Molecular basis and regulation of pathogenicity and patulin biosynthesis in Penicillium expansum

Effect of antifungal proteins (AFPs) on the viability of heat-resistant fungi (HRFs) and the preservation of fruit juices

The control of heat-resistant fungi (HRFs), which cause spoilage of heat-treated fruit products, is considered a challenge for the fruit juice and beverage industry and requires new strategies for the development of antifungal compounds. In this study, four antifungal proteins (AFPs) from Penicillium digitatum (PdAfpB) and Penicillium expansum (PeAfpA, PeAfpB and PeAfpC), were evaluated against conidia from a representative collection of HRFs. A total of 19 strains from 16 different species belonging to the genera Aspergillus, Hamigera, Paecilomyces, Rasamsonia, Sarocladium, Talaromyces and Thermoascus were included in the study. PeAfpA and PdAfpB exhibited potent antifungal activity in synthetic media, completely inhibiting the growth of most of the fungi evaluated in the range of 0.5-32 μg/mL. The efficacy of the four AFPs was also tested in fruit juices against ascospores of five HRFs relevant to the food industry, including P. fulvus, P. niveus, P. variotii, A. fischeri and T. flavus. PdAfpB was the most effective protein in fruit juices, since it completely inhibited the growth of the five species tested in at least one of the fruit juices evaluated. This is the first study to demonstrate the activity of AFPs against fungal ascospores. Finally, a challenge test study showed that PdAfpB, at a concentration of 32 μg/mL, protected apple fruit juice artificially inoculated with ascospores of P. variotii for 17 days, highlighting the potential of the protein as a preservative in the fruit juice industry.

Set1/COMPASS regulates growth, pathogenicity, and patulin biosynthesis of Penicillium expansum via H3K4 methylation and the interaction with PeVelB

INTRODUCTION

Penicillium expansum is a harmful plant fungal pathogen that causes blue mold disease and produces mycotoxin patulin, leading to huge economic losses and food safety hazard. Set1 associated complex Set1/COMPASS deposits the methylation at lysine 4 of histone H3, which is associated with gene expression in diverse biological processes of fungi. However, the function and underlying mechanisms of Set1/COMPASS are poorly defined in P. expansum.

OBJECTIVES

The study aimed to identify Set1/COMPASS and investigate its regulation mechanisms on growth, pathogenicity, and patulin biosynthesis of P. expansum.

METHODS

Analyses of phylogenetic relationship, conserved structural domain, and gene deletion were used to identify components of Set1/COMPASS. Phenotype analysis and stress tolerance test of gene deletion mutants were conducted to analyze the function of these components. Yeast two-hybrid, Co-Immunoprecipitation (Co-IP), and point mutation were performed to verify the protein interaction. Western blot was conducted for detection of H3K4 methylation levels.

RESULTS

P. expansum owns six components of Set1/COMPASS besides PeSet1. Absence of each component resulted in reduction of H3K4 methylation levels and impaired growth, pathogenicity, and patulin biosynthesis, as well as altered stress responses of P. expansum. One component PeBre2p was found to interact with the conserved global regulator PeVelB (VelvetLike protein B) at Asp294 of PeBre2p. This interaction affected fungal growth and utilization of fructose, lactose, glycine, and proline in P. expansum.

CONCLUSION

This study revealed the important roles of Set1/COMPASS in P. expansum and clarified for the first time the combined regulation of PeBre2p and PeVelB in fungal growth and nutrition utilization. These results will provide potential targets for the control of blue mold disease.

Effects of temperature, pH, and relative humidity on the growth of Penicillium paneum OM1 isolated from pears and its patulin production

Patulin is a mycotoxin produced by several species of Penicillium sp., Aspergillus sp., and Byssochlamys sp. on apples and pears. Most studies have been focused on Penicillium expansum, a common postharvest pathogen, but little is known about the characteristics of Penicillium paneum. In the present study, we evaluated the effects of temperature, pH, and relative humidity (RH) on the growth of P. paneum OM1, which was isolated from pears, and its patulin production. The fungal strain showed the highest growth rate at 25 °C and pH 4.5 on pear puree agar medium (PPAM) under 97 % RH, while it produced the highest amount of patulin at 20 °C and pH 4.5 on PPAM under 97 % RH. Moreover, RT-qPCR analysis of relative expression levels of 5 patulin biosynthetic genes (patA, patE, patK, patL, and patN) in P. paneum OM1 exhibited that the expression of the 4 patulin biosynthetic genes except patL was up-regulated in YES medium (patulin conducive), while it was not in PDB medium (patulin non-conducive). Our data demonstrated that the 3 major environmental parameters had significant impact on the growth of P. paneum OM1 and its patulin production. These results could be exploited to prevent patulin contamination by P. paneum OM1 during pear storage.

Determination and analysis of patulin in apples, hawthorns, and their products by high-performance liquid chromatography

This study aimed to establish a high-performance liquid chromatography (HPLC) method to investigate the residues of patulin in apples, hawthorns, and their products. A total of 400 samples were collected from online shopping plats and supermarkets in China, including apples (n = 50), hawthorns (n = 50), and their products (apple juice, apple puree, apple jam, hawthorn juice, hawthorn chips, and hawthorn rolls, n = 300). In this experiment, this method had good linearity and a recovery of 82.3-94.4% for patulin. The limit of detection (LOD) was 0.2 µg/kg for liquid samples, while it was 0.3 µg/kg for solid and semi-fluid samples. The frequencies of patulin were 79.8% in 400 samples, and the patulin concentration is from 0.6 to 126.0 µg/kg. Two samples (0.5%) for patulin exceeded the regulatory limit (50 µg/kg) in 400 samples. The frequencies of patulin in kinds of samples were 32.0-98.0% (p < 0.05), and the percentage of samples exceeding the limit was not more than 2.0%. The frequencies of patulin in domestic samples were 83.0%, while they were 57.7% in imported samples. Two domestic samples (0.6%) contained patulin above the regulatory limit, while none of the imported samples exceeded the limit. Among the online and offline samples, the frequencies of patulin were 76.4 and 82.1%. Two online samples (1.0%) for patulin exceeded the regulatory limit, whereas none of the offline samples exceeded the limit. These results showed it is important to monitor regularly the content of patulin in apples, hawthorns, and their products to ensure consumer food safety.

Wide transcriptional outlook to uncover Penicillium expansum genes underlying fungal incompatible infection

Pathogenesis of P. expansum involved different processes and one of them is the recognition between pathogen-host, which in the case of P. expansum is preferably pome fruit. In this work, the possible mechanisms connected to host recognition are addressed through the generation of a subtractive library carried out during the incompatible P. expansum-orange interaction in the initial stages of infection. The generated library was analyzed by massive sequencing and bioinformatic analysis. Of the identified genes, a total of 24 were selected for subsequent expression analysis by RT-qPCR in two incompatible interaction situations. The characterization of the overexpressed genes revealed the presence of CWDEs, ATPases, aldolases, detoxifying enzymes and virulent determinants that could act as effectors related to fungal virulence independently of the host. However, several identified genes, which could not be associated with the virulence of P. expansum under compatible conditions, were related to enzymes to obtain the nutrients necessary for the growth and development of the pathogen under stress conditions through basal metabolism that contributes to expand the range of adaptation of the pathogen to the environment and different hosts.

Patulin Biodegradation Mechanism Study in Pichia guilliermondii S15-8 Based on PgSDR-A5D9S1

Patulin contamination has become a bottleneck problem in the safe production of fruit products, although biodegradation technology shows potential application value in patulin control. In the present study, the patulin biodegradation mechanism in a probiotic yeast, Pichia guilliermondii S15-8, was investigated. Firstly, the short-chain dehydrogenase PgSDR encoded by gene A5D9S1 was identified as a patulin degradation enzyme, through RNA sequencing and verification by qRT-PCR. Subsequently, the exogenous expression system of the degradation protein PgSDR-A5D9S1 in E. coli was successfully constructed and demonstrated a more significant patulin tolerance and degradation ability. Furthermore, the structure of PgSDR-A5D9S1 and its active binding sites with patulin were predicted via molecular docking analysis. In addition, the heat-excited protein HSF1 was predicted as the transcription factor regulating the patulin degradation protein PgSDR-A5D9S1, which may provide clues for the further analysis of the molecular regulation mechanism of patulin degradation. This study provides a theoretical basis and technical support for the industrial application of biodegradable functional strains.

Biodegradation of patulin in fresh pear juice by an aldo-keto reductase from Meyerozyma guilliermondii

Bio-enzymes have shown broad application prospects in controlling mycotoxins due to their strong specificity, fast reaction rate and mild reaction conditions. However, the number of enzymes isolated, purified and characterized to degrade patulin (PAT) is limited. We expressed an aldo-keto reductase (MgAKR) from Meyerozyma guilliermondii in Escherichia coli. The results demonstrated that the purified MgAKR could convert PAT into ascladiol in vitro with NADPH serving as a coenzyme. Adding 300 μg/mL MgAKR resulted in an 88 % reduction of PAT in fresh pear juice without affecting its quality in the biodegradation process. The site-directed mutagenesis suggested that the interaction between MgAKR and PAT occurred through the active sites of Lys242 and Leu240. This study serves as a valuable theoretical reference for the development of enzymes aimed at detoxifying PAT in fruit and their derivatives.

Immunosuppressive effects of the mycotoxin patulin in macrophages

Patulin (PAT) is a fungi-derived secondary metabolite produced by numerous fungal species, especially within Aspergillus, Byssochlamys, and Penicillium genera, amongst which P. expansum is the foremost producer. Similar to other fungi-derived metabolites, PAT has been shown to have diverse biological features. Initially, PAT was used as an effective antimicrobial agent against Gram-negative and Gram-positive bacteria. Then, PAT has been shown to possess immunosuppressive properties encompassing humoral and cellular immune response, immune cell function and activation, phagocytosis, nitric oxide and reactive oxygen species production, cytokine release, and nuclear factor-κB and mitogen-activated protein kinases activation. Macrophages are a heterogeneous population of immune cells widely distributed throughout organs and connective tissue. The chief function of macrophages is to engulf and destroy foreign bodies through phagocytosis; this ability was fundamental to his discovery. However, macrophages play other well-established roles in immunity. Thus, considering the central role of macrophages in the immune response, we review the immunosuppressive effects of PAT in macrophages and provide the possible mechanisms of action.

Infection of postharvest pear by Penicillium expansum is facilitated by the glycoside hydrolase (eglB) gene

The primary reason for postharvest loss is blue mold disease which is mainly caused by Penicillium expansum. Strategies for disease control greatly depend on the understanding of mechanisms of pathogen-fruit interaction. A member of the glycoside hydrolase family, β-glucosidase 1b (eglB), in P. expansum was significantly upregulated during postharvest pear infection. Glycoside hydrolases are a large group of enzymes that can degrade plant cell wall polymers. High homology was found between the glycoside hydrolase superfamily in P. expansum. Functional characterization and analysis of eglB were performed via gene knockout and complementation analysis. Although eglB deletion had no notable effect on P. expansum colony shape or microscopic morphology, it did reduce the production of fungal hyphae, thereby reducing P. expansum's sporulation and patulin (PAT) accumulation. Moreover, the deletion of eglB (ΔeglB) reduced P. expansum pathogenicity in pears. The growth, conidia production, PAT accumulation, and pathogenicity abilities of ΔeglB were restored to that of wild-type P. expansum by complementation of eglB (ΔeglB-C). These findings indicate that eglB contributes to P. expansum's development and pathogenicity. This research is a contribution to the identification of key effectors of fungal pathogenicity for use as targets in fruit safety strategies.

Exploring the Biocontrol Capability of Non-Mycotoxigenic Strains of Penicillium expansum

Penicillium expansum is one the major postharvest pathogens of pome fruit during postharvest handling and storage. This fungus also produces patulin, which is a highly toxic mycotoxin that can contaminate infected fruits and their derived products and whose levels are regulated in many countries. In this study, we investigated the biocontrol potential of non-mycotoxigenic strains of Penicillium expansum against a mycotoxigenic strain. We analyzed the competitive behavior of two knockout mutants that were unable to produce patulin. The first mutant (∆patK) involved the deletion of the patK gene, which is the initial gene in patulin biosynthesis. The second mutant (∆veA) involved the deletion of veA, which is a global regulator of primary and secondary metabolism. At the phenotypic level, the ∆patK mutant exhibited similar phenotypic characteristics to the wild-type strain. In contrast, the ∆veA mutant displayed altered growth characteristics compared with the wild type, including reduced conidiation and abnormal conidiophores. Neither mutant produced patulin under the tested conditions. Under various stress conditions, the ∆veA mutants exhibited reduced growth and conidiation when exposed to stressors, including cell membrane stress, oxidative stress, osmotic stress, and different pH values. However, no significant changes were observed in the ∆patK mutant. In competitive growth experiments, the presence of non-mycotoxigenic strains reduced the population of the wild-type strain during in vitro growth. Furthermore, the addition of either of the non-mycotoxigenic strains resulted in a significant decrease in patulin levels. Overall, our results suggest the potential use of non-mycotoxigenic mutants, particularly ∆patK mutants, as biocontrol agents to reduce patulin contamination in food and feed.

A receptor-like kinase SlFERL mediates immune responses of tomato to Botrytis cinerea by recognizing BcPG1 and fine-tuning MAPK signaling

FERONIA (FER) is a receptor-like kinase showing versatile functions during plant growth, development, and responses to environmental stimuli. However, its functions during the interaction between fruit and necrotrophic fungal pathogens are still unclear. Combining reverse genetic approaches, physiological assays, co-immunoprecipitation, protein phosphorylation identification, and site-directed mutagenesis, we reported a tomato FER homolog SlFERL (Solanum lycopersicum FERONIA Like) involved in the immune responses to Botrytis cinerea invasion. The results indicated that SlFERL extracellular domain recognized and interacted with the secreted virulence protein BcPG1 from B. cinerea, further revealed that SlFERL triggered downstream signaling by phosphorylating SlMAP3K18 at Thr45, Ser49, Ser76, and Ser135. Moreover, we verified that SlMAP2K2 and SlMAP2K4 synergistically contributed to immune response of tomato to B. cinerea, in which SlFERL-SlMAP3K18 module substantially modulated protein level and/or kinase activity of SlMAP2K2/SlMAP2K4. These findings reveal a new pattern-triggered immune pathway, indicating that SlFERL participates in the immune responses to B. cinerea invasion via recognizing BcPG1 and fine-tuning MAPK signaling.

Visualization detection of mycotoxin patulin in fruit juices by a small-molecule fluorescent probe

The mycotoxin patulin is a common contaminant in rotten fruits, posing severe food safety risks and threats to human health. Developing a convenient, sensitive and reliable method for patulin detection is of utmost importance but remains challenging. In this study, we have successfully designed and synthesized a small-molecule fluorescent probe, FITC-Lys, which demonstrates good sensitivity in detecting patulin. Upon contact with patulin, the terminal Lys group of the FITC-Lys probe reacts with patulin, resulting in the formation of the fluorescein dimer that subsequently quenches fluorescence. This variation of fluorescence enables the visualization and sensitive detection of patulin. The probe exhibits good sensitivity with a low LOD of 8 ng mL-1 for the fluorescence spectrum method and a LOD of 12 ng mL-1 for the fluorescence imaging method. Moreover, we have validated the probe's capability for patulin detection in apple and pear juices, achieving good recoveries ranging from 98.60% to 103.80%. Notably, the probe FITC-Lys is the first small-molecule fluorescent probe that has proven successful in visualizing patulin in juices derived from decayed apples and pears. Consequently, this probe holds great potential as a practical tool for monitoring patulin in foodstuffs, thereby contributing to enhanced food safety standards.

Fungal and mycotoxin contaminants in cannabis and hemp flowers: implications for consumer health and directions for further research

Medicinal and recreational uses of Cannabis sativa, commonly known as cannabis or hemp, has increased following its legalization in certain regions of the world. Cannabis and hemp plants interact with a community of microbes (i.e., the phytobiome), which can influence various aspects of the host plant. The fungal composition of the C. sativa phytobiome (i.e., mycobiome) currently consists of over 100 species of fungi, which includes phytopathogens, epiphytes, and endophytes, This mycobiome has often been understudied in research aimed at evaluating the safety of cannabis products for humans. Medical research has historically focused instead on substance use and medicinal uses of the plant. Because several components of the mycobiome are reported to produce toxic secondary metabolites (i.e., mycotoxins) that can potentially affect the health of humans and animals and initiate opportunistic infections in immunocompromised patients, there is a need to determine the potential health risks that these contaminants could pose for consumers. This review discusses the mycobiome of cannabis and hemp flowers with a focus on plant-infecting and toxigenic fungi that are most commonly found and are of potential concern (e.g., Aspergillus, Penicillium, Fusarium, and Mucor spp.). We review current regulations for molds and mycotoxins worldwide and review assessment methods including culture-based assays, liquid chromatography, immuno-based technologies, and emerging technologies for these contaminants. We also discuss approaches to reduce fungal contaminants on cannabis and hemp and identify future research needs for contaminant detection, data dissemination, and management approaches. These approaches are designed to yield safer products for all consumers.

PeAP1-mediated oxidative stress response plays an important role in the growth and pathogenicity of Penicillium expansum

Penicillium expansum is the causal agent of post-harvest blue mold in various fruits and serves as a model for understanding fungal pathogenicity and mycotoxin production. The relevance of oxidative stress response in the growth and virulence of P. expansum has been largely unexplored. Here, we identify the transcriptional factor PeAP1 as a regulator of oxidative stress response in P. expansum. Gene expression and protein abundance of PeAP1, as well as its nuclear localization, are specifically induced by H2O2. Deletion of PeAP1 results in increased sensitivity to H2O2, and PeAP1 mutants exhibit a variety of defects in hyphal growth and virulence. PeAP1 prevents the accumulation of both intracellular H2O2 during vegetative growth and host-derived H2O2 during biotrophic growth. Application of an antioxidant glutathione and a NADPH oxidase inhibitor, diphenylene iodonium, to the PeAP1 mutant partially restored fungal growth and virulence. RNA sequencing analysis revealed 144 H2O2-induced PeAP1 target genes, including four antioxidant-related genes, PeGST1, PePrx1, PePrx2, and PeTRX2, that were also demonstrated to be involved in oxidative stress response and/or virulence. Collectively, our results demonstrate the global regulatory role of PeAP1 in response to oxidative stress and provide insights into the critical role of the PeAP1-mediated oxidative stress response to regulate growth and virulence of P. expansum. IMPORTANCE Reactive oxygen species are the core of host plant defense and also play a vital role in the successful invasion of host plants by pathogenic fungi. Despite its importance, the relevance of oxidative stress response in fungal growth and virulence is poorly understood in P. expansum. In this study, we reveal that the transcription factor PeAP1 acts as a central regulator of oxidative stress response in P. expansum and that there is a major link between PeAP1-mediated oxidative stress response and fungal growth and virulence. To explore the underlying mechanisms, we performed comparative transcriptomic studies and identified a number of H2O2-induced PeAP1 target genes, including four novel ones, PePrx1, PePrx2, PeGST1, and PeTRX2, whose functions were linked to PeAP1 and pathogenicity. These findings provide novel insights into the regulation mechanism of PeAP1 on growth and virulence, which might offer promising targets for control of blue mold and patulin contamination.

Therapeutic Potential of Marine Probiotics: A Survey on the Anticancer and Antibacterial Effects of Pseudoalteromonas spp

Due to the increasing limitations and negative impacts of the current options for preventing and managing diseases, including chemotherapeutic drugs and radiation, alternative therapies are needed, especially ones utilizing and maximizing natural products (NPs). NPs abound with diverse bioactive primary and secondary metabolites and compounds with therapeutic properties. Marine probiotics are beneficial microorganisms that inhabit marine environments and can benefit their hosts by improving health, growth, and disease resistance. Several studies have shown they possess potential bioactive and therapeutic actions against diverse disease conditions, thus opening the way for possible exploitation of their benefits through their application. Pseudoalteromonas spp. are a widely distributed heterotrophic, flagellated, non-spore-forming, rod-shaped, and gram-negative marine probiotic bacteria species with reported therapeutic capabilities, including anti-cancer and -bacterial effects. This review discusses the basic concepts of marine probiotics and their therapeutic effects. Additionally, a survey of the anticancer and antibacterial effects of Pseudoalteromonas spp. is presented. Finally, marine probiotic production, advances, prospects, and future perspectives is presented.

Ena Proteins Respond to PacC-Mediated pH Signaling Pathway and Play a Crucial Role in Patulin Biosynthesis

Penicillium expansum is a main producer of patulin that causes severe postharvest decay and food safety issues in the fruit industry. Development, pathogenicity, and patulin production of P. expansum are strongly influenced by the PacC-pH signaling pathway. Global transcription factor PacC regulates various fungal biological processes through a complicated molecular network. In the present study, three Ena family genes (PeEnas), PeEnaA, PeEnaB, and PeEnaC, as important downstream targets of PePacC, were identified in P. expansum. Deletion of PeEnaA, PeEnaB, and PeEnaC showed little effect on mycelial growth under alkaline or high salinity conditions, but double and triple deletion of these genes impaired the virulence of P. expansum on apple fruit. Notably, patulin biosynthesis of P. expansum was distinctly inhibited in the deletion mutants of PeEnas. PeEnas regulated expressions of the patulin gene cluster, AP1, CreA, Sge1, and Hog1 at the transcriptional level and played roles in maintaining membrane potential. Overexpression of PeEnaC in ΔPePacC restored the patulin production defect of ΔPePacC. Our results indicated that, as downstream targets of PePacC, the PeEna family proteins play a crucial role in patulin biosynthesis in P. expansum.

Current Insights in Fungal Importance-A Comprehensive Review

Besides plants and animals, the Fungi kingdom describes several species characterized by various forms and applications. They can be found in all habitats and play an essential role in the excellent functioning of the ecosystem, for example, as decomposers of plant material for the cycling of carbon and nutrients or as symbionts of plants. Furthermore, fungi have been used in many sectors for centuries, from producing food, beverages, and medications. Recently, they have gained significant recognition for protecting the environment, agriculture, and several industrial applications. The current article intends to review the beneficial roles of fungi used for a vast range of applications, such as the production of several enzymes and pigments, applications regarding food and pharmaceutical industries, the environment, and research domains, as well as the negative impacts of fungi (secondary metabolites production, etiological agents of diseases in plants, animals, and humans, as well as deteriogenic agents).

Immobilized short-chain dehydrogenase/reductase on Fe3O4 particles acts as a magnetically recoverable biocatalyst component in patulin bio-detoxification system

Patulin is one of the most important mycotoxins that contaminates fruit-derived products and causes acute or chronic toxicity in humans. In the present study, a novel patulin-degrading enzyme preparation was developed by taking a short-chain dehydrogenase/reductase and covalently linking it to dopamine/polyethyleneimine co-deposited magnetic Fe₃O₄ particles. Optimum immobilization provided 63% immobilization efficiency and 62% activity recovery. Moreover, the immobilization protocol substantially improved thermal and storage stabilities, proteolysis resistance, and reusability. Using reduced nicotinamide adenine dinucleotide phosphate as a cofactor, the immobilized enzyme exhibited a detoxification rate of 100% in phosphate-buffered saline and a detoxification rate of more than 80% in apple juice. The immobilized enzyme did not cause adverse effects on juice quality and could be magnetically separated quickly after detoxification to ensure convenient recycling. Moreover, it did not exhibit cytotoxicity against a human gastric mucosal epithelial cell line at a concentration of 100 mg/L. Consequently, the immobilized enzyme as a biocatalyst had the characteristics of high efficiency, stability, safety, and easy separation, establishing the first step in building a bio-detoxification system to control patulin contamination in juice and beverage products.

Genomes of four Streptomyces strains reveal insights into putative new species and pathogenicity of scab-causing organisms

Genomes of four Streptomyces isolates, two putative new species (Streptomyces sp. JH14 and Streptomyces sp. JH34) and two non thaxtomin-producing pathogens (Streptomyces sp. JH002 and Streptomyces sp. JH010) isolated from potato fields in Colombia were selected to investigate their taxonomic classification, their pathogenicity, and the production of unique secondary metabolites of Streptomycetes inhabiting potato crops in this region. The average nucleotide identity (ANI) value calculated between Streptomyces sp. JH34 and its closest relatives (92.23%) classified this isolate as a new species. However, Streptomyces sp. JH14 could not be classified as a new species due to the lack of genomic data of closely related strains. Phylogenetic analysis based on 231 single-copy core genes, confirmed that the two pathogenic isolates (Streptomyces sp. JH010 and JH002) belong to Streptomyces pratensis and Streptomyces xiamenensis, respectively, are distant from the most well-known pathogenic species, and belong to two different lineages. We did not find orthogroups of protein-coding genes characteristic of scab-causing Streptomycetes shared by all known pathogenic species. Most genes involved in biosynthesis of known virulence factors are not present in the scab-causing isolates (Streptomyces sp. JH002 and Streptomyces sp. JH010). However, Tat-system substrates likely involved in pathogenicity in Streptomyces sp. JH002 and Streptomyces sp. JH010 were identified. Lastly, the presence of a putative mono-ADP-ribosyl transferase, homologous to the virulence factor scabin, was confirmed in Streptomyces sp. JH002. The described pathogenic isolates likely produce virulence factors uncommon in Streptomyces species, including a histidine phosphatase and a metalloprotease potentially produced by Streptomyces sp. JH002, and a pectinesterase, potentially produced by Streptomyces sp. JH010. Biosynthetic gene clusters (BGCs) showed the presence of clusters associated with the synthesis of medicinal compounds and BGCs potentially linked to pathogenicity in Streptomyces sp. JH010 and JH002. Interestingly, BGCs that have not been previously reported were also found. Our findings suggest that the four isolates produce novel secondary metabolites and metabolites with medicinal properties.

Histone H3K4 Methyltransferase PeSet1 Regulates Colonization, Patulin Biosynthesis, and Stress Responses of Penicillium expansum

Fruit blue mold disease and patulin contamination caused by Penicillium expansum lead to huge economic losses and food safety concerns worldwide. Many genes have been proven to be involved in the regulation of pathogenic and toxigenic processes of P. expansum. Histone H3 lysine 4 (H3K4) methylation is well recognized for its association with chromatin regulation and gene transcription. However, it is not clear whether H3K4 methylation is related to infection and patulin biosynthesis in Penicillium. Here, we characterized PeSet1, which is responsible for H3K4me1/me2/me3 in P. expansum. The deletion of PeSet1 caused severe defects in hyphal growth, conidiation, colonization, patulin biosynthesis, and stress responses. Moreover, we demonstrated that PeSet1 is involved in the regulation of patulin biosynthesis by mediating the expression of patulin cluster genes and crucial global regulatory factors. Likewise, PeSet1 positively regulated key genes in β-1,3-glucan biosynthesis and the reactive oxygen species scavenging process to modulate cell wall integrity and oxidative stress responses, respectively. Collectively, we have proven for the first time the function of Set1 in patulin biosynthesis and the crucial role of Set1 in colonization and stress responses in P. expansum. IMPORTANCE Penicillium expansum is one of the most important plant fungal pathogens, which not only causes blue mold rot in various fruits, leading to huge decay losses, but also produces mycotoxin patulin, posing a threat to human health. Both pathogenesis and patulin biosynthesis in P. expansum are regulated by complex and sophisticated networks. We focused on the epigenetic modification and identified a conserved histone H3K4 methyltransferase PeSet1 in P. expansum. Our work revealed the important role of PeSet1 in growth, development, colonization, patulin production, and stress responses of P. expansum. In particular, we originally described the regulation of Set1 on patulin biosynthetic pathway. These findings will provide new targets for the prevention and control of blue mold disease and patulin contamination.

AaCaMKs Positively Regulate Development, Infection Structure Differentiation and Pathogenicity in Alternaria alternata, Causal Agent of Pear Black Spot

Calcium/calmodulin-dependent protein kinase (CaMK), a key downstream target protein in the Ca²⁺ signaling pathway of eukaryotes, plays an important regulatory role in the growth, development and pathogenicity of plant fungi. Three AaCaMKs (AaCaMK1, AaCaMK2 and AaCaMK3) with conserved PKC_like superfamily domains, ATP binding sites and ACT sites have been cloned from Alternaria alternata, However, their regulatory mechanism in A. alternata remains unclear. In this study, the function of the AaCaMKs in the development, infection structure differentiation and pathogenicity of A. alternata was elucidated through targeted gene disruption. The single disruption of AaCaMKs had no impact on the vegetative growth and spore morphology but significantly influenced hyphae growth, sporulation, biomass accumulation and melanin biosynthesis. Further expression analysis revealed that the AaCaMKs were up-regulated during the infection structure differentiation of A. alternata on hydrophobic and pear wax substrates. In vitro and in vivo analysis further revealed that the deletion of a single AaCaMKs gene significantly reduced the A. alternata conidial germination, appressorium formation and infection hyphae formation. In addition, pharmacological analysis confirmed that the CaMK specific inhibitor, KN93, inhibited conidial germination and appressorium formation in A. alternata. Meanwhile, the AaCaMKs genes deficiency significantly reduced the A. alternata pathogenicity. These results demonstrate that AaCaMKs regulate the development, infection structure differentiation and pathogenicity of A. alternata and provide potential targets for new effective fungicides.

Comprehensive review on patulin and Alternaria toxins in fruit and derived products

Mycotoxins are toxic secondary metabolites produced by certain fungi, which can contaminate various food commodities, including fruits and their derived products. Patulin and Alternaria toxins are among the most commonly encountered mycotoxins in fruit and their derived products. In this review, the sources, toxicity, and regulations related to these mycotoxins, as well as their detection and mitigation strategies are widely discussed. Patulin is a mycotoxin produced mainly by the fungal genera Penicillium, Aspergillus, and Byssochlamys. Alternaria toxins, produced by fungi in the Alternaria genus, are another common group of mycotoxins found in fruits and fruit products. The most prevalent Alternaria toxins are alternariol (AOH) and alternariol monomethyl ether (AME). These mycotoxins are of concern due to their potential negative effects on human health. Ingesting fruits contaminated with these mycotoxins can cause acute and chronic health problems. Detection of patulin and Alternaria toxins in fruit and their derived products can be challenging due to their low concentrations and the complexity of the food matrices. Common analytical methods, good agricultural practices, and contamination monitoring of these mycotoxins are important for safe consumption of fruits and derived products. And Future research will continue to explore new methods for detecting and managing these mycotoxins, with the ultimate goal of ensuring the safety and quality of fruits and derived product supply.

Current and future trends in the biocontrol of postharvest diseases

Postharvest diseases of fruits and vegetables cause significant economic losses to producers and marketing firms. Many of these diseases are caused by necrotrophic fungal pathogens that require wounded or injured tissues to establish an infection. Biocontrol of postharvest diseases is an evolving science that has moved from the traditional paradigm of one organism controlling another organism to viewing biocontrol as a system involving the biocontrol agent, the pathogen, the host, the physical environment, and most recently the resident microflora. Thus, the paradigm has shifted from one of simplicity to complexity. The present review provides an overview of how the field of postharvest biocontrol has evolved over the past 40 years, a brief review of the biology of necrotrophic pathogens, the discovery of BCAs, their commercialization, and mechanisms of action. Most importantly, current research on the use of marker-assisted-selection, the fruit microbiome and its relationship to the pathobiome, and the use of double-stranded RNA as a biocontrol strategy is discussed. These latter subjects represent evolving trends in postharvest biocontrol research and suggestions for future research are presented.

Modulation of extracellular Penicillium expansum-driven acidification by Papiliotrema terrestris affects biosynthesis of patulin and has a possible role in biocontrol activity

The active regulation of extracellular pH is critical for the virulence of fungal pathogens. Penicillium expansum is the causal agent of green-blue mold on stored pome fruits and during its infection process acidifies the host tissues by secreting organic acids. P. expansum is also the main producer of patulin (PAT), a mycotoxin found in pome fruit-based products and that represents a serious health hazard for its potential carcinogenicity. While it is known that PAT biosynthesis in P. expansum is regulated by nutritional factors such as carbon and nitrogen and by the pH, the mechanistic effects of biocontrol on PAT production by P. expansum are not known. In this work, we assessed how optimal and suboptimal concentrations of the biocontrol agent (BCA) Papiliotrema terrestris LS28 affect both extracellular pH and PAT biosynthesis in P. expansum. In wounded apples, the optimal and suboptimal concentrations of the BCA provided almost complete and partial protection from P. expansum infection, respectively, and reduced PAT contamination in both cases. However, the suboptimal concentration of the BCA increased the specific mycotoxigenic activity by P. expansum. In vitro, the rate of PAT biosynthesis was strictly related to the extracellular pH, with the highest amount of PAT detected in the pH range 4–7, whereas only traces were detectable at pH 3. Moreover, both in vitro and in apple wounds the BCA counteracted the extracellular P. expansum-driven acidification maintaining extracellular pH around 4, which is within the pH range that is optimal for PAT biosynthesis. Conversely, in the absence of LS28 the pathogen-driven acidification led to rapidly achieving acidic pH values (<3) that lie outside of the optimal pH range for PAT biosynthesis. Taken together, these results suggest that pH modulation by LS28 is important to counteract the host tissue acidification and, therefore, the virulence of P. expansum. On the other hand, the buffering of P. expansum-driven acidification provided by the BCA increases the specific rate of PAT biosynthesis through the extension of the time interval at which the pH value lies within the optimal range for PAT biosynthesis. Nevertheless, the antagonistic effect provided by the BCA greatly reduced the total amount of PAT.

Occurrence of Patulin and Polyphenol Profile of Croatian Traditional and Conventional Apple Cultivars during Storage

Apples and apple-based products are among the most consumed fruits around the world. However, they are susceptible to infection with the fungi Penicilium expansum. In addition to the reduction of apple quality, secondary metabolism of this fungus produces a mycotoxin patulin that has a negative effect on human health. Currently, there is no available research in the literature on the resistance of Croatian traditional apple cultivars to contamination with P. expansum, and consequently, on the patulin content in apples and apple juice produced from those apples. Although the mechanism of apple resistance to fungal diseases has not yet been sufficiently investigated, some studies have shown that polyphenolic compounds have some impact on fungi growth. In order to contribute with new knowledge, this research deals with monitoring the growth of P. expansum on apples, patulin detection by LC/MS-MS, determination of polyphenol profile by validated HPLC method, and determining the effect of polyphenolic compounds on fungi growth and patulin production during apple storage. The results of this study have shown that Croatian traditional apple cultivars harvested from family farm Horvatić contain higher concentration of polyphenolic compounds and higher antioxidant activity. At the same time, they showed more resistance to infection by P. expansum than conventional ones. The higher content of dihydrochalcones and flavanols encouraged the biosynthesis of patulin in examined cultivars. However, the higher content of non-flavonoids such as 2-6 dimethoxybenzoic acid, 4-hydroxycinnamic acid and chlorogenic acid leads to decrease in content of patulin. In conclusion, it seems that content of polyphenols and patulin production are correlated.

Highly efficient removal of patulin using immobilized enzymes of Pseudomonas aeruginosa TF-06 entrapped in calcium alginate beads

Patulin is a toxic secondary metabolite produced by several moulds, which contaminates fruits and their products posing serious threats to human health. Though several microorganisms and enzymes have been reported to effectively degrade patulin, separation of them from fruit juice challenges the commercial applications. Here, a Pseudomonas aeruginosa strain TF-06 was isolated, its patulin degradation mechanism and optimum conditions for enzyme immobilization were investigated. The results indicated that TF-06 could degrade patulin into non-cytotoxic E/Z-ascladiol mainly by the activity of intracellular enzymes. For easy separation of enzymes, calcium alginate was selected for immobilization of intracellular enzymes from TF-06. The immobilized enzyme beads were effective in detoxification of patulin in apple juice. The mitigation rate was reached 95%, while there was no negative effect on juice quality. The study provides a promising way to resolve the issue of enzyme separation during mycotoxin biological detoxification in fruit juice.

Recent advances in research on biocontrol of postharvest fungal decay in apples

Apple is the largest fruit crop produced in temperate regions and is a popular fruit worldwide. It is, however, susceptible to a variety of postharvest fungal pathogens, including Penicillium expansum, Botrytis cinerea, Botryosphaeria dothidea, Monilia spp., and Alternaria spp. Decays resulting from fungal infections severely reduce apple quality and marketable yield. Biological control utilizing bacterial and fungal antagonists is an eco-friendly and effective method of managing postharvest decay in horticultural crops. In the current review, research on the pathogenesis of major decay fungi and isolation of antagonists used to manage postharvest decay in apple is presented. The mode of action of postharvest biocontrol agents (BCAs), including recent molecular and genomic studies, is also discussed. Recent research on the apple microbiome and its relationship to disease management is highlighted, and the use of additives and physical treatments to enhance biocontrol efficacy of BCAs is reviewed. Biological control is a critical component of an integrated management system for the sustainable approaches to apple production. Additional research will be required to explore the feasibility of developing beneficial microbial consortia and novel antimicrobial compounds derived from BCAs for postharvest disease management, as well as genetic approaches, such as the use of CRISPR/Cas9 technology.

More than a Virulence Factor: Patulin Is a Non-Host-Specific Toxin that Inhibits Postharvest Phytopathogens and Requires Efflux for Penicillium Tolerance

Mycotoxin contamination is a leading cause of food spoilage and waste on a global scale. Patulin, a mycotoxin produced by Penicillium spp. during postharvest pome fruit decay, causes acute and chronic effects in humans, withstands pasteurization, and is not eliminated by fermentation. While much is known about the impact of patulin on human health, there are significant knowledge gaps concerning the effect of patulin during postharvest fruit-pathogen interactions. Application of patulin on six apple cultivars reproduced some blue mold symptoms that were cultivar-independent and dose-dependent. Identical symptoms were also observed in pear and mandarin orange. Six Penicillium isolates exposed to exogenous patulin exhibited delayed germination after 24 h, yet all produced viable colonies in 7 days. However, four common postharvest phytopathogenic fungi were completely inhibited by patulin during conidial germination and growth, suggesting the toxin is important for Penicillium to dominate the postharvest niche. Using clorgyline, a broad-spectrum efflux pump inhibitor, we demonstrated that efflux plays a role in Penicillium auto-resistance to patulin during conidial germination. The work presented here contributes new knowledge of patulin auto-resistance, its mode of action, and inhibitory role in fungal-fungal interactions. Our findings provide a solid foundation to develop toxin and decay mitigation approaches.

Study on the mechanism of inhibiting patulin production by fengycin

Penicillium expansum is the main cause of apple rot. Besides, it can also produce mycotoxin patulin (PAT). Therefore, the search for substances that can inhibit the activity and toxigenicity of P. expansum has become a hot research topic. This study investigates the inhibitory effects of fengycin on patulin production in P. expansum. P. expansum was cultured under different environments with different concentrations of fengycin. The patulin content produced per unit weight of P. expansum mycelium was detected and determined by high pressure liquid chromatography (HPLC). Synergy brands (SYBR) GreenI Real-time PCR was used to detect the expression levels of 6-methylsalicylic acid synthase (6-MSAS) and isoepoxydon dehydrogenase (IDH), which were the key genes of producing patulin of P. expansum mycelium, in the conditions treated by fengycin and untreated. After fengycin treatments, not only the patulin content in every unit weight of P. expansum mycelium but also the expression level of 6-MSAS decreased significantly. The expression level of 6-MSAS of treatment was 0.11 folds of control. However, the expression level of IDH treated by fengycin decreased slightly. Fengycin could inhibit the P. expansum from producing patulin by downregulating the expression of key synthetic genes 6-MSAS.

Application of recyclable CRISPR/Cas9 tools for targeted genome editing in the postharvest pathogenic fungi Penicillium digitatum and Penicillium expansum

Penicillium digitatum and Penicillium expansum are plant pathogenic fungi that cause the green and blue mold diseases, respectively, leading to serious postharvest economic losses worldwide. Moreover, P. expansum can produce mycotoxins, which are hazardous compounds to human and animal health. The development of tools that allow multiple and precise genetic manipulation of these species is crucial for the functional characterization of their genes. In this sense, CRISPR/Cas9 represents an excellent opportunity for genome editing due to its efficiency, accuracy and versatility. In this study, we developed protoplast generation and transformation protocols and applied them to implement the CRISPR/Cas9 technology in both species for the first time. For this, we used a self-replicative, recyclable AMA1-based plasmid which allows unlimited number of genomic modifications without the limitation of integrative selection markers. As test case, we successfully targeted the wetA gene, which encodes a regulator of conidiophore development. Finally, CRISPR/Cas9-derived ΔwetA strains were analyzed. Mutants showed reduced axenic growth, differential pathogenicity and altered conidiogenesis and germination. Additionally, P. digitatum and P. expansum ΔwetA mutants showed distinct sensitivity to fungal antifungal proteins (AFPs), which are small, cationic, cysteine-rich proteins that have become interesting antifungals to be applied in agriculture, medicine and in the food industry. With this work, we demonstrate the feasibility of the CRISPR/Cas9 system, expanding the repertoire of genetic engineering tools available for these two important postharvest pathogens and open up the possibility to adapt them to other economically relevant phytopathogenic fungi, for which toolkits for genetic modifications are often limited.

Penicillium chrysogenum, a Vintage Model with a Cutting-Edge Profile in Biotechnology

The discovery of penicillin entailed a decisive breakthrough in medicine. No other medical advance has ever had the same impact in the clinical practise. The fungus Penicillium chrysogenum (reclassified as P. rubens) has been used for industrial production of penicillin ever since the forties of the past century; industrial biotechnology developed hand in hand with it, and currently P. chrysogenum is a thoroughly studied model for secondary metabolite production and regulation. In addition to its role as penicillin producer, recent synthetic biology advances have put P. chrysogenum on the path to become a cell factory for the production of metabolites with biotechnological interest. In this review, we tell the history of P. chrysogenum, from the discovery of penicillin and the first isolation of strains with high production capacity to the most recent research advances with the fungus. We will describe how classical strain improvement programs achieved the goal of increasing production and how the development of different molecular tools allowed further improvements. The discovery of the penicillin gene cluster, the origin of the penicillin genes, the regulation of penicillin production, and a compilation of other P. chrysogenum secondary metabolites will also be covered and updated in this work.

Penicillium expansum Impact and Patulin Accumulation on Conventional and Traditional Apple Cultivars

Penicillium expansum is a necrotrophic plant pathogen among the most ubiquitous fungi disseminated worldwide. It causes blue mould rot in apples during storage, transport and sale, threatening human health by secreting patulin, a toxic secondary metabolite that contaminates apples and apple-derived products. Nevertheless, there is still a lack of sufficient data regarding the resistance of different apple cultivars to P. expansum, especially ancient ones, which showed to possess certain resistance to plant diseases. In this work, we investigated the polyphenol profile of 12 traditional and 8 conventional apple cultivar and their resistance to P. expansum CBS 325.48. Eight polyphenolic compounds were detected; the most prominent were catechin, epicatechin and gallic acid. The highest content of catechin was detected in ‘Apistar’—91.26 mg/100 g of fresh weight (FW), epicatechin in ‘Bobovac’—67.00 mg/100 g of FW, and gallic acid in ‘Bobovac’ and ‘Kraljevčica’—8.35 and 7.40 mg/100 g of FW, respectively. The highest content of patulin was detected in ‘Kraljevčica’ followed by ‘Apistar’—1687 and 1435 µg/kg, respectively. In apple cultivars ‘Brčko’, ‘Adamčica’ and ‘Idared’, patulin was not detected. Furthermore, the patulin content was positively correlated with gallic acid (r = 0.4226; p = 0.002), catechin (r = 0.3717; p = 0.008) and epicatechin (r = 0.3305; p = 0.019). This fact indicates that higher contents of gallic acid, catechin and epicatechin negatively affected and boost patulin concentration in examined apple cultivars. This can be related to the prooxidant activity of polyphenolic compounds and sensitivity of P. expansum to the disturbance of oxidative status.

Arginine Methyltransferase PeRmtC Regulates Development and Pathogenicity of Penicilliumexpansum via Mediating Key Genes in Conidiation and Secondary Metabolism

Penicillium expansum is one of the most common and destructive post-harvest fungal pathogens that can cause blue mold rot and produce mycotoxins in fruit, leading to significant post-harvest loss and food safety concerns. Arginine methylation by protein arginine methyltransferases (PRMTs) modulates various cellular processes in many eukaryotes. However, the functions of PRMTs are largely unknown in post-harvest fungal pathogens. To explore their roles in P. expansum, we identified four PRMTs (PeRmtA, PeRmtB, PeRmtC, and PeRmt2). The single deletion of PeRmtA, PeRmtB, or PeRmt2 had minor or no impact on the P. expansum phenotype while deletion of PeRmtC resulted in decreased conidiation, delayed conidial germination, impaired pathogenicity and pigment biosynthesis, and altered tolerance to environmental stresses. Further research showed that PeRmtC could regulate two core regulatory genes, PeBrlA and PeAbaA, in conidiation, a series of backbone genes in secondary metabolism, and affect the symmetric ω-N^G, N’^G-dimethylarginine (sDMA) modification of proteins with molecular weights of primarily 16–17 kDa. Collectively, this work functionally characterized four PRMTs in P. expansum and showed the important roles of PeRmtC in the development, pathogenicity, and secondary metabolism of P. expansum.

Recent advances in Penicillium expansum infection mechanisms and current methods in controlling P. expansum in postharvest apples

One of the most significant challenges associated with postharvest apple deterioration is the blue mold caused by Penicillium expansum, which leads to considerable economic losses to apple production industries. Apple fruits are susceptible to mold infection owing to their high nutrient and water content, and current physical control methods can delay but cannot completely inhibit P. expansum growth. Biological control methods present promising alternatives; however, they are not always cost effective and have application restrictions. P. expansum infection not only enhances disease pathogenicity, but also inhibits the expression of host-related defense genes. The implementation of new ways to investigate and control P. expansum are expected with the advent of omics technology. Advances in these techniques, together with molecular biology approaches such as targeted gene deletion and whole genome sequencing, will lead to a better understanding of the P. expansum infectious machinery. Here, we review the progress of research on the blue mold disease caused by P. expansum in apples, including physiological and molecular infection mechanisms, as well as various methods to control this common plant pathogen.

PeMetR-mediated sulfur assimilation is essential for virulence and patulin biosynthesis in Penicillium expansum

Penicillium expansum, as the causal agent of blue mould and a main producer of mycotoxin patulin, is a global concern for economic and food safety. To date, the nutritional requirements of the pathogen during infection and patulin biosynthesis are poorly understood. Here, we genetically characterized the role of the bZIP transcription factor PeMetR in sulfur metabolism, virulence and patulin biosynthesis of P. expansum. The PeMetR regulator is crucial for normal germination and growth on inorganic S-sources but dispensable for utilization of organic S-sources. Accordingly, it is involved in regulating the expression of genes in sulfur assimilation pathway rather than methionine metabolic processes. Disruption of PeMetR resulted in a complete loss of virulence on various fruits. Additionally, the mutant showed a remarkably reduced ability to produce patulin. Exogenous methionine could partially or completely rescue the impaired phenotypes of the mutant. Inactivation of the sulfur assimilation pathway genes, PesA, PesB, PesC, PesF, generated growth, virulence and patulin production defects similar to those of ΔPeMetR. Overall, our study provides evidence that PeMetR-mediated sulfur assimilation is essential for growth and infection and shows for the first time that regulation of sulfur assimilation affects biosynthesis of an important mycotoxin patulin in P. expansum.

Eco-friendly management of postharvest fungal decays in kiwifruit

Kiwifruit is purchased by consumers worldwide and is increasing in demand. Unfortunately, kiwifruit is susceptible to postharvest decay caused by a variety of fungal pathogens, including Botrytis cinerea, Penicillium expansum, Alternaria alternata, Botryosphaeria dothidea, and Diaporthe spp. Among these pathogens, B. cinerea is the most prevalent and devastating. Infections by these fungal pathogens result in a deterioration in fruit quality and a reduction in marketable yield. Eco-friendly methods to control kiwifruit postharvest decay have been explored as alternatives to the use of synthetic fungicides. In this review, we provide an overview and discuss the virulence and pathogenesis of fungi that are causal agents of kiwifruit decay, especially B. cinerea, including recent molecular and genomic studies. Advances in pre- and postharvest measures for postharvest decay management, including biological control, physical applications, the use of natural compounds and plant hormones, and the use of combined methods, are also reviewed. Eco-friendly control measures are a critical component of an integrated management approach for sustainable production of kiwifruit. The need for further research on the use of microbial consortia for the management of postharvest diseases of kiwifruit is also discussed.

Patulin in food: A mycotoxin concern for human health and its management strategies

The mycotoxin patulin is primarily produced as a secondary metabolite by numerous fungal species and predominantly by Aspergillus, Byssochlamys, and Penicillium species. It is generally associated with fungal infected food materials. Penicillium expansum is considered the only fungal species liable for patulin contamination in pome fruits, especially in apples and apple-based products. This toxin in food poses serious health concerns and economic threat, which has aroused the need to adopt effective detection and mitigation strategies. Understanding its origin sources and biosynthetic mechanism stands essential for efficiently designing a management strategy against this fungal contamination. This review aims to present an updated outline of the sources of patulin occurrence in different foods and their biosynthetic mechanisms. It further provides information regarding the detrimental effects of patulin on human and agriculture as well as its effective detection, management, and control strategies.

Function of pH-dependent transcription factor PacC in regulating development, pathogenicity, and mycotoxin biosynthesis of phytopathogenic fungi

pH, as one of the most important environmental factors, affects various biological processes in pathogenic fungi. Sensing and responding to fluctuations in ambient pH are essential for these fungi to complete their life cycle. Fungi have evolved a complicated and conserved system, the so-called Pal-pH pathway, to regulate genes and adapt to alterations in ambient pH. PacC is the dominant transcription factor in the Pal-pH pathway and regulates various biological processes. The regulatory mode of PacC has been extensively studied in Aspergillus nidulans and is generally conserved in other fungal species, including numerous phytopathogenic fungi. However, species-specific alterations have been reported. This review summarizes recent advances in the regulatory mechanisms of PacC and its role in controlling development, pathogenicity, and mycotoxin biosynthesis in phytopathogenic fungi. Potential applications of these findings and some unresolved questions are also discussed.

Cinnamon Oil Inhibits Penicillium expansum Growth by Disturbing the Carbohydrate Metabolic Process

Penicillium expansum is a major postharvest pathogen that mainly threatens the global pome fruit industry and causes great economic losses annually. In the present study, the antifungal effects and potential mechanism of cinnamon oil against P. expansum were investigated. Results indicated that 0.25 mg L⁻¹ cinnamon oil could efficiently inhibit the spore germination, conidial production, mycelial accumulation, and expansion of P. expansum. In addition, it could effectively control blue mold rots induced by P. expansum in apples. Cinnamon oil could also reduce the expression of genes involved in patulin biosynthesis. Through a proteomic quantitative analysis, a total of 146 differentially expressed proteins (DEPs) involved in the carbohydrate metabolic process, most of which were down-regulated, were noticed for their large number and functional significance. Meanwhile, the expressions of 14 candidate genes corresponding to DEPs and the activities of six key regulatory enzymes (involving in cellulose hydrolyzation, Krebs circle, glycolysis, and pentose phosphate pathway) showed a similar trend in protein levels. In addition, extracellular carbohydrate consumption, intracellular carbohydrate accumulation, and ATP production of P. expansum under cinnamon oil stress were significantly decreased. Basing on the correlated and mutually authenticated results, we speculated that disturbing the fungal carbohydrate metabolic process would be partly responsible for the inhibitory effects of cinnamon oil on P. expansum growth. The findings would provide new insights into the antimicrobial mode of cinnamon oil.

Characterization of a short-chain dehydrogenase/reductase and its function in patulin biodegradation in apple juice

Biodegradation based on microbial enzymes is considered to be one of the promising ways for controlling patulin contamination. However, few patulin degrading enzymes have been isolated and characterized until now. Here, a short-chain dehydrogenase/reductase (SDR) gene, CgSDR, was cloned from a yeast strain Candida guilliermondii, and expressed in Escherichia coli. The expression of CgSDR conferred a strong patulin tolerance and degradation ability to E. coli, and purified CgSDR could transform patulin into E-ascladiol in vitro with NADPH as a coenzyme. Moreover, addition of CgSDR at 150 μg/mL could reduce 80% of patulin in apple juice and the biodegradation process did not affect the quality of the apple juice. A molecular docking analysis and site-directed mutagenesis indicated that CgSDR might interact with patulin via VAL188 as an active binding sites. The findings provide new insights for developing enzymic formulations for mycotoxin detoxification in fruit derived products.

Versatile Roles of the Receptor-Like Kinase Feronia in Plant Growth, Development and Host-Pathogen Interaction

As a member of the Catharanthus roseus receptor-like kinase 1-like (CrRLK1L) protein kinase subfamily, FERONIA (FER) has emerged as a versatile player regulating multifaceted functions in growth and development, as well as responses to environmental factors and pathogens. With the concerted efforts of researchers, the molecular mechanism underlying FER-dependent signaling has been gradually elucidated. A number of cellular processes regulated by FER-ligand interactions have been extensively reported, implying cell type-specific mechanisms for FER. Here, we provide a review on the roles of FER in male-female gametophyte recognition, cell elongation, hormonal signaling, stress responses, responses to fungi and bacteria, and present a brief outlook for future efforts.