose catabolic pathway. In this study we investigated the possible interaction between XlnR, AraR and GalR in pentose and/or D-galactose catabolism in A. nidulans. Growth phenotypes and metabolic gene expression profiles were studied in single, double and triple disruptant A. nidulans strains of the genes encoding these paralogous transcription factors. Our results demonstrate that AraR and XlnR not only control pentose catabolic pathway genes, but also genes of the oxido-reductive D-galactose catabolic pathway. This suggests an interaction between three transcriptional regulators in D-galactose catabolism. Conversely, GalR is not involved in regulation of pentose catabolism, but controls only genes of the oxido-reductive D-galactose catabolic pathway.
Highlights
Filamentous fungi are able to degrade structural plant cell wall polysaccharides and catabolize the released monosaccharides [1]
In this study we investigated possible genetic interaction between three paralogous sugar-specific transcriptional factors (TFs) (XlnR, AraR and GalR) in A. nidulans
We have presented evidence that the D-galactose oxido-reductive pathway is co-regulated by at least three TFs in A. nidulans (Fig 8)
Summary
Filamentous fungi are able to degrade structural plant cell wall polysaccharides (e.g. xylan and pectin) and catabolize the released monosaccharides [1]. The production of the enzymes needed for polysaccharide degradation is controlled by transcriptional regulators Some of these regulators have been identified and characterized in Aspergillus, such as the transcriptional activators AraR, GalR and XlnR [2,3,4]. These regulators are most likely induced by L-arabinose/L-arabitol, D-galactose and D-xylose, respectively, and control the metabolic conversion of these monosaccharides. This provides the fungus with a quick and controllable system that responds to the polymers present in the environment.
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