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Fungal Genet Biol. 2019 Feb;123:53-59. doi: 10.1016/j.fgb.2018.11.004. Epub 2018 Nov 26.

l-Arabinose induces d-galactose catabolism via the Leloir pathway in Aspergillus nidulans.

Author information

1
Department of Biochemical Engineering, Faculty of Science and Technology, University of Debrecen, Egyetem tér 1, H-4032 Debrecen, Hungary.
2
Fungal Physiology, Westerdijk Fungal Biodiversity Institute & Fungal Molecular Physiology, Utrecht University, Uppsalalaan 8, 3584 CT Utrecht, the Netherlands.
3
Department of Biochemical Engineering, Faculty of Science and Technology, University of Debrecen, Egyetem tér 1, H-4032 Debrecen, Hungary. Electronic address: kicsizsoka@yahoo.com.

Abstract

l-Arabinose and d-galactose are the principal constituents of l-arabinogalactan, and also co-occur in other hemicelluloses and pectins. In this work we hypothesized that similar to the induction of relevant glycoside hydrolases by monomers liberated from these plant heteropolymers, their respective catabolisms in saprophytic and phytopathogenic fungi may respond to the presence of the other sugar to promote synergistic use of the complex growth substrate. We showed that these two sugars are indeed consumed simultaneously by Aspergillus nidulans, while l-arabinose is utilised faster in the presence than in the absence of d-galactose. Furthermore, the first two genes of the Leloir pathway for d-galactose catabolism - encoding d-galactose 1-epimerase and galactokinase - are induced more rapidly by l-arabinose than by d-galactose eventhough deletion mutants thereof grow as well as a wild type strain on the pentose. d-Galactose 1-epimerase is hyperinduced by l-arabinose, d-xylose and l-arabitol but not by xylitol. The results suggest that in A. nidulans, l-arabinose and d-xylose - both requiring NADPH for their catabolisation - actively promote the enzyme infrastructure necessary to convert β-d-galactopyranose via the Leloir pathway with its α-anomer specific enzymes, into β-d-glucose-6-phosphate (the starting substrate of the oxidative part of the pentose phosphate pathway) even in the absence of d-galactose.

KEYWORDS:

Galactokinase gene; Galactose 1-epimerase gene; Induction of transcription; Mixed carbon source synergism; d-Galactose; l-Arabinose

PMID:
30496805
DOI:
10.1016/j.fgb.2018.11.004
[Indexed for MEDLINE]

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