Abstract
BackgroundHeterochromatin protein 1 (HP1, homologue HepA in Penicillium oxalicum) binding is associated with a highly compact chromatin state accompanied by gene silencing or repression. HP1 loss leads to the derepression of gene expression. We investigated HepA roles in regulating cellulolytic enzyme gene expression, as an increasingly number of studies have suggested that cellulolytic enzyme gene expression is not only regulated by transcription factors, but is also affected by the chromatin status.ResultsAmong the genes that exhibited significant differences between the hepA deletion strain (ΔhepA) and the wild type (WT), most (95.0 %) were upregulated in ΔhepA compared with WT. The expression of the key transcription factor for cellulolytic enzyme gene (e.g., repressor CreA and activator ClrB) increased significantly. However, the deletion of hepA led to downregulation of prominent extracellular cellulolytic enzyme genes. Among the top 10 extracellular glycoside hydrolases (Amy15A, Amy13A, Cel7A/CBHI, Cel61A, Chi18A, Cel3A/BGLI, Xyn10A, Cel7B/EGI, Cel5B/EGII, and Cel6A/CBHII), in which secretion amount is from the highest to the tenth in P. oxalicum secretome, eight genes, including two amylase genes (amy15A and amy13A), all five cellulase genes (cel7A/cbh1, cel6A/cbh2, cel7B/eg1, cel5B/eg2, and cel3A/bgl1), and the cellulose-active LPMO gene (cel61A) expression were downregulated. Results of chromatin accessibility real-time PCR (CHART-PCR) showed that the chromatin of all three tested upstream regions opened specifically because of the deletion of hepA in the case of two prominent cellulase genes cel7A/cbh1 and cel7B/eg1. However, the open chromatin status did not occur along with the activation of cellulolytic enzyme gene expression. The overexpression of hepA upregulated the cellulolytic enzyme gene expression without chromatin modification. The overexpression of hepA remarkably activated the cellulolytic enzyme synthesis, not only in WT (~150 % filter paper activity (FPA) increase), but also in the industry strain RE-10 (~20–30 % FPA increase).ConclusionsHepA is required for chromatin condensation of prominent cellulase genes. However, the opening of chromatin mediated by the deletion of hepA was not positively correlated with cellulolytic enzyme gene activation. HepA is actually a positive regulator for cellulolytic enzyme gene expression and could be a promising target for genetic modification to improve cellulolytic enzyme synthesis.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-016-0624-9) contains supplementary material, which is available to authorized users.
Highlights
Heterochromatin protein 1 (HP1, homologue HepA in Penicillium oxalicum) binding is associated with a highly compact chromatin state accompanied by gene silencing or repression
Another chromatin-associated protein (T. reesei ID 107641), which has a bromodomain, a module found in many chromatin-associated proteins and which plays a key role in chromatin remodeling, was reported to bear the highest expression in T. reesei Δcre1 when the strain was cultivated in cellulose and is thought to result in an alteration of chromatin structure that change the expression of genes related to lignocelluloses degradation [14]
The chromatin organization modifier domain (CHD) is involved in the interaction with H3K9-methylated nucleosomes required for chromatin binding, whereas chromo shadow domain (CSD) mainly mediates interaction with other heterochromatin proteins [28]
Summary
Heterochromatin protein 1 (HP1, homologue HepA in Penicillium oxalicum) binding is associated with a highly compact chromatin state accompanied by gene silencing or repression. Two types of nucleosome modifiers exist, those that remodel the nucleosomes, such as ATP-dependent activity of SWI/ SNF [10], and those that add chemical groups to the tails of histone, such as histone methyltransferases or histone acetyltransferases [11] This modification can “loosen” the chromatin structure, rendering it accessible and capable of binding the transcriptional machinery [12]. The helicase gene snf, which is a component of yeast Swi/Snf multisubunit chromatin remodeling complex, was found to be upregulated significantly in T. reesei Δcre mutant and thought to be involved in the cellulase gene repression by Cre at a high growth rate [13] Another chromatin-associated protein (T. reesei ID 107641), which has a bromodomain, a module found in many chromatin-associated proteins and which plays a key role in chromatin remodeling, was reported to bear the highest expression in T. reesei Δcre when the strain was cultivated in cellulose and is thought to result in an alteration of chromatin structure that change the expression of genes related to lignocelluloses degradation [14]. This histone modification could be recognized by the heterochromatin protein 1 (HP1) [18]
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