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Trehalose is required for the acquisition of tolerance to a variety of stresses in the filamentous fungus Aspergillus nidulans

Unité Microbiologie et Environnement, Institut Pasteur, 25 rue du Docteur Roux, 75724 Paris Cedex 15, France¹
Flanders Interuniversity Institute for Biotechnology, VIB and Laboratory of Molecular Cell Biology, Katholieke Universiteit Leuven, Kardinaal Mercierlaan 92, B-3001 Leuven-Heverlee, Flanders, Belgium²
Molecular Genetics of Industrial Micro-organisms, Wageningen University, Dreijenlaan 2, 6703HA Wageningen, The Netherlands³

Author for correspondence: Christophe d’Enfert. Tel: +33 1 40 61 32 57. Fax: +33 1 45 68 87 90. e-mail: denfert{at}pasteur.fr

Trehalose is a non-reducing disaccharide found at high concentrations in Aspergillus nidulans conidia and rapidly degraded upon induction of conidial germination. Furthermore, trehalose is accumulated in response to a heat shock or to an oxidative shock. The authors have characterized the A. nidulans tpsA gene encoding trehalose-6-phosphate synthase, which catalyses the first step in trehalose biosynthesis. Expression of tpsA in a Saccharomyces cerevisiae tps1 mutant revealed that the tpsA gene product is a functional equivalent of the yeast Tps1 trehalose-6-phosphate synthase. The A. nidulans tpsA-null mutant does not produce trehalose during conidiation or in response to various stress conditions. While germlings of the tpsA mutant show an increased sensitivity to moderate stress conditions (growth at 45 °C or in the presence of 2 mM H₂O₂), they display a response to severe stress (60 min at 50 °C or in the presence of 100 mM H₂O₂) similar to that of wild-type germlings. Furthermore, conidia of the tpsA mutant show a rapid loss of viability upon storage. These results are consistent with a role of trehalose in the acquisition of stress tolerance. Inactivation of the tpsA gene also results in increased steady-state levels of sugar phosphates but does not prevent growth on rapidly metabolizable carbon sources (glucose, fructose) as seen in Saccharomyces cerevisiae. This suggests that trehalose 6-phosphate is a physiological inhibitor of hexokinase but that this control is not essential for proper glycolytic flux in A. nidulans. Interestingly, tpsA transcription is not induced in response to heat shock or during conidiation, indicating that trehalose accumulation is probably due to a post-translational activation process of the trehalose 6-phosphate synthase.

Keywords: trehalose 6-phosphate synthase, spore germination, glycolysis, heat stress, oxidative stress, hexokinase

Abbreviations: EST, expressed sequence tag; 5-FOA, 5-fluoro-orotic acid; T6P, trehalose 6-phosphate; T6PP, trehalose-6-phosphate phosphatase; T6PS, trehalose-6-phosphate synthase

The GenBank accession number for the sequence reported in this paper is AF043230.

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