The Transcriptional Repressor TupA in Aspergillus niger Is Involved in Controlling Gene Expression Related to Cell Wall Biosynthesis, Development, and Nitrogen Source Availability

Abstract

The Tup1-Cyc8 (Ssn6) complex is a well characterized and conserved general transcriptional repressor complex in eukaryotic cells. Here, we report the identification of the Tup1 (TupA) homolog in the filamentous fungus Aspergillus niger in a genetic screen for mutants with a constitutive expression of the agsA gene. The agsA gene encodes a putative alpha-glucan synthase, which is induced in response to cell wall stress in A. niger. Apart from the constitutive expression of agsA, the selected mutant was also found to produce an unknown pigment at high temperatures. Complementation analysis with a genomic library showed that the tupA gene could complement the phenotypes of the mutant. Screening of a collection of 240 mutants with constitutive expression of agsA identified sixteen additional pigment-secreting mutants, which were all mutated in the tupA gene. The phenotypes of the tupA mutants were very similar to the phenotypes of a tupA deletion strain. Further analysis of the tupA-17 mutant and the ΔtupA mutant revealed that TupA is also required for normal growth and morphogenesis. The production of the pigment at 37°C is nitrogen source-dependent and repressed by ammonium. Genome-wide expression analysis of the tupA mutant during exponential growth revealed derepression of a large group of diverse genes, including genes related to development and cell wall biosynthesis, and also protease-encoding genes that are normally repressed by ammonium. Comparison of the transcriptome of up-regulated genes in the tupA mutant showed limited overlap with the transcriptome of caspofungin-induced cell wall stress-related genes, suggesting that TupA is not a general suppressor of cell wall stress-induced genes. We propose that TupA is an important repressor of genes related to development and nitrogen metabolism.

The interaction of induction and repression mechanisms in the regulation of galacturonic acid-induced genes in Aspergillus niger

“…As pgxC is still partially repressed by glucose even in de creA mutant, an alternative repression mechanism might play a role. Although we could not link the TupA general repressor protein to glucose repression in A. niger (Schachtschabel et al, 2013), we cannot exclude a possible involvement of TupA in pgxC repression and this possibility will be addressed in future experiments. Finally, the promoter reporter strains in the DcreA background that still require an inducer for growth (pgaX, pgxB and pgxC) allow forward genetic screens for inducer-independent mutants.…”

MoTup1 is required for growth, conidiogenesis and pathogenicity of Magnaporthe oryzae

“…D). As Tup1 could regulate the expression of a series of cell wall biosynthesis‐associated genes in A. niger (Schachtschabel et al ., ), we examined the expression of these genes and found that they were down‐regulated in the Δ Motup1 mutant. The expression of the β‐1,3‐glucan synthase MoFKS1 (MGG_00865) (Fujikawa et al ., ) was also repressed in the Δ Motup1 mutant.…”

“…In addition to the genes found above, MoTup1 also regulates the expression of genes related to metabolism through the Tup1–Cyc8 complex (Keleher et al ., ; Schachtschabel et al ., ). We therefore examined the expression of the genes known to be involved in metabolism.…”

“…Neurospore crassa Rco1, the homologue of Tup1, is required for hyphal fusion, normal hyphal morphology, and asexual and sexual development (Vandeputte et al ., ). In Aspergillus niger , TupA is also involved in growth, spore production and nitrogen metabolism, and TupA also controls the expression of a series of genes associated with cell wall biosynthesis and development (Schachtschabel et al ., ).…”

A Transcriptome Meta-Analysis Proposes Novel Biological Roles for the Antifungal Protein AnAFP in Aspergillus niger

“…Finally, deletion of two transcription factors important for securing cell wall integrity of A . niger (RlmA, [44]; TupA, [47] did also not affect anafp expression. Likewise, confrontation of A .…”