Annual Conference 2025 of the Association for General and Applied Microbiology - Jahrestagung 2025 der Vereinigung für Allgemeine und Angewandte Mikrobiologie

Chair

Sensing and Sugar Transporting in Trichoderma reesei

FG Fungal biology and biotechnology

The filamentous fungus Trichoderma reesei is extensively used in the biofuel industry due to its remarkable ability to deconstruct lignocellulosic biomass, a critical process in bioethanol production. This fungus employs various sugar transporters, such as Tr44175 and Tr69957, to facilitate the uptake of key carbohydrates like cellobiose and sophorose, which are essential for regulating the expression of cellulolytic enzymes and thereby enhancing cellulose hydrolysis. Moreover, studies on membrane proteins with CFEM domains, such as Tr111205, have shown that they not only improve sugar uptake but also play roles in osmotic stress response and cell wall integrity. Molecular docking analyses indicate that these proteins have a high specificity for binding sugars, optimizing metabolic efficiency across diverse lignocellulosic substrates, including sugarcane bagasse. These findings expand our knowledge of nutrient sensing in T. reesei and suggest strategies for strain engineering to boost enzyme production, which could significantly reduce costs in industrial bioprocessing.

Invited lecture

Prof. , Dr.

Insights into the Localization and Structural Composition of Lipid Rafts in Schizophyllum commune

Lipid rafts are dynamic microdomains within the cell membrane. They contain high levels of sterols, sphingolipids, and specific proteins associated with lipid rafts. These domains act as platforms for signal transduction, membrane trafficking, protein sorting, and polarized growth (Alvarez et al., 2007). The filamentous basidiomycete Schizophyllum commune requires polarized growth, which depends on the transport of proteins and lipids to the hyphal tip through vesicle trafficking. Rafts contain specific proteins like stomatin and striatin. They play a crucial role in cell signalling and signal transduction. Further striatin is known for its protein-protein interactions with caveolin, a well-known raft related protein. The aim of this work is to investigate the composition of raft domains and the localization and function of rafts in S. commune using two raft-associated proteins: stomatin and striatin. To analyse the overall membrane composition, we performed LC-MS measurements. Sterol-enriched raft domains were visualized by Filipin staining. Further, stomatin and striatin were labelled with the fluorescence proteins dTomato and eGFP, respectively, and visualized by laser scanning microscopy. To investigate the role of stomatin and striatin, we performed a knockout followed by RNA sequencing. The deletion of either stomatin and striatin in S. commune impacted the organism regarding morphological and genetic changes. The RNAseq results of S. commune Δsto showed an upregulation of several cell signalling groups like GPI-anchored proteins, MAPKs, and GPCRs. Further results showed a high effect on membrane-related genes and several membrane transporter groups. The deletion of striatin in S. commune seems to play a significant role in S. commune, especially in the dikaryotic life stage. The study has shown that raft-associated proteins of S. commune play an important role in hyphal growth, cell signalling, membrane stabilization, and membrane-related components. Enhancing our understanding of the structure and functionality of membrane microdomains in microorganisms could potentially provide valuable insights into mating, the interaction of organisms, and the pathogenesis process. Alvarez, F. J., Douglas, L. M., & Konopka, J. B. (2007). Sterol-Rich Plasma Membrane Domains in Fungi. Eukaryotic Cell, 6(5).

Short lecture

Fungal Argonaute proteins mediate bidirectional cross-kingdom RNA interference during host infection

Cross-kingdom RNA interference (ck-RNAi) is an emerging topic in host-pathogen interaction studies. Previously, it was shown that the fungal pathogen Botrytis cinerea transfers small RNAs into its host cells to suppress plant immunity genes for infection1, 2. However, the molecular factors that are involved in ck-RNAi remain largely unknown. We recently developed a GFP ckRNAi "switch-on" reporter tool in transgenic plants to track for the first time RNA communication in real-time during infection3. With this tool, we discovered Botrytis Argonaute (BcAGO)1 and BcAGO2 proteins are required for small RNA delivery into plants during fungal-induced ck-RNAi. Moreover, BcAGO co-immunopurification and small RNA sequencing revealed that tomato plants also send small RNAs into B. cinerea that bind to the Botrytis AGOs. These tomato small RNAs are active in silencing fungal virulence gene expression as a defence response mechanism. In conclusion, we provide strong evidence for bidirectional cross-kingdom RNA communication during fungal-plant interaction, and AGOs are key factors in this communication mechanism. 1 Weiberg, A. et al. Fungal small RNAs suppress plant immunity by hijacking host RNA interference pathways. Science 342, 118-123 (2013). 2 Wang, M., Weiberg, A., Dellota, E., Jr., Yamane, D. & Jin, H. Botrytis small RNA Bc-siR37 suppresses plant defense genes by cross-kingdom RNAi. RNA Biol 14, 421-428 (2017). 3 Cheng, A. P. et al. A fungal RNA-dependent RNA polymerase is a novel player in plant infection and cross-kingdom RNA interference. PLoS Pathog 19, e1011885 (2023).

Understanding and harnessing the carbon catabolic potential of Fomes fomentarius for industrial applications

Fomes fomentarius is a promising candidate for fungal mycelium-based composite material production. However, its application in industry is hampered by a limited knowledge of its carbon catabolism. To accelerate the development of an industrially feasible composite production process based on F. fomentarius, we have grown it under 24 cultivation conditions, analysed gene expression patterns during substrate degradation, and constructed gene co-expression networks. Our analyses suggest that genes encoding putative lignocellulolytic CAZymes have been the subject of gene family expansion followed by transcriptional divergence, which will have contributed to niche specificity and metabolic robustness. Transcriptional regulation might be directed by two putative regulators, CalA and CalB, that we have identified using gene co-expression networks. A subset of CAZyme-encoding genes were found to be arranged in a novel type of metabolic gene cluster, termed contiguous co-expression clusters, that have not been described previously in fungi. This discovery has given us further insight into the transcriptional organisation and regulation of F. fomentarius genes. Lastly, we identified 35 sugar transporters in silico. Applying SPOT, a state-of-the-art model, we predicted potential substrates and analysed their respective gene expression patterns, the results of which indicate that sugar transporters in F. fomentarius might be promiscuous towards more than one substrate. By carrying out gene expression analysis and constructing co-expression networks focused on F. fomentarius carbon catabolism, we have been able to single out target genes for future studies aiming to optimise substrate utilisation. Ultimately, this insight will facilitate strain improvement approaches of F. fomentarius for industrial applications.

G-protein coupled receptors regulate morphological development in the plant pathogen Ustilago maydis

G-protein-coupled receptors (GPCRs) are the largest class of eukaryotic receptor proteins that regulate physiology and are important drug targets in humans. Although GPCRs are present in fungi and might be similarly druggable, they are far less understood than their human counterparts. This is of particular interest, as pathogenic fungi are gaining increasing attention, as human-, animal- and plant diseases caused by fungi are on the rise. Therefore, a mechanistic understanding of fungal GPCRs is crucially lacking. In my project, we investigate the contribution of GPCRs to the pathogenicity of the basidiomycete fungus Ustilago maydis. In a first step, more than 30 previously undescribed proteins that share structural similarity with 7-transmembrane GPCRs were discovered on the genome of U. maydis. These potential GPCRs are highly diverse on the sequence level and many are not conserved in well-studied ascomycete fungi and might be an adaptation to its specific plant-pathogenic lifestyle. A closer inspection of the expression profiles of the GPCR candidates showed that many are differentially expressed during infection of the host Zea mays. We therefore hypothesize that these receptors enable the fungus to detect host-specific signals but likely also metabolites. Some of these stimuli might also be important for regulating the dimorphic switch from yeast-like sporidia to infectious hyphae in U. maydis. To first gain more knowledge on their potential functions, we not only performed a structure-guided categorization of the receptors but also used structure prediction tools to predict interactions between the receptors and the four Gα-subunits of U. maydis. We are currently implementing a yeast reporter system that allows us to identify different ligands recognized by the receptors and understand the importance of these signals for pathogenic development of U. maydis. Since GPCR signal transduction is linked to the secondary messenger cAMP, we also determined cAMP levels revealing that different GPCR deletion backgrounds are decreased in cAMP. These results further suggest that some of the studied receptors are indeed GPCRs and linked to the cAMP signaling pathway of U. maydis. Our research will contribute to a better understanding of fungal GPCRs in terms of signal transduction, its link to cAMP levels and overall pathogenicity in U. maydis. These findings will provide a basis for detailed GPCR-ligand interactions and enhance our understanding of signal perception in pathogenic basidiomycete fungi.

FG Fungal biology and biotechnology
Signaling across membranes

Appointment

Chair

Programme

FG Fungal biology and biotechnologySignaling across membranes

Appointment

Chair

Programme

FG Fungal biology and biotechnology
Signaling across membranes