Genetic Analysis of Four Sexual Differentiation Process Proteins (isp4/SDPs) in Chaetomium thermophilum and Thermomyces lanuginosus Reveals Their Distinct Roles in Development

Responses of the Mushroom Pleurotus ostreatus under Different CO2 Concentration by Comparative Proteomic Analyses

Background: Pleurotus ostreatus is a popular edible mushroom in East Asian markets. Research on the responses of P. ostreatus under different carbon dioxide concentrations is limited. Methods: Label-free LC-MS/MS quantitative proteomics analysis technique was adopted to obtain the protein expression profiles of P. ostreatus fruiting body pileus collected under different carbon dioxide concentrations. The Pearson correlation coefficient analysis and principal component analysis were performed to reveal the correlation among samples. The differentially expressed proteins (DEPs) were organized. Gene ontology analysis was performed to divide the DEPs into different metabolic processes and pathways. Results: The expansion of stipes was inhibited in the high CO₂ group compared with that in the low CO₂ group. There were 415 DEPs (131 up- and 284 down-regulated) in P. ostreatus PH11 treated with 1% CO₂ concentration compared with P. ostreatus under atmospheric conditions. Proteins related to hydrolase activity, including several amidohydrolases and cell wall synthesis proteins, were highly expressed under high CO₂ concentration. Most of the kinases and elongation factors were significantly down-regulated under high CO₂ concentration. The results suggest that the metabolic regulation and development processes were inhibited under high CO₂ concentrations. In addition, the sexual differentiation process protein Isp4 was inhibited under high CO₂ concentrations, indicating that the sexual reproductive process was also inhibited under high CO₂ concentrations, which is inconsistent with the small fruiting body pileus under high CO₂ concentrations. Conclusions: This research reports the proteome analysis of commercially relevant edible fungi P. ostreatus under different carbon dioxide concentrations. This study deepens our understanding of the mechanism for CO₂-induced morphological change in the P. ostreatus fruiting body, which will facilitate the artificial cultivation of edible mushrooms.

A Homologous Recombination System to Generate Epitope-Tagged Target Genes in Chaetomium thermophilum: A Genetic Approach to Investigate Native Thermostable Proteins

Chaetomium thermophilum is an attractive eukaryotic model organism which, due to its unusually high temperature tolerance (optimal growth at 50-52 °C), has a thermostable proteome that can be exploited for biochemical, structural and biotechnological applications. Site directed gene manipulation for the expression of labeled target genes is a desirable approach to study the structure and function of thermostable proteins and their organization in complexes, which has not been established for this thermophile yet. Here, we describe the development of a homologous recombination system to epitope-tag chromosomal genes of interest in Chaetomium thermophilum with the goal to exploit the derived thermostable fusion proteins for tandem-affinity purification. This genetic approach was facilitated by the engineering of suitable strains, in which factors of the non-homologous end-joining pathway were deleted, thereby improving the efficiency of homologous integration at specific gene loci. Following this strategy, we could demonstrate that gene tagging via homologous recombination improved the yield of purified bait proteins and co-precipitated factors, paving the way for related studies in fundamental research and industrial applications.

Insights into the cellulose degradation mechanism of the thermophilic fungus Chaetomium thermophilum based on integrated functional omics

BACKGROUND

Lignocellulose is the most abundant and renewable biomass resource on the planet. Lignocellulose can be converted into biofuels and high-value compounds; however, its recalcitrance makes its breakdown a challenge. Lytic polysaccharide monooxygenases (LPMOs) offer tremendous promise for the degradation of recalcitrant polysaccharides. Chaetomium thermophilum, having many LPMO-coding genes, is a dominant thermophilic fungus in cellulose-rich and self-heating habitats. This study explores the genome, secretomes and transcript levels of specific genes of C. thermophilum.

RESULTS

The genome of C. thermophilum encoded a comprehensive set of cellulose- and xylan-degrading enzymes, especially 18 AA9 LPMOs that belonged to different subfamilies. Extracellular secretomes showed that arabinose and microcrystalline cellulose (MCC) could specifically induce the secretion of carbohydrate-active enzymes (CAZymes), especially AA9 LPMOs, by C. thermophilum under different carbon sources. Temporal analyses of secretomes and transcripts revealed that arabinose induced the secretion of xylanases by C. thermophilum, which was obviously different from other common filamentous fungi. MCC could efficiently induce the specific secretion of LPMO2s, possibly because the insert in loop3 on the substrate-binding surface of LPMO2s strengthened its binding capacity to cellulose. LPMO2s, cellobio hydrolases (CBHs) and cellobiose dehydrogenases (CDHs) were cosecreted, forming an efficient cellulose degradation system of oxidases and hydrolases under thermophilic conditions.

CONCLUSIONS

The specific expression of LPMO2s and cosecretion of hydrolases and oxidases by the thermophilic fungus C. thermophilum play an important role in cellulose degradation. This insight increases our understanding of the cellulose degradation under thermophilic conditions and may inspire the design of the optimal enzyme cocktails for more efficient exploration of biomass resources in industrial applications.