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Genome-wide transcriptional response of Aspergillus nidulans to heterologous protein production

ABSTRACT: Filamentous fungi are important factories in the production and secretion of homologous and heterologous lignocellulolytic enzymes, however the regulation of protein secretion in these organisms need to be further explored. In order to investigate this regulation, Aspergillus nidulans recombinant strains were analyzed by transcriptomics. We designed three A. nidulans recombinant strains producing the following heterologous proteins: alpha-arabinofuranosidase (AbfA), beta-glucosidase (BglC) and thermophilic mannanase (1542). The heterologous genes abfA and bglC were highly expressed, while the levels of 1542 mRNA were similar to the reference gene. An indirect relationship between mRNA and the levels of protein secretion was observed, suggesting that transcription is not a bottleneck in these systems. Based on the general analysis of RNA-seq of the recombinant strains, it was possible to observe a predominant up-regulation response. Moreover, biological processes related to metabolism, protein with binding function and cellular transport were overrepresented. We also observed the unconventional splicing of hacA for the recombinant A. nidulansAbfA and A. nidulans1542, indicating some level of unfolded protein response. The global analysis showed mild stress at 2 h induction of heterologous protein production, which was normalized after 8 h. Our results provide insights to understand how A. nidulans adapts to the overproduction of heterologous proteins.

ORGANISM(S): Aspergillus nidulans

PROVIDER: GSE101522 | GEO | 2020/07/14

REPOSITORIES: GEO

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Project description:Thermothelomyces thermophilus, formerly known as Myceliophthora thermophila, is used in industry to produce lignocellulolytic enzymes and heterologous proteins. However, the transcriptional network driving the expression of these proteins remains elusive. As a first step to systematically uncover this network, we investigated growth, protein secretion, and transcriptomic fingerprints of strains deficient in the cellulolytic transcriptional regulators Clr1, Clr2, and Clr4, respectively. The genes encoding Clr1, Clr2, and Clr4 were individually deleted using split marker or the CRISPR/Cas12a technology and the resulting strains as well as the parental strain were cultivated in bioreactors under chemostat conditions using glucose as carbon source. During steady state conditions, cellulose was added instead of glucose to study the genetic and cellular responses in all four strains to the shift in carbon source availability. Notably, the clr1 and clr2 deletion strains were unable to continue to grow on cellulose, demonstrating a key role of both regulators in cellulose catabolism. Their transcriptomic fingerprints uncovered not only a lack of cellulase gene expression but also reduced expression of genes predicted to encode hemicellulases, pectinases, and esterases. In contrast, the growth of the clr4 deletion strain was very similar compared to the parental strain. However, a much stronger expression of cellulases, hemicellulases, pectinases, and esterases was observed. The data gained in this study suggest that both transcriptional regulators Clr1 and Clr2 activate the expression of genes predicted to encode cellulases as well as hemicellulases, pectinases, and esterases. They further suggest that Clr1 controls the basal expression of cellulases and initiates the main lignocellulolytic response to cellulose via induction of clr2 expression. In contrast, Clr4 seems to act as a repressor of the lignocellulolytic response presumably via controlling clr2 expression. Comparative transcriptomics in all four strains revealed potentially new regulators in carbohydrate catabolism and lignocellulolytic enzyme expression that define a candidate gene list for future analyses.

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Genome-wide transcriptional response of Aspergillus nidulans to heterologous protein production

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