Comparative RNA-seq based transcriptomic analysis of Aspergillus nidulans recombinant strains overproducing heterologous glycoside hydrolases

Abstract

Filamentous fungi are important cell factories for 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 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. There was an indirect relationship between mRNA and the protein secretion levels, suggesting that transcription is not a bottleneck in these systems. Based on the general RNA-seq analysis 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 enriched. We also observed the unconventional splicing of hacA for the recombinant strains A. nidulansAbfA and A.nidulans1542, indicating some level of unfolded protein response. The global analysis showed mild stress after 2 h induction of heterologous protein production, which normalized after 8 h. Our results provide insights to understand how A. nidulans adapts to the overproduction of heterologous proteins.