The filamentous fungus Trichoderma reesei is adapted to nutrient-poor environments, in which it uses extracellular
cellulases to obtain
glucose from the available
cellulose biomass. We have isolated and characterized Trhxt1, a putative
glucose transporter gene, as judged by the
glucose accumulation phenotype of a DeltaTrhxt1 mutant. This gene is repressed at high
glucose concentrations and expressed at micromolar levels and in the absence of
glucose. The gene is also induced during the growth of T. reesei on
cellulose when the
glucose concentration generated from the hydrolysis of
cellulose present in the culture medium is in the micromolar range. We also show that
oxygen availability controls the expression of the Trxht1 gene. In this regard, the gene is down-regulated by
hypoxia and also by the inhibition of the flow of electrons through the respiratory chain using
antimycin A. Intriguingly,
anoxia but not
hypoxia strongly induces the expression of the gene in the presence of an otherwise repressive concentration of
glucose. These results indicate that although the absence of repressing concentrations of
glucose and an active respiratory chain are required for Trhxt1 expression under normoxic conditions these physiological processes have no effect on the expression of this gene under an anoxic state. Thus, our results highlight the presence of a novel coordinated interaction between
oxygen and the regulatory circuit for
glucose repression under anoxic conditions.