Transcriptional Activation of the Aspergillus nidulans gpdA Promoter by Osmotic Signals

Abstract

ABSTRACT A differentially expressed gpdA cDNA clone was isolated from NaCl-adapted Aspergillus nidulans (FGSC359) and identified as glyceraldehyde-3-phosphate dehydrogenase ( gpdA ) on the basis of its nucleotide sequence. The level of gpdA RNA substantially increased in cultures gradually adapted to NaCl but was greatly reduced in cultures exposed briefly to a high concentration of NaCl. A pyrG auxotroph of A. nidulans (A773) was cotransformed with a gpdA-uidA construct and a plasmid containing the Neurospora crassa pyr4 gene as a selectable marker. One pyrG + β-glucuronidase-positive (GUS + ) transformant was selected, and stable integration of the gpdA-uidA construct into the genome was confirmed by Southern blot analysis. Gradual adaptation to increasing concentrations of NaCl resulted in an increase in GUS activity to 2.7-fold. GUS activity was reduced after a 2-h exposure of an unadapted culture to 2 M NaCl but gradually increased to a maximum of twofold after 24 h. GUS activity also increased by 8.4-fold in Na 2 SO 4 -adapted cultures, 4.9-fold in polyethylene glycol-adapted cultures, and 7.5-fold in KCl-adapted cultures. These results are consistent with the hypothesis that the A. nidulans gpdA promoter is transcriptionally activated by osmotic signals.