Sensing and transduction of nutritional and chemical signals in filamentous fungi: Impact on cell development and secondary metabolites biosynthesis

The nematode-trapping fungus Arthrobotrys oligospora detects prey pheromones via G protein-coupled receptors

The ability to sense prey-derived cues is essential for predatory lifestyles. Under low-nutrient conditions, Arthrobotrys oligospora and other nematode-trapping fungi develop dedicated structures for nematode capture when exposed to nematode-derived cues, including a conserved family of pheromones, the ascarosides. A. oligospora senses ascarosides via conserved MAPK and cAMP-PKA pathways; however, the upstream receptors remain unknown. Here, using genomic, transcriptomic and functional analyses, we identified two families of G protein-coupled receptors (GPCRs) involved in sensing distinct nematode-derived cues. GPCRs homologous to yeast glucose receptors are required for ascaroside sensing, whereas Pth11-like GPCRs contribute to ascaroside-independent nematode sensing. Both GPCR classes activate conserved cAMP-PKA signalling to trigger trap development. This work demonstrates that predatory fungi use multiple GPCRs to sense several distinct nematode-derived cues for prey recognition and to enable a switch to a predatory lifestyle. Identification of these receptors reveals the molecular mechanisms of cross-kingdom communication via conserved pheromones also sensed by plants and animals.

Glucose and HODEs regulate Aspergillus ochraceus quorum sensing through the GprC-AcyA pathway

Aspergillus ochraceus is the traditional ochratoxin A (OTA)-producing fungus with density-dependent behaviors, which is known as quorum sensing (QS) that is mediated by signaling molecules. Individual cells trend to adapt environmental changes in a "whole" flora through communications, allowing fungus to occupy an important ecological niche. Signals perception, transmission, and feedback are all rely on a signal network that constituted by membrane receptors and intracellular effectors. However, the interference of density information in signal transduction, which regulates most life activities of Aspergillus, have yet to be elucidated. Here we show that the G protein-coupled receptor (GPCR) to cAMP pathway is responsible for transmitting density information, and regulates the key point in life cycle of A. ochraceus. Firstly, the quorum sensing phenomenon of A. ochraceus is confirmed, and identified the density threshold is 103 spores/mL, which represents the low density that produces the most OTA in a series quorum density. Moreover, the GprC that classified as sugar sensor, and intracellular adenylate cyclase (AcyA)-cAMP-PKA pathway that in response to ligands glucose and HODEs are verified. Furthermore, GprC and AcyA regulate the primary metabolism as well as secondary metabolism, and further affects the growth of A. ochraceus during the entire life cycle. These studies highlight a crucial G protein signaling pathway for cell communication that is mediated by carbohydrate and oxylipins, and clarified a comprehensive effect of fungal development, which include the direct gene regulation and indirect substrate or energy supply. Our work revealed more signal molecules that mediated density information and connected effects on important adaptive behaviors of Aspergillus ochraceus, hoping to achieve comprehensive prevention and control of mycotoxin pollution from interrupting cell communication.

Penicillium chrysogenum: Beyond the penicillin

Almost one century after the Sir Alexander Fleming's fortuitous discovery of penicillin and the identification of the fungal producer as Penicillium notatum, later Penicillium chrysogenum (currently reidentified as Penicillium rubens), the molecular mechanisms behind the massive production of penicillin titers by industrial strains could be considered almost fully characterized. However, this filamentous fungus is not only circumscribed to penicillin, and instead, it seems to be full of surprises, thereby producing important metabolites and providing expanded biotechnological applications. This review, in addition to summarizing the classical role of P. chrysogenum as penicillin producer, highlights its ability to generate an array of additional bioactive secondary metabolites and enzymes, together with the use of this microorganism in relevant biotechnological processes, such as bioremediation, biocontrol, production of bioactive nanoparticles and compounds with pharmaceutical interest, revalorization of agricultural and food-derived wastes or the enhancement of food industrial processes and the agricultural production.

Molecular warfare between pathogenic Fusarium oxysporum R1 and host Crocus sativus L. unraveled by dual transcriptomics

KEY MESSAGE

Phenylpropanoid biosynthesis and plant-pathogen interaction pathways in saffron and cell wall degrading enzymes in Fusarium oxysporum R1 are key players involved in the interaction. Fusarium oxysporum causes corm rot in saffron (Crocus sativus L.), which is one of the most devastating fungal diseases impacting saffron yield globally. Though the corm rot agent and its symptoms are known widely, little is known about the defense mechanism of saffron in response to Fusarium oxysporum infection at molecular level. Therefore, the current study reports saffron-Fusarium oxysporum R1 (Fox R1) interaction at the molecular level using dual a transcriptomics approach. The results indicated the activation of various defense related pathways such as the mitogen activated protein kinase pathway (MAPK), plant-hormone signaling pathways, plant-pathogen interaction pathway, phenylpropanoid biosynthesis pathway and PR protein synthesis in the host during the interaction. The activation of pathways is involved in the hypersensitive response, production of various secondary metabolites, strengthening of the host cell wall, systemic acquired resistance etc. Concurrently, in the pathogen, 60 genes reported to be linked to pathogenicity and virulence has been identified during the invasion. The expression of genes encoding plant cell wall degrading enzymes, various transcription factors and effector proteins indicated the strong pathogenicity of Fusarium oxysporum R1. Based on the results obtained, the putative molecular mechanism of the saffron-Fox R1 interaction was identified. As saffron is a male sterile plant, and can only be improved by genetic manipulation, this work will serve as a foundation for identifying genes that can be used to create saffron varieties, resistant to Fusarium oxysporum infection.

Targeting of Specialized Metabolites Biosynthetic Enzymes to Membranes and Vesicles by Posttranslational Palmitoylation: A Mechanism of Non-Conventional Traffic and Secretion of Fungal Metabolites

In nature, the formation of specialized (secondary) metabolites is associated with the late stages of fungal development. Enzymes involved in the biosynthesis of secondary metabolites in fungi are located in distinct subcellular compartments including the cytosol, peroxisomes, endosomes, endoplasmic reticulum, different types of vesicles, the plasma membrane and the cell wall space. The enzymes traffic between these subcellular compartments and the secretion through the plasma membrane are still unclear in the biosynthetic processes of most of these metabolites. Recent reports indicate that some of these enzymes initially located in the cytosol are later modified by posttranslational acylation and these modifications may target them to membrane vesicle systems. Many posttranslational modifications play key roles in the enzymatic function of different proteins in the cell. These modifications are very important in the modulation of regulatory proteins, in targeting of proteins, intracellular traffic and metabolites secretion. Particularly interesting are the protein modifications by palmitoylation, prenylation and miristoylation. Palmitoylation is a thiol group-acylation (S-acylation) of proteins by palmitic acid (C16) that is attached to the SH group of a conserved cysteine in proteins. Palmitoylation serves to target acylated proteins to the cytosolic surface of cell membranes, e.g., to the smooth endoplasmic reticulum, whereas the so-called toxisomes are formed in trichothecene biosynthesis. Palmitoylation of the initial enzymes involved in the biosynthesis of melanin serves to target them to endosomes and later to the conidia, whereas other non-palmitoylated laccases are secreted directly by the conventional secretory pathway to the cell wall space where they perform the last step(s) of melanin biosynthesis. Six other enzymes involved in the biosynthesis of endocrosin, gliotoxin and fumitremorgin believed to be cytosolic are also targeted to vesicles, although it is unclear if they are palmitoylated. Bioinformatic analysis suggests that palmitoylation may be frequent in the modification and targeting of polyketide synthetases and non-ribosomal peptide synthetases. The endosomes may integrate other small vesicles with different cargo proteins, forming multivesicular bodies that finally fuse with the plasma membrane during secretion. Another important effect of palmitoylation is that it regulates calcium metabolism by posttranslational modification of the phosphatase calcineurin. Mutants defective in the Akr1 palmitoyl transferase in several fungi are affected in calcium transport and homeostasis, thus impacting on the biosynthesis of calcium-regulated specialized metabolites. The palmitoylation of secondary metabolites biosynthetic enzymes and their temporal distribution respond to the conidiation signaling mechanism. In summary, this posttranslational modification drives the spatial traffic of the biosynthetic enzymes between the subcellular organelles and the plasma membrane. This article reviews the molecular mechanism of palmitoylation and the known fungal palmitoyl transferases. This novel information opens new ways to improve the biosynthesis of the bioactive metabolites and to increase its secretion in fungi.

Every road leads to Rome: diverse biosynthetic regulation of plant cell wall-degrading enzymes in filamentous fungi Penicillium oxalicum and Trichoderma reesei

Cellulases and xylanases are plant cell wall-degrading enzymes (CWDEs) that are critical to sustainable bioproduction based on renewable lignocellulosic biomass to reduce carbon dioxide emission. Currently, these enzymes are mainly produced from filamentous fungi, especially Trichoderma reesei and Penicillium oxalicum. However, an in-depth comparison of these two producers has not been performed. Although both P. oxalicum and T. reesei harbor CWDE systems, they exhibit distinct features regulating the production of these enzymes, mainly through different transcriptional regulatory networks. This review presents the strikingly different modes of genome-wide regulation of cellulase and xylanase biosynthesis in P. oxalicum and T. reesei, including sugar transporters, signal transduction cascades, transcription factors, chromatin remodeling, and three-dimensional organization of chromosomes. In addition, different molecular breeding approaches employed, based on the understanding of the regulatory networks, are summarized. This review highlights the existence of very different regulatory modes leading to the efficient regulation of CWDE production in filamentous fungi, akin to the adage that "every road leads to Rome." An understanding of this divergence may help further improvements in fungal enzyme production through the metabolic engineering and synthetic biology of certain fungal species.

Endocrine Effect of Some Mycotoxins on Humans: A Clinical Review of the Ways to Mitigate the Action of Mycotoxins

Fungi such as Aspergillus spp. and Fusarium spp., which are commonly found in the environment, pose a serious global health problem. This study aims to present the results of epidemiological studies, including clinical cases, on the relationship between human exposure to some mycotoxins, especially zearalenone and aflatoxin, and the occurrence of reproductive disorders. In addition, examples of methods to reduce human exposure to mycotoxins are presented. In March 2023, various databases (PubMed, Google Scholar, EMBASE and Web of Science) were systematically searched using Google Chrome to identify studies evaluating the association between exposure to mycotoxins and the occurrence of complications related to impaired fertility or cancer incidence. The analysed data indicate that exposure to the evaluated mycotoxins is widespread and correlates strongly with precocious puberty, reduced fertility and increased cancer incidence in women and men worldwide. There is evidence to suggest that exposure to the Aspergillus mycotoxin aflatoxin (AF) during pregnancy can impair intrauterine foetal growth, promote neonatal jaundice and cause perinatal death and preterm birth. In contrast, exposure to the Fusarium mycotoxin zearalenone (ZEA) leads to precocious sexual development, infertility, the development of malformations and the development of breast cancer. Unfortunately, the development of methods (biological, chemical or physical) to completely eliminate exposure to mycotoxins has limited practical application. The threat to human health from mycotoxins is real and further research is needed to improve our knowledge and specific public health interventions.

Interaction of calcium responsive proteins and transcriptional factors with the PHO regulon in yeasts and fungi

Phosphate and calcium ions are nutrients that play key roles in growth, differentiation and the production of bioactive secondary metabolites in filamentous fungi. Phosphate concentration regulates the biosynthesis of hundreds of fungal metabolites. The central mechanisms of phosphate transport and regulation, mediated by the master Pho4 transcriptional factor are known, but many aspects of the control of gene expression need further research. High ATP concentration in the cells leads to inositol pyrophosphate molecules formation, such as IP3 and IP7, that act as phosphorylation status reporters. Calcium ions are intracellular messengers in eukaryotic organisms and calcium homeostasis follows elaborated patterns in response to different nutritional and environmental factors, including cross-talking with phosphate concentrations. A large part of the intracellular calcium is stored in vacuoles and other organelles forming complexes with polyphosphate. The free cytosolic calcium concentration is maintained by transport from the external medium or by release from the store organelles through calcium permeable transient receptor potential (TRP) ion channels. Calcium ions, particularly the free cytosolic calcium levels, control the biosynthesis of fungal metabolites by two mechanisms, 1) direct interaction of calcium-bound calmodulin with antibiotic synthesizing enzymes, and 2) by the calmodulin-calcineurin signaling cascade. Control of very different secondary metabolites, including pathogenicity determinants, are mediated by calcium through the Crz1 factor. Several interactions between calcium homeostasis and phosphate have been demonstrated in the last decade: 1) The inositol pyrophosphate IP3 triggers the release of calcium ions from internal stores into the cytosol, 2) Expression of the high affinity phosphate transporter Pho89, a Na+/phosphate symporter, is controlled by Crz1. Also, mutants defective in the calcium permeable TRPCa7-like of Saccharomyces cerevisiae shown impaired expression of Pho89. This information suggests that CrzA and Pho89 play key roles in the interaction of phosphate and calcium regulatory pathways, 3) Finally, acidocalcisomes organelles have been found in mycorrhiza and in some melanin producing fungi that show similar characteristics as protozoa calcisomes. In these organelles there is a close interaction between orthophosphate, pyrophosphate and polyphosphate and calcium ions that are absorbed in the polyanionic polyphosphate matrix. These advances open new perspectives for the control of fungal metabolism.

Looking outside the box: a comparative cross-kingdom view on the cell biology of the three major lineages of eukaryotic multicellular life

Many cell biological facts that can be found in dedicated scientific textbooks are based on findings originally made in humans and/or other mammals, including respective tissue culture systems. They are often presented as if they were universally valid, neglecting that many aspects differ-in part considerably-between the three major kingdoms of multicellular eukaryotic life, comprising animals, plants and fungi. Here, we provide a comparative cross-kingdom view on the basic cell biology across these lineages, highlighting in particular essential differences in cellular structures and processes between phyla. We focus on key dissimilarities in cellular organization, e.g. regarding cell size and shape, the composition of the extracellular matrix, the types of cell-cell junctions, the presence of specific membrane-bound organelles and the organization of the cytoskeleton. We further highlight essential disparities in important cellular processes such as signal transduction, intracellular transport, cell cycle regulation, apoptosis and cytokinesis. Our comprehensive cross-kingdom comparison emphasizes overlaps but also marked differences between the major lineages of the three kingdoms and, thus, adds to a more holistic view of multicellular eukaryotic cell biology.

Selection of rhizosphere communities of diverse rotation crops reveals unique core microbiome associated with reduced banana Fusarium wilt disease

Crop rotation can assemble distinct core microbiota as functionally specific barriers against the invasion of banana Fusarium oxysporum pathogens. However, the taxonomic identity of rotation-unique core taxa and their legacy effects are poorly understood under field conditions. Pepper and eggplant rotations were employed to reveal rotation crop- and banana-unique antagonistic core taxa by in situ tracking of the soil microbiome assembly patterns for 2 yr. The rotation crop-unique antagonistic taxa were isolated and functionally verified by culture-dependent techniques, high-throughput sequencing, and pot experiments. Pepper and eggplant rotations resulted in eight and one rotation-unique antagonistic core taxa out of 12 507 microbial taxa, respectively. These nine antagonistic taxa were retained the following year and significantly decreased banana wilt disease incidence via legacy effects, although the cultivated strains were exclusively of the genera Bacillus and Pseudomonas. The fermentation broth and volatiles of these two taxa showed strong antagonistic activity, and pot experiments demonstrated high suppression of wilt disease and significant promotion of banana growth. Our study provides a mechanistic understanding of the identification of rotation crop-unique antagonistic taxa and highlights the importance of targeted cultivation of beneficial microorganisms for optimizing crop rotation-based scenarios in support of banana agriculture sustainability.

Dual Transcriptomics Reveals Interspecific Interactions between the Mycoparasite Calcarisporium cordycipiticola and Its Host Cordyceps militaris

Calcarisporium cordycipiticola is a mycoparasite of the edible fungus Cordyceps militaris, and mycoparasitism causes devastating diseases of mushrooms. In this study, dual-transcriptomic analysis was performed to reveal interspecific interactions between the mycoparasite C. cordycipiticola and its host C. militaris. At 4 and 8 days postinfection (dpi), 2,959 and 2,077 differentially expressed genes (DEGs) of C. cordycipiticola and 914 and 1,548 DEGs of C. militaris were identified compared with the mycelial stage, respectively, indicating that C. cordycipiticola responded more quickly than C. militaris. Lectins of the pathogen may play a role in the recognition of fungal prey. Both Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses showed that primary metabolism was vigorous for the pathogen to colonize the host and that the pathogen's attack substantially altered C. militaris' primary metabolism. C. cordycipiticola upregulated some carbohydrate-active enzyme (CAZyme) genes, including CBM18, GH18, GH16, and GH76, for degrading the host cell wall and defending against host immunity. C. militaris produced excessive reactive oxygen species (ROS) to respond to the infection. The GO term "heme binding" was the only shared term enriched at both stages at 4 and 8 dpi, indicating that iron was important for both the pathogen and the host. The uptake of iron by pathogens through multiple pathways promoted colonization and removed high ROS levels produced by the host. The transcription levels of Cmhsp78, Cmhsp70, and Cmhyd1 in C. militaris responded quickly, and these genes have potential as candidates for the breeding of resistant varieties. This study provides clues for understanding the interactions between a mycoparasite and its mushroom host and will be helpful for the breeding of resistant varieties and disease prevention and control for this edible fungus. IMPORTANCE White mildew disease caused by Calcarisporium cordycipiticola is devastating for the fruiting body cultivation of Cordyceps militaris, a popular and highly valued edible fungus. Here, the pathogenic mechanisms of C. cordycipiticola, the responses of C. militaris to the infection, and the interaction of these two phylogenetically close species were revealed by time course dual-transcriptome profiles. In general, the host C. militaris responds more slowly than the pathogen C. cordycipiticola. For the first time, we found that iron was important for both the mycoparasite and the host. C. cordycipiticola takes up iron by multiple pathways to promote colonization and remove high ROS levels produced by the host. The rapidly responding genes Cmhsp70, Cmhsp78, and Cmhyd1 in C. militaris may have the potential as candidate genes for the breeding of resistant varieties. This study expands our understanding of the mycoparasitic interactions of two species from sister families and will be helpful for the breeding of and disease prevention and control in mushrooms.

Molecular Characterization of Phospholipase C in Infection Structure Differentiation Induced by Pear Fruit Surface Signals, Stress Responses, Secondary Metabolism, and Virulence of Alternaria alternata

Fungal pathogens use plant surface physiochemical signals to trigger specific developmental processes. To assess the role of phospholipase C (PLC) in mediating plant stimuli sensing of Alternaria alternata, the function of three PLC genes was characterized by constructing ΔAaPLC mutants. Here we showed that fruit wax-coated surfaces significantly induced appressorium formation in A. alternata and mutants. Germination of ΔAaPLC mutants did not differ from the wild type. Deletion of AaPLC1 led to the decrease of appressorium formation and infected hyphae, but the degree of reduction varies between the different types of waxes, with the strongest response to pear wax. Appressorium formation and infected hyphae of the ΔAaPLC1 mutant on dewaxed onion epidermis mounted with pear wax (θ4) were reduced by 14.5 and 65.7% after 8 h incubation, while ΔAaPLC2 and ΔAaPLC3 formed the same infection hyphae as wild type. In addition, AaPLC1 mutation caused pleiotropic effects on fungal biological function, including growth deficiency, changes in stress tolerance, weakening of pathogenicity to the host, as well as destruction of mycotoxin synthesis. Both AaPLC2 and AaPLC3 genes were found to have some effects on stress response and mycotoxin production. Taken together, AaPLC genes differentially regulate the growth, stress response, pathogenicity, and secondary metabolism of A. alternata.

Tools for adapting to a complex habitat: G-protein coupled receptors in Trichoderma

Sensing the environment and interpretation of the received signals are crucial competences of living organisms in order to properly adapt to their habitat, succeed in competition and to reproduce. G-protein coupled receptors (GPCRs) are members of a large family of sensors for extracellular signals and represent the starting point of complex signaling cascades regulating a plethora of intracellular physiological processes and output pathways in fungi. In Trichoderma spp. current research involves a wide range of topics from enzyme production, light response and secondary metabolism to sexual and asexual development as well as biocontrol, all of which require delicate balancing of resources in response to the environmental challenges or biotechnological needs at hand, which are crucially impacted by the surroundings of the fungi and their intercellular signaling cascades triggering a precisely tailored response. In this review we summarize recent findings on sensing by GPCRs in Trichoderma, including the function of pheromone receptors, glucose sensing by CSG1 and CSG2, regulation of secondary metabolism by GPR8 and impacts on mycoparasitism by GPR1. Additionally, we provide an overview on structural determinants, posttranslational modifications and interactions for regulation, activation and signal termination of GPCRs in order to inspire future in depth analyses of their function and to understand previous regulatory outcomes of natural and biotechnological processes modulated or enabled by GPCRs.

Recent advances in metabolic regulation and bioengineering of gibberellic acid biosynthesis in Fusarium fujikuroi

The plant growth hormone gibberellic acid (GA₃), as one of the representative secondary metabolites, is widely used in agriculture, horticulture and brewing industry. GA₃ is detected in both plants and several fungi with the ability to stimulate plant growth. Currently, the main mode of industrial production of GA₃ is depended on the microbial fermentation via long-period submerged fermentation using Fusarium fujikuroi as the only producing strain, qualified for its natural productivity. However, the demand of large-sale industrialization of GA₃ was still restricted by the low productivity. The biosynthetic route of GA₃ in F. fujikuroi is now well-defined. Furthermore, the multi-level regulation mechanisms involved in the whole network of GA₃ production have also been gradually unveiled by the past two decades based on the identification and characterization of several global regulators and their mutual functions. Combined with the quick development of genetic manipulation techniques, the rational modification of producing strain F. fujikuroi development become practical for higher productivity achievement. Herein, we review the latest advances in the molecular regulation of GA₃ biosynthesis in F. fujikuroi and conclude a comprehensive network involving nitrogen depression, global regulator, histone modification and G protein signaling pathway. Correspondingly, the bioengineering strategies covering conventional random mutation, genetic manipulating platform development, metabolic edition and fermentation optimization were also systematically proposed.

The G-protein coupled receptor GPRK contributes to fungal development and full virulence in Metarhizium robertsii

G-protein-coupled receptor K (GPRK), which is a class VI fungal G-protein-coupled receptor (GPCR), plays a critical role in plant immunity against pathogens by mediating the endocytic pathway, influencing metabolism in response to environmental signals, and regulating asexual reproduction and pathogenic development. However, the function of these proteins in entomopathogenic fungi has rarely been investigated. Accordingly, we characterized MrGPRK, a GPCR in the entomopathogenic fungus Metarhizium robertsii containing a C-terminal seven-transmembrane and a conserved regulator of G protein signaling domain, and found that it localized to endosomes. Mutant phenotype assays showed that a ΔMrGprk strain displayed increased defects in radial growth (~28%) and decreased conidial production (~80%) compared with a wild-type strain. Decreased conidiation rates coincided well with the repression of conidiation-related regulatory genes, including three key conidial transcription factors: brlA, abaA, and wetA. MrGprk deficiency impaired full virulence (both topical and injectable inoculations). Further analysis demonstrated that deleting fungal MrGprk decreased the rates of appressorium formation and suppressed the transcription of several genes contributing to appressorial turgor pressure, cuticle penetration, and pH regulation. Additionally, the ΔMrGprk strain showed higher cyclic (cAMP) levels, suggesting that this GPCR is critical for cAMP signal transduction. In summary, MrGPRK was found to contribute to vegetative growth, conidial production, and full virulence of M. robertsii. These findings are conducive to a better understanding of the roles of GPCRs in the development and pathogenicity of entomopathogenic fungi.

Fungal G-Protein-Coupled Receptors: A Promising Mediator of the Impact of Extracellular Signals on Biosynthesis of Ochratoxin A

G-protein-coupled receptors (GPCRs) are transmembrane receptors involved in transducing signals from the external environment inside the cell, which enables fungi to coordinate cell transport, metabolism, and growth to promote their survival, reproduction, and virulence. There are 14 classes of GPCRs in fungi involved in sensing various ligands. In this paper, the synthesis of mycotoxins that are GPCR-mediated is discussed with respect to ligands, environmental stimuli, and intra-/interspecific communication. Despite their apparent importance in fungal biology, very little is known about the role of ochratoxin A (OTA) biosynthesis by Aspergillus ochraceus and the ligands that are involved. Fortunately, increasing evidence shows that the GPCR that involves the AF/ST (sterigmatocystin) pathway in fungi belongs to the same genus. Therefore, we speculate that GPCRs play an important role in a variety of environmental signals and downstream pathways in OTA biosynthesis. The verification of this inference will result in a more controllable GPCR target for control of fungal contamination in the future.

Involvement of phospholipase PLA2 in production of cellulase and xylanase by Penicillium oxalicum

Phospholipases play vital roles in immune and inflammatory responses in mammals and plants; however, knowledge of phospholipase functions in fungi is limited. In this study, we investigated the effects of deleting predicted phospholipase genes on cellulase and xylanase production, and morphological phenotype, in Penicillium oxalicum. Individual deletion of nine of the ten predicted phospholipase genes resulted in alteration of cellulase and xylanase production, and the morphological phenotypes, to various degrees. The mutant ∆POX07277 lost 22.5 to 82.8% of cellulase (i.e., filter paper cellulase, carboxymethylcellulase, and p-nitrophenyl-β-cellobiosidase) and xylanase production, whereas p-nitrophenyl-β-glucopyranosidase production increased by 5.8-127.8 fold. POX07277 (P. oxalicum gene No. 07277) was predicted to encode phospholipase A2 and was found to negatively affect the sporulation of P. oxalicum. Comparative transcriptomic and quantitative reverse transcription-PCR analysis indicated that POX07277 dynamically affected the expression of cellulase and xylanase genes and the regulatory genes for fungal sporulation, under micro-crystalline cellulose induction. POX07277 was required for the expression of the known regulatory gene PoxCxrB (cellulolytic and xylanolytic regulator B in P. oxalicum), which is involved in cellulase and xylanase gene expression in P. oxalicum. Conversely, POX07277 expression was regulated by PoxCxrB. These findings will aid the understanding of phospholipase functions and provide novel insights into the mechanism of fungal cellulase and xylanase gene expression. KEY POINTS : • The roles of phospholipases were investigated in Penicillium oxalicum. • POX07277 (PLA₂) is required for the expression of cellulase and xylanase genes. • PoxCxrB dynamically regulated POX07277 expression.

Entomogenous fungi isolated from Cryptotympana atrata with antibacterial and antifungal activity

Although many entomogenous fungi have been discovered over the years, few studies on the crude extracts of fungi isolated from Cryptotympana atrata with antibacterial and antifungal activity were reported. In this study, total twenty entomogenous fungi were isolated for the first time. And among of them, two pure cultures were identified as Purpureocillium lilacinum and Aspergillus fumigatus with apparent morphology, microscopic identification and 18S rRNA gene sequence. The active strains were fermented to optimize in six different culture media at three different pH values. The antibacterial and antifungal activities of the metabolites were more potent and efficient in Fungal medium 3^# at a pH of 6.2 than in the other tested media or at the other tested pH values. Total seven human pathogens and one insect pathogen were used to evaluate the antibacterial and antifungal activity of crude extracts, among which 25% of the extracts exhibited antifungal activity against Verticillium lecanii, while 33.3% and 47.2% of the extracts exhibited antibacterial activity against the important human pathogens Staphylococcus aureus and Bacillus cereus, respectively. The range of the MICs was from 15.6 to 250 μg mL^-1, and 35% of the fungal metabolites exhibited antibacterial activity against Pseudomonas aeruginosa, Bacillus thuringiensis and Enterobacter aerogenes at 1000 μg mL^-1 except the previously described antibacterial activities. Furthermore, the phylogenetic relationships of the two identified fungi were also constructed. In brief, it is the first reporting about enthompathogenic fungi from Cryptotympana atrata and provides candidate strains with potential use as biological agents and against multidrug-resistant organisms.

Identification of a key G-protein coupled receptor in mediating appressorium formation and fungal virulence against insects

Fungal G-protein coupled receptors (GPCRs) play essential roles in sensing environmental cues including host signals. The study of GPCR in mediating fungus-insect interactions is still limited. Here we report the evolution of GPCR genes encoded in the entomopathogenic Metarhizium species and found the expansion of Pth11-like GPCRs in the generalist species with a wide host range. By deletion of ten candidate genes MrGpr1-MrGpr10 selected from the six obtained subfamilies in the generalist M. robertsii, we found that each of them played a varied level of roles in mediating appressorium formation. In particular, deletion of MrGpr8 resulted in the failure of appressorium formation on different substrates and the loss of virulence during topical infection of insects but not during injection assays when compared with the wild-type (WT) strain. Further analysis revealed that disruption of MrGpr8 substantially impaired the nucleus translocation of the mitogen-activated protein kinase (MAPK) Mero-Fus3 but not the MAPK Mero-Slt2 during appressorium formation. We also found that the defect of AMrGpr8 could not be rescued with the addition of cyclic AMP for appressorium formation. Relative to the WT, differential expression of the selected genes have also been detected in AMrGpr8. The results of this study may benefit the understanding of fungus-interactions mediated by GPCRs.

Omics Approaches Applied to Penicillium chrysogenum and Penicillin Production: Revealing the Secrets of Improved Productivity

Penicillin biosynthesis by Penicillium chrysogenum is one of the best-characterized biological processes from the genetic, molecular, biochemical, and subcellular points of view. Several omics studies have been carried out in this filamentous fungus during the last decade, which have contributed to gathering a deep knowledge about the molecular mechanisms underlying improved productivity in industrial strains. The information provided by these studies is extremely useful for enhancing the production of penicillin or other bioactive secondary metabolites by means of Biotechnology or Synthetic Biology.

Transcriptomic analysis reveals MAPK signaling pathways affect the autolysis in baker's yeast

Yeast autolysis refers to the process in which cells degrade and release intracellular contents under specific conditions by endogenous enzymes such as proteases, nucleases and lipid enzymes. Protein-rich baker's yeast is widely used to produce yeast extract in food industry, however, the molecular mechanism related to baker's yeast autolysis is still unclear. In this study, RNA-seq technology and biochemical analysis were performed to analyze the autolysis processes in baker's yeast. The differentially expressed genes (DEGs), 27 autolysis-related euKaryotic Ortholog Groups (KOG) and three types of autolysis-induced Gene Ontology (GO) were identified and analyzed in detail. A total of 143 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways under autolysis were also assigned. Interestingly, the DEGs were significantly enriched in the mitogen-activated protein kinase (MAPK) signaling pathways and metabolic pathways, and key genes MID2, MTL1, SLT2, PTP2, HKR1 and GPD1 may play important roles in autolysis. Further quantitative PCR was performed to verify the expression pattern in baker's yeast autolysis. Together, all these results indicated that MAPK pathways might play an essential role during autolysis process through inhibiting the metabolism and disrupting cell wall in baker's yeast. This result may provide important clues for the in-depth interpretation of the yeast autolysis mechanism.

Transport systems, intracellular traffic of intermediates and secretion of β-lactam antibiotics in fungi

Fungal secondary metabolites are synthesized by complex biosynthetic pathways catalized by enzymes located in different subcellular compartments, thus requiring traffic of precursors and intermediates between them. The β-lactam antibiotics penicillin and cephalosporin C serve as an excellent model to understand the molecular mechanisms that control the subcellular localization of secondary metabolites biosynthetic enzymes. Optimal functioning of the β-lactam biosynthetic enzymes relies on a sophisticated temporal and spatial organization of the enzymes, the intermediates and the final products. The first and second enzymes of the penicillin pathway, ACV synthetase and IPN synthase, in Penicillium chrysogenum and Aspergillus nidulans are cytosolic. In contrast, the last two enzymes of the penicillin pathway, phenylacetyl-CoA ligase and isopenicillin N acyltransferase, are located in peroxisomes working as a tandem at their optimal pH that coincides with the peroxisomes pH. Two MFS transporters, PenM and PaaT have been found to be involved in the import of the intermediates isopenicillin N and phenylacetic acid, respectively, into peroxisomes. Similar compartmentalization of intermediates occurs in Acremonium chrysogenum; two enzymes isopenicillin N-CoA ligase and isopenicillin N-CoA epimerase, that catalyse the conversion of isopenicillin N in penicillin N, are located in peroxisomes. Two genes encoding MFS transporters, cefP and cefM, are located in the early cephalosporin gene cluster. These transporters have been localized in peroxisomes by confocal fluorescence microscopy. A third gene of A. chrysogenum, cefT, encodes an MFS protein, located in the cell membrane involved in the secretion of cephalosporin C, although cefT-disrupted mutants are still able to export cephalosporin by redundant transporters. The secretion of penicillin from peroxisomes to the extracellular medium is still unclear. Attempts have been made to identify a gene encoding the penicillin secretion protein among the 48 ABC-transporters of P. chrysogenum. The highly efficient secretion system that exports penicillin against a concentration gradient may involve active penicillin extrusion systems mediated by vesicles that fuse to the cell membrane. However, there is no correlation of pexophagy with penicillin or cephalosporin formation since inactivation of pexophagy leads to increased penicillin or cephalosporin biosynthesis due to preservation of peroxisomes. The penicillin biosynthesis finding shows that in order to increase biosynthesis of novel secondary metabolites it is essential to adequately target enzymes to organelles.

Weighted Gene Co-expression Network Analysis Identifies Critical Genes for the Production of Cellulase and Xylanase in Penicillium oxalicum

Genes involved in cellular processes undergo environment-dependent co-regulation, but the co-expression patterns of fungal cellulase and xylanase-encoding genes remain unclear. Here, we identified two novel carbon sources, methylcellulose and 2-hydroxyethyl cellulose, which efficiently induced the secretion of cellulases and xylanases in Penicillium oxalicum. Comparative transcriptomic analyses identified carbon source-specific transcriptional patterns, mainly including major cellulase and xylanase-encoding genes, genes involved in glycolysis/gluconeogenesis and the tricarboxylic acid cycle, and genes encoding transcription factors, transporters and G protein-coupled receptors. Moreover, the weighted correlation network analysis of time-course transcriptomes, generated 17 highly connected modules. Module MEivory, comprising 120 members, included major cellulase and xylanase-encoding genes, genes encoding the key regulators PoxClrB and PoxXlnR, and a cellodextrin transporter POX06051/CdtC, which were tightly correlated with the filter-paper cellulase, carboxymethylcellulase and xylanase activities in P. oxalicum. An expression kinetic analysis indicated that members in MEivory were activated integrally by carbon sources, but their expressional levels were carbon source- and/or induction duration-dependent. Three uncharacterized regulatory genes in MEivory were identified, which regulate the production of cellulases and xylanases in P. oxalicum. These findings provide insights into the mechanisms associated with the synthesis and secretion of fungal cellulases and xylanases, and a guide for P. oxalicum application in biotechnology.

Aflatoxin Biosynthesis and Genetic Regulation: A Review

The study of fungal species evolved radically with the development of molecular techniques and produced new evidence to understand specific fungal mechanisms such as the production of toxic secondary metabolites. Taking advantage of these technologies to improve food safety, the molecular study of toxinogenic species can help elucidate the mechanisms underlying toxin production and enable the development of new effective strategies to control fungal toxicity. Numerous studies have been made on genes involved in aflatoxin B1 (AFB1) production, one of the most hazardous carcinogenic toxins for humans and animals. The current review presents the roles of these different genes and their possible impact on AFB1 production. We focus on the toxinogenic strains Aspergillus flavus and A. parasiticus, primary contaminants and major producers of AFB1 in crops. However, genetic reports on A. nidulans are also included because of the capacity of this fungus to produce sterigmatocystin, the penultimate stable metabolite during AFB1 production. The aim of this review is to provide a general overview of the AFB1 enzymatic biosynthesis pathway and its link with the genes belonging to the AFB1 cluster. It also aims to illustrate the role of global environmental factors on aflatoxin production and the recent data that demonstrate an interconnection between genes regulated by these environmental signals and aflatoxin biosynthetic pathway.