VeA and MvlA repression of the cryptic orsellinic acid gene cluster in Aspergillus nidulans involves histone 3 acetylation

Abstract

Summary A perplexing aspect of fungal secondary metabolite gene clusters is that most clusters remain ‘silent’ under common laboratory growth conditions where activation is obtained through gene manipulation or encounters with environmental signals. Few proteins have been found involved in repression of silent clusters. Through multicopy suppressor mutagenesis, we have identified a novel cluster suppressor in Aspergillus nidulans, MvlA (modulator of veA loss). Genetic assessment of MvlA mutants revealed the role of both itself and VeA (but not the VeA partner LaeA) in the suppression of the cryptic ors gene cluster producing orsellinic acid and its F9775 derivatives. Loss of veA upregulates F9775A and F9775B production and this increase is reduced 4~5 fold when an overexpression mvlA (OE::mvlA) allele is introduced into the ΔveA background. Previous studies have implicated a positive role for GcnE (H3K9 acetyltransferase of the SAGA/ADA complex) in ors cluster expression and here we find expression of gcnE is upregulated in ΔveA and suppressed by OE::mvlA in the ΔveA background. H3K9 acetylation levels of ors cluster genes correlated with gcnE expression and F9775 production in ΔveA and OE::mvlAΔveA strains. Finally, deletion of gcnE in the ΔveA background abolishes ors cluster activation and F9775 production. Together, this work supports a role for VeA and MvlA in modifying SAGA/ADA complex activity.

The Histone Acetyltransferase GcnE (GCN5) Plays a Central Role in the Regulation ofAspergillusAsexual Development

“…An interesting case is polyketide orsellinic acid, which is produced by A. nidulans in response to the interaction with a streptomycete species in a GcnE-dependent manner (Nützmann et al 2011). Synthesis of orsellinic acid derivatives F9775A and -B, which is induced in a ΔveA strain, is lost in the double-mutant ΔgcnE ΔveA (Bok et al 2013). Thus, the reported role of GcnE in the regulation of secondary metabolism is consistent with our microarray expression analysis.…”

“…In previous work, we and others have established that histone acetylation plays only a minor role in the regulation of some selected primary metabolic systems (Reyes-Dominguez et al 2008;Georgakopoulos et al 2012) but significantly regulates secondary metabolism (Shwab et al 2007;Nützmann et al 2011Nützmann et al , 2013Bok et al 2013). Data presented here enlarge our picture of GcnE function to a genome-wide scale, and from these experiments it is becoming clear that GcnE is a minor regulator of primary metabolism but an essential component in driving A. nidulans developmental processes.…”

“…Only recently, the relevance of chromatin-based silencing of secondary metabolite gene clusters was recognized in several Aspergillus and Fusarium species (Shwab et al 2007;Bok et al 2009;Lee et al 2009;Reyes-Dominguez et al 2010; Strauss and ReyesDominguez 2011). For example, it has been demonstrated that acetylation of histone H3 is required for the synthesis of secondary metabolites in A. nidulans (Reyes-Dominguez et al 2010;Nützmann et al 2011;Bok et al 2013;Nützmann et al 2013). Reduction of heterochromatin marks leads to higher secondary metabolite production in Aspergillus and Fusarium species (Reyes-Dominguez et al 2010, and it has also been found that it de-represses silent clusters, leading to the production of novel metabolites (Bok et al 2009).…”

Revitalization of a Forward Genetic Screen Identifies Three New Regulators of Fungal Secondary Metabolism in the Genus Aspergillus

“…This is important for interpretation of these results, as one would expect that a saturated genetic screen would have also discovered additional genes in the velvet complex (VeA and VelB). However, it is understandable that mutations in veA or velB would have been missed in a visual screen due to the presence of increased levels of orsellinic acid produced by these mutants, which makes the strains look very dark in color and masks NOR pigmentation (57). Consistently, deletions of both laeA and mcsA result in loss of ST in addition to other pigments produced by the fungus, thereby making the mutants more easily distinguishable in a visual NOR screen.…”

Breaking the silence: new strategies for discovering novel natural products

“…Traditional promoter knock-in strategies based on homologous double-crossover recombination are often time-consuming and labor-intensive especially when applied to streptomycetes [18,19]. Recently we developed a highly efficient clustered, regularly interspaced, short palindromic repeat (CRISPR)/CRISPR-associated protein 9 (Cas9) system for multiplex genome editing in streptomycetes, either targeting at precise gene deletion [20] or promoter knock-in [21 •• ].…”