Abstract
The Aspergillus nidulans xprG gene encodes a putative transcriptional activator that is a member of the Ndt80 family in the p53-like superfamily of proteins. Previous studies have shown that XprG controls the production of extracellular proteases in response to starvation. We undertook transcriptional profiling to investigate whether XprG has a wider role as a global regulator of the carbon nutrient stress response. Our microarray data showed that the expression of a large number of genes, including genes involved in secondary metabolism, development, high-affinity glucose uptake and autolysis, were altered in an xprG Δ null mutant. Many of these genes are known to be regulated in response to carbon starvation. We confirmed that sterigmatocystin and penicillin production is reduced in xprG - mutants. The loss of fungal mass and secretion of pigments that accompanies fungal autolysis in response to nutrient depletion was accelerated in an xprG1 gain-of-function mutant and decreased or absent in an xprG - mutant. The results support the hypothesis that XprG plays a major role in the response to carbon limitation and that nutrient sensing may represent one of the ancestral roles for the p53-like superfamily. Disruption of the AN6015 gene, which encodes a second Ndt80-like protein, showed that it is required for sexual reproduction in A. nidulans .
Highlights
XprG and two non-catalytic hexokinase-like proteins (HxkC and HxkD) were first identified as regulators of extracellular protease production in Aspergillus nidulans through genetic analysis[1,2,3]
Transcriptional profiling A. nidulans microarrays provided by the Pathogen Functional Genomics Resource Center (PFGRC) were used to compare transcript levels in an xprG+ strain and an xprGD null strain after transfer to medium containing glucose as a carbon source or medium lacking a carbon source for 16 h
More than 37% of the 197 probes that hybridized to transcripts that were significantly up-regulated during carbon starvation, were down-regulated in the xprGD1 mutant
Summary
XprG and two non-catalytic hexokinase-like proteins (HxkC and HxkD) were first identified as regulators of extracellular protease production in Aspergillus nidulans through genetic analysis[1,2,3]. In A. nidulans, extracellular proteases are produced in response to carbon, nitrogen or sulfur starvation[4]. Genetic evidence indicates that XprG activates expression of extracellular protease genes in response to nutrient stress and that HxkC and HxkD are negative regulators of XprG1–3,5,6. The hxkCD1 and hxkDD3 null mutations and the xprG1 gain-of-function mutation increase production of extracellular proteases[1,2,3,5]. Loss-of-function mutations in xprG abolish carbon-starvation-induced production of extracellular proteases and are epistatic to the hxkCD1 and hxkDD3 null mutations[3,6,7]. There is evidence that XprG could be involved in a general response to starvation
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