Comparison and characterization of α-amylase inducers in Aspergillus nidulans based on nuclear localization of AmyR

Abstract

AmyR, a fungal transcriptional activator responsible for induction of amylolytic genes in Aspergillus nidulans, localizes to the nucleus in response to the physiological inducer isomaltose. Maltose, kojibiose, and D-glucose were also found to trigger the nuclear localization of GFP-AmyR. Isomaltose- and kojibiose-triggered nuclear localization was not inhibited by the glucosidase inhibitor, castanospermine, while maltose-triggered localization was inhibited. Thus, maltose itself does not appear to be an direct inducer, but its degraded or transglycosylated product does. Non-metabolizable D-glucose analogues were also able to trigger the nuclear localization, implying that these sugars, except maltose, directly function as the inducers of AmyR nuclear entry. The inducing activity of D-glucose was 4 orders-of-magnitude weaker compared with isomaltose. Although D-glucose has the ability to induce a-amylase production, this activity would generally be masked by CreA-dependent carbon catabolite repression. Significant induction of a-amylase by D-glucose was observed in creA-defective A. nidulans. © Springer-Verlag 2012.