Identification of new signalling peptides through a genome-wide survey of 250 fungal secretomes

Fungal Cell Wall-Associated Effectors: Sensing, Integration, Suppression, and Protection

The cell wall (CW) of plant-interacting fungi, as the direct interface with host plants, plays a crucial role in fungal development. A number of secreted proteins are directly associated with the fungal CW, either through covalent or non-covalent interactions, and serve a range of important functions. In the context of plant-fungal interactions many are important for fungal development in the host environment and may therefore be considered fungal CW-associated effectors (CWAEs). Key CWAE functions include integrating chemical/physical signals to direct hyphal growth, interfering with plant immunity, and providing protection against plant defenses. In recent years, a diverse range of mechanisms have been reported that underpin their roles, with some CWAEs harboring conserved motifs or functional domains, while others are reported to have novel features. As such, the current understanding regarding fungal CWAEs is systematically presented here from the perspective of their biological functions in plant-fungal interactions. An overview of the fungal CW architecture and the mechanisms by which proteins are secreted, modified, and incorporated into the CW is first presented to provide context for their biological roles. Some CWAE functions are reported across a broad range of pathosystems or symbiotic/mutualistic associations. Prominent are the chitin interacting-effectors that facilitate fungal CW modification, protection, or suppression of host immune responses. However, several alternative functions are now reported and are presented and discussed. CWAEs can play diverse roles, some possibly unique to fungal lineages and others conserved across a broad range of plant-interacting fungi. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

A non-pheromone GPCR is essential for meiosis and ascosporogenesis in the wheat scab fungus

Meiosis is essential for generating genetic diversity and sexual spores, but the regulation of meiosis and ascosporogenesis is not clear in filamentous fungi, in which dikaryotic and diploid cells formed inside fruiting bodies are not free living and independent of pheromones or pheromone receptors. In this study, Gia1, a non-pheromone GPCR (G protein-coupled receptor) with sexual-specific expression in Fusarium graminearum, is found to be essential for ascosporogenesis. The gia1 mutant was normal in perithecium development, crozier formation, and karyogamy but failed to undergo meiosis, which could be partially rescued by a dominant active mutation in GPA1 and activation of the Gpmk1 pathway. GIA1 orthologs have conserved functions in regulating meiosis and ascosporogenesis in Sordariomycetes. GIA1 has a paralog, GIP1, in F. graminearum and other Hypocreales species which is essential for perithecium formation. GIP1 differed from GIA1 in expression profiles and downstream signaling during sexual reproduction. Whereas the C-terminal tail and IR3 were important for intracellular signaling, the N-terminal region and EL3 of Gia1 were responsible for recognizing its ligand, which is likely a protein enriched in developing perithecia, particularly in the gia1 mutant. Taken together, these results showed that GIA1 encodes a non-pheromone GPCR that regulates the entry into meiosis and ascosporogenesis via the downstream Gpmk1 MAP kinase pathway in F. graminearum and other filamentous ascomycetes.

Peptide signaling through leucine-rich repeat receptor kinases: insight into land plant evolution

Multicellular organisms need mechanisms for communication between cells so that they can fulfill their purpose in the organism as a whole. Over the last two decades, several small post-translationally modified peptides (PTMPs) have been identified as components of cell-to-cell signaling modules in flowering plants. Such peptides most often influence growth and development of organs not universally conserved among land plants. PTMPs have been matched to subfamily XI leucine-rich repeat receptor-like kinases with > 20 repeats. Phylogenetic analyses, facilitated by recently published genomic sequences of non-flowering plants, have identified seven clades of such receptors with a history back to the common ancestor of bryophytes and vascular plants. This raises a number of questions: When did peptide signaling arise during land plant evolution? Have orthologous peptide-receptor pairs preserved their biological functions? Has peptide signaling contributed to major innovations, such as stomata, vasculature, roots, seeds, and flowers? Using genomic, genetic, biochemical, and structural data and non-angiosperm model species, it is now possible to address these questions. The vast number of peptides that have not yet found their partners suggests furthermore that we have far more to learn about peptide signaling in the coming decades.

How to improve the production of peptidyl compounds in filamentous fungi

Peptidyl compounds produced by filamentous fungi, which are nonribosomal peptides (NRPs) and ribosomally synthesized and post-translationally modified peptides (RiPPs), are rich sources of bioactive compounds with a wide variety of structures. Some of these peptidyl compounds are useful as pharmaceuticals and pesticides. However, for industrial use, their low production often becomes an obstacle, and various approaches have been challenged to overcome this weakness. In this article, we summarize the successful attempts to increase the production of NRPs and RiPPs in filamentous fungi and present our perspectives on how to improve it further.

Structural and Functional Analysis of Peptides Derived from KEX2-Processed Repeat Proteins in Agaricomycetes Using Reverse Genetics and Peptidomics

Bioactivities of fungal peptides are of interest for basic research and therapeutic drug development. Some of these peptides are derived from "KEX2-processed repeat proteins" (KEPs), a recently defined class of precursor proteins that contain multiple peptide cores flanked by KEX2 protease cleavage sites. Genome mining has revealed that KEPs are widespread in the fungal kingdom. Their functions are largely unknown. Here, we present the first in-depth structural and functional analysis of KEPs in a basidiomycete. We bioinformatically identified KEP-encoding genes in the genome of the model agaricomycete Coprinopsis cinerea and established a detection protocol for the derived peptides by overexpressing the C. cinerea KEPs in the yeast Pichia pastoris. Using this protocol, which includes peptide extraction and mass spectrometry with data analysis using the search engine Mascot, we confirmed the presence of several KEP-derived peptides in C. cinerea, as well as in the edible mushrooms Lentinula edodes, Pleurotus ostreatus, and Pleurotus eryngii. While CRISPR-mediated knockout of C. cinerea kep genes did not result in any detectable phenotype, knockout of kex genes caused defects in mycelial growth and fruiting body formation. These results suggest that KEP-derived peptides may play a role in the interaction of C. cinerea with the biotic environment and that the KEP-processing KEX proteases target a variety of substrates in agaricomycetes, including some important for mycelial growth and differentiation. IMPORTANCE Two recent bioinformatics studies have demonstrated that KEX2-processed repeat proteins are widespread in the fungal kingdom. However, despite the prevalence of KEPs in fungal genomes, only few KEP-derived peptides have been detected and studied so far. Here, we present a protocol for the extraction and structural characterization of KEP-derived peptides from fungal culture supernatants and tissues. The protocol was successfully used to detect several linear and minimally modified KEP-derived peptides in the agaricomycetes C. cinerea, L. edodes, P. ostreatus, and P. eryngii. Our study establishes a new protocol for the targeted search of KEP-derived peptides in fungi, which will hopefully lead to the discovery of more of these interesting fungal peptides and allow a further characterization of KEPs.

A Functional Carbohydrate Degrading Enzyme Potentially Acquired by Horizontal Gene Transfer in the Genome of the Soil Invertebrate Folsomia candida

Horizontal gene transfer (HGT) is defined as the acquisition by an organism of hereditary material from a phylogenetically unrelated organism. This process is mostly observed among bacteria and archaea, and considered less likely between microbes and multicellular eukaryotes. However, recent studies provide compelling evidence of the evolutionary importance of HGT in eukaryotes, driving functional innovation. Here, we study an HGT event in Folsomia candida (Collembola, Hexapoda) of a carbohydrate-active enzyme homologous to glycosyl hydrase group 43 (GH43). The gene encodes an N-terminal signal peptide, targeting the product for excretion, which suggests that it contributes to the diversity of digestive capacities of the detritivore host. The predicted α-L-arabinofuranosidase shows high similarity to genes in two other Collembola, an insect and a tardigrade. The gene was cloned and expressed in Escherichia coli using a cell-free protein expression system. The expressed protein showed activity against p-nitrophenyl-α-L-arabinofuranoside. Our work provides evidence for functional activity of an HGT gene in a soil-living detritivore, most likely from a bacterial donor, with genuine eukaryotic properties, such as a signal peptide. Co-evolution of metazoan GH43 genes with the Panarthropoda phylogeny suggests the HGT event took place early in the evolution of this ecdysozoan lineage.

Secretome Analysis of Macrophomina phaseolina Identifies an Array of Putative Virulence Factors Responsible for Charcoal Rot Disease in Plants

Macrophomina phaseolina is a global devastating necrotrophic fungal pathogen. It causes charcoal rot disease in more than 500 host plants including major food crops, pulse crops, fiber crops, and oil crops. Despite having the whole-genome sequence of M. phaseolina, understanding the M. phaseolina genome-based plant–pathogen interactions is limited in the absence of direct experimental proof of secretion. Thus, it is essential to understand the host–microbe interaction and the disease pathogenesis, which can ensure global agricultural crop production and security. An in silico–predicted secretome of M. phaseolina is unable to represent the actual secretome. We could identify 117 proteins present in the secretome of M. phaseolina using liquid chromatography–electrospray ionization–tandem mass spectrometry. Data are available via ProteomeXchange with identifier PXD032749. An array of putative virulence factors of M. phaseolina were identified in the present study using solid-state culture. Similar virulence factors have been reported in other plant pathogenic fungi also. Among the secretory fungal proteins with positive economic impacts, lignocellulolytic enzymes are of prime importance. Further, we validated our results by detecting the cell wall–degrading enzymes xylanase, endoglucanase, and amylase in the secretome of M. phaseolina. The present study may provide a better understanding about the necrotrophic fungi M. phaseolina, which modulate the host plant defense barriers using secretory proteins.

Prediction of effector proteins and their implications in pathogenicity of phytopathogenic filamentous fungi: A review

Plant pathogenic fungi encode and secrete effector proteins to promote pathogenesis. In recent years, the important role of effector proteins in fungi and plant host interactions has become increasingly prominent. In this review, the functional characterization and molecular mechanisms by which fungal effector proteins modulate biological processes and suppress the defense of plant hosts are discussed, with an emphasis on cell localization during fungal infection. This paper also provides a comprehensive review of bioinformatic and experimental methods that are currently available for the identification of fungal effector proteins. We additionally summarize the secretion pathways and the methods for verifying the presence effector proteins in plant host cells. For future research, comparative genomic studies of different pathogens with varying life cycles will allow comprehensive and systematic identification of effector proteins. Additionally, functional analysis of effector protein interactions with a wider range of hosts (especially non-model crops) will provide more detailed repertoires of fungal effectors. Identifying effector proteins and verifying their functions will improve our understanding of their role in causing disease and in turn guide future strategies for combatting fungal infections.

Out for a RiPP: challenges and advances in genome mining of ribosomal peptides from fungi

Covering up to June 2021Ribosomally synthesized and post-translationally modified peptides (RiPPs) from fungi are an underexplored class of natural products, despite their propensity for diverse bioactivities and unique structural features. Surveys of fungal genomes for biosynthetic gene clusters encoding RiPPs have been limited in their scope due to our incomplete understanding of fungal RiPP biosynthesis. Through recent discoveries, along with earlier research, a clearer picture has been emerging of the biosynthetic principles that underpin fungal RiPP pathways. In this Highlight, we trace the approaches that have been used for discovering currently known fungal RiPPs and show that all of them can be assigned to one of three distinct families based on hallmarks of their biosynthesis, which are in turn imprinted on their corresponding gene clusters. We hope that our systematic exposition of fungal RiPP structural and gene cluster features will facilitate more comprehensive approaches to genome mining efforts in the future.

A targeted bioinformatics approach identifies highly variable cell surface proteins that are unique to Glomeromycotina

Diversity in arbuscular mycorrhizal fungi (AMF) contributes to biodiversity and resilience in natural environments and healthy agricultural systems. Functional complementarity exists among species of AMF in symbiosis with their plant hosts, but the molecular basis of this is not known. We hypothesise this is in part due to the difficulties that current sequence assembly methodologies have assembling sequences for intrinsically disordered proteins (IDPs) due to their low sequence complexity. IDPs are potential candidates for functional complementarity because they often exist as extended (non-globular) proteins providing additional amino acids for molecular interactions. Rhizophagus irregularis arabinogalactan-protein-like proteins (AGLs) are small secreted IDPs with no known orthologues in AMF or other fungi. We developed a targeted bioinformatics approach to identify highly variable AGLs/IDPs in RNA-sequence datasets. The approach includes a modified multiple k-mer assembly approach (Oases) to identify candidate sequences, followed by targeted sequence capture and assembly (mirabait-mira). All AMF species analysed, including the ancestral family Paraglomeraceae, have small families of proteins rich in disorder promoting amino acids such as proline and glycine, or glycine and asparagine. Glycine- and asparagine-rich proteins also were found in Geosiphon pyriformis (an obligate symbiont of a cyanobacterium), from the same subphylum (Glomeromycotina) as AMF. The sequence diversity of AGLs likely translates to functional diversity, based on predicted physical properties of tandem repeats (elastic, amyloid, or interchangeable) and their broad pI ranges. We envisage that AGLs/IDPs could contribute to functional complementarity in AMF through processes such as self-recognition, retention of nutrients, soil stability, and water movement.

The crystal structure of SnTox3 from the necrotrophic fungus Parastagonospora nodorum reveals a unique effector fold and provides insight into Snn3 recognition and pro-domain protease processing of fungal effectors

Plant pathogens cause disease through secreted effector proteins, which act to promote infection. Typically, the sequences of effectors provide little functional information and further targeted experimentation is required. Here, we utilized a structure/function approach to study SnTox3, an effector from the necrotrophic fungal pathogen Parastagonospora nodorum, which causes cell death in wheat-lines carrying the sensitivity gene Snn3. We developed a workflow for the production of SnTox3 in a heterologous host that enabled crystal structure determination and functional studies. We show this approach can be successfully applied to study effectors from other pathogenic fungi. The β-barrel fold of SnTox3 is a novel fold among fungal effectors. Structure-guided mutagenesis enabled the identification of residues required for Snn3 recognition. SnTox3 is a pre-pro-protein, and the pro-domain of SnTox3 can be cleaved in vitro by the protease Kex2. Complementing this, an in silico study uncovered the prevalence of a conserved motif (LxxR) in an expanded set of putative pro-domain-containing fungal effectors, some of which can be cleaved by Kex2 in vitro. Our in vitro and in silico study suggests that Kex2-processed pro-domain (designated here as K2PP) effectors are common in fungi and this may have broad implications for the approaches used to study their functions.

The crystal structure of SnTox3 from the necrotrophic fungus Parastagonospora nodorum reveals a unique effector fold and provides insight into Snn3 recognition and pro-domain protease processing of fungal effectors

Plant pathogens cause disease through secreted effector proteins, which act to promote infection. Typically, the sequences of effectors provide little functional information and further targeted experimentation is required. Here, we utilized a structure/function approach to study SnTox3, an effector from the necrotrophic fungal pathogen Parastagonospora nodorum, which causes cell death in wheat-lines carrying the sensitivity gene Snn3. We developed a workflow for the production of SnTox3 in a heterologous host that enabled crystal structure determination and functional studies. We show this approach can be successfully applied to study effectors from other pathogenic fungi. The β-barrel fold of SnTox3 is a novel fold among fungal effectors. Structure-guided mutagenesis enabled the identification of residues required for Snn3 recognition. SnTox3 is a pre-pro-protein, and the pro-domain of SnTox3 can be cleaved in vitro by the protease Kex2. Complementing this, an in silico study uncovered the prevalence of a conserved motif (LxxR) in an expanded set of putative pro-domain-containing fungal effectors, some of which can be cleaved by Kex2 in vitro. Our in vitro and in silico study suggests that Kex2-processed pro-domain (designated here as K2PP) effectors are common in fungi and this may have broad implications for the approaches used to study their functions.

Transcription factor control of virulence in phytopathogenic fungi

Plant-pathogenic fungi are a significant threat to economic and food security worldwide. Novel protection strategies are required and therefore it is critical we understand the mechanisms by which these pathogens cause disease. Virulence factors and pathogenicity genes have been identified, but in many cases their roles remain elusive. It is becoming increasingly clear that gene regulation is vital to enable plant infection and transcription factors play an essential role. Efforts to determine their regulatory functions in plant-pathogenic fungi have expanded since the annotation of fungal genomes revealed the ubiquity of transcription factors from a broad range of families. This review establishes the significance of transcription factors as regulatory elements in plant-pathogenic fungi and provides a systematic overview of those that have been functionally characterized. Detailed analysis is provided on regulators from well-characterized families controlling various aspects of fungal metabolism, development, stress tolerance, and the production of virulence factors such as effectors and secondary metabolites. This covers conserved transcription factors with either specialized or nonspecialized roles, as well as recently identified regulators targeting key virulence pathways. Fundamental knowledge of transcription factor regulation in plant-pathogenic fungi provides avenues to identify novel virulence factors and improve our understanding of the regulatory networks linked to pathogen evolution, while transcription factors can themselves be specifically targeted for disease control. Areas requiring further insight regarding the molecular mechanisms and/or specific classes of transcription factors are identified, and direction for future investigation is presented.

Effectors of Plant Necrotrophic Fungi

Plant diseases caused by necrotrophic fungal pathogens result in large economic losses in field crop production worldwide. Effectors are important players of plant-pathogen interaction and deployed by pathogens to facilitate plant colonization and nutrient acquisition. Compared to biotrophic and hemibiotrophic fungal pathogens, effector biology is poorly understood for necrotrophic fungal pathogens. Recent bioinformatics advances have accelerated the prediction and discovery of effectors from necrotrophic fungi, and their functional context is currently being clarified. In this review we examine effectors utilized by necrotrophic fungi and hemibiotrophic fungi in the latter stages of disease development, including plant cell death manipulation. We define "effectors" as secreted proteins and other molecules that affect plant physiology in ways that contribute to disease establishment and progression. Studying and understanding the mechanisms of necrotrophic effectors is critical for identifying avenues of genetic intervention that could lead to improved resistance to these pathogens in plants.

Secretomes of medically important fungi reflect morphological and phylogenetic diversity

Secretome represents a main target for understanding the mechanisms of fungal adaptation. In the present study, we focus on the secretomes of fungi associated with infections in humans and other mammals in order to explore relationships between the diverse morphological and phylogenetic groups. Almost all the mammalian pathogenic fungi analyzed have secretome sizes smaller than 1000 proteins and, secreted proteins comprise between 5% and 10% of the total proteome. As expected, the correlation pattern between the secretome size and the total proteome was similar to that described in previous secretome studies of fungi. With regard to the morphological groups, minimum secretome sizes of less than 250 secreted proteins and low values for the fraction of secreted proteins are shown in mammalian pathogenic fungi with reduced proteomes such as microsporidia, atypical fungi and some species of yeasts and yeast-like fungi (Malassezia). On the other hand, filamentous fungi have significantly more secreted proteins and the highest numbers are present in species of filamentous fungi that also are plant or insect pathogens (Fusarium verticilloides, Fusarium oxysporum and Basidiobolus meristosporus). With respect to phylogeny, there are also variations in secretome size across fungal subphyla: Microsporidia, Taphrinomycotina, Ustilagomycotina and Saccharomycotina contain small secretomes; whereas larger secretomes are found in Agaricomycotina, Pezizomycotina, Mucoromycotina and Entomophthoromycotina. Finally, principal component analysis (PCA) was conducted on the complete secretomes. The PCA results revealed that, in general, secretomes of fungi belonging to the same morphological group or subphyla cluster together. In conclusion, our results point out that in medically important fungi there is a relationship between the secretome and the morphological group or phylogenetic classification.

Peptides derived from Kex2-processed repeat proteins are widely distributed and highly diverse in the Fungi kingdom

BACKGROUND

Recently, a gene cluster responsible for biosynthesis of ustiloxin in Aspergillus flavus was identified as the first case of a ribosomally synthesized and post-translationally modified peptide (RiPP) synthetic pathway in Ascomycota. RiPPs are biosynthesized from precursor peptides, which are processed to produce the RiPP backbone (core peptides) for further modifications such as methylation and cyclization. Ustiloxin precursor peptide has two distinctive features: a signal peptide for translocation into the endoplasmic reticulum and highly repeated core sequences cleaved by Kex2 protease in the Golgi apparatus. On the basis of these characteristics, the ustiloxin-type RiPP precursor peptides or Kex2-processed repeat proteins (KEPs) in strains belonging to the Fungi kingdom were computationally surveyed, in order to investigate the distribution and putative functions of KEPs in fungal ecology.

RESULTS

In total, 7878 KEPs were detected in 1345 of 1461 strains belonging to 8 phyla. The average number of KEPs per strain was 5.25 in Ascomycota and 5.30 in Basidiomycota, but only 1.35 in the class Saccharomycetes (Ascomycota) and 1.00 in the class Tremellomycetes (Basidiomycota). The KEPs were classified into 838 types and 2560 stand-alone ones, which had no homologs. Nearly 200 types were distributed in more than one genus, and 14 types in more than one phylum. These types included yeast α-mating factors and fungal pheromones. Genes for 22% KEPs were accompanied by genes for DUF3328-domain-containing proteins, which are indispensable for cyclization of the core peptides. DUF3328-domain-containing protein genes were located at an average distance of 3.09 genes from KEP genes. Genes for almost all (with three exceptions) KEPs annotated as yeast α-mating factors or fungal pheromones were not accompanied by DUF3328-domain-containing protein genes.

CONCLUSION

KEPs are widely distributed in the Fungi kingdom, but their repeated sequences are highly diverse. From these results and some examples, a hypothesis was raised that KEPs initially evolved as unmodified linear peptides (e.g., mating factors), and then those that adopted a modified cyclic form emerged (e.g., toxins) to utilize their strong bioactivity against predators and competitive microorganisms.

Novel approach in whole genome mining and transcriptome analysis reveal conserved RiPPs in Trichoderma spp

BACKGROUND

Ribosomally synthesized and post-translationally modified peptides (RiPPs) are a highly diverse group of secondary metabolites (SM) of bacterial and fungal origin. While RiPPs have been intensively studied in bacteria, little is known about fungal RiPPs. In Fungi only six classes of RiPPs are described. Current strategies for genome mining are based on these six known classes. However, the genes involved in the biosynthesis of theses RiPPs are normally organized in biosynthetic gene clusters (BGC) in fungi.

RESULTS

Here we describe a comprehensive strategy to mine fungal genomes for RiPPs by combining and adapting existing tools (e.g. antiSMASH and RiPPMiner) followed by extensive manual curation based on conserved domain identification, (comparative) phylogenetic analysis, and RNASeq data. Deploying this strategy, we could successfully rediscover already known fungal RiPPs. Further, we analysed four fungal genomes from the Trichoderma genus. We were able to find novel potential RiPP BGCs in Trichoderma using our unconventional mining approach.

CONCLUSION

We demonstrate that the unusual mining approach using tools developed for bacteria can be used in fungi, when carefully curated. Our study is the first report of the potential of Trichoderma to produce RiPPs, the detected clusters encode novel uncharacterized RiPPs. The method described in our study will lead to further mining efforts in all subdivisions of the fungal kingdom.

The Multiple Facets of Plant-Fungal Interactions Revealed Through Plant and Fungal Secretomics

The plant secretome is usually considered in the frame of proteomics, aiming at characterizing extracellular proteins, their biological roles and the mechanisms accounting for their secretion in the extracellular space. In this review, we aim to highlight recent results pertaining to secretion through the conventional and unconventional protein secretion pathways notably those involving plant exosomes or extracellular vesicles. Furthermore, plants are well known to actively secrete a large array of different molecules from polymers (e.g. extracellular RNA and DNA) to small compounds (e.g. ATP, phytochemicals, secondary metabolites, phytohormones). All of these play pivotal roles in plant-fungi (or oomycetes) interactions, both for beneficial (mycorrhizal fungi) and deleterious outcomes (pathogens) for the plant. For instance, recent work reveals that such secretion of small molecules by roots is of paramount importance to sculpt the rhizospheric microbiota. Our aim in this review is to extend the definition of the plant and fungal secretomes to a broader sense to better understand the functioning of the plant/microorganisms holobiont. Fundamental perspectives will be brought to light along with the novel tools that should support establishing an environment-friendly and sustainable agriculture.

G-protein-coupled Receptors in Fungi

G-protein-coupled receptors (GPCRs) are the largest family of transmembrane receptors in fungi. These receptors have an important role in the transduction of extracellular signals into intracellular sites in response to diverse stimuli. They enable fungi to coordinate cell function and metabolism, thereby promoting their survival and propagation, and sense certain fundamentally conserved elements, such as nutrients, pheromones, and stress, for adaptation to their niches, environmental stresses, and host environment, causing disease and pathogen virulence. This chapter highlights the role of GPCRs in fungi in coordinating cell function and metabolism. Fungal cells sense the molecular interactions between extracellular signals. Their respective sensory systems are described here in detail.

Discovery of novel fungal RiPP biosynthetic pathways and their application for the development of peptide therapeutics

Bioactive peptide natural products are an important source of therapeutics. Prominent examples are the antibiotic penicillin and the immunosuppressant cyclosporine which are both produced by fungi and have revolutionized modern medicine. Peptide biosynthesis can occur either non-ribosomally via large enzymes referred to as non-ribosomal peptide synthetases (NRPS) or ribosomally. Ribosomal peptides are synthesized as part of a larger precursor peptide where they are posttranslationally modified and subsequently proteolytically released. Such peptide natural products are referred to as ribosomally synthesized and posttranslationally modified peptides (RiPPs). Their biosynthetic pathways have recently received a lot of attention, both from a basic and applied research point of view, due to the discoveries of several novel posttranslational modifications of the peptide backbone. Some of these modifications were so far only known from NRPSs and significantly increase the chemical space covered by this class of peptide natural products. Latter feature, in combination with the promiscuity of the modifying enzymes and the genetic encoding of the peptide sequence, makes RiPP biosynthetic pathways attractive for synthetic biology approaches to identify novel peptide therapeutics via screening of de novo generated peptide libraries and, thus, exploit bioactive peptide natural products beyond their direct use as therapeutics. This review focuses on the recent discovery and characterization of novel RiPP biosynthetic pathways in fungi and their possible application for the development of novel peptide therapeutics.